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Ricardo Benavente - One of the best experts on this subject based on the ideXlab platform.
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Disassembly of the synaptonemal complex in chicken oocytes analyzed by super-resolution microscopy.
Chromosoma, 2019Co-Authors: Roberta B. Sciurano, María Inés Pigozzi, Ricardo BenaventeAbstract:The synaptonemal complex is an evolutionarily conserved, supramolecular structure that holds the homologous chromosomes together during the pachytene stage of the first meiotic prophase. Among vertebrates, synaptonemal complex dynamics has been analyzed in mouse spermatocytes following the assembly of its components from leptotene to pachytene stages. With few exceptions, a detailed study of the disassembly of SCs and the behavior of SC components at recombination sites at the onset of diplotene has not been accomplished. Here, we describe for the first time the progressive disassembly of the SC in chicken oocytes during the initial steps of desynapsis using immunolocalization of specific SC proteins and super-resolution microscopy. We found that transverse filament protein SYCP1 and central element component SYCE3 remain associated with the lateral elements at the beginning of chromosomal axis separation. As the separation between lateral elements widens, these proteins eventually disappear, without any evidence of subsequent association. Our observations support the idea that post-translational modifications of the central region components have a role at the initial phases of the SC disassembly. At the crossover sites, signaled by persistent MLH1 foci, the central region proteins are no longer detected when the SYCP3-positive lateral elements are widely separated. These findings are indicative that SC disassembly follows a general pattern along the desynaptic bivalents. The present work shows that the use of avian oocytes at prophase I provides a valuable model to explore the time course and chromosomal localization of SC proteins and its relationship with local changes along meiotic bivalents.
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Protein SYCP2 Is an Ancient Component of the Metazoan Synaptonemal Complex
Cytogenetic and genome research, 2015Co-Authors: Johanna Fraune, Manfred Alsheimer, Josef Redolfi, Céline Brochier-armanet, Ricardo BenaventeAbstract:During the first meiotic prophase, chromosome synapsis is mediated by the synaptonemal complex (SC), an evolutionarily conserved meiosis-specific structure. In mammals, 7 SC protein components have been identified so far. Despite some controversy in the past, we have shown that SC proteins are ancient in metazoans and very likely formed an ancestral SC structure in the ancestor of metazoans. Protein components SYCP1, SYCP3, SYCE2, and TEX12 were identified in basal-branching metazoans, while other components (SYCE1 and SYCE3) are more recent elements. However, the evolutionary history of mammalian SYCP2 is not known. Here, we investigated this aspect with the aid of bioinformatic tools as well as with RNA and protein expression analysis. We conclude that SYCP2 belongs to the group of ancient SC proteins that was already present in the common ancestor of metazoans more than 500 million years ago.
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Phylogenies of Central Element Proteins Reveal the Dynamic Evolutionary History of the Mammalian Synaptonemal Complex: Ancient and Recent Components
Genetics, 2013Co-Authors: Johanna Fraune, Manfred Alsheimer, Céline Brochier-armanet, Ricardo BenaventeAbstract:During meiosis, the stable pairing of the homologous chromosomes is mediated by the assembly of the synaptonemal complex (SC). Its tripartite structure is well conserved in Metazoa and consists of two lateral elements (LEs) and a central region (CR) that in turn is formed by several transverse filaments (TFs) and a central element (CE). In a previous article, we have shown that not only the structure, but also the major structural proteins SYCP1 (TFs) and SYCP3 (LEs) of the mammalian SC are conserved in metazoan evolution. In continuation of this work, we now investigated the evolution of the mammalian CE-specific proteins using phylogenetic and biochemical/cytological approaches. In analogy to the observations made for SYCP1 and SYCP3, we did not detect homologs of the mammalian CE proteins in insects or nematodes, but in several other metazoan clades. We were able to identify homologs of three mammalian CE proteins in several vertebrate and invertebrate species, for two of these proteins down to the basal-branching phylum of Cnidaria. Our approaches indicate that the SC arose only once, but evolved dynamically during diversification of Metazoa. Certain proteins appear to be ancient in animals, but successive addition of further components as well as protein loss and/or replacements have also taken place in some lineages.
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Hydra meiosis reveals unexpected conservation of structural synaptonemal complex proteins across metazoans
Proceedings of the National Academy of Sciences of the United States of America, 2012Co-Authors: Johanna Fraune, Manfred Alsheimer, Jean-nicolas Volff, Karoline Busch, Sebastian Fraune, Thomas C. G. Bosch, Ricardo BenaventeAbstract:The synaptonemal complex (SC) is a key structure of meiosis, mediating the stable pairing (synapsis) of homologous chromosomes during prophase I. Its remarkable tripartite structure is evolutionarily well conserved and can be found in almost all sexually reproducing organisms. However, comparison of the different SC protein components in the common meiosis model organisms Saccharomyces cerevisiae, Arabidopsis thaliana, Caenorhabditis elegans, Drosophila melanogaster, and Mus musculus revealed no sequence homology. This discrepancy challenged the hypothesis that the SC arose only once in evolution. To pursue this matter we focused on the evolution of SYCP1 and SYCP3, the two major structural SC proteins of mammals. Remarkably, our comparative bioinformatic and expression studies revealed that SYCP1 and SYCP3 are also components of the SC in the basal metazoan Hydra. In contrast to previous assumptions, we therefore conclude that SYCP1 and SYCP3 form monophyletic groups of orthologous proteins across metazoans.
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Synaptonemal Complex Protein SYCP3 Exists in Two Isoforms Showing Different Conservation in Mammalian Evolution
Cytogenetic and genome research, 2010Co-Authors: Manfred Alsheimer, Andrea Baier, Sabine Schramm, Wolfgang Schütz, Ricardo BenaventeAbstract:Meiosis-specific protein SYCP3 is a major structural component of synaptonemal complex (SC) lateral elements. SYCP3 is rather well conserved in vertebrates. However, some differences in SYCP3 expressi
Christer Hoog - One of the best experts on this subject based on the ideXlab platform.
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Synaptonemal Complex Components Persist at Centromeres and Are Required for Homologous Centromere Pairing in Mouse Spermatocytes
PLOS Genetics, 2012Co-Authors: C. Gastón Bisig, Michel F. Guiraldelli, Anna Kouznetsova, Harry Scherthan, Dean S. Dawson, Christer Hoog, Roberto J. PezzaAbstract:Recent studies in simple model organisms have shown that centromere pairing is important for ensuring high-fidelity meiotic chromosome segregation. However, this process and the mechanisms regulating it in higher eukaryotes are unknown. Here we present the first detailed study of meiotic centromere pairing in mouse spermatogenesis and link it with key events of the G2/metaphase I transition. In mouse we observed no evidence of the persistent coupling of centromeres that has been observed in several model organisms. We do however find that telomeres associate in non-homologous pairs or small groups in B type spermatogonia and pre-leptotene spermatocytes, and this association is disrupted by deletion of the synaptonemal complex component SYCP3. Intriguingly, we found that, in mid prophase, chromosome synapsis is not initiated at centromeres, and centromeric regions are the last to pair in the zygotene-pachytene transition. In late prophase, we first identified the proteins that reside at paired centromeres. We found that components of the central and lateral element and transverse filaments of the synaptonemal complex are retained at paired centromeres after disassembly of the synaptonemal complex along diplotene chromosome arms. The absence of SYCP1 prevents centromere pairing in knockout mouse spermatocytes. The localization dynamics of SYCP1 and SYCP3 suggest that they play different roles in promoting homologous centromere pairing. SYCP1 remains only at paired centromeres coincident with the time at which some kinetochore proteins begin loading at centromeres, consistent with a role in assembly of meiosis-specific kinetochores. After removal of SYCP1 from centromeres, SYCP3 then accumulates at paired centromeres where it may promote bi-orientation of homologous centromeres. We propose that, in addition to their roles as synaptonemal complex components, SYCP1 and SYCP3 act at the centromeres to promote the establishment and/or maintenance of centromere pairing and, by doing so, improve the segregation fidelity of mammalian meiotic chromosomes.
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Phosphorylation of chromosome core components may serve as axis marks for the status of chromosomal events during mammalian meiosis.
PLoS genetics, 2012Co-Authors: Tomoyuki Fukuda, John C. Schimenti, Florencia Pratto, James M. A. Turner, R. Daniel Camerini-otero, Christer HoogAbstract:Meiotic recombination and chromosome synapsis between homologous chromosomes are essential for proper chromosome segregation at the first meiotic division. While recombination and synapsis, as well as checkpoints that monitor these two events, take place in the context of a prophase I-specific axial chromosome structure, it remains unclear how chromosome axis components contribute to these processes. We show here that many protein components of the meiotic chromosome axis, including SYCP2, SYCP3, HORMAD1, HORMAD2, SMC3, STAG3, and REC8, become post-translationally modified by phosphorylation during the prophase I stage. We found that HORMAD1 and SMC3 are phosphorylated at a consensus site for the ATM/ATR checkpoint kinase and that the phosphorylated forms of HORMAD1 and SMC3 localize preferentially to unsynapsed chromosomal regions where synapsis has not yet occurred, but not to synapsed or desynapsed regions. We investigated the genetic requirements for the phosphorylation events and revealed that the phosphorylation levels of HORMAD1, HORMAD2, and SMC3 are dramatically reduced in the absence of initiation of meiotic recombination, whereas BRCA1 and SYCP3 are required for normal levels of phosphorylation of HORMAD1 and HORMAD2, but not of SMC3. Interestingly, reduced HORMAD1 and HORMAD2 phosphorylation is associated with impaired targeting of the MSUC (meiotic silencing of unsynapsed chromatin) machinery to unsynapsed chromosomes, suggesting that these post-translational events contribute to the regulation of the synapsis surveillance system. We propose that modifications of chromosome axis components serve as signals that facilitate chromosomal events including recombination, checkpoint control, transcription, and synapsis regulation.
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The Mouse Cohesin-Associated Protein PDS5B Is Expressed in Testicular Cells and Is Associated with the Meiotic Chromosome Axes
Genes, 2010Co-Authors: Tomoyuki Fukuda, Christer HoogAbstract:During the first meiotic prophase, the cohesin complex is localized to the chromosome axis and contributes to chromosome organization, pairing, synapsis, and recombination. The PDS5 protein, an accessory factor of the cohesin complex, is known to be a component of meiotic chromosome cores in fungi and to be implicated in meiotic chromosome structure and function. We found by immunoblotting experiments that a mammalian PDS5 protein, PDS5B, is abundantly expressed in mouse testis compared to other tissues. Immunofluorescence labeling experiments revealed that PDS5B is highly expressed in spermatogonia and that most PDS5B is depleted from chromatin as cells enter meiosis. During the first meiotic prophase, PDS5B associates with the axial cores of chromosomes. The axial association of PDS5B was observed also in the absence of synaptonemal complex proteins, such as SYCP1 and SYCP3, suggesting that PDS5B is an integral part of the chromosome axis as defined by the cohesin complex. These results suggest that PDS5B modulates cohesin functions in spermatocytes as well as in spermatogonia, contributing to meiotic chromosome structure and function.
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Disruption of pairing and synapsis of chromosomes causes stage-specific apoptosis of male meiotic cells.
Theriogenology, 2007Co-Authors: Geert Hamer, Anna Kouznetsova, Ivana Novak, Christer HoogAbstract:During meiosis, DNA replication is followed by two successive rounds of chromosome segregation (meiosis I and II), which give rise to genetically diverse haploid gametes. The prophase of the first meiotic division is highly regulated and alignment and synapsis of the homologous chromosomes during this stage are mediated by the synaptonemal complex. Incorrect assembly of the synaptonemal complex results in cell death, impaired meiotic recombination and aneuploidy. Oocytes with meiotic defects often survive the first meiotic prophase and give rise to aneuploid gametes. Similarly affected spermatocytes, on the other hand, almost always undergo apoptosis at a male-specific meiotic checkpoint, located specifically at epithelial stage IV during spermatogenesis. Many examples of this stage IV-specific arrest have been described for several genetic mouse models in which DNA repair or meiotic recombination are abrogated. Interestingly, in C. elegans, meiotic recombination and synapsis are monitored by two separate checkpoint pathways. Therefore we studied spermatogenesis in several knockout mice (Sycp1(-/-), SYCP3(-/-), Smc1beta(-/-) and SYCP3/Sycp1 and SYCP3/Smc1beta double-knockouts) that are specifically defective in meiotic pairing and synapsis. Like for recombination defects, we found that all these genotypes also specifically arrest at epithelial stage IV. It seems that the epithelial stage IV checkpoint eliminates spermatocytes that fail a certain quality check, being either synapsis or DNA damage related.
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mouse embryonic stem cells form follicle like ovarian structures but do not progress through meiosis
Stem Cells, 2006Co-Authors: Ivana Novak, Daniel A Lightfoot, Hong Wang, Annika Eriksson, Ensaf Mahdy, Christer HoogAbstract:Several recent studies have suggested that mouse embryonic stem cells (ESCs) can differentiate into female and male germ cells in vitro. The meiotic process in germ cell-like cells derived from ESCs has not been studied in detail, but it has been reported that synaptonemal complex protein-3 (SYCP3) is expressed in these cells. Here, we have carefully evaluated the meiotic process in germ cell-like cells derived from ESCs, using a panel of meiosis-specific markers that identify distinct meiotic signatures unique to meiotic prophase I development in vivo. We find that whereas SYCP3 is expressed in germ cell-like cells, other meiotic proteins, such as SYCP1, SYCP2, STAG3 (stromal antigen 3), REC8 (meiotic protein similar to the rad21 cohesins), and SMC1 (structural maintenance of chromosomes-1)-β, are not expressed. The nuclear distribution of SYCP3 in the germ cell-like cells is highly abnormal and not associated with the chromosomes of these cells. Fluorescence in situ hybridization analysis shows that the SYCP3-positive germ cell-like cells do not contain synapsed homologous chromosomes but instead display a chromosomal organization normally found in somatic cells. The absence of expression of essential meiotic proteins and a normal meiotic chromosomal organization strongly suggests that the germ cell-like cells formed from ESCs fail to progress through meiosis.
Roberta B. Sciurano - One of the best experts on this subject based on the ideXlab platform.
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Disassembly of the synaptonemal complex in chicken oocytes analyzed by super-resolution microscopy.
Chromosoma, 2019Co-Authors: Roberta B. Sciurano, María Inés Pigozzi, Ricardo BenaventeAbstract:The synaptonemal complex is an evolutionarily conserved, supramolecular structure that holds the homologous chromosomes together during the pachytene stage of the first meiotic prophase. Among vertebrates, synaptonemal complex dynamics has been analyzed in mouse spermatocytes following the assembly of its components from leptotene to pachytene stages. With few exceptions, a detailed study of the disassembly of SCs and the behavior of SC components at recombination sites at the onset of diplotene has not been accomplished. Here, we describe for the first time the progressive disassembly of the SC in chicken oocytes during the initial steps of desynapsis using immunolocalization of specific SC proteins and super-resolution microscopy. We found that transverse filament protein SYCP1 and central element component SYCE3 remain associated with the lateral elements at the beginning of chromosomal axis separation. As the separation between lateral elements widens, these proteins eventually disappear, without any evidence of subsequent association. Our observations support the idea that post-translational modifications of the central region components have a role at the initial phases of the SC disassembly. At the crossover sites, signaled by persistent MLH1 foci, the central region proteins are no longer detected when the SYCP3-positive lateral elements are widely separated. These findings are indicative that SC disassembly follows a general pattern along the desynaptic bivalents. The present work shows that the use of avian oocytes at prophase I provides a valuable model to explore the time course and chromosomal localization of SC proteins and its relationship with local changes along meiotic bivalents.
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The XY Body of the Cat (Felis catus): Structural Differentiations and Protein Immunolocalization.
Cytogenetic and genome research, 2017Co-Authors: Roberta B. Sciurano, Geraldine De Luca, I. Mónica Rahn, Alberto J. SolariAbstract:The heteromorphic X and Y chromosomes behave in a special way in mammalian spermatocytes; they form the XY body and synapse only partially. The aim of this article was to study the origin and the role of the special differentiations in the XY pair of the domestic cat during pachytene by analyzing its fine structural characteristics and the immunolocalization of the main meiotic proteins SYCP3, SYCP1, SYCE3, SMC3, γ-H2AX, BRCA1, H3K27me3, and MLH1. The cat XY body shows particularly striking structures: an extreme degree of axial fibrillation in late pachynema and a special location of SYCP3-containing fibrils, bridging different regions of the main X axis, as well as one bridge at the inner end of the pairing region that colocalizes with the single mandatory MLH1 focus. There are sequential changes, first bullous expansions, then subdivision into fibrils, all involving axial thickening. The chromatin of the XY body presents the usual features of meiotic sex chromosome inactivation. An analysis of the XY body of many eutherians and metatherians suggests that axial thickenings are primitive features. The sequential changes in the mass and location of SYCP3-containing fibers vary among the clades because of specific processes of axial assembly/disassembly occurring in different species.
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Synapsis, recombination, and chromatin remodeling in the XY body of armadillos
Chromosome Research, 2012Co-Authors: Roberta B. Sciurano, Mónica I. Rahn, Luis Rossi, Juan Pablo Luaces, María Susana Merani, Alberto J. SolariAbstract:Three xenarthrans species Chaetophractus villosus , Chaetophractus vellerosus , and Zaedyus pichiy have been used for the analysis of the structure, behavior, and immunochemical features of the XY body during pachytene. In all these species, the sex chromosomes form an XY body easily identifiable in thin sections by the special and regular packing of the chromatin fibers of the internal region of the XY body (“differential” regions) and those of the peripheral region (synaptic region). Spermatocyte spreads show a complete synapsis between the X- and the Y-axis, which lasts up to the end of pachytene. From the early pachytene substages to the late ones, the X-axis develops prominent branches, which in late pachytene span the synaptic region. Synapsis is regular as shown by SYCP1 labeling. Axial development is followed by SYCP3 labeling and in the asynaptic region of the X-axis by BRCA1. Gamma-H2AX labels exclusively the differential (asynaptic) region of the X chromosome. A single focus is labeled by MLH1 in the synaptic region. The location of this MLH1 focus spans from 0.3 to 1.6 μm from the telomere in the analyzed xenarthrans, covering approximately half of the Y-axis length. It is concluded that xenarthrans, as basal placental mammals, harbor the largest pseudoautosomal regions of presently analyzed mammals, and shows the typical features of meiotic sex chromosome inactivation (MSCI).
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Protein immunolocalization supports the presence of identical mechanisms of XY body formation in eutherians and marsupials.
Chromosome research : an international journal on the molecular supramolecular and evolutionary aspects of chromosome biology, 2007Co-Authors: María José Franco, Roberta B. Sciurano, Alberto J. SolariAbstract:The meiotic sex chromosomes of the American marsupials Monodelphis dimidiata and Didelphis albiventris were studied with electron microscopy (EM) and with immunofluorescence localization of meiotic proteins SYCP1 and SYCP3, and proteins essential for meiotic sex chromosome inactivation (MSCI), γ-H2AX and BRCA1. The chromatin of the non-synaptic X and Y chromosomes contains γ-H2AX, first as foci and then as homogeneous staining at late stages. The thick and split X and Y axes are labelled with BRCA1 except at one terminus. The bulgings of the axes contain SYCP1 as well as the inner side of the dense plate. The evenly spaced and highly packed chromatin fibres of the conjoined XY body in these species have the same behaviour and the same components (γ-H2AX in the chromatin, BRCA1 in the axes) as in the XY body of eutherian species. These observations and recent data from the literature suggest that XY body formation is ancestral to the metatherian–eutherian divergence.
Harry Scherthan - One of the best experts on this subject based on the ideXlab platform.
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Synaptonemal Complex Components Persist at Centromeres and Are Required for Homologous Centromere Pairing in Mouse Spermatocytes
PLOS Genetics, 2012Co-Authors: C. Gastón Bisig, Michel F. Guiraldelli, Anna Kouznetsova, Harry Scherthan, Dean S. Dawson, Christer Hoog, Roberto J. PezzaAbstract:Recent studies in simple model organisms have shown that centromere pairing is important for ensuring high-fidelity meiotic chromosome segregation. However, this process and the mechanisms regulating it in higher eukaryotes are unknown. Here we present the first detailed study of meiotic centromere pairing in mouse spermatogenesis and link it with key events of the G2/metaphase I transition. In mouse we observed no evidence of the persistent coupling of centromeres that has been observed in several model organisms. We do however find that telomeres associate in non-homologous pairs or small groups in B type spermatogonia and pre-leptotene spermatocytes, and this association is disrupted by deletion of the synaptonemal complex component SYCP3. Intriguingly, we found that, in mid prophase, chromosome synapsis is not initiated at centromeres, and centromeric regions are the last to pair in the zygotene-pachytene transition. In late prophase, we first identified the proteins that reside at paired centromeres. We found that components of the central and lateral element and transverse filaments of the synaptonemal complex are retained at paired centromeres after disassembly of the synaptonemal complex along diplotene chromosome arms. The absence of SYCP1 prevents centromere pairing in knockout mouse spermatocytes. The localization dynamics of SYCP1 and SYCP3 suggest that they play different roles in promoting homologous centromere pairing. SYCP1 remains only at paired centromeres coincident with the time at which some kinetochore proteins begin loading at centromeres, consistent with a role in assembly of meiosis-specific kinetochores. After removal of SYCP1 from centromeres, SYCP3 then accumulates at paired centromeres where it may promote bi-orientation of homologous centromeres. We propose that, in addition to their roles as synaptonemal complex components, SYCP1 and SYCP3 act at the centromeres to promote the establishment and/or maintenance of centromere pairing and, by doing so, improve the segregation fidelity of mammalian meiotic chromosomes.
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Female-specific features of recombinational double-stranded DNA repair in relation to synapsis and telomere dynamics in human oocytes
Chromosoma, 2004Co-Authors: I. Roig, B. Liebe, J. Egozcue, Ll. Cabero, M. Garcia, Harry ScherthanAbstract:Chromosome segregation errors are a significant cause of aneuploidy among human neonates and often result from errors in female meiosis that occur during fetal life. For the latter reason, little is known about chromosome dynamics during female prophase I. Here, we analyzed chromosome reorganization, and centromere and telomere dynamics in meiosis in the human female by immunofluorescent staining of the SYCP3 and SYCP1 synaptonemal complex proteins and the course of recombinational DNA repair by IF of phospho-histone H2A.X (γ-H2AX), RPA and MLH1 recombination proteins. We found that SYCP3, but not SYCP1, aggregates appear in the preleptotene nucleus and some persist up to pachytene. Telomere clustering (bouquet stage) in oocytes lasted from late-leptotene to early pachytene—significantly longer than in the male. Leptotene and zygotene oocytes and spermatocytes showed strong γ-H2AX labeling, while γ-H2AX patches, which colocalized with RPA, were present on SYCP1-tagged pachytene SCs. This was rarely seen in the male and may suggest that synapsis installs faster with respect to progression of recombinational double-strand break repair or that the latter is slower in the female. It is speculated that the presence of γ-H2AX into pachytene highlights female-specific peculiarities of recombination, chromosome behavior and checkpoint control that may contribute to female susceptibility for aneuploidy.
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Telomere Attachment, Meiotic Chromosome Condensation, Pairing, and Bouquet Stage Duration Are Modified in Spermatocytes Lacking Axial Elements
Molecular biology of the cell, 2003Co-Authors: Bodo Liebe, Manfred Alsheimer, Christer Hoog, Ricardo Benavente, Harry ScherthanAbstract:During the extended prophase to the meiosis I division, chromosomes assemble axial elements (AE) along replicated sister chromatids whose ends attach to the inner nuclear membrane (NM) via a specialized conical thickening. Here, we show at the EM level that in SYCP3 - / - spermatocyte chromosomes lack the AE and the conical end thickening, but still they attach their telomeres to the inner NM with an electron-dense plate that contains T 2 AG 3 repeats. Immunofluorescence detected telomere proteins, SCP2, and the meiosis-specific cohesin STAG3 at the SYCP3 - / - telomere. Bouquet stage spermatocytes were approximately threefold enriched, and the number of telomere but not centromere signals was reduced to the haploid in advanced SYCP3 - / - spermatocytes, which indicates a special mode of homolog pairing at the mammalian telomere. Fluorescence in situ hybridization with mouse chromosome 8- and 12-specific subsatellite probes uncovered reduced levels of regional homolog pairing, whereas painting of chromosomes 13 revealed partial or complete juxtapositioning of homologs; however, condensation of SYCP3 - / - bivalents was defective. Electron microscopic analysis of AE-deficient spermatocytes revealed that transverse filaments formed short structures reminiscent of the synaptonemal complex central region, which likely mediate stable homolog pairing. It appears that the AE is required for chromosome condensation, rapid exit from the bouquet stage, and fine-tuning of homolog pairing.
Sean M. Burgess - One of the best experts on this subject based on the ideXlab platform.
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spo11 -/- males fail to properly synapse homologous chromosomes, and exhibit high numbers of engaged telomeres during meiosis I.
2019Co-Authors: Yana P. Blokhina, An D. Nguyen, Bruce W. Draper, Sean M. BurgessAbstract:A: 1A-5B: spo11 -/- nuclear surface spreads stained for SYCP3 (green), Sycp1 (blue), telomeres (Tel; magenta), and DNA (DAPI, blue). 1C-5C: Magnified (Mag) images are from regions indicated by white boxes in the panels above. Telomere associations are seen at all stages (arrowheads); Short stretches of Sycp1 are seen in some mutant cells (short arrows). Scale bar = 5μm. B: Numbers of engaged telomeres in WT vs. spo11 -/- cells. The mutant cells were categorized based on similarity to WT SYCP3 loading extent. Post-LZ refers to all cells that were classified as pre-pachytene or pachytene in WT and equivalent cells in spo11 mutants. The data was pooled from two experiments done on different days (set 1, orange circles; set 2, green diamonds). P values were acquired using unpaired t test with Welch’s correction. For * p ≤ 0.0314, and for **** p < 0.0001. While WT telomere engagements are reduced at later stages, the telomere engagements in spo11-/- are maintained. C: Dot plot of BAC distance measurements in WT and spo11 -/- males (in μm). In the WT during the early stages when the average SYCP3 lines are short (< 2 μm), the BAC signals are unpaired; As meiosis progresses and the SYCP3 lines elongate (> 2 μm), the BAC signals exhibit pairing (p = 0.0004, unpaired t test with Welch’s correction). In the spo11 -/- males the BAC signals remain unpaired even with extended SYCP3 axes.
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Interlocks and de-synapsed chromosomes in male zebrafish meiosis I.
2019Co-Authors: Yana P. Blokhina, An D. Nguyen, Bruce W. Draper, Sean M. BurgessAbstract:1A-6C: Examples of nuclear surface spreads showing interlocks (arrows) and de-synapsed chromosomes (triple arrows) at the late zygotene to pachytene stage where most chromosomes are synapsed. In some cases, de-synapsed chromosomes have another chromosome passing through them (arrowheads). 1D-6D: Magnification (Mag) images are from regions indicated by white boxes in the merge panels. SYCP3 (green), Sycp1 (blue), Telomeres (Tel; magenta). Scale bar = 5μm.
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Homologous chromosome synapsis and pairing in female zebrafish meiosis I.
2019Co-Authors: Yana P. Blokhina, An D. Nguyen, Bruce W. Draper, Sean M. BurgessAbstract:1A-5B: SYCP3 (green) loading and synapsis (Sycp1; blue), begin near telomeres (Tel; magenta) and progress inwards, similarly to what is seen in zebrafish males. 6A-8A: BAC (red), SYCP3 (green), Sycp1 (blue), Telomeres (Tel; magenta). 6B-8B: Same images as 6A-8A with only the BAC shown (gray; arrowheads). Scale bar = 5 μm.
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spo11 -/- females fail to properly synapse homologous chromosomes.
2019Co-Authors: Yana P. Blokhina, An D. Nguyen, Bruce W. Draper, Sean M. BurgessAbstract:1A-4B: spo11 -/- nuclear surface spreads stained for SYCP3 (green), Sycp1 (blue), telomeres (Tel; magenta), and DNA (DAPI, blue). While SYCP3 loading proceeds, chromosomes are not synapsed. Scale bar = 5μm).
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Measurements of SYCP3 vs.
2019Co-Authors: Yana P. Blokhina, An D. Nguyen, Bruce W. Draper, Sean M. BurgessAbstract:Sycp1 length, numbers of engaged telomeres, and numbers of co-alignments in male zebrafish meiosis I. A: Average SYCP3 length vs. average Sycp1 length. Each circle represents the average of all measurements in one nucleus (n = 30 nuclei). B: Total SYCP3 length vs. total Sycp1 length in the same cells shown in A. Stages of meiosis are defined by total length of Sycp1: leptotene (L, Sycp1 = 0 μm; yellow); leptotene to zygotene transition (L/EZ, Sycp1 = 1–10 μm; blue); early to mid-zygotene (EZ/MZ, Sycp1 = 10–50 μm; pink); mid to late zygotene (MZ/LZ, Sycp1 = 50–100 μm; purple); late zygotene (LZ, Sycp1 > 100 μm; cyan). C: Numbers of engaged telomeres per cell, where one engaged telomere end is an SYCP3 line with its telomere associated with a potentially non-homologous telomere end. Each point represents one cell. The data was pooled from two experiments done on different days (set 1, orange circles; set 2, green diamonds). The highest numbers of engaged telomere ends were observed in L and L/EZ stages after which point there was a significant decrease in engaged telomere ends in the EZ/MZ category, p < 0.0001 (unpaired t test with Welch’s correction), however, some number of engaged ends were maintained throughout prophase I. D: Examples of funnel and pinch co-alignment configurations. In the funnel configuration the co-alignment is directly adjacent to the telomeres; in the pinch configuration the co-alignment is not directly adjacent to the telomeres. White arrows point to the co-aligned regions. The blue arrow points to a pinch configuration where SC has already started to form (not counted as co-aligned). E: Total numbers of co-alignments in different stage cells of meiosis I prophase. Each point represents one cell. F: Numbers of co-alignments (0–5) in individual cells in WT (n = 24) and spo11 -/- (n = 32) males. The LZ class was excluded from the WT representation as at this stage synapsis has typically initiated at the majority of telomere ends. spo11 -/- cells, where synapsis is mostly abolished, were assessed for co-alignment if they appeared to have SYCP3 lines of similar lengths to the leptotene and zygotene classes of WT.
