The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Masayuki Yamamoto - One of the best experts on this subject based on the ideXlab platform.
-
spindle pole body components are reorganized during fission yeast meiosis
Molecular Biology of the Cell, 2012Co-Authors: Midori Ohta, Masamitsu Sato, Masayuki YamamotoAbstract:c Kazusa DNA Research Institute, 2-6-7 Kazusa-kamatari, Kisarazu, Chiba 292-0818, Japan ABSTRACT During meiosis, the centrosome/spindle pole body (SPB) must be regulated in a manner distinct from that of mitosis to achieve a specialized cell division that will produce gametes. In this paper, we demonstrate that several SPB components are localized to SPBs in a meiosis-specific manner in the fission yeast Schizosaccharomyces pombe. SPB compo- nents, such as Cut12, Pcp1, and Spo15, which stay on the SPB during the mitotic cell cycle, disassociate from the SPB during meiotic prophase and then return to the SPB immediately before the onset of meiosis I. Interestingly, the polo kinase Plo1, which normally localizes to the SPB during mitosis, is excluded from them in meiotic prophase, when meiosis-specific, horse-tail nuclear movement occurs. We found that exclusion of Plo1 during this period was essential to properly remodel SPBs, because artificial targeting of Plo1 to SPBs resulted in an overduplication of SPBs. We also found that the centrin Cdc31 was required for meiotic SPB remodeling. Thus Plo1 and a centrin play central roles in the meiotic SPB remodeling, which is essential for generating the proper number of meiotic SPBs and, thereby provide unique characteristics to meiotic divisions.
-
Spindle pole body components are reorganized during fission yeast meiosis
Molecular Biology of the Cell, 2012Co-Authors: Midori Ohta, Masamitsu Sato, Masayuki YamamotoAbstract:During meiosis, the centrosome/spindle pole body (SPB) must be regulated in a manner distinct from that of mitosis to achieve a specialized cell division that will produce gametes. In this paper, we demonstrate that several SPB components are localized to SPBs in a meiosis-specific manner in the fission yeast Schizosaccharomyces pombe. SPB components, such as Cut12, Pcp1, and Spo15, which stay on the SPB during the mitotic cell cycle, disassociate from the SPB during meiotic prophase and then return to the SPB immediately before the onset of meiosis I. Interestingly, the polo kinase Plo1, which normally localizes to the SPB during mitosis, is excluded from them in meiotic prophase, when meiosis-specific, horse-tail nuclear movement occurs. We found that exclusion of Plo1 during this period was essential to properly remodel SPBs, because artificial targeting of Plo1 to SPBs resulted in an overduplication of SPBs. We also found that the centrin Cdc31 was required for meiotic SPB remodeling. Thus Plo1 and a centrin play central roles in the meiotic SPB remodeling, which is essential for generating the proper number of meiotic SPBs and, thereby provide unique characteristics to meiotic divisions.
-
Protein phosphatase 4 is required for centrosome maturation in mitosis and sperm meiosis in C. elegans.
Journal of cell science, 2002Co-Authors: Eisuke Sumiyoshi, Asako Sugimoto, Masayuki YamamotoAbstract:The centrosome consists of two centrioles surrounded by the pericentriolar material (PCM). In late G2 phase, centrosomes enlarge by recruiting extra PCM, and concomitantly its microtubule nucleation activity increases dramatically. The regulatory mechanisms of this dynamic change of centrosomes are not well understood. Protein phosphatase 4 (PP4) is known to localize to mitotic centrosomes in mammals and Drosophila. An involvement of PP4 in the mitotic spindle assembly has been implicated in Drosophila, but in vivo functions of PP4 in other organisms are largely unknown. Here we characterize two Caenorhabditis elegans PP4 genes, named pph-4.1 and pph-4.2. Inhibition of the function of each gene by RNA-mediated interference (RNAi) revealed that PPH-4.1 was essential for embryogenesis but PPH-4.2 was not. More specifically, PPH-4.1 was required for the formation of spindles in mitosis and sperm meiosis. However, this phosphatase was apparently dispensable for female meiotic divisions, which do not depend on centrosomes. In the cell depleted of pph-4.1 activity, localization of gamma-tubulin and a Polo-like kinase homologue to the centrosome was severely disturbed. Immunofluorescence staining revealed that PPH-4.1 was present at centrosomes from prophase to telophase, but not during interphase. These results indicate that PPH-4.1 is a centrosomal protein involved in the recruitment of PCM components to the centrosome, and is essential for the activation of microtubule nucleation potential of the centrosome. Furthermore, chiasmata between homologous chromosomes were often absent in oocytes that lacked pph-4.1 activity. Thus, besides promoting spindle formation, PPH-4.1 appears to play a role in either the establishment or the maintenance of chiasmata during meiotic prophase I.
-
A protein phosphatase 4 homologue, PPH-4.1, is essential for centrosome maturation in mitosis and sperm meiosis in C. elegans
West Coast Worm Meeting, 2002Co-Authors: Eisuke Sumiyoshi, Asako Sugimoto, Fumio Motegi, Masayuki YamamotoAbstract:The centrosome is the primary microtubule organizing center in eukaryotic cells. Centrosomes mature during the G2/M transition, accumulating the pericentriolar materials (PCM) that direct the assembly of microtubules. The regulation of this dynamic change of centrosomes remains largely unknown. Protein phosphatase 4 is known to localize to mitotic centrosomes in mammals and Drosophila, but its in vivo functions are not well understood. Here, we report that one of the two C. elegans protein phosphatase 4 homologues, PPH-4.1, is required for centrosome maturation. RNAi analysis revealed that PPH-4.1 was required for the formation of spindles in mitosis and sperm meiosis, while it was dispensable for female meiotic divisions, which do not depend on centrosomes. In mitotic pph-4.1(RNAi) embryos, localization of gamma-tubulin and a Polo-like kinase homologue to the centrosome was severely disrupted. Immunofluorescence staining revealed that PPH-4.1 was present at centrosomes from prophase to telophase, but not during interphase. Depolymerization of astral microtubules by nocodazole or cold treatment did not affect the centrosomal localization of PPH-4.1, suggesting that localization of PPH-4.1 to centrosomes is not dependent on microtubules. These results indicate that PPH-4.1 is involved in the recruitment of PCM components to the centrosome, and is essential for the activation of microtubule nucleation potential of the centrosome. We are currently examining the mechanisms of cell cycle-dependent localization of PPH-4.1 on centrosomes. Besides the centrosomal phenotypes, absence of chiasmata between homologous chromosomes was often observed in oocytes of pph-4.1(RNAi) animals. Thus, in addition to spindle formation, PPH-4.1 appears to play a role in either the establishment or the maintenance of chiasmata during meiotic prophase I.
Kim Nasmyth - One of the best experts on this subject based on the ideXlab platform.
-
Condensin confers the longitudinal rigidity of chromosomes
Nature Cell Biology, 2015Co-Authors: Martin Houlard, Jonathan Godwin, Jean Metson, Tatsuya Hirano, Kim NasmythAbstract:In addition to inter-chromatid cohesion, mitotic and meiotic chromatids must have three physical properties: compaction into ‘threads’ roughly co-linear with their DNA sequence, intra-chromatid cohesion determining their rigidity, and a mechanism to promote sister chromatid disentanglement. A fundamental issue in chromosome biology is whether a single molecular process accounts for all three features. There is universal agreement that a pair of Smc–kleisin complexes called condensin I and II facilitate sister chromatid disentanglement, but whether they also confer thread formation or longitudinal rigidity is either controversial or has never been directly addressed respectively. We show here that condensin II (beta-kleisin) has an essential role in all three processes during meiosis I in mouse oocytes and that its function overlaps with that of condensin I (gamma-kleisin), which is otherwise redundant. Pre-assembled meiotic bivalents unravel when condensin is inactivated by TEV cleavage, proving that it actually holds chromatin fibres together. By inactivating condensin I or II before the first meiotic division in mouse oocytes, Nasmyth and colleagues demonstrate that condensin is needed for chromatin thread formation and chromosome rigidity.
-
Condensin confers the longitudinal rigidity of chromosomes
Nature Cell Biology, 2015Co-Authors: Martin Houlard, Jonathan Godwin, Jean Metson, Jibak Lee, Tatsuya Hirano, Kim NasmythAbstract:In addition to inter-chromatid cohesion, mitotic and meiotic chromatids must have three physical properties: compaction into 'threads' roughly co-linear with their DNA sequence, intra-chromatid cohesion determining their rigidity, and a mechanism to promote sister chromatid disentanglement. A fundamental issue in chromosome biology is whether a single molecular process accounts for all three features. There is universal agreement that a pair of Smc-kleisin complexes called condensin I and II facilitate sister chromatid disentanglement, but whether they also confer thread formation or longitudinal rigidity is either controversial or has never been directly addressed respectively. We show here that condensin II (beta-kleisin) has an essential role in all three processes during meiosis I in mouse oocytes and that its function overlaps with that of condensin I (gamma-kleisin), which is otherwise redundant. Pre-assembled meiotic bivalents unravel when condensin is inactivated by TEV cleavage, proving that it actually holds chromatin fibres together.
-
Maintenance of cohesin at centromeres after meiosis I in budding yeast requires a kinetochore-associated protein related to MEI-S332.
Current Biology, 2004Co-Authors: Vittorio L. Katis, Kirsten P. Rabitsch, Marta Galova, Juraj Gregan, Kim NasmythAbstract:Abstract Background: The halving of chromosome number that occurs during meiosis depends on three factors. First, homologs must pair and recombine. Second, sister centromeres must attach to microtubules that emanate from the same spindle pole, which ensures that homologous maternal and paternal pairs can be pulled in opposite directions (called homolog biorientation). Third, cohesion between sister centromeres must persist after the first meiotic division to enable their biorientation at the second. Results: A screen performed in fission yeast to identify meiotic chromosome missegregation mutants has identified a conserved protein called Sgo1 that is required to maintain sister chromatid cohesion after the first meiotic division. We describe here an orthologous protein in the budding yeast S. cerevisiae (Sc), which has not only meiotic but also mitotic chromosome segregation functions. Deletion of Sc SGO1 not only causes frequent homolog nondisjunction at meiosis I but also random segregation of sister centromeres at meiosis II. Meiotic cohesion fails to persist at centromeres after the first meiotic division, and sister centromeres frequently separate precociously. Sgo1 is a kinetochore-associated protein whose abundance declines at anaphase I but, nevertheless, persists on chromatin until anaphase II. Conclusions: The finding that Sgo1 is localized to the centromere at the time of the first division suggests that it may play a direct role in preventing the removal of centromeric cohesin. The similarity in sequence composition, chromosomal location, and mutant phenotypes of sgo1 mutants in two distant yeasts with that of MEI-S332 in Drosophila suggests that these proteins define an orthologous family conserved in most eukaryotic lineages.
-
Un Ménage à Quatre: The Molecular Biology of Chromosome Segregation in Meiosis
Cell, 2003Co-Authors: Mark Petronczki, Maria F. Siomos, Kim NasmythAbstract:Sexually reproducing organisms rely on the precise reduction of chromosome number during a specialized cell division called meiosis. Whereas mitosis produces diploid daughter cells from diploid cells, meiosis generates haploid gametes from diploid precursors. The molecular mechanisms controlling chromosome transmission during both divisions have started to be delineated. This review focuses on the four fundamental differences between mitotic and meiotic chromosome segregation that allow the ordered reduction of chromosome number in meiosis: (1) reciprocal recombination and formation of chiasmata between homologous chromosomes, (2) suppression of sister kinetochore biorientation, (3) protection of centromeric cohesion, and (4) inhibition of DNA replication between the two meiotic divisions.
Chikashi Shimoda - One of the best experts on this subject based on the ideXlab platform.
-
s pombe sporulation specific coiled coil protein spo15p is localized to the spindle pole body and essential for its modification
Journal of Cell Science, 2000Co-Authors: Shigeaki Ikemoto, Taro Nakamura, Michiko Kubo, Chikashi ShimodaAbstract:Spindle pole bodies in the fission yeast Schizosaccharomyces pombe are required during meiosis, not only for spindle formation but also for the assembly of forespore membranes. The spo15 mutant is defective in the formation of forespore membranes, which develop into spore envelopes. The spo15 + gene encodes a protein with a predicted molecular mass of 223 kDa, containing potential coiled-coil regions. The spo15 gene disruptant was not lethal, but was defective in spore formation. Northern and western analyses indicated that spo15 + was expressed not only in meiotic cells but also in vegetative cells. When the spo15-GFP fusion gene was expressed by the authentic spo15 promoter during vegetative growth and sporulation, the fusion protein colocalized with Sad1p, which is a component of spindle pole bodies. Meiotic divisions proceeded in spo15Δ cells with kinetics similar to those in wild-type cells. In addition, the morphology of the mitotic and meiotic spindles and the nuclear segregation were normal in spo15Δ. Intriguingly, transformation of spindle pole bodies from a punctate to a crescent form prior to forespore membrane formation was not observed in spo15Δ cells. We conclude that Spo15p is associated with spindle pole bodies throughout the life cycle and plays an indispensable role in the initiation of spore membrane formation. SUMMARY
-
S. pombe sporulation-specific coiled-coil protein Spo15p is localized to the spindle pole body and essential for its modification.
Journal of Cell Science, 2000Co-Authors: Shigeaki Ikemoto, Taro Nakamura, Michiko Kubo, Chikashi ShimodaAbstract:Spindle pole bodies in the fission yeast Schizosaccharomyces pombe are required during meiosis, not only for spindle formation but also for the assembly of forespore membranes. The spo15 mutant is defective in the formation of forespore membranes, which develop into spore envelopes. The spo15(+)gene encodes a protein with a predicted molecular mass of 223 kDa, containing potential coiled-coil regions. The spo15 gene disruptant was not lethal, but was defective in spore formation. Northern and western analyses indicated that spo15(+) was expressed not only in meiotic cells but also in vegetative cells. When the spo15-GFP fusion gene was expressed by the authentic spo15 promoter during vegetative growth and sporulation, the fusion protein colocalized with Sad1p, which is a component of spindle pole bodies. Meiotic divisions proceeded in spo15delta cells with kinetics similar to those in wild-type cells. In addition, the morphology of the mitotic and meiotic spindles and the nuclear segregation were normal in spo15delta. Intriguingly, transformation of spindle pole bodies from a punctate to a crescent form prior to forespore membrane formation was not observed in spo15delta cells. We conclude that Spo15p is associated with spindle pole bodies throughout the life cycle and plays an indispensable role in the initiation of spore membrane formation.
Søren S.l. Andersen - One of the best experts on this subject based on the ideXlab platform.
-
Mitotic chromatin regulates phosphorylation of Stathmin/Op18
Nature, 1997Co-Authors: Søren S.l. Andersen, Anthony J. Ashford, Rgis Tournebize, Olivier Gavet, Andr Sobel, Anthony A. Hyman, Eric KarsentiAbstract:Meiotic and mitotic spindles are required for the even segregation of duplicated chromosomes to the two daughter cells. The mechanism of spindle assembly is not fully understood, but two have been proposed that are not mutually exclusive1,2,3. The ‘search and capture’ model suggests that dynamic microtubules become progressively captured and stabilized by the kinetochores on chromosomes, leading to spindle assembly3,4. The ‘local stabilization’ model proposes that chromosomes change the state of the cytoplasm around them, making it more favourable to microtubule polymerization2,5,6,7,8,9. It has been shown10,11 that Stathmin/Op18 inhibits microtubule polymerization in vitro by interaction with tubulin12, and that overexpression in tissue culture cells of non-phosphorylatable mutants of Stathmin/Op18 prevents the assembly of mitotic spindles13. We have used Xenopus egg extracts and magnetic chromatin beads14 to show that mitotic chromatin induces phosphorylation of Stathmin/Op18. We have also shown that Stathmin/Op18 is one of the factors regulated by mitotic chromatin that governs preferential microtubule growth around chromosomes during spindle assembly.
-
mitotic chromatin regulates phosphorylation of stathmin op18
Nature, 1997Co-Authors: Søren S.l. Andersen, Anthony J. Ashford, Rgis Tournebize, Olivier Gavet, Andr Sobel, Anthony A. Hyman, Eric KarsentiAbstract:Meiotic and mitotic spindles are required for the even segregation of duplicated chromosomes to the two daughter cells. The mechanism of spindle assembly is not fully understood, but two have been proposed that are not mutually exclusive1,2,3. The ‘search and capture’ model suggests that dynamic microtubules become progressively captured and stabilized by the kinetochores on chromosomes, leading to spindle assembly3,4. The ‘local stabilization’ model proposes that chromosomes change the state of the cytoplasm around them, making it more favourable to microtubule polymerization2,5,6,7,8,9. It has been shown10,11 that Stathmin/Op18 inhibits microtubule polymerization in vitro by interaction with tubulin12, and that overexpression in tissue culture cells of non-phosphorylatable mutants of Stathmin/Op18 prevents the assembly of mitotic spindles13. We have used Xenopus egg extracts and magnetic chromatin beads14 to show that mitotic chromatin induces phosphorylation of Stathmin/Op18. We have also shown that Stathmin/Op18 is one of the factors regulated by mitotic chromatin that governs preferential microtubule growth around chromosomes during spindle assembly.
Eric Karsenti - One of the best experts on this subject based on the ideXlab platform.
-
Mitotic chromatin regulates phosphorylation of Stathmin/Op18
Nature, 1997Co-Authors: Søren S.l. Andersen, Anthony J. Ashford, Rgis Tournebize, Olivier Gavet, Andr Sobel, Anthony A. Hyman, Eric KarsentiAbstract:Meiotic and mitotic spindles are required for the even segregation of duplicated chromosomes to the two daughter cells. The mechanism of spindle assembly is not fully understood, but two have been proposed that are not mutually exclusive1,2,3. The ‘search and capture’ model suggests that dynamic microtubules become progressively captured and stabilized by the kinetochores on chromosomes, leading to spindle assembly3,4. The ‘local stabilization’ model proposes that chromosomes change the state of the cytoplasm around them, making it more favourable to microtubule polymerization2,5,6,7,8,9. It has been shown10,11 that Stathmin/Op18 inhibits microtubule polymerization in vitro by interaction with tubulin12, and that overexpression in tissue culture cells of non-phosphorylatable mutants of Stathmin/Op18 prevents the assembly of mitotic spindles13. We have used Xenopus egg extracts and magnetic chromatin beads14 to show that mitotic chromatin induces phosphorylation of Stathmin/Op18. We have also shown that Stathmin/Op18 is one of the factors regulated by mitotic chromatin that governs preferential microtubule growth around chromosomes during spindle assembly.
-
mitotic chromatin regulates phosphorylation of stathmin op18
Nature, 1997Co-Authors: Søren S.l. Andersen, Anthony J. Ashford, Rgis Tournebize, Olivier Gavet, Andr Sobel, Anthony A. Hyman, Eric KarsentiAbstract:Meiotic and mitotic spindles are required for the even segregation of duplicated chromosomes to the two daughter cells. The mechanism of spindle assembly is not fully understood, but two have been proposed that are not mutually exclusive1,2,3. The ‘search and capture’ model suggests that dynamic microtubules become progressively captured and stabilized by the kinetochores on chromosomes, leading to spindle assembly3,4. The ‘local stabilization’ model proposes that chromosomes change the state of the cytoplasm around them, making it more favourable to microtubule polymerization2,5,6,7,8,9. It has been shown10,11 that Stathmin/Op18 inhibits microtubule polymerization in vitro by interaction with tubulin12, and that overexpression in tissue culture cells of non-phosphorylatable mutants of Stathmin/Op18 prevents the assembly of mitotic spindles13. We have used Xenopus egg extracts and magnetic chromatin beads14 to show that mitotic chromatin induces phosphorylation of Stathmin/Op18. We have also shown that Stathmin/Op18 is one of the factors regulated by mitotic chromatin that governs preferential microtubule growth around chromosomes during spindle assembly.
