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Results for “Synaptonemal Complex”

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PubMed1975

Electron microscopic observations on the meiotic karyotype of diploid and tetraploid Saccharomyces cerevisiae.

Certain strains of Saccharomyces cerevisiae contain visible segments of synaptonemal complex which are apparent components of bivalents in pachytene of meiotic prophase. The synaptonemal complex has the typical width in the frontal plane but is unusually thin in the sagittal plane, thus accounting for its poor visibility. Amorphous densities situated adjacent to the central element occur at intervals suggesting their coincidence with sites of crossing over. Reconstruction of the synaptonemal complex from serial sections has permitted karyotypic analysis. The number of segments of synaptonemal complex and the distribution of their legths is consistent with the genetic map. Two, possibly three, segments enter the nucleolus as if bearing sequences encoding ribosomal RNA. Reconstruction of tetraploid nuclei reveals an approximate doubling of the diploid chromosome number and confirms the pattern of nucleolar entry. Quadrivalent pairing is evident between the pairs of synaptonemal complex segments in the tetraploid nuclei.

Cell Nucleus↗

PubMed1984

Synaptonemal complex-associated centromeres and recombination nodules in plant meiocytes prepared by an improved surface-spreading technique.

An improved method of preparing two-dimensional surface spreads of plant synaptonemal complexes (SCs) is described. This technique produces clear preparations of SCs and, in addition, consistently reveals both centromeres and recombination nodules (RNs) in PTA-stained preparations viewed by electron microscopy. A preliminary study of RN number and distribution in Allium fistulosum indicates that they faithfully reflect the positions of cross-over exchange events as revealed by chiasmata.

Cell Nucleus↗

PubMed1980

Time of recombination in the Drosophila melanogaster oocyte. II. Electron microscopic and genetic studies of a temperature-sensitive recombination mutant.

A test has been carried out to determine if the restrictive temperature (31 degrees) acts to reduce recombination in the temperature-sensitive recombination-deficient genotype rec-l26/rec-l16 by reducing or eliminating the synaptonemal complex. Measurements of the length of synaptonemal complexes in heat-treated and untreated stage 1 oocytes, following termination of the temperature-sensitive period, reveal less than a 5% difference, with the greater length present in the treated oocytes. Alterations are not observed in synaptonemal complex distribution within the nucleus or in its fine structure. Parallel genetic studies confirm earlier observations that the restrictive temperature, whose action is confined to a 36-h sensitive period virtually coextensive with premeiotic-S, drastically reduces recombination to approximately 10% of normal. The results are most simply interpreted to mean that the restrictive temperatures acts directly on the recombination process.

Animals↗

PubMed2003

The pairing of X and Y chromosomes during meiotic prophase in the marsupial species Thylamys elegans is maintained by a dense plate developed from their axial elements.

Unlike eutherian males, pairing of the sex chromosomes in marsupial males during the first meiotic prophase is not mediated by a synaptonemal complex. Instead, a specific structure, the dense plate, develops during pachytene between the sex chromosomes. We have investigated the development and structural nature of this asynaptic association in males of the marsupial species Thylamys elegans by means of immunolabelling and electron microscopy techniques. Our results show that the behaviour of male marsupial sex chromosomes during first meiotic prophase is complex, involving modifications of their structure and/or composition. Pairing of the sex chromosomes and formation of the dense plate take place in mid pachytene, paralleling morphological changes in the sex chromosomal axial elements. Components of the central element of the synaptonemal complex were not found in the sex body, in agreement with ultrastructural studies that reported the absence of a canonical tripartite synaptonemal complex between male marsupial sex chromosomes. Interestingly, the dense plate is labelled with antibodies against the SCP3 protein of the lateral elements of the synaptonemal complex. Moreover, as sex chromosome axial elements decrease in mass throughout mid-late pachytene, the dense plate increases, suggesting that material moves from the axial elements to the dense plate. Additionally, both sex chromosome axial elements and the dense plate have proteins that are specifically phosphorylated, as revealed by their labelling with the MPM-2 antibody, indicating that they undergo a chromosome-specific regulation process throughout first meiotic prophase. We propose that the unique modifications of the composition and structure of the axial elements of the sex chromosomes in meiotic prophase may result in the prescription of synaptonemal complex formation between male marsupial sex chromosomes, where the dense plate is an extension of the axial elements of sex chromosomes. This replaces synapsis to maintain X and Y association during first meiotic prophase.

Animals↗

PubMed1989

Genetic control of chromosome synapsis in yeast meiosis.

Both meiosis-specific and general recombination functions, recruited from the mitotic cell cycle, are required for elevated levels of recombination and for chromosome synapsis (assembly of the synaptonemal complex) during yeast meiosis. The meiosis-specific SPO11 gene (previously shown to be required for meiotic recombination) has been isolated and shown to be essential for synaptonemal complex formation but not for DNA metabolism during the vegetative cell cycle. In contrast, the RAD52 gene is required for mitotic and meiotic recombination but not for synaptonemal complex assembly. These data suggest that the synaptonemal complex may be necessary but is clearly not sufficient for meiotic recombination. Cytological analysis of spread meiotic nuclei demonstrates that chromosome behavior in yeast is comparable with that observed in larger eukaryotes. These spread preparations support the immunocytological localization of specific proteins in meiotic nuclei. This combination of genetic, molecular cloning, and cytological approaches in a single experimental system provides a means of addressing the role of specific gene products and nuclear structures in meiotic chromosome behavior.

Chromosomes, Fungal↗

PubMed1999

Mitotic and meiotic analysis in Arctocephalus australis (Otariidae).

The karyotype with C-, G- and NOR-banding of Arctocephalus australis is reported for the first time. The chromosomal number is 2n = 36. The X chromosome, identified in G-banded metaphases from males, is metacentric and the Y chromosome is a minute chromosome, also metacentric. Pachytene spermatocytes were used for synaptonemal complexes analysis with a surface spreading technique. A total of 17 autosomal synaptonemal complexes are observed plus the XY pair. During early pachytene, the X and Y axes are thickened and remain unpaired. As pachytene advances, a short SC is formed between the gonosomes, as it is common among eutherian mammals. The particular asymmetrical appearance of the synaptonemal complex in the sex pair is described and compared to other cases among mammals.

Animals↗

PubMed2000

STAG3, a novel gene encoding a protein involved in meiotic chromosome pairing and location of STAG3-related genes flanking the Williams-Beuren syndrome deletion.

Chromatin rearrangements in the meiotic prophase are characterized by the assembly and disassembly of synaptonemal complexes (SC), a protein structure that stabilizes the pairing of homologous chromosomes in prophase. We report the identification of human and mouse cDNA coding for stromalin 3 (STAG3), a new mammalian stromalin member of the synaptonemal complex. The stromalins are a group of highly conserved proteins, represented in several organisms from yeast to humans. Stromalins are characterized by the stromalin conservative domain (SCD), a specific motif found in all proteins of the family described to date. STAG3 is expressed specifically in testis, and immunolocalization experiments show that STAG3 is associated to the synaptonemal complex. As the protein encoded by the homologous gene (Scc3p) in Saccharomyces cerevisiae was found to be a subunit of a cohesin complex that binds chromosomes until the onset of anaphase, our data suggest that STAG3 is involved in chromosome pairing and maintenance of synaptonemal complex structure during the pachytene phase of meiosis in a cohesin-like manner. We have mapped the human STAG3 gene to the 7q22 region of chromosome 7; six human STAG3-related genes have also been mapped: two at 7q22 near the functional gene, one at 7q11.22, and three at 7q11.23, two of them flanking the breakpoints commonly associated with the Williams-Beuren syndrome (WBS) deletion. Since the WBS deletion occurs as a consequence of unequal meiotic crossing over, we suggest that STAG3 duplications predispose to germline chromosomal rearrangement within this region.

Amino Acid Sequence↗

PubMed1996

Targeted gene disruption of Hsp70-2 results in failed meiosis, germ cell apoptosis, and male infertility.

In addition to the five 70-kDa heat shock proteins (HSP70) common to germ cells and somatic tissues of mammals, spermatogenic cells synthesize HSP70-2 during meiosis. To determine if this unique stress protein has a critical role in meiosis, we used gene-targeting techniques to disrupt Hsp70-2 in mice. Male mice homozygous for the mutant allele (Hsp70-2 -/-) did not synthesize HSP70-2, lacked postmeiotic spermatids and mature sperm, and were infertile. However, neither meiosis nor fertility was affected in female Hsp70-2 -/- mice. We previously found that HSP70-2 is associated with synaptonemal complexes in the nucleus of meiotic spermatocytes from mice and hamsters. While synaptonemal complexes assembled in Hsp70-2 -/- spermatocytes, structural abnormalities became apparent in these cells by late prophase, and development rarely progressed to the meiotic divisions. Furthermore, analysis of nuclei and genomic DNA indicated that the failure of meiosis in Hsp70-2 -/- mice was coincident with a dramatic increase in spermatocyte apoptosis. These results suggest that HSP70-2 participates in synaptonemal complex function during meiosis in male germ cells and is linked to mechanisms that inhibit apoptosis.

Animals↗

PubMed2003

Destructive effect of DNA topoisomerase II inhibitor vepesid on mouse spermatogenesis.

Inhibition of DNA topoisomerase II with vepesid induced structural and functional reorganization of chromatin in meiotically dividing spermatocytes I, which later led to the block of their differentiation and long-lasting disorders in spermatogenesis. Vepesid induced decondensation of spermatocyte I chromatin, block of desynapsis, and elongation of lateral elements of spermatocyte autosome synaptonemal complexes during late pachytene and diplotene of meiosis. This confirms the involvement of type II DNA topoisomerase in chromatin condensation and homologous chromosome desynapsis at the stage of diplotene and the role of this enzyme in structural organization of the synaptonemal complex. Vepesid induced the formation of dichotomy and breaks of the pericentromer regions of subelements of lateral elements of the autosomal synaptonemal complexes; the number of cells with associations of axial elements of sex chromosomes with autosomal synaptonemal complexes increased, univalents of autosomes and sex chromosomes appeared. Mesna, a modifier of toxic effects of antitumor drugs, had no toxic effect on spermatogenic cells. Mesna reduced the lethal effect of vepesid during combined treatment, but did not ensure long-term protection of spermatogenesis.

Animals↗

PubMed1992

The evolution of meiosis.

Meiosis is too complex to have arisen at once full blown and a stepwise scheme is proposed for its evolution, where each step is believed to have provided an immediate selective advantage: (1) The first step in this tentative sequence is the development of a haploidization process by means of a rapid series of mitotic non-disjunctions, turned on under conditions where haploidy is favored. The non-disjunctions may have resulted from a conditional mutation which caused sister centromere cohesiveness in the past mitotic metaphase. (2) Next probably came the formation of rudimentary synaptonemal complex type structures, first at Holliday-type configurations and later extending from these along chromosome pairs. These structures between homologues, though costly to produce and maintain, may have directly served the disjunctive function by setting the stage for the production of haploidy in one division, under conditions where it was advantageous. (3) Then secondarily acquired functions of the synaptonemal complex or structures associated with it may have promoted greatly increased crossover frequency, in part at least by increasing the frequency of the isomerization-type reaction. The resulting recombination of linked genes could have been advantageous under some conditions. (4) Finally, it is proposed that the capability was acquired for enhanced association of sister chromatids during the period between pachytene and anaphase I to give rise to chiasma-mediated disjunction, so that the relatively costly synaptonemal complex maintenance until anaphase I could be abandoned without losing disjunctive capability. It is implied that the modern synaptonemal complex is a structure which embodies a number of separately encoded proteins and that secondary structures and functions are associated with close homologue pairing. This scheme is based upon observable cytological and molecular characteristics of modern organisms.

Animals↗

PubMed2002

Asy1, a protein required for meiotic chromosome synapsis, localizes to axis-associated chromatin in Arabidopsis and Brassica.

The Arabidopsis thaliana ASY1 gene is essential for homologous chromosome synapsis. Antibodies specific to Asy1 protein and its homologue BoAsy1 from the related crop species Brassica oleracea have been used to investigate the temporal expression and localization of the protein in both species. Asy1 is initially detected in pollen mother cells during meiotic interphase as numerous punctate foci distributed over the chromatin. As leptotene progresses the signal appears to be increasingly continuous and is closely associated with the axial elements but not to the extended chromatin loops associated with them. By the end of zygotene the signal extends almost the entire length of the synapsed homologues, although not to the telomeres. The protein begins to disappear as the homologues desynapse, until by late diplotene it is no longer associated with the chromosomes. Immunogold labelling in conjunction with electron microscopy established that Asy1 localizes to regions of chromatin that associate with the axial/lateral elements of meiotic chromosomes rather than being a component of the synaptonemal complex itself. These data together with the previously observed asynaptic phenotype of the asy1 mutant suggest that Asy1 is required for morphogenesis of the synaptonemal complex, possibly by defining regions of chromatin that associate with the developing synaptonemal complex structure.

Arabidopsis↗

PubMed1982

Ultrastructural characterization of the meiotic prophase. A tool in the assessment of radiation damage in man.

The three-dimensional reconstruction of meiotic nuclei from serial sections micrographed in the electron microscope has provided information about man and several other organisms that is not obtainable by light microscopy or biochemical analysis. At zygotene, the previously unpaired chromosomes align and form synaptonemal complexes between homologous chromosome segments either by progressive initiation from the telomeres or by interstitial recognition. Chromosome and bivalent interlocking at zygotene is a regular phenomenon and occurs at a frequency of 0.7-4.0 per nucleus in samples of meiocytes analyzed from different organisms. This frequency is reduced to 0.1 per nucleus at pachytene. The interlockings are resolved by breakage and precise rejoining of the broken ends. This breakage and rejoining can also occur in the absence of the DNA nicking and repair involved in crossing-over. The synaptonemal complexes combining homologous chromosome segments are stabilized by recombination nodules, after which a second round of synaptonemal complex formation between as yet unpaired or unstably paired chromosome segments occurs, apparently for optimization of bivalent formation. Non-homologous pairing with the synaptonemal complex can take place in this phase of pachytene. Continuity between recombination nodules and chromatin chiasmata has been traced at the ultrastructural level but not all nodules lead to chiasmata. The distributions of recombination nodules among the bivalents and along the bivalents at successive stages of meiotic prophase show that the nodules are placed at random at early-zygotene after which bivalents without nodules have preference for the acquisition of these structures. Chiasma interference appears as a consequence of the limited number of recombination nodules available together with a decreased affinity of a bivalent arm with a nodule for additional ones. The relevance of these observations in the study of genetic damage by radiation is discussed.

Aneuploidy↗

PubMed2006

Abnormal progression through meiosis in men with nonobstructive azoospermia.

OBJECTIVE: To study meiotic abnormalities in men with nonobstructive azoospermia. DESIGN: Analysis of synaptonemal complex and recombination in testicular tissue. SETTING: Research laboratory. PATIENT(S): Twenty-nine men with nonobstructive azoospermia and 12 men with normal spermatogenesis. INTERVENTION(S): Testicular tissues were processed with immunofluorescent staining using antibodies against proteins associated with synaptonemal complex and recombination events. MAIN OUTCOME MEASURE(S): Synaptonemal complex configuration and recombination in meiosis I. RESULT(S): In patients with nonobstructive azoospermia, a marked heterogeneity in spermatogenesis was found: nearly half of them had a complete absence of meiotic cells, one case had germ cells arrested at the zygotene stage of meiotic prophase, and, in general, the rest had impaired fidelity of chromosome synapsis and recombination in pachytene cells. Compared with controls, these patients had significantly more cells in leptotene/zygotene and higher frequencies of unpaired chromosome regions in pachytene. Significantly reduced recombination, an increased frequency of achiasmate autosome bivalents, and sex univalents in pachytene were also observed in these patients with nonobstructive azoospermia. CONCLUSION(S): Defects in chromosome synapsis and decreased recombination during meiotic prophase may have led to spermatogenesis arrest and contributed in part to the unexplained infertility in these patients.

Adaptor Proteins, Signal Transducing↗

PubMed2003

Meiosis in the golden hamster: a confocal microscopy and flow cytometric analysis.

In this study, confocal microscopy and flow-cytometry were utilized to follow meiosis in hamster spermatogenesis. Confocal microscopy was used as an analytical tool to observe spermatocytes inside the tubules following meiotic progression consecutively at defined spermatogenic stages. To study spermatocyte differentiation, the structure of the synaptonemal complex was studied in detail at various stages of hamster spermatogenesis using the antibody against SC3 (the protein of axial/lateral element). The synaptonemal complex was observed from the leptotene stage until the first meiotic division with maximal staining in mid-pachytene spermatocytes, suggesting a role for SC3 at this postrecombinational stage. In addition, 3-dimensional (3D) images of synaptonemal complex were observed, providing information about spatial distribution of the chromosomes within the nuclei of spermatocytes at different stages of meiosis. Changes in spermatocyte sizes and DNA condensation allowed assessment of meiosis by flow cytometry. Changes in chromatin condensation at different stages of hamster meiosis were followed, revealing decondensation from early to late pachytene stages. The analysis also allowed a comparing of chromatin status of mitotic and meiotic chromosomes, confirming the less compact structure of the latter, possibly connected to increased transcriptional activity during meiosis.

Animals↗

PubMed2003

Relationship of DNA double-strand breaks to synapsis in Drosophila.

The relationship between synaptonemal complex formation (synapsis) and double-strand break formation (recombination initiation) differs between organisms. Although double-strand break creation is required for normal synapsis in Saccharomyces cerevisiae and the mouse, it is not necessary for synapsis in Drosophila and Caenorhabditis elegans. To investigate the timing of and requirements for double-strand break formation during Drosophila meiosis, we used an antibody that recognizes a histone modification at double-strand break sites, phosphorylation of HIS2AV (gamma-HIS2AV). Our results support the hypothesis that double-strand break formation occurs after synapsis. Interestingly, we detected a low (10-25% of wildtype) number of gamma-HIS2AV foci in c(3)G mutants, which fail to assemble synaptonemal complex, suggesting that there may be both synaptonemal complex-dependent and synaptonemal complex-independent mechanisms for generating double-strand breaks. Furthermore, mutations in Drosophila Rad54 (okr) and Rad51 (spnB) homologs cause delayed and prolonged gamma-HIS2AV staining, suggesting that double-strand break repair is delayed but not eliminated in these mutants. There may also be an interaction between the recruitment of repair proteins and phosphorylation.

Animals↗

PubMed2006

Effect of the quinolone coccidiostat decoquinate on the rearrangement of chromosomes of Eimeria tenella.

The present report concerns our attempts to further study the effect of quinolone coccidiostats on the sporulation of Eimeria tenella oocysts by analyzing the meiotic behaviour of the chromosomes. To that end, synaptonemal complexes were analyzed by TEM applied to intact meiotic chromosomes. These were isolated after disruption of oocysts, which were harvested from decoquinate-medicated and non-medicated (control) birds. In oocysts from control birds, synaptonemal complexes appeared as the 14 bivalents of the normal karyotype. However, in oocysts from medicated birds, our synaptonemal complex analysis revealed a reciprocal translocation, which was observed as an irregular pairing of chromosome axes 5 and 12 resulting in quadrivalent and trivalent configurations. This finding suggests breakage points in chromosomes 5 and 12 and exchange of chromosomal segments. Furthermore, breakpoints in chromosome 12 resulted in telomere deletion. The chromosomal aberrations described in the present study may result in reduced sporulation since chromosomes involved in translocations segregate abnormally during meiosis. In addition, the results reported provide new evidence of the inhibitory effect of quinolones on the sporulation of E. tenella oocysts, since sporocysts were not formed.

Animals↗

PubMed1989

Nucleolar structures in chromosome and SC preparations from human oocytes at first meiotic prophase.

We describe a comparative study of the behavior of nucleolar structures and their relationship with nucleolar chromosomes and synaptonemal complexes at first meiotic prophase of human oocytes in an attempt to elucidate the nature of this cellular organization and to learn more about maternal nondisjunction. The number of main nucleoli varies along the different stages of prophase I and is usually low. It shows an increase from leptotene to pachytene and a decrease from pachytene to diplotene related to a decrease and an increase of main nucleoli volume, respectively. The methodology employed has enabled us to analyze in detail dark bodies, round bodies, dense bodies, and main nucleoli in chromosome or synaptonemal complex spreads. The relationship between nucleolar chromosomes or synaptonemal complexes and the nucleoli implies the existence, in a very reduced space, of chromosomal regions that contain homologous sequences and that are often unpaired. This situation may facilitate the production of heterologous pairing and chromosomal exchanges between nonhomologous chromosomes and finally result in aneuploidy. Thus, the situation explained above together with the differences between the oocyte and spermatocyte NOR cycles could be one of the reasons for the higher incidence of aneuploidies of maternal origin at meiosis I.

Cell Nucleolus↗

PubMed1988

Chromosomal pairing in deer mice heterozygous for the presence of heterochromatic short arms.

The pattern of chromosomal pairing was analyzed in male deer mice (Peromyscus maniculatus and Peromyscus sitkensis) heterozygous for the presence of heterochromatic short arms. G- and C-banding of somatic metaphases indicated that the presence of heterochromatic short arms increased the length of chromosome 4 by 15% in P. sitkensis and that of chromosome 8 by 9% in P. maniculatus. Analysis of silver-stained late zygotene and early pachytene nuclei revealed a low frequency of unequal axial lengths in the synaptonemal complexes corresponding to the heteromorphic bivalents. All mid- and late pachytene nuclei, however, exhibited fully paired synaptonemal complexes with equalized axial lengths. These observations suggest the existence of an adjustment mechanism which functions to equalize the lengths of the two axes of the heteromorphic synaptonemal complex.

Animals↗