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  • 1.
    Appelgren, Henrik
    et al.
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institute.
    Kniola, Barbara
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institute.
    Ekwall, Karl
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institute.
    Distinct centromere domain structures with separate functions demonstrated in live fission yeast cells2003Inngår i: Journal of Cell Science, ISSN 0021-9533, E-ISSN 1477-9137, Vol. 116, nr 19, s. 4035-4042Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fission yeast (Saccharomyces pombe) centromere DNA is organized in a central core region flanked on either side by a region of outer repeat (otr) sequences. The otr region is known to be heterochromatic and bound by the Swi6 protein whereas the central core region contains an unusual chromatin structure involving the histone H3 variant Cnp1 (S. pombe CENP-A). The central core is the base for formation of the kinetochore structure whereas the flanking region is important for sister centromere cohesion. We have previously shown that the ultrastructural domain structure of S. pombe centromeres in interphase is similar to that of human centromeres. Here we demonstrate that S. pombe centromeres are organized in cytologically distinct domains even in mitosis. Fluorescence in situ hybridization of fixed metaphase cells revealed that the otr regions of the centromere were still held together by cohesion even after the sister kinetochores had separated. In live cells, the central cores and kinetochores of sister chromosomes could be distinguished from one Another when they were subjected to mitotic tension. The function of the different centromeric domains was addressed. Transacting mutations affecting the kinetochore (nuf2) central core domain (mis6) and the heterochromatin domain (rik1) were analyzed in live cells. In interphase, both nuf2 and mis6 caused declustering of centromeres from the spindle pole body whereas centromere clustering was normal in rik1 despite an apparent decondensation defect. The declustering of centromeres in mis6 cells correlated with loss the Ndc80 kinetochore marker protein from the centromeres. Interestingly the declustered centromeres were still restricted to the nuclear periphery thus revealing a kinetochore-independent peripheral localization mechanism for heterochromatin. Time-lapse microscopy of live mis6 and nuf2-1 mutant cells in mitosis showed similar severe misaggregation phenotypes whereas the rik1 mutants showed a mild cohesion defect. Thus, S. pombe centromeres have two distinguishable domains even during mitosis, and our functional analyses support the previous observations that the kinetochore/central core and the heterochromatin domains have distinct functions both in interphase and mitosis.

  • 2.
    Arabi, Azadeh
    et al.
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institute.
    Rustum, Cecilia
    Södertörns högskola, Avdelning Naturvetenskap. Stockholm University.
    Hallberg, Einar
    Södertörns högskola, Avdelning Naturvetenskap.
    Wright, Anthony P H
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institute.
    Accumulation of c-Myc and proteasomes at the nucleoli of cells containing elevated c-Myc protein levels2003Inngår i: Journal of Cell Science, ISSN 0021-9533, E-ISSN 1477-9137, Vol. 116, nr 9, s. 1707-1717Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    c-Myc is a predominately nuclear transcription factor that is a substrate for rapid turnover by the proteasome system. Cancer-related mutations in c-Myc lead to defects in its degradation and thereby contribute to the increase in its cellular level that is associated with the disease. Little is known about the mechanisms that target c-Myc to the proteasomes. By using a GFP fusion protein and live analysis we show that c-Myc shuttles between the nucleus and cytoplasm and thus it could be degraded in either compartment. Strikingly, at elevated levels of expression c-Myc accumulates at nucleoli in some cells, consistent with saturation of a nucleolus-associated degradation system in these cells. This idea is further supported by the observation that proteasome inhibitor treatment causes accumulation of c-Myc at the nucleoli of essentially all cells. Under these conditions c-Myc is relatively stably associated with the nucleolus, as would be expected if the nucleolus functions as a sequestration/degradation site for excess c-Myc. Furthermore, during elevated c-Myc expression or proteasome inhibition, nucleoli that are associated with c-Myc also accumulate proteasomes. c-Myc and proteasomes co-localise in intranucleolar regions distinct from the dense fibrillar component of the nucleolus. Based on these results we propose a model for c-Myc downregulation where c-Myc is sequestered at the nucleoli. Sequestration of c-Myc is accompanied by recruitment of proteasomes and may lead to subsequent degradation.

  • 3.
    Arabi, Azadeh
    et al.
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Institutet.
    Wu, Siqin
    SLU.
    Ridderstråle, Karin
    SLU.
    Bierhoff, Holger
    German Cancer Research Center, Heidelberg, Germany.
    Shiue, Chiounan
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Institutet.
    Fatyol, Karoly
    German Cancer Research Center, Heidelberg, Germany.
    Fahlén, Sara
    SLU.
    Hydbring, Per
    SLU.
    Söderberg, Ola
    Uppsala universitet.
    Grummt, Ingrid
    German Cancer Research Center, Heidelberg, Germany.
    Larsson, Lars-Gunnar
    SLU.
    Wright, Anthony P H
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Institutet.
    c-Myc associates with ribosomal DNA and activates RNA polymerase I transcription2005Inngår i: Nature Cell Biology, ISSN 1465-7392, E-ISSN 1476-4679, Vol. 7, nr 3, s. 303-310Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The c-Myc oncoprotein regulates transcription of genes that are associated with cell growth, proliferation and apoptosis(1). c-Myc levels are modulated by ubiquitin/proteasome-mediated degradation(1). Proteasome inhibition leads to c-Myc accumulation within nucleoli(2), indicating that c-Myc might have a nucleolar function. Here we show that the proteins c-Myc and Max interact in nucleoli and are associated with ribosomal DNA. This association is increased upon activation of quiescent cells and is followed by recruitment of the Myc cofactor TRRAP, enhanced histone acetylation, recruitment of RNA polymerase I (Pol I), and activation of rDNA transcription. Using small interfering RNAs (siRNAs) against c-Myc and an inhibitor of Myc - Max interactions, we demonstrate that c-Myc is required for activating rDNA transcription in response to mitogenic signals. Furthermore, using the ligand-activated MycER ( ER, oestrogen receptor) system, we show that c-Myc can activate Pol I transcription in the absence of Pol II transcription. These results suggest that c-Myc coordinates the activity of all three nuclear RNA polymerases, and thereby plays a key role in regulating ribosome biogenesis and cell growth.

  • 4. Bakhiet, M
    et al.
    Tjernlund, A
    Mousa, A
    Gad, Annica
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institute.
    Strömblad, Staffan
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institute.
    Kuziel, W A
    Seiger, A
    Andersson, J
    RANTES promotes growth and survival of human first-trimester forebrain astrocytes2001Inngår i: Nature Cell Biology, ISSN 1465-7392, E-ISSN 1476-4679, Vol. 3, nr 2, s. 150-157Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have examined the role of alpha and beta chemokines in the promotion of the ontogenetic development of the brain. RANTES was expressed preferentially in human fetal astrocytes in an age-dependent manner. Astrocytes from 5-week-old brains showed high proliferation and reduced survival, whereas 10-week-old astrocytes exhibited opposite effects. These effects were suppressed by anti-RANTES or anti-RANTES receptor antibodies and were enhanced by recombinant RANTES. RANTES induced tyrosine phosphorylation of several cellular proteins and nuclear translocation of STAT-1 in astrocytes. Interferons (IFN-gamma) was required for RANTES effects because RANTES induced IFN-gamma, and only 10-week-old astrocytes expressed the IFN-gamma receptor. Blocking of IFN-gamma with antibody reversed the effects of RANTES, indicating that cytokine/chemokine networks are critically involved in brain development.

  • 5. Bao, W J
    et al.
    Thullberg, M
    Zhang, H Q
    Onischenko, A
    Strömblad, Staffan
    Södertörns högskola, Avdelning Naturvetenskap.
    Cell attachment to the extracellular matrix induces proteasomal degradation of p21(CIP1) via Cdc42/Rac1 signaling2002Inngår i: Molecular and Cellular Biology, ISSN 0270-7306, E-ISSN 1098-5549, Vol. 22, nr 13, s. 4587-4597Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The cyclin-dependent kinase 2 (Cdk2) inhibitors p21(CIP1) and p27(KIP1) are negatively regulated by anchorage during cell proliferation, but it is unclear how integrin signaling may affect these Cdk2 inhibitors. Here, we demonstrate that integrin ligation led to rapid reduction of p21(CIp1) and p27(KIP1) protein levels in three distinct cell types upon attachment to various extracellular matrix (ECM) proteins, including fibronectin (FN), or to immobilized agonistic anti-integrin monoclonal antibodies. Cell attachment to FN did not rapidly influence p21(CIp1) mRNA levels, while the protein stability of p21(CIp1) was decreased. Importantly, the down-regulation of p21(CIP1) and p27(KIP1) was completely blocked by three distinct proteasome inhibitors, demonstrating that integrin ligation induced proteasomal degradation of these Cdk2 inhibitors. Interestingly, ECM-induced proteasomal proteolysis of a ubiquitination-deficient p21(CIP1) mutant (p21K6R) also occurred, showing that the proteasomal degradation of p21(CIP1) was ubiquitin independent. Concomitant with our finding that the small GTPases Cdc42 and Rac1 were activated by attachment to FN, constitutively active (ca) Cdc42 and ca Rac1 promoted down-regulation of p21(CIP1). However, dominant negative (dn) Cdc42 and do Rac1 mutants blocked the anchorage-induced degradation of p21(CIP1), suggesting that an integrin-induced Cdc42/Rac1 signaling pathway activates proteasomal degradation of p21(CIP1). Our results indicate that integrin-regulated proteasomal proteolysis might contribute to anchorage-dependent cell cycle control.

  • 6.
    Bartish, Galyna
    Södertörns högskola, Institutionen för livsvetenskaper. Stockholms universitet, Wenner-Grens institut.
    Elongation factor 2: A key component of the translation machinery in eukaryotes: Properties of yeast elongation factor 2 studied in vivo2008Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Synthesis of proteins is performed by the ribosome, a large ribonucleoprotein complex. Apart from the ribosome, numerous protein factors participate in this process. Elongation factor 2 (eEF2) is one of these factors. eEF2 is an essential protein with a mol. mass of about 100 kDa. The amino acid sequence of eEF2 is highly conserved in different organisms. eEF2 from S. cerevisiae contains 842 amino acids. The role of eEF2 in protein synthesis is to participate in the translocation of tRNAs from the A- and P-sites on the ribosome to the P- and E-sites. This movement of tRNAs is accompanied by a simultaneous movement of mRNA by one codon. eEF2 consists of six domains referred to as domains G, G′ and II-V, belongs to the G-protein super-family and possesses all structural motifs characterizing proteins in this family. eEF2 binds to the ribosome in complex with GTP. After GTP hydrolysis and translocation, it leaves the ribosome bound to GDP. The rate of protein synthesis in the cell can be regulated by phosphorylation of eEF2. Phosphorylation occurs on two threonine residues, situated in the G domain of the factor. Phosphorylation of eEF2 is catalysed by Rck2-kinase in yeast which is activated in response to osmotic stress. Despite the high degree of conservation of the threonine residues, they are not essential for yeast cell under normal growth conditions. However, under mild osmotic stress the growth rate of the cells lacking threonine residues was decreased. Region where threonine residues are located, called Switch I. Cryo-EM reconstruction shows that this region adopts ordered conformation when the eEF2•GTP complex is bound to the ribosome but became structurally disordered upon GTP hydrolysis. Mutagenesis of individual amino acids in Switch I resulted in both functional and non-functional eEF2 depending on the site of mutation and the substituting amino acid. Both functional and non-functional Switch I mutants were able to bind to the ribosome, indicating that mutations did not abolish the capacity of the factor to bind GTP. Yeast eEF2 with Switch I region from E. coli was able to substitute the wild type protein in vivo, though the growth rate of these cells was severely impaired. The eEF2-dependent GTP hydrolysis can be activated by ribosome from heterologous sources as seen in vitro. However, eEF2 from A. thaliana, D. melanogaster and S. solfataricus could not substi-tute yeast eEF2 in vivo. This may indicate additional roles of eEF2 in the yeast cell, apart from translocation itself.

  • 7.
    Bartish, Galyna
    et al.
    Södertörns högskola, Institutionen för livsvetenskaper. Stockholm University.
    Moradi, Hossein
    Södertörns högskola, Institutionen för livsvetenskaper. Stockholm University.
    Nygård, Odd
    Södertörns högskola, Institutionen för livsvetenskaper.
    Amino acids Thr56 and Thr58 are not essential for elongation factor 2 function in yeast2007Inngår i: The FEBS Journal, ISSN 1742-464X, E-ISSN 1742-4658, Vol. 274, nr 20, s. 5285-5297Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Yeast elongation factor 2 is an essential protein that contains two highly conserved threonine residues, T56 and T58, that could potentially be phosphorylated by the Rck2 kinase in response to environmental stress. The importance of residues T56 and T58 for elongation factor 2 function in yeast was studied using site directed mutagenesis and functional complementation. Mutations T56D, T56G, T56K, T56N and T56V resulted in nonfunctional elongation factor 2 whereas mutated factor carrying point mutations T56M, T56C, T56S, T58S and T58V was functional. Expression of mutants T56C, T56S and T58S was associated with reduced growth rate. The double mutants T56M/T58W and T56M/T58V were also functional but the latter mutant caused increased cell death and considerably reduced growth rate. The results suggest that the physiological role of T56 and T58 as phosphorylation targets is of little importance in yeast under standard growth conditions. Yeast cells expressing mutants T56C and T56S were less able to cope with environmental stress induced by increased growth temperatures. Similarly, cells expressing mutants T56M and T56M/T58W were less capable of adapting to increased osmolarity whereas cells expressing mutant T58V behaved normally. All mutants tested were retained their ability to bind to ribosomes in vivo. However, mutants T56D, T56G and T56K were under-represented on the ribosome, suggesting that these nonfunctional forms of elongation factor 2 were less capable of competing with wild-type elongation factor 2 in ribosome binding. The presence of nonfunctional but ribosome binding forms of elongation factor 2 did not affect the growth rate of yeast cells also expressing wild-type elongation factor 2.

  • 8. Beckman, M
    et al.
    Kihlmark, Madeleine
    Södertörns högskola, Institutionen för kemi, biologi, geografi och miljövetenskap.
    Iverfeldt, K
    Hallberg, Einar
    Södertörns högskola, Institutionen för kemi, biologi, geografi och miljövetenskap.
    Degradation of GFP-labelled POM121, a non-invasive sensor of nuclear apoptosis, precedes clustering of nuclear pores and externalisation of phosphatidylserine2004Inngår i: Apoptosis (London), ISSN 1360-8185, E-ISSN 1573-675X, Vol. 9, nr 3, s. 363-368Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The nuclear pore membrane protein POM121 is specifically degraded during apoptosis by a caspase-3-dependent process enabling early detection of apoptosis in living cells expressing POM121-GFP. Here we further investigated temporal aspects of apoptotic degradation of POM121-GFP. We demonstrate that decreased POM121-GFP fluorescence precedes annexin V-labelling of apoptotic cells. This indicates that degradation of the nuclear pore complex starts prior to redistribution of plasma membrane phosphatidylserine, which serves as a signal for phagocytotic elimination of apoptotic cells. Furthermore, a caspase-resistant GFP-labelled mutant of POM121 resisted degradation even in late apoptosis and was detected in clustered nuclear pores. Thus, it can be concluded that loss of POM121-GFP is a specific sensor of the activation of caspase-3-dependent proteolysis at the nuclear pores.

  • 9. Bernard, Pascal
    et al.
    Schmidt, Christine Katrin
    Vaur, Sabine
    Dheur, Sonia
    Drogat, Julie
    Genier, Sylvie
    Ekwall, Karl
    Södertörns högskola, Institutionen för livsvetenskaper.
    Uhlmann, Frank
    Javerzat, Jean-Paul
    Cell-cycle regulation of cohesin stability along fission yeast chromosomes2008Inngår i: EMBO Journal, ISSN 0261-4189, E-ISSN 1460-2075, Vol. 27, nr 1, s. 111-121Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Sister chromatid cohesion is mediated by cohesin, but the process of cohesion establishment during S-phase is still enigmatic. In mammalian cells, cohesin binding to chromatin is dynamic in G1, but becomes stabilized during S-phase. Whether the regulation of cohesin stability is integral to the process of cohesion establishment is unknown. Here, we provide evidence that fission yeast cohesin also displays dynamic behavior. Cohesin association with G1 chromosomes requires continued activity of the cohesin loader Mis4/Ssl3, suggesting that repeated loading cycles maintain cohesin binding. Cohesin instability in G1 depends on wpl1, the fission yeast ortholog of mammalian Wapl, suggestive of a conserved mechanism that controls cohesin stability on chromosomes. wpl1 is nonessential, indicating that a change in wpl1-dependent cohesin dynamics is dispensable for cohesion establishment. Instead, we find that cohesin stability increases at the time of S-phase in a reaction that can be uncoupled from DNA replication. Hence, cohesin stabilization might be a pre-requisite for cohesion establishment rather than its consequence.

  • 10.
    Buch, Charlotta
    et al.
    Södertörns högskola, Institutionen för livsvetenskaper.
    Lindberg, Robert
    Södertörns högskola, Institutionen för livsvetenskaper.
    Figueroa, Ricardo
    Södertörns högskola, Institutionen för livsvetenskaper.
    Gudise, Santhosh
    Södertörns högskola, Institutionen för livsvetenskaper.
    Onischenko, Evgeny
    Hallberg, Einar
    Södertörns högskola, Institutionen för livsvetenskaper.
    An integral protein of the inner nuclear membrane localizes to the mitotic spindle in mammalian cells2009Inngår i: Journal of Cell Science, ISSN 0021-9533, E-ISSN 1477-9137, Vol. 122, nr 12, s. 2100-2107Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Here, we characterize a transmembrane protein of the nuclear envelope that we name spindle-associated membrane protein 1 (Samp1). The protein is conserved in metazoa and fission yeast and is homologous to Net5 in rat and Ima1 in Schizosaccharomyces pombe. We show that, in human cells, the protein is a membrane-spanning polypeptide with an apparent molecular mass of 43 kDa. This is consistent with a predicted polypeptide of 392 amino acids that has five transmembrane segments and its C-terminus exposed to the nucleoplasm. During interphase, Samp1 was specifically distributed in the inner nuclear membrane. Post-transcriptional silencing of Samp1 expression resulted in separation of centrosomes from the nuclear envelope, indicating that it is functionally connected to the cytoskeleton. At the onset of mitosis, most of the protein dispersed out into the ER, as expected. However, during mitosis, a significant fraction of the protein specifically localized to the polar regions of the mitotic spindle. We demonstrate for the first time, in human cells, the existence of a membranous structure overlapping with the mitotic spindle. Interestingly, another integral inner nuclear membrane protein, emerin, was absent from the spindle-associated membranes. Thus, Samp1 defines a specific membrane domain associated with the mitotic spindle.

  • 11.
    Burglin, Thomas R
    Södertörns högskola, Avdelning Naturvetenskap.
    The homeobox genes of Encephalitozoon cuniculi (Microsporidia) reveal a putative mating-type locus2003Inngår i: Development, Genes and Evolution, ISSN 0949-944X, E-ISSN 1432-041X, Vol. 213, nr 1, s. 50-52Artikkel i tidsskrift (Fagfellevurdert)
  • 12. Carmichael, J B
    et al.
    Provost, P
    Ekwall, Karl
    Södertörns högskola, Institutionen för kemi, biologi, geografi och miljövetenskap.
    Hobman, T C
    Ago1 and Dcr1, two core components of the RNA interference pathway, functionally diverge from Rdp1 in regulating cell cycle events in Schizosaccharomyces pombe2004Inngår i: Molecular Biology of the Cell, ISSN 1059-1524, E-ISSN 1939-4586, Vol. 15, nr 3, s. 1425-1435Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the fission yeast Schizosaccharomyces pombe, three genes that function in the RNA interference (RNAi) pathway, ago1(+), dcr1(+), and rdp1(+), have recently been shown to be important for timely formation of heterochromatin and accurate chromosome segregation. In the present study, we present evidence that null mutants for ago1(+) and dcr1(+) but not rdp1(+), exhibit abnormal cytokinesis, cell cycle arrest deficiencies, and mating defects. Subsequent analyses showed that ago1(+) and dcr1(+) are required for regulated hyperphosphorylation of Cdc2 when encountering genotoxic insults. Because rdp1(+) is dispensable for this process, the functions of ago1(+) and dcr1(+) in this pathway are presumably independent of their roles in RNAi-mediated heterochromatin formation and chromosome segregation. This was further supported by the finding that ago1(+) is a multicopy suppressor of the S-M checkpoint deficiency and cytokinesis defects associated with loss of Dcr1 function, but not for the chromosome segregation defects of this mutant. Accordingly, we conclude that Dcr1-dependent production of small interfering RNAs is not required for enactment and/or maintenance of certain cell cycle checkpoints and that Ago1 and Dcr1 functionally diverge from Rdp1 to control cell cycle events in fission yeast. Finally, exogenous expression of hGERp95/EIF2C2/hAgo2, a human Ago1 homolog implicated in posttranscriptional gene silencing, compensated for the loss of ago1(+) function in S. pombe. This suggests that PPD proteins may also be important for regulation of cell cycle events in higher eukaryotes.

  • 13.
    Daigle, N
    et al.
    European Molecular Biology Laboratory (EMBL), Heidelberg, Germany.
    Beaudouin, J
    European Molecular Biology Laboratory (EMBL), Heidelberg, Germany.
    Hartnell, L
    NIH Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD), National Institutes of Health (NIH) - USA.
    Imreh, Gabriela
    Södertörns högskola, Avdelning Naturvetenskap.
    Hallberg, Einar
    Södertörns högskola, Avdelning Naturvetenskap.
    Lippincott-Schwartz, J
    NIH Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD), National Institutes of Health (NIH) - USA.
    Ellenberg, J
    European Molecular Biology Laboratory (EMBL), Heidelberg, Germany.
    Nuclear pore complexes form immobile networks and have a very low turnover in live mammalian cells2001Inngår i: Journal of Cell Biology, ISSN 0021-9525, E-ISSN 1540-8140, Vol. 154, nr 1, s. 71-84Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The nuclear pore complex (NPC) and its relationship to the nuclear envelope (NE) was characterized in living cells using POM121-green fluorescent protein (GFP) and GFP-Nup153, and GFP-lamin B1. No independent movement of single pore complexes was found within the plane of the NE in interphase. Only large arrays of NPCs moved slowly and synchronously during global changes in nuclear shape, strongly suggesting mechanical connections which form an NPC network. The nuclear lamina exhibited identical movements. NPC turnover measured by fluorescence recovery after photobleaching of POM121 was less than once per cell cycle. Nup153 association with NPCs was dynamic and turnover of this nucleoporin was three orders of magnitude faster. Overexpression of both nucleoporins induced the formation of annulate lamellae (AL) in the endoplasmic reticulum (ER). Turnover of AL pore complexes was much higher than in the NE (once every 2.5 min). During mitosis, POM121 and Nup153 were completely dispersed and mobile in the ER (POM121) or cytosol (Nup153) in metaphase, and rapidly redistributed to an immobilized pool around chromatin in late anaphase. Assembly and immobilization of both nucleoporins occurred before detectable recruitment of lamin B1, which is thus unlikely to mediate initiation of NPC assembly at the end of mitosis.

  • 14.
    Djupedal, Ingela
    et al.
    Södertörns högskola, Institutionen för livsvetenskaper.
    Ekwall, Karl
    Södertörns högskola, Institutionen för livsvetenskaper, Molekylärbiologi.
    Epigenetics: heterochromatin meets RNAi2009Inngår i: Cell Research, ISSN 1001-0602, E-ISSN 1748-7838, Vol. 19, nr 3, s. 282-295Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The term epigenetics refers to heritable changes not encoded by DNA. The organization of DNA into chromatin fibers affects gene expression in a heritable manner and is therefore one mechanism of epigenetic inheritance. Large parts of eukaryotic genomes consist of constitutively highly condensed heterochromatin, important for maintaining genome integrity but also for silencing of genes within. Small RNA, together with factors typically associated with RNA interference (RNAi) targets homologous DNA sequences and recruits factors that modify the chromatin, commonly resulting in formation of heterochromatin and silencing of target genes. The scope of this review is to provide an overview of the roles of small RNA and the RNAi components, Dicer, Argonaute and RNA dependent polymerases in epigenetic inheritance via heterochromatin formation, exemplified with pathways from unicellular eukaryotes, plants and animals.

  • 15.
    Djupedal, Ingela
    et al.
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Institutet.
    Kos-Braun, Isabelle C.
    University of Edinburgh, Edinburgh, UK / Universität Heidelberg, Heidelberg, Germany.
    Mosher, Rebecca A.
    University of Cambridge, Cambridge, UK.
    Söderholm, Niklas
    Karolinska Institutet.
    Simmer, Femke
    University of Edinburgh, Edinburgh, UK.
    Hardcastle, Thomas J.
    University of Cambridge, Cambridge, UK.
    Fender, Aurelie
    Uppsala universitet.
    Heidrich, Nadja
    Uppsala universitet.
    Kagansky, Alexander
    University of Edinburgh, Edinburgh, UK.
    Bayne, Elizabeth
    University of Edinburgh, Edinburgh, UK.
    Wagner, E. Gerhart H.
    Uppala universitet.
    Baulcombe, David C.
    University of Cambridge, Cambridge, UK.
    Allshire, Robin C.
    University of Edinburgh, Edinburgh, UK.
    Ekwall, Karl
    Södertörns högskola, Institutionen för livsvetenskaper, Molekylärbiologi. Karolinska Institutet.
    Analysis of small RNA in fission yeast; centromeric siRNAs are potentially generated through a structured RNA2009Inngår i: EMBO Journal, ISSN 0261-4189, E-ISSN 1460-2075, Vol. 28, nr 24, s. 3832-3844Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The formation of heterochromatin at the centromeres in fission yeast depends on transcription of the outer repeats. These transcripts are processed into siRNAs that target homologous loci for heterochromatin formation. Here, high throughput sequencing of small RNA provides a comprehensive analysis of centromere-derived small RNAs. We found that the centromeric small RNAs are Dcr1 dependent, carry 50-monophosphates and are associated with Ago1. The majority of centromeric small RNAs originate from two remarkably well-conserved sequences that are present in all centromeres. The high degree of similarity suggests that this non-coding sequence in itself may be of importance. Consistent with this, secondary structure-probing experiments indicate that this centromeric RNA is partially double-stranded and is processed by Dicer in vitro. We further demonstrate the existence of small centromeric RNA in rdp1D cells. Our data suggest a pathway for siRNA generation that is distinct from the well-documented model involving RITS/RDRC. We propose that primary transcripts fold into hairpin-like structures that may be processed by Dcr1 into siRNAs, and that these siRNAs may initiate heterochromatin formation independent of RDRC activity. The EMBO Journal (2009) 28, 3832-3844. doi: 10.1038/emboj.2009.351; Published online 26 November 2009

  • 16.
    Djupedal, Ingela
    et al.
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Institutet.
    Portoso, M
    University of Edinburgh, Edinburgh, UK.
    Spåhr, H
    Karolinska Institutet.
    Bonilla, Carolina
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Institutet.
    Gustafsson, C M
    Karolinska Institutet.
    Allshire, R C
    University of Edinburgh, Edinburgh, UK.
    Ekwall, Karl
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Institutet.
    RNA Pol II subunit Rpb7 promotes centromeric transcription and RNAi-directed chromatin silencing2005Inngår i: Genes & Development, ISSN 0890-9369, E-ISSN 1549-5477, Vol. 19, nr 19, s. 2301-2306Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fission yeast centromeric repeats are transcribed into small interfering RNA (siRNA) precursors (pre-siRNAs), which are processed by Dicer to direct heterochromatin formation. Recently, Rpb1 and Rpb2 subunits of RNA polymerase II (RNA Pol II) were shown to mediate RNA interference (RNAi)-directed chromatin modification but did not affect pre-siRNA levels. Here we show that another Pol II subunit, Rpb7 has a specific role in presiRNA transcription. We define a centromeric presiRNA promoter from which initiation is exquisitely sensitive to the rpb7-G150D mutation. In contrast to other Pol II subunits, Rpb7 promotes pre-siRNA transcription required for RNAi-directed chromatin silencing.

  • 17.
    Durand-Dubief, Mickael
    et al.
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Institutet.
    Sinha, Indranil
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Institutet.
    Fagerström-Billai, Fredrik
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Institutet.
    Bonilla, Carolina
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Institutet.
    Wright, Anthony
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Instiutet.
    Grunstein, Michael
    University of California, Los Angeles, CA, USA.
    Ekwall, Karl
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Institutet.
    Specific functions for the fission yeast Sirtuins Hst2 and Hst4 in gene regulation and retrotransposon silencing2007Inngår i: EMBO Journal, ISSN 0261-4189, E-ISSN 1460-2075, Vol. 26, nr 10, s. 2477-2488Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Expression profiling, ChiP-CHIP and phenotypic analysis were used to investigate the functional relationships of class III NAD(+)-dependent HDACs (Sirtuins) in fission yeast. We detected significant histone acetylation increases in Sirtuin mutants at their specific genomic binding targets and were thus able to identify an in vivo substrate preference for each Sirtuin. At heterochromatic loci, we demonstrate that although Hst2 is mainly cytoplasmic, a nuclear pool of Hst2 colocalizes with the other Sirtuins at silent regions (cen, mat, tel, rDNA), and that like the other Sirtuins, Hst2 is required for rDNA and centromeric silencing. Interestingly we found specific functions for the fission yeast Sirtuins Hst2 and Hst4 in gene regulation. Hst2 directly represses genes involved in transport and membrane function, whereas Hst4 represses amino-acid biosynthesis genes and Tf2 retrotransposons. A specific role for Hst4 in Tf2 50 mRNA processing was revealed. Thus, Sirtuins share functions at many genomic targets, but Hst2 and Hst4 have also evolved unique functions in gene regulation.

  • 18.
    Efimenko, Evgeni
    et al.
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Institute.
    Blacque, Oliver E.
    Simon Fraser University, Burnaby, British Columbia, Canada.
    Ou, Guangshuo
    University of California, Davis, USA.
    Haycraft, Courtney J.
    University of Alabama at Birmingham Medical Center, Birmingham, USA.
    Yoder, Bradley K.
    University of Alabama at Birmingham Medical Center, Birmingham, USA.
    Scholey, Jonathan M.
    University of California, Davis, USA.
    Leroux, Michel R.
    Simon Fraser University, Burnaby, British Columbia, Canada.
    Swoboda, Peter
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Instiute.
    Caenorhabditis elegans DYF-2, an orthologue of human WDR19, is a component of the intraflagellar transport machinery in sensory Cilia2006Inngår i: Molecular Biology of the Cell, ISSN 1059-1524, E-ISSN 1939-4586, Vol. 17, nr 11, s. 4801-4811Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The intraflagellar transport (IFT) machinery required to build functional cilia consists of a multisubunit complex whose molecular composition, organization, and function are poorly understood. Here, we describe a novel tryptophan-aspartic acid (WD) repeat (WDR) containing IFT protein from Caenorhabditis elegans, DYF-2, that plays a critical role in maintaining the structural and functional integrity of the IFT machinery. We determined the identity of the dyf-2 gene by transgenic rescue of mutant phenotypes and by sequencing of mutant alleles. Loss of DYF-2 function selectively affects the assembly and motility of different IFT components and leads to defects in cilia structure and chemosensation in the nematode. Based on these observations, and the analysis of DYF-2 movement in a Bardet-Biedl syndrome mutant with partially disrupted IFT particles, we conclude that DYF-2 can associate with IFT particle complex B. At the same time, mutations in dyf-2 can interfere with the function of complex A components, suggesting an important role of this protein in the assembly of the IFT particle as a whole. Importantly, the mouse orthologue of DYF-2, WDR19, also localizes to cilia, pointing to an important evolutionarily conserved role for this WDR protein in cilia development and function.

  • 19.
    Ekwall, Karl
    Södertörns högskola, Institutionen för kemi, biologi, geografi och miljövetenskap. Karolinska Institute.
    The RITS complex - A direct link between small RNA and heterochromatin2004Inngår i: Molecular Cell, ISSN 1097-2765, E-ISSN 1097-4164, Vol. 13, nr 3, s. 304-305Artikkel i tidsskrift (Fagfellevurdert)
  • 20.
    Eriksson, Charlotta
    et al.
    Södertörns högskola, Institutionen för kemi, biologi, geografi och miljövetenskap. Karolinska Institute.
    Rustum, Cecilia
    Södertörns högskola, Institutionen för kemi, biologi, geografi och miljövetenskap. Stockholm University.
    Hallberg, Einar
    Södertörns högskola, Institutionen för kemi, biologi, geografi och miljövetenskap.
    Dynamic properties of nuclear pore complex proteins in gp210 deficient cells2004Inngår i: FEBS Letters, ISSN 0014-5793, E-ISSN 1873-3468, Vol. 572, nr 1-3, s. 261-265Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Gp210, an integral membrane protein of the nuclear pore complex (NPC), is believed to be involved in NPC biogenesis. To test this hypothesis, we have investigated dynamic properties of the NPC and distribution of NPC proteins in NIH/ 3T3 cells lacking gp210. POM121 (the other integral NPC protein) and NUP107 (of the NUP107/160 complex) were correctly distributed at the nuclear pores in the absence of gp210. Furthermore, fluorescence recovery after photobleaching experiments showed that POM121 and NUP107 remained stably associated at the NPCs. We conclude that gp210 cannot be required for incorporation of POM121 or NUP107 or be required for maintaining NPC stability.

  • 21. Eriksson, S
    et al.
    Nygren, Jonas
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institute.
    Ahnström, G
    Matrix association of early- and late-replicating chromatin studied by single-cell electrophoresis2002Inngår i: Biochimica et Biophysica Acta. Molecular Cell Research, ISSN 0167-4889, E-ISSN 1879-2596, Vol. 1590, nr 1-3, s. 103-108Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    CHO-K1 cells were synchronized at the G(1)/S border by mitotic shake-off and aphidicolin incubation. Pulse-labeling with tritium was done at 30 min, 2 or 5 h into the S-phase, with chase incubations for different times in non-radioactive medium. The cells were subjected to neutral microelectrophoresis to extend the DNA into "comets," after which the label was visualized through autoradiography. At zero chase time, all label was positioned in the head. The displacement of label into the tails increased with time, reaching a maximum at about 5 h after the pulse. A lag phase of 2 - 3 It was observed for the early-labeled cells before the displacement started. Also, more label was released after overnight serum starvation, but this was reversed through a 3-h incubation at normal growth conditions. It was found that late-replicating chromatin is organized in larger domains than early-replicating chromatin, and DNA polymerase seems to be an important organizer. Early-replicating chromatin has other important attachments to the nuclear matrix, dependent on metabolic activity.

  • 22. Facanha, A L O
    et al.
    Appelgren, Henrik
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institutet.
    Tabish, Mohammad
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institutet.
    Okorokov, L
    Ekwall, Karl
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institutet.
    The endoplasmic reticulum cation P-type ATPase Cta4p is required for control of cell shape and microtubule dynamics2002Inngår i: Journal of Cell Biology, ISSN 0021-9525, E-ISSN 1540-8140, Vol. 157, nr 6, s. 1029-1039Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Here we describe the phenotypic characterization of the cta(4+) gene, encoding a novel member of the P4 family of P-type ATPases of fission yeast. The cta4Delta mutant is temperature sensitive and cold sensitive lethal and displays several morphological defects in cell polarity and cytokinesis. Microtubules are generally destabilized in cells lacking Cta4p. The microtubule length is decreased, and the number of microtubules per cell is increased. This is concomitant with an increase in the number of microtubule catastrophe events in the midzone of the cell. These defects are likely due to a general imbalance in cation homeostasis. Immunofluorescence microscopy and membrane fractionation experiments revealed that green fluorescent protein-tagged Cta4 localizes to the ER. Fluorescence resonance energy transfer experiments in living cells using the yellow cameleon indicator for Ca2+ indicated that Cta4p regulates the cellular Ca2+ concentration. Thus, our results reveal a link between cation homeostasis and the control of cell shape, microtubule dynamics, and cytokinesis, and appoint Ca2+ as a key ion in controlling these processes.

  • 23.
    Fagerström-Billai, Fredrik
    et al.
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Institutet.
    Wright, Anthony P H
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Institutet.
    Functional comparison of the Tup11 and Tup12 transcriptional corepressors in fission yeast2005Inngår i: Molecular and Cellular Biology, ISSN 0270-7306, E-ISSN 1098-5549, Vol. 25, nr 2, s. 716-727Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Gene duplication is considered an important evolutionary mechanism. Unlike many characterized species, the fission yeast Schizosaccharomyces pombe contains two paralogous genes, tup11(+) and tup12(+), that encode transcriptional corepressors similar to the well-characterized budding yeast Tup1 protein. Previous reports have suggested that Tup11 and Tup12 proteins play redundant roles. Consistently, we show that the two Tup proteins can interact together when expressed at normal levels and that each can independently interact with the Ssn6 protein, as seen for Tup1 in budding yeast. However, tup11(-) and tup12(-) mutants have different phenotypes on media containing KCl and CaCl2. Consistent with the functional difference between tup11(-) and tup12- mutants, we identified a number of genes in genome-wide gene expression experiments that are differentially affected by mutations in the tup11(+) and tup12(+) genes. Many of these genes are differentially derepressed in tup11(-) mutants and are over-represented in genes that have previously been shown to respond to a range of different stress conditions. Genes specifically derepressed in tup12(-) mutants require the Ssn6 protein for their repression. As for Tupl.2, Ssn6 is also required for efficient adaptation to KCI- and CaCl2-mediated stress. We conclude that Tup11 and Tup12 are at least partly functionally diverged and suggest that the Tup12 and Ssn6 proteins have adopted a specific role in regulation of the stress response.

  • 24. Funk, C
    et al.
    Wiklund, R
    Schröder, Wolfgang P
    Södertörns högskola, Avdelning Naturvetenskap.
    Jansson, C
    D1' centers are less efficient than normal photosystem II centers2001Inngår i: FEBS Letters, ISSN 0014-5793, E-ISSN 1873-3468, Vol. 505, nr 1, s. 113-117Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    One prominent difference between the photosystem II (PSII) reaction center protein D1 ' in Synechocystis 6803 and normal D1 is the replacement of Phe-186 in D1 with leucine in D1 '. Mutants of Synechocystis 6803 producing only D1 ', or containing engineered D1 proteins with Phe-186 substitutions, were analyzed by 77 K fluorescence emission spectra, chlorophyll a fluorescence induction yield and decay kinetics, and flash-induced oxygen evolution. Compared to D1-containing PSII centers, D1 ' centers exhibited a 50% reduction in variable chlorophyll a fluorescence yield, while the flash-induced O-2 evolution pattern was unaffected. In the F186 mutants, both the P680(+)/Q(A)(-) recombination and O-2 oscillation pattern were noticeably perturbed.

  • 25.
    Gallio, Marco
    et al.
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institutet.
    Kylsten, Per
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institutet.
    Providencia may help find a function for a novel, widespread protein family2000Inngår i: Current Biology, ISSN 0960-9822, E-ISSN 1879-0445, Vol. 10, nr 19, s. R693-R694Artikkel i tidsskrift (Fagfellevurdert)
  • 26. Granlund, Irene
    et al.
    Storm, Patrik
    Schubert, Maria
    Södertörns högskola, Institutionen för livsvetenskaper.
    Garcia-Cerdan, Jose G.
    Funk, Christiane
    Schröder, Wolfgang P.
    The TL29 Protein is Lumen Located, Associated with PSII and Not an Ascorbate Peroxidase2009Inngår i: Plant and Cell Physiology, ISSN 0032-0781, E-ISSN 1471-9053, Vol. 50, nr 11, s. 1898-1910Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The TL29 protein is one of the more abundant proteins in the thylakoid lumen of plant chloroplasts. Based on its sequence homology to ascorbate peroxidases, but without any supporting biochemical evidence, TL29 was suggested to be involved in the plant defense system against reactive oxygen species and consequently renamed to APX4. Our in vivo and in vitro analyses failed to show any peroxidase activity associated with TL29; it bound neither heme nor ascorbate. Recombinant overexpressed TL29 had no ascorbate-dependent peroxidase activity, and various mutational analyses aiming to convert TL29 into an ascorbate peroxidase failed. Furthermore, in the thylakoid lumen no such activity could be associated with TL29 and, additionally, TL29 knock-out mutants did not show any decreased peroxidase activity or increased content of radical oxygen species when grown under light stress. Instead we could show that TL29 is a lumen-located component associated with PSII.

  • 27. Grimm, T
    et al.
    Teglund, Stephan
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institutet.
    Tackels, D
    Sangiorgi, E
    Gurrieri, F
    Schwartz, C
    Toftgard, R
    Genomic organization and embryonic expression of Suppressor of Fused, a candidate gene for the split-hand/split-foot malformation type 32001Inngår i: FEBS Letters, ISSN 0014-5793, E-ISSN 1873-3468, Vol. 505, nr 1, s. 13-17Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The genes for human and mouse Suppressor of Fused (SU(FU)/Su(Fu)) in the Hedgehog signaling pathway were characterized and found to contain 12 exons. Human SU(FU) localized on chromosome 10q24-25 between the markers D10S192 and AFM183XB12. We detected three additional SU(FU) isoforms, two of which have lost their ability to interact with the transcription factor GLI1. Expression analysis using whole mount in situ hybridization revealed strong expression of Su(Fu) in various mouse embryonic tissues. SU(FU) was considered a candidate gene for the split-hand/split-foot malformation type 3 (SHFM3). However, no alterations in the SU(FU) gene were found in SHFM3 patients.

  • 28. Högstrand, K.
    et al.
    Böhme, Jan
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institute.
    DNA damage caused by etoposide and γ-irradiation induces gene conversion of the MHC in a mouse non-germline testis cell line1999Inngår i: Mutation research, ISSN 0027-5107, E-ISSN 1873-135X, Vol. 423, nr 1-2, s. 155-169Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have explored the effects of γ-irradiation and etoposide on the gene conversion frequency between the endogenous major histocompatibility complex class II genes Abk and Ebd in a mouse testis cell line of non-germline origin with a polymerase chain reaction assay. Both γ-rays and etoposide were shown to increase the gene conversion frequency with up to 15-fold compared to untreated cells. Etoposide, which is an agent that stabilise a cleavable complex between DNA and DNA topoisomerase II, shows an increased induction of gene conversion events with increased dose of etoposide. Cells treated with γ-rays, which induce strand breaks, had an increased gene conversion frequency when they were subjected to low doses of irradiation, but increasing doses of irradiation did not lead to an increase of gene conversion events, which might reflect differences in the repair process depending on the extent and nature of the DNA damage. These results where DNA damage was shown to be able to induce gene conversion of endogenous genes in mouse testis cells suggests that the DNA repair system could be involved in the molecular genetic mechanism that results in gene conversion in higher eukaryotes like mammals.

  • 29. Högstrand, K
    et al.
    Böhme, Jan
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institute / Stockholm University.
    Gene conversion of major histocompatibility complex genes in the mouse spermatogenesis is a premeiotic event1997Inngår i: Molecular Biology of the Cell, ISSN 1059-1524, E-ISSN 1939-4586, Vol. 8, nr 12, s. 2511-2517Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The molecular genetic mechanism of gene conversion in higher eukaryotes remains unknown. We find it of considerable interest to determine when during spermatogenesis gene conversion occurs. We have therefore purified pachytene spermatocytes and haploid spermatocytes from adult mice and analyzed these fractions for the presence of gene conversion products resulting from the transfer between the major histocompatibility complex class II genes Ebd and Abk in a polymerase chain reaction assay. We have further isolated spermatogenic cells from prepubescent mice and analyzed them for the presence of the same gene conversion products. We can detect gene conversion products in testis cells as early as in 8-d-old mice where the only existing spermatogenic cells are spermatogonia. The frequency of gene conversion products remains the same as the cells reach meiosis in 18-d-old mice, and is unchanged after meiosis is completed in haploid spermatocytes. Gene conversion of this specific fragment therefore appears to be a premeiotic event and, consequently, relies on genetic mechanisms other than normal meiotic recombination.

  • 30.
    Imreh, Gabriela
    et al.
    Södertörns högskola, Avdelning Naturvetenskap. Stockholm University.
    Hallberg, Einar
    Södertörns högskola, Avdelning Naturvetenskap.
    An integral membrane protein from the nuclear pore complex is also present in the annulate lamellae: Implications for annulate lamella formation2000Inngår i: Experimental Cell Research, ISSN 0014-4827, E-ISSN 1090-2422, Vol. 259, nr 1, s. 180-190Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Annulate lamellae (AL) are cytoplasmic arrays of stacked membrane cisternae containing densely packed pore complexes which are similar in structure to the nuclear pore complexes (NPCs) and thus referred to as annulate lamella pore complexes (ALPCs). We have recently shown that the integral nuclear pore membrane protein POM121 tagged with green fluorescent protein was correctly targeted to the nuclear pores (H. Soderqvist et al., 1997, fur. J. Biochem. 250, 808-813). Here we have investigated if POM121 fused to three tandem molecules of yellow fluorescent protein YFP) (POM121-YFP3,) also was able to distribute in the extensive and well-characterized Al; of RC37 and BMGE cells. Transfected RC37 or BMGE cells displayed YFP fluorescence around the nuclear envelope, as well. as in the cytoplasmic AL structures. The YFP fluorescence colocalized perfectly with immunostaining using antibodies specific for different NPC proteins. The AL of both transfected and untransfected BMGE cells resisted extractions with Tx-100 and 250 mM NaCl, but were completely solubilized at 450 mM NaCl. Loss of YFP fluorescence and immunostaining for other NPC proteins correlated under all extraction conditions tested, suggesting that overexpressed POM121-YFP3, had become an integrated part both of the NPCs and of the ALPCs. Furthermore, we have generated a stable BHK cell line expressing POM121YFP(3,) located exclusively at the nuclear pores. Treatment with vinblastine sulfate, which induces formation of Al; in a variety of cells, resulted in distribution of POM121-YFP3, into cytoplasmic foci colocalizing with immunostaining for peripheral NPC proteins. Taken together, the results show that YFP-tagged POM121 is able to distribute in drug-induced or naturally occurring AL, suggesting that POM121 is a natural constituent of ALPCs. In COS cells, which normally lack or have very little AT-I, YFP-tagged POM121 distributed in the nuclear pores when expressed at low levels. However, at high expression levels the YFP fluorescence also distributed in a number of brightly fluorescing cytoplasmic dots or foci, which were not present in untransfected cells. This was also true for untagged POM121. The cytoplasmic foci varied in size from 0.1 to 2 mu m and were distinctly located in the immediate vicinity of ER cisternae (without colocalizing) and also contained other nuclear pore proteins, indicating that they may represent cytoplasmic AL. This idea is supported by time-lapse studies of postmitotic assembly of these structures. This raises the question of the role of POM121 in ALPC and NPC biogenesis.

  • 31.
    Imreh, Gabriela
    et al.
    Södertörns högskola, Avdelning Naturvetenskap. Stockholm University.
    Maksel, Danuta
    Södertörns högskola, Avdelning Naturvetenskap.
    de Monvel, J B
    Branden, L
    Hallberg, Einar
    Södertörns högskola, Avdelning Naturvetenskap.
    ER retention may play a role in sorting of the nuclear pore membrane protein POM1212003Inngår i: Experimental Cell Research, ISSN 0014-4827, E-ISSN 1090-2422, Vol. 284, nr 2, s. 173-184Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Integral membrane proteins of the nuclear envelope (NE) are synthesized on the rough endoplasmic reticulum (ER) and following free diffusion in the continuous ER/NE membrane system are targeted to their proper destinations due to interactions of specific domains with other components of the NE. By studying the intracellular distribution and dynamics of a deletion mutant of an integral membrane protein of the nuclear pores, POM121, which lacks the pore-targeting domain, we investigated if ER retention plays a role in sorting of integral membrane proteins to the nuclear envelope. A nascent membrane protein lacking sorting determinants is believed to diffuse laterally in the continuous ER/NE lipid bilayer and expected to follow vesicular traffic to the plasma membrane. The GFP-tagged deletion mutant, POM121(1-129)-GFP, specifically distributed within the ER membrane, but was completely absent from the Golgi compartment and the plasma membrane. Experiments using fluorescence recovery after photobleaching (FRAP) and fluorescence loss in photobleaching (FLIP) demonstrated that despite having very high mobility within the whole ER network (D = 0.41 +/- 0.11 mum(2)/s) POM121(1-129)-GFP was unable to exit the ER. It was also not detected in post-ER compartments of cells incubated at 15degreesC. Taken together, these experiments show that amino acids 1-129 of POM121 are able to retain GFP in the ER membrane and suggest that this retention occurs by a direct mechanism rather than by a retrieval mechanism. Our data suggest that ER retention might be important for sorting of POM121 to the nuclear pores.

  • 32.
    Jenvert, Rose-Marie
    Södertörns högskola, Institutionen för livsvetenskaper. Stockholms universitet.
    The ribosome, stringent factor and the bacterial stringent response2007Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The stringent response plays a significant role in the survival of bacteria during different environmental conditions. It is activated by the binding of stringent factor (SF) to stalled ribosomes that have an unacylated tRNA in the ribosomal A-site which leads to the synthesis of (p)ppGpp. ppGpp binds to the RNA polymerase, resulting in a rapid down-regulation of rRNA and tRNA transcription and up-regulation of mRNAs coding for enzymes involved in amino acid biosynthesis. The importance of the A-site and unacylated tRNA in the activation of SF was confirmed by chemical modification and subsequent primer extension experiments (footprinting experiments) which showed that binding of SF to ribosomes resulted in the protection of regions in 23S rRNA, the A-loop and helix 89 that are involved in the binding of the A-site tRNA. An in vitro assay showed that the ribosomal protein L11 and its flexible N-terminal part was important in the activation of SF. Interestingly the N-terminal part of L11 was shown to activate SF on its own and this activation was dependent on both ribosomes and an unacylated tRNA in the A-site. The N-terminal part of L11 was suggested to mediate an interaction between ribosome-bound SF and the unacylated tRNA in the A-site or interact with SF and the unacylated tRNA independently of each other. Footprinting experiments showed that SF bound to the ribosome protected bases in the L11 binding domain of the ribosome that were not involved in an interaction with ribosomal protein L11. The sarcin/ricin loop, in close contact with the L11 binding domain on the ribosome and essential for the binding and activation of translation elongation factors was also found to be protected by the binding of SF. Altogether the presented results suggest that SF binds to the factor-binding stalk of the ribosome and that activation of SF is dependent on the flexible N-terminal domain of L11 and an interaction of SF with the unacylated tRNA in the A-site of the 50S subunit.

  • 33. Jimenez, A
    et al.
    Johansson, C
    Ljung, J
    Sagemark, Johan
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institutet.
    Berndt, Kurt D
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institutet.
    Ren, B
    Tibbelin, G
    Ladenstein, R
    Kieselbach, T
    Holmgren, A
    Gustafsson, J A
    Miranda-Vizuete, A
    Human spermatid-specific thioredoxin-1 (Sptrx-1) is a two-domain protein with oxidizing activity2002Inngår i: FEBS Letters, ISSN 0014-5793, E-ISSN 1873-3468, Vol. 530, nr 1-3, s. 79-84Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spermatid-specific thioredoxin-1 (Sptrx-1) is the first member of the thioredoxin family of proteins with a tissue-specific expression pattern, found exclusively in the tail of elongating spermatids and spermatozoa. We describe here further biochemical characterization of human Sptrx-1 protein structure and enzymatic activity. In gel filtration chromatography human Sptrx-1 eluates as a 400 kDa protein consistent with either an oligomeric form, not maintained by intermolecular disulfide bonding, and/or a highly asymmetrical structure. Analysis of circular dichroism spectra of fragments 1-360 and 361-469 and comparison to spectra of full-length Sptrx-1 supports a two-domain organization with a largely unstructured N-terminal domain and a folded thioredoxin-like C-terminal domain. Functionally, Sptrx-1 behaves as an oxidant in vitro when using selenite, but not oxidized glutathione, as electron acceptor. This oxidizing enzymatic activity suggests that Sptrx-1 might govern the stabilization (by disulfide cross-linking) of the different structures in the developing tail of spermatids and spermatozoa.

  • 34.
    Johnsson, Anna
    et al.
    Södertörns högskola, Institutionen för livsvetenskaper, Molekylärbiologi. Karolinska Institutet.
    Durand-Dubief, Mickael
    Karolinska Intitutet.
    Xue-Franzen, Yongtao
    Södertörns högskola, Institutionen för livsvetenskaper, Molekylärbiologi. Karolinska Institutet.
    Rönnerblad, Michelle
    Karolinska Institutet.
    Ekwall, Karl
    Södertörns högskola, Institutionen för livsvetenskaper, Molekylärbiologi. Karolinska Institutet.
    Wright, Anthony P. H.
    Södertörns högskola, Institutionen för livsvetenskaper, Molekylärbiologi. Karolinska Institutet.
    HAT-HDAC interplay modulates global histone H3K14 acetylation in gene-coding regions during stress2009Inngår i: EMBO Reports, ISSN 1469-221X, E-ISSN 1469-3178, Vol. 10, nr 9, s. 1009-1014Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Histone acetylation and deacetylation are important for gene regulation. The histone acetyltransferase, Gcn5, is an activator of transcriptional initiation that is recruited to gene promoters. Here, we map genome-wide Gcn5 occupancy and histone H3K14ac at high resolution. Gcn5 is predominantly localized to coding regions of highly transcribed genes, where it collaborates antagonistically with the class-II histone deacetylase, Clr3, to modulate H3K14ac levels and transcriptional elongation. An interplay between Gcn5 and Clr3 is crucial for the regulation of many stress-response genes. Our findings suggest a new role for Gcn5 during transcriptional elongation, in addition to its known role in transcriptional initiation.

  • 35.
    Johnsson, Anna E.
    et al.
    Södertörns högskola, Institutionen för livsvetenskaper, Molekylärbiologi.
    Wright, Anthony P. H.
    Södertörns högskola, Institutionen för livsvetenskaper, Molekylärbiologi.
    The role of specific HAT-HDAC interactions in transcriptional elongation2010Inngår i: Cell Cycle, ISSN 1538-4101, E-ISSN 1551-4005, Vol. 9, nr 3, s. 467-471Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We previously reported genome-wide evidence that the Gcn5 histone cetyltransferase (HAT) is located in the transcribed region of highly xpressed genes and that it plays an important role in transcriptional longation in the fission yeast, Schizosaccharomyces pombe (EMBO Reports 009; 10: 1009-14). Furthermore, the specific interplay between Gcn5 and he Clr3 histone deacetylase (HDAC) controls the acetylation levels of ysine-14 in histone H3 in the same class of highly expressed genes. utants of histone H3 that cannot be acetylated at residue 14 show imilar stress phenotypes to those observed for mutants lacking Gcn5. In his Extra View article we review these findings in relation to related iterature and extend important aspects of the original study. Notably, cn5 and Gcn5-dependent acetylation of histone H3K14 tend to be more nriched in the upstream regions of genes that require Gcn5 for correct xpression compared to genes that are independent of Gcn5. This suggests critical role of Gcn5 in the transcriptional initiation of these enes. Gcn5 is however most highly enriched in the transcribed regions f these gene sets but there is no difference between Gcn5-dependent and cn5-independent gene sets. Thus we suggest that Gcn5 plays an important ut redundant role in the transcriptional elongation of these genes. The ir2 HDAC has a similar genomic localization and enzymatic activity to lr3. We studied gcn5 Delta sir2 Delta double mutants that do not show a uppressed phenotype in relation to gcn5 Delta single mutants, compared o gcn5 Delta clr3 Delta mutants that do, in order to better understand he specificity of the interplay between Gcn5 and Clr3. In some classes f non-highly expressed genes the clr3 Delta mutant tends to restore evels of histone H3K14 acetylation in the double mutant strain more ffectively than sir2 Delta.

  • 36.
    Kieselbach, T
    et al.
    Karolinska Institutet.
    Bystedt, Maria
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institutet.
    Hynds, P
    University of Warwick, UK.
    Robinson, C
    University of Warwick, UK.
    Schröder, Wolfgang P
    Södertörns högskola, Avdelning Naturvetenskap.
    A peroxidase homologue and novel plastocyanin located by proteomics to the Arabidopsis chloroplast thylakoid lumen2000Inngår i: FEBS Letters, ISSN 0014-5793, E-ISSN 1873-3468, Vol. 480, nr 2-3, s. 271-276Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A study by two-dimensional electrophoresis showed that the soluble, lumenal fraction of Arabidopsis thaliana thylakoids can be resolved into 300 protein spots. After subtraction of low-intensity spots and accounting for low-level stromal contamination, the number of more abundant, lumenal proteins was estimated to be between 30 and 60. Two of these proteins have been identified: a novel plastocyanin that also was the predominant component of the total plastocyanin pool, and a putative ascorbate peroxidase. Import studies shamed that these proteins are routed to the thylakoid lumen by the Sec- and delta pH-dependent translocation pathways, respectively, In addition, novel isoforms of PsbO and PsbQ were identified.

  • 37.
    Kihlmark, Madeleine
    et al.
    Södertörns högskola, Avdelning Naturvetenskap.
    Imreh, Gabriela
    Södertörns högskola, Avdelning Naturvetenskap.
    Hallberg, Einar
    Södertörns högskola, Avdelning Naturvetenskap.
    Sequential degradation of proteins from the nuclear envelope during apoptosis2001Inngår i: Journal of Cell Science, ISSN 0021-9533, E-ISSN 1477-9137, Vol. 114, nr 20, s. 3643-3653Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have produced new antibodies specific for the integral pore membrane protein POM121. Using these antibodies we show that during apoptosis POM121 becomes proteolytically degraded in a caspase-dependent manner. The POM121 antibodies and antibodies specific for other proteins of the nuclear envelope were used in a comparative study of nuclear apoptosis in staurosporine-treated buffalo rat liver cells. Nuclei from these cells were classified in three different stages of apoptotic progression: stage I, moderately condensed chromatin surrounded by a smooth nuclear periphery; stage II, compact patches of condensed chromatin collapsing against a smooth nuclear periphery; stage III, round compact chromatin bodies surrounded by grape-shaped nuclear periphery. We have performed double labeling immunofluorescence microscopy of individual apoptotic cells and quantitative immunoblotting analysis of total proteins from apoptotic cell cultures. The results showed that degradation of nuclear envelope marker proteins occurred in a specific order. POM121 degradation occurred surprisingly early and was initiated before nucleosomal DNA degradation could be detected using TUNEL assay and completed before clustering of the nuclear pores. POM121 was eliminated significantly more rapid compared with NUP153 (a peripheral protein located in the nucleoplasmic basket of the nuclear pore complex) and lamin B (a component of the nuclear lamina). Disappearance of NUP153 and lamin B was coincident with onset of DNA fragmentation and clustering of nuclear pores. By contrast, the peripheral NPC protein p62 was degraded much later. The results suggest that degradation of POM121 may be an important early step in propagation of nuclear apoptosis.

  • 38.
    Kihlmark, Madeleine
    et al.
    Södertörns högskola, Institutionen för kemi, biologi, geografi och miljövetenskap. Stockholm University.
    Rustum, Cecilia
    Södertörns högskola, Institutionen för kemi, biologi, geografi och miljövetenskap. Stockholm University.
    Eriksson, Charlotta
    Södertörns högskola, Institutionen för kemi, biologi, geografi och miljövetenskap. Karolinska Institutet.
    Beckman, M
    Stockholm University.
    Iverfeldt, K
    Stockholm University.
    Hallberg, Einar
    Södertörns högskola, Institutionen för kemi, biologi, geografi och miljövetenskap.
    Correlation between nucleocytoplasmic transport and caspase-3-dependent dismantling of nuclear pores during apoptosis2004Inngår i: Experimental Cell Research, ISSN 0014-4827, E-ISSN 1090-2422, Vol. 293, nr 2, s. 346-356Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During apoptosis (also called programmed cell death), the chromatin condenses and the DNA is cleaved into oligonucleosomal fragments. Caspases are believed to play a major role in nuclear apoptosis. However, the relation between dismantling of nuclear pores, disruption of the nucleocytoplasmic barrier, and nuclear entry of caspases is unclear. We have analyzed nuclear import of the green fluorescent protein fused to a nuclear localization signal (GFP-NLS) in tissue culture cells undergoing apoptosis. Decreased nuclear accumulation of GFP-NLS could be detected at the onset of nuclear apoptosis manifested as dramatic condensation and redistribution of chromatin toward the nuclear periphery. At this step, dismantling of nuclear pores was already evident as indicated by proteolysis of the nuclear pore membrane protein POM121. Thus, disruption of nuclear compartmentalization correlated with early signs of nuclear pore damage. Both these events clearly preceded massive DNA fragmentation, detected by TUNEL assay. Furthermore, we show that in apoptotic cells, POM121 is specifically cleaved at aspartate-531 in its large C-terminal portion by a caspase-3-dependent mechanism. Cleavage of the C-terminal portion of POM121, which is adjoining the nuclear pore complex, is likely to disrupt interactions with other nuclear pore proteins affecting the stability of the pore complex. A temporal correlation of apoptotic events supports a model where caspase-dependent disassembly of nuclear pores and disruption of the nucleocytoplasmic barrier paves the way for nuclear entry of caspases and subsequent activation of CAD-mediated DNA fragmentation.

  • 39.
    Kniola, Barbara
    et al.
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institutet.
    O'Toole, E
    McIntosh, J R
    Mellone, B
    Allshire, R
    Mengarelli, S
    Hultenby, K
    Ekwall, Karl
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institutet.
    The domain structure of centromeres is conserved from fission yeast to humans2001Inngår i: Molecular Biology of the Cell, ISSN 1059-1524, E-ISSN 1939-4586, Vol. 12, nr 9, s. 2767-2775Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The centromeric DNA of fission yeast is arranged with a central core flanked by repeated sequences. The centromere-associated proteins, Mis6p and Cnp1p (SpCENP-A), associate exclusively with central core DNA, whereas the Swi6 protein binds the surrounding repeats. Here, electron microscopy and immunofluorescence light microscopy reveal that the central core and flanking regions occupy distinct positions within a heterochromatic domain. An "anchor" structure containing the Ndc80 protein resides between this heterochromatic domain and the spindle pole body. The organization of centromere-associated proteins in fission yeast is reminiscent of the multilayered structures of human kinetochores, indicating that such domain structure is conserved in eukaryotes.

  • 40.
    Koroxenidou, Lena
    et al.
    Södertörns högskola, Institutionen för livsvetenskaper.
    Ohlson, Lena C. E.
    Södertörns högskola, Institutionen för livsvetenskaper.
    Porsch Hällström, Inger
    Södertörns högskola, Institutionen för livsvetenskaper.
    Long-term 17 alpha-ethinyl estradiol treatment decreases cyclin E and cdk2 expression, reduces cdk2 kinase activity and inhibits S phase entry in regenerating rat liver2005Inngår i: Journal of Hepatology, ISSN 0168-8278, E-ISSN 1600-0641, Vol. 43, nr 3, s. 478-484Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background/Aims: The synthetic estrogen 17 alpha-ethinyl estradiol (EE), a potent tumor promoter in rat liver, stimulates growth during short-term treatment but inhibits hepatocyte proliferation upon prolonged treatment. To identify the molecular targets of the mitoinhibitory effect of EE, the expression of proteins regulating G(1)- and S-progression were analyzed during the first cell cycle in EE-treated female Wistar rats. Methods: Long-term (60 days) EE treatment. Immunohistochemical staining for proliferation cell nuclear antigen (PCNA) to detect cells in S phase and quantification of mitosis. Western blot to monitor protein expression. Cdk2 kinase assay to examine histone H1 phosphorylation. Results: EE reduced the number of cells in S phase and mitosis by about 70%. Cyclin D-1 and D-3 were unaffected, while cdk4 was moderately decreased. Cyclin E and cdk2 were markedly decreased with concomitant marked reduction of cdk2 kinase activity. EE also decreased cyclin A and increased G(1) levels of p53 and p21. Conclusions: EE causes a cell cycle block before S-phase. The reduction of the cdk2 kinase activity, essential for G(1)/S-transition, might be involved in the cell cycle block. Also, EE treatment results in p53 activation and upregulation of the cdk inhibitor p21 that might contribute to the G(1) arrest.

  • 41. Lejeune, Erwan
    et al.
    Bortfeld, Miriam
    White, Sharon A.
    Pidoux, Alison L.
    Ekwall, Karl
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Institute.
    Allshire, Robin C.
    Ladurner, Andreas G.
    The chromatin-remodeling factor FACT contributes to centromeric heterochromatin independently of RNAi2007Inngår i: Current Biology, ISSN 0960-9822, E-ISSN 1879-0445, Vol. 17, nr 14, s. 1219-1224Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Centromeres exert vital cellular functions in mitosis and meiosis. A specialized histone and other chromatin-bound factors nucleate a dynamic protein assembly that is required for the proper segregation of sister chromatids. In several organisms, including the fission yeast, Schizosaccharomyces pombe, the RNAi pathway contributes to the formation of silent chromatin in pericentromeric regions. Little is known about how chromatin-remodeling factors contribute to heterochromatic integrity and centromere function. Here we show that the histone chaperone and remodeling complex FACT is required for centromeric-heterochromatin integrity and accurate chromosome segregation. We show that Spt16 and Pob3 are two subunits of the S. pombe FACT complex. Surprisingly, yeast strains deleted for pob3+ are viable and alleviate gene silencing at centromeric repeats and at the silent mating-type locus. Importantly, like heterochromatin and RNAi pathway mutants, Pob3 null strains exhibit lagging chromosomes on anaphase spindles. Whereas the processing of centromeric RNA transcripts into siRNAs is maintained in Pob3 mutants, Swi6-association with the centromere is reduced. Our studies provide the first experimental evidence for a role of the RNA polymerase II cofactor FACT in heterochromatin integrity and in centromere function.

  • 42. Lundholm, L
    et al.
    Bryzgalova, G
    Gao, H
    Portwood, N
    Fält, S
    Berndt, Kurt D
    Karolinska Institutet.
    Dicker, A
    Galuska, D
    Zierath, J R
    Gustafsson, J Å
    Efendic, S
    Dahlman-Wright, K
    Khan, A
    The estrogen receptor {alpha}-selective agonist propyl pyrazole triol improves glucose tolerance in ob/ob mice; potential molecular mechanisms2008Inngår i: Journal of Endocrinology, ISSN 0022-0795, E-ISSN 1479-6805, Vol. 199, nr 2, s. 275-286Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of this study was to validate the role of estrogen receptor alpha (ERalpha) signaling in the regulation of glucose metabolism, and to compare the molecular events upon treatment with the ERalpha-selective agonist propyl pyrazole triol (PPT) or 17beta-estradiol (E(2)) in ob/ob mice. Female ob/ob mice were treated with PPT, E(2) or vehicle for 7 or 30 days. Intraperitoneal glucose and insulin tolerance tests were performed, and insulin secretion was determined from isolated islets. Glucose uptake was assayed in isolated skeletal muscle and adipocytes. Gene expression profiling in the liver was performed using Affymetrix microarrays, and the expression of selected genes was studied by real-time PCR analysis. PPT and E(2) treatment improved glucose tolerance and insulin sensitivity. Fasting blood glucose levels decreased after 30 days of PPT and E(2) treatment. However, PPT and E(2) had no effect on insulin secretion from isolated islets. Basal and insulin-stimulated glucose uptake in skeletal muscle and adipose tissue were similar in PPT and vehicle-treated ob/ob mice. Hepatic lipid content was decreased after E(2) treatment. In the liver, treatment with E(2) and PPT increased and decreased the respective expression levels of the transcription factor signal transducer and activator of transcription 3, and of glucose-6-phosphatase. In summary, our data demonstrate that PPT exerts anti-diabetic effects, and these effects are mediated via ERalpha.

  • 43. Lundström, A
    et al.
    Gallio, Marco
    Södertörns högskola, Institutionen för kemi, biologi, geografi och miljövetenskap.
    Englund, C
    Steneberg, P
    Hemphälä, J
    Aspenström, P
    Keleman, K
    Falileeva, L
    Dickson, B J
    Samakovlis, C
    Vilse, a conserved Rac/Cdc42 GAP mediating Robo repulsion in tracheal cells and axons2004Inngår i: Genes & Development, ISSN 0890-9369, E-ISSN 1549-5477, Vol. 18, nr 17, s. 2161-2171Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Slit proteins steer the migration of many cell types through their binding to Robo receptors, but how Robo controls cell motility is not clear. We describe the functional analysis of vilse, a Drosophila gene required for Robo repulsion in epithelial cells and axons. Vilse defines a conserved family of RhoGAPs (Rho GTPase-activating proteins), with representatives in flies and vertebrates. The phenotypes of vilse mutants resemble the tracheal and axonal phenotypes of Slit and Robo mutants at the CNS midline. Dosage-sensitive genetic interactions between vilse, slit, and robo mutants suggest that vilse is a component of robo signaling. Moreover, overexpression of Vilse in the trachea of robo mutants ameliorates the phenotypes of robo, indicating that Vilse acts downstream of Robo to mediate midline repulsion. Vilse and its human homolog bind directly to the intracellular domains of the corresponding Robo receptors and promote the hydrolysis of RacGTP and, less efficiently, of Cdc42GTP. These results together with genetic interaction experiments with robo, vilse, and rac mutants suggest a mechanism whereby Robo repulsion is mediated by the localized inactivation of Rac through Vilse.

  • 44.
    Miranda-Vizuete, A
    et al.
    Karolinska Institute.
    Spyrou, Giannis
    Södertörns högskola, Avdelning Naturvetenskap. Karolinska Institute.
    Genomic organization and identification of a novel alternative splicing variant of mouse mitochondrial thioredoxin reductase (TrxR2) gene2002Inngår i: Molecules and Cells, ISSN 1016-8478, E-ISSN 0219-1032, Vol. 13, nr 3, s. 488-492Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Eukaryotic mitochondria are equipped with a complete thioredoxin system, composed of thioredoxin and thioredoxin reductase, which has been implicated in the protection against the reactive oxygen intermediates generated during the respiratory process in this organelle. Like its cytosolic counterpart, mammalian mitochondrial thioredoxin reductase is a homodimeric selenoprotein. We report here the genomic organization of the mouse mitochondrial thioredoxin gene (TrxR2) that spans 53 kb and consists of 18 exons ranging from 20 to 210 bp. All splicing sites conformed to the GT/AG rule with the exon-intron boundaries located exactly at the same position as the human TrxR2 gene, the only mammalian mitochondrial thioredoxin reductase gene whose genomic structure has been elucidated to date. In addition, we have identified a novel mRNA splicing variant lacking intron 14 resulting in a protein subunit with a shorter interface domain This new splicing variant provides a frame work for further analysis of this important enzyme as its predicted homodimeric conformation can now be expanded to a putative heterodimeric structure as well as a small subunit homodimer with the obvious implications at the regulatory level.

  • 45.
    Miranda-Vizuete, Antonio
    et al.
    Södertörns högskola, Institutionen för livsvetenskaper.
    Fierro Gonzalez, Juan Carlos
    Södertörns högskola, Institutionen för livsvetenskaper.
    Gahmon, Gabriele
    Burghoorn, Jan
    Södertörns högskola, Institutionen för livsvetenskaper.
    Navas, Plácido
    Swoboda, Peter
    Södertörns högskola, Institutionen för livsvetenskaper.
    Lifespan decrease in a Caenorhabditis elegans mutant lacking TRX-1, a thioredoxin expressed in ASJ sensory neurons2006Inngår i: FEBS Letters, ISSN 0014-5793, E-ISSN 1873-3468, Vol. 580, nr 2, s. 484-490Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Thioredoxins are a class of small proteins that play a key role in regulating many cellular redox processes. We report here the characterization of the first member of the thioredoxin family in metazoans that is mainly associated with neurons. The Caenorhabditis elegans gene B0228.5 encodes a thioredoxin (TRX-1) that is expressed in ASJ ciliated sensory neurons, and to some extent also in the posterior-most intestinal cells. TRX-1 is active at reducing protein disulfides in the presence of a heterologous thioredoxin reductase. A mutant worm strain carrying a null allele of the trx-1 gene displays a reproducible decrease in both mean and maximum lifespan when compared to wild-type. The identification and characterization of TRX-1 paves the way to use C elegans as an in vivo model to study the role of thioredoxins in lifespan and nervous system physiology and pathology.

  • 46. Muhlenbock, Per
    et al.
    Szechynska-Hebda, Magdalena
    Plaszczyca, Marian
    Baudo, Marcela
    Mullineaux, Philip M.
    Parker, Jane E.
    Karpinska, Barbara
    Södertörns högskola, Institutionen för livsvetenskaper, Biologi. Södertörns högskola, Institutionen för livsvetenskaper, Molekylärbiologi.
    Karpinski, Stanislaw
    Chloroplast Signaling and LESION SIMULATING DISEASE1 Regulate Crosstalk between Light Acclimation and Immunity in Arabidopsis2008Inngår i: The Plant Cell, ISSN 1040-4651, E-ISSN 1532-298X, Vol. 20, nr 9, s. 2339-2356Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Plants are simultaneously exposed to abiotic and biotic hazards. Here, we show that local and systemic acclimation in Arabidopsis thaliana leaves in response to excess excitation energy (EEE) is associated with cell death and is regulated by specific redox changes of the plastoquinone (PQ) pool. These redox changes cause a rapid decrease of stomatal conductance, global induction of ASCORBATE PEROXIDASE2 and PATHOGEN RESISTANCE1, and increased production of reactive oxygen species (ROS) and ethylene that signals through ETHYLENE INSENSITIVE2 (EIN2). We provide evidence that multiple hormonal/ROS signaling pathways regulate the plant's response to EEE and that EEE stimulates systemic acquired resistance and basal defenses to virulent biotrophic bacteria. In the Arabidopsis LESION SIMULATING DISEASE1 (lsd1) null mutant that is deregulated for EEE acclimation responses, propagation of EEE-induced programmed cell death depends on the plant defense regulators ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1) and PHYTOALEXIN DEFICIENT4 (PAD4). We find that EDS1 and PAD4 operate upstream of ethylene and ROS production in the EEE response. The data suggest that the balanced activities of LSD1, EDS1, PAD4, and EIN2 regulate signaling of programmed cell death, light acclimation, and holistic defense responses that are initiated, at least in part, by redox changes of the PQ pool.

  • 47.
    Olsson, Ida
    et al.
    Södertörns högskola, Institutionen för livsvetenskaper.
    Berrez, Jean-Marc
    Södertörns högskola, Institutionen för livsvetenskaper.
    Leipus, Arunas
    CHORI, Children's Hospital Oakland Research Institute, Oakland, USA / Umeå University.
    Östlund, Cecilia
    Columbia University, New York, USA.
    Mutvei, Ann
    Södertörns högskola, Institutionen för livsvetenskaper.
    The arginine methyltransferase Rmt2 is enriched in the nucleus and co-purifies with the nuclear porins Nup49, Nup57 and Nup1002007Inngår i: Experimental Cell Research, ISSN 0014-4827, E-ISSN 1090-2422, Vol. 313, nr 9, s. 1778-1789Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Arginine methylation is a post-translational modification of proteins implicated in RNA processing, protein compartmentalization, signal transduction, transcriptional regulation and DNA repair. In a screen for proteins associated with the nuclear envelope in the yeast Saccharomyces cerevisiae, we have identified the arginine methyltransferase Rmt2, previously shown to methylate the ribosomal protein L12. By indirect immunofluorescence and subcellular fractionations we demonstrate here that Rmt2 has nuclear and cytoplasmic localizations. Biochemical analysis of a fraction enriched in nuclei reveals that nuclear Rmt2 is resistant to extractions with salt and detergent, indicating an association with structural components. This was supported by affinity purification experiments with TAP-tagged Rmt2. Rmt2 was found to co-purify with the nucleoporins Nup49, Nup57 and Nup100, revealing a novel link between arginine methyltransferases and the nuclear pore complex. In addition, a genome-wide transcription study of the rmt2 Delta mutant shows significant downregulation of the transcription of MYO1, encoding the Type II myosin heavy chain required for cytokinesis and cell separation.

  • 48.
    Onischenko, Evgeny A.
    et al.
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Institute.
    Crafoord, Ellinor
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Institute.
    Hallberg, Einar
    Södertörns högskola, Institutionen för livsvetenskaper.
    Phosphomimetic mutation of the mitotically phosphorylated serine 1880 compromises the interaction of the transmembrane nucleoporin gp210 with the nuclear pore complex2007Inngår i: Experimental Cell Research, ISSN 0014-4827, E-ISSN 1090-2422, Vol. 313, nr 12, s. 2744-2751Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The nuclear pore complexes (NPCs) reversibly disassemble and reassemble during mitosis. Disassembly of the NPC is accompanied by phosphorylation of many nucleoporins although the function of this is not clear. It was previously shown that in the transmembrane nucleoporin gp210 a single serine residue at position 1880 is specifically phosphorylated during mitosis. Using amino acid substitution combined with live cell imaging, time-lapse microscopy and FRAP, we investigated the role of serine 1880 in binding of gp210 to the NPC in vivo An alanine subtitutions mutant (S1880A) was significantly more dynamic at the NPC compared to the wild-type protein, suggesting that serine 1880 is important for binding of gp210 to the NPC. Moreover a glutamate substitution (S1880E) closely mimicking phosphorylated serine specifically interfered with incorporation of gp210 into the NPC and compromised its post-mitotic recruitment to the nuclear envelope of daughter nuclei. our findings are consistent with the idea that mitotic phosphorylation acts to dissociate gp210 from the structural elements of the NPC.

  • 49.
    Onischenko, Evgeny A
    et al.
    Södertörns högskola, Institutionen för kemi, biologi, geografi och miljövetenskap. Karolinska Institute.
    Gubanova, N V
    Institute of Cytology and Genetics, Novosibirsk, Russia.
    Kieselbach, T
    Karolinska Institute.
    Kiseleva, E V
    Institute of Cytology and Genetics, Novosibirsk, Russia.
    Hallberg, Einar
    Södertörns högskola, Institutionen för kemi, biologi, geografi och miljövetenskap.
    Annulate lamellae play only a minor role in the storage of excess nucleoporins in Drosophila embryos2004Inngår i: Traffic: the International Journal of Intracellular Transport, ISSN 1398-9219, E-ISSN 1600-0854, Vol. 5, nr 3, s. 152-164Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The nuclear pore complexes (NPCs), multiprotein assemblies embedded in the nuclear envelope, conduct nucleo-cytoplasmic traffic of macromolecules. Mimics of NPCs, called annulate lamellae pore complexes (ALPCs), are usually found in cytoplasmic membranous stacks in oocytes and early embryonic cells. They are believed to constitute storage compartments for excess premade nucleoporins. To evaluate the extent to which ALPCs store nucleoporins in early embryonic cells we took advantage of syncytial Drosophila embryos, containing both AL and rapidly proliferating nuclei in the common cytoplasm. Electron microscopic morphometric analysis showed that the number of ALPCs did not decrease to compensate for the growing number of NPCs during syncytial development. We performed Western blot analysis to quantify seven different nucleoporins and analyzed their intraembryonal distribution by confocal microscopy and subcellular fractionation. Syncytial embryos contained a large maternally contributed stockpile of nucleoporins. However, even during interphases, only a small fraction of the excess nucleoporins was assembled into ALPCs, whereas the major fraction was soluble and contained at least one phosphorylated nucleoporin. We conclude that in Drosophila embryos ALPCs play only a minor role in storing the excess maternally contributed nucleoporins. Factors that may prevent nucleoporins from assembly into ALPCs are discussed.

  • 50.
    Onischenko, Evgeny A
    et al.
    Södertörns högskola, Institutionen för livsvetenskaper. Karolinska Institutet.
    Gubanova, N V
    Institute of Cytology and Genetics, Novosibirsk, Russia.
    Kiseleva, E V
    Institute of Cytology and Genetics, Novosibirsk, Russia.
    Hallberg, Einar
    Södertörns högskola, Institutionen för livsvetenskaper.
    Cdk1 and okadaic acid-sensitive phosphatases control assembly of nuclear pore complexes in Drosophila embryos2005Inngår i: Molecular Biology of the Cell, ISSN 1059-1524, E-ISSN 1939-4586, Vol. 16, nr 11, s. 5152-5162Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Disassembly and reassembly of the nuclear pore complexes (NPCs) is one of the major events during open mitosis in higher eukaryotes. However, how this process is controlled by the mitotic machinery is not clear. To investigate this we developed a novel in vivo model system based on syncytial Drosophila embryos. We microinjected different mitotic effectors into the embryonic cytoplasm and monitored the dynamics of disassembly/reassembly of NPCs in live embryos using fluorescently labeled wheat germ agglutinin (WGA) or in fixed embryos using electron microscopy and immunostaining techniques. We found that in live embryos Cdk1 activity was necessary and sufficient to induce disassembly of NPCs as well as their cytoplasmic mimics: annulate lamellae pore complexes (ALPCs). Cdk1 activity was also required for keeping NPCs and ALPCs disassembled during mitosis. In Agreement recombinant Cdk1/cyclin B was able to induce phosphorylation and dissociation of nucleoporins from the NPCs in vitro. Conversely, reassembly of NPCs and ALPCs was dependent on the activity of protein phosphatases, sensitive to okadaic acid (OA). Our findings suggest a model where mitotic disassembly/reassembly of the NPCs is regulated by a dynamic equilibrium of Cdk1 and OA-sensitive phosphatase activities and provide evidence that mitotic phosphorylation mediates disassembly of the NPC.

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