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Results for “Synaptonemal Complex”

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PubMed1989

Two kinds of "recombination nodules" in Neurospora crassa.

Two morphological types of recombination nodules, termed early and late, are recognized in Neurospora crassa. Eighty nuclei at different substages were used to determine numbers of nodules per nucleus, distribution of nodules along the nucleolus-organizing chromosome, and distribution of nodules among the two largest chromosomes. Early nodules appear at the synaptonemal complex at early zygotene and increase in number during zygotene until a dramatic reduction occurs at zygotene-pachytene transition. Thereafter early nodules are steadily eliminated until they disappear by diplotene. Late nodules are also present during zygotene. Their number doubles at the zygotene-pachytene transition and stays at this level until diplotene. The total number of nodules is rather constant through zygotene and pachytene. Distribution of bivalents with 0, 1, 2, etc. nodules follows a Poisson distribution at zygotene, but not at pachytene, where variance is less than the mean, indicating positive interference. Nodules are distributed nonrandomly along the nucleolus-organizer bivalent. The pattern differs slightly in nuclei of different origin. Nuclei with unusual synaptonemal complexes sustain normal levels of recombination by having the same amount of nodules as normal nuclei. In abnormal nuclei nodules are preferentially associated with normal segments. It is proposed that early nodules do not participate in any form of recombination but have a role in finding an appropriate site for a crossing-over event. Morphological change to the late type indicates that the site has been reached and the exchange event can be mediated by the late nodule.

Chromosomes↗

PubMed2003

In silico search for functionally similar proteins involved in meiosis and recombination in evolutionarily distant organisms.

Evolutionarily distant organisms have not only orthologs, but also nonhomologous proteins that build functionally similar subcellular structures. For instance, this is true with protein components of the synaptonemal complex (SC), a universal ultrastructure that ensures the successful pairing and recombination of homologous chromosomes during meiosis. We aimed at developing a method to search databases for genes that code for such nonhomologous but functionally analogous proteins. Advantage was taken of the ultrastructural parameters of SC and the conformation of SC proteins responsible for these. Proteins involved in SC central space are known to be similar in secondary structure. Using published data, we found a highly significant correlation between the width of the SC central space and the length of rod-shaped central domain of mammalian and yeast intermediate proteins forming transversal filaments in the SC central space. Basing on this, we suggested a method for searching genome databases of distant organisms for genes whose virtual proteins meet the above correlation requirement. Our recent finding of the Drosophila melanogaster CG17604 gene coding for synaptonemal complex transversal filament protein received experimental support from another lab. With the same strategy, we showed that the Arabidopsis thaliana and Caenorhabditis elegans genomes contain unique genes coding for such proteins.

Animals↗

PubMed1998

Heterogeneity and meiotic behaviour of B and sex chromosomes, banding patterns and localization of (TTAGGG)n sequences by fluorescence in situ hybridization in the neotropical water rat Nectomys (Rodentia, Cricetidae).

A cytogenetic study using fluorescence in situ hybridization (FISH) of telomere probes, CBG, GTG and RBG banding patterns and synaptonemal complex data was carried out in 41 specimens of Nectomys from three Brazilian states: Pernambuco, Mato Grosso and São Paulo. The specimens presented 2n = 52, 53, 56 and 57, and the differences in chromosome number were due to the presence of three different supernumeraries and also to the occurrence of tandem fusions. The tandem fusions involved chromosome pairs 3 + 11 and 5 + 24 from karyotype with 2n = 56 that originated pairs 1 and 4 in specimens with 2n = 52. Sex chromosome polymorphism was also detected, and the X presented three different morphologies, which could be explained by heterochromatin addition/deletion. FISH results revealed interstitial telomeric bands (ITBs) in a submetacentric B, but no ITB was detected in the chromosomes originated by tandem fusion. The supernumeraries presented a remarkable heterogeneity of size and morphology, constitutive heterochromatin pattern and localization of telomeric sequences. Synaptonemal complex by light and electron microscopy showed the supernumerary as an autopaired univalent. The sex chromosome pairing in meiotic cells involved the heterochromatic short arm of the X chromosome and the short arm of the Y chromosome.

Animals↗

PubMed2001

Synaptic pattern of sex complements and sperm head malformation in X-autosome translocation carrier bulls.

Testicular activity and semen characteristics of bulls carrying an X-autosome translocation t(Xp +;23q-) revealed all stages of spermatogenesis although their semen consisted of few and, exclusively, of malformed spermatozoa. Chromosome painting on metaphase spreads of their mother and synaptonemal complex analysis on these and normal bulls were carried out to test whether the location and meiotic pairing behaviour of the rearranged segments could have contributed to the sperm head malformation and oligospermia in our X-autosome translocation (X-AT) carrier bulls. Spermatocytes of X-AT carriers displayed the rearranged chromosomes in a univalent-trivalent association, with 23q- always remaining as a univalent and Xp + in synapsis with normal chromosome 23 and the Y chromosome. Chromosome painting studies to test whether the total absence of meiocytes showing a quadrivalent is due to the non-reciprocal nature of this translocation, identified Xp sequence homology with the distal end of 23q- confirming its relocation to the terminal segment of 23q-. Our synaptonemal complex analyses also confirmed that the bovine pseudo-autosomal region (PAR) is at the distal ends of Xq and Yp and further revealed that over 85% of spermatocytes of X-AT carriers (and up to 13% of spermatocytes of normal bulls) sustain a Y-axis break adjacent to the PAR. Although the exact cause of a Y-axis break in bovine spermatocytes is not known at present, we believe that the break and possible loss of Yq in such high proportions of spermatocytes of X-AT carriers could have contributed to the sperm head malformation and oligospermia in our X-AT carrier bulls.

Animals↗

PubMed1993

A conditional allele of the Saccharomyces cerevisiae HOP1 gene is suppressed by overexpression of two other meiosis-specific genes: RED1 and REC104.

The HOP1 gene of Saccharomyces cerevisiae is believed to encode a protein component of the synaptonemal complex, the structure formed when homologous chromosomes synapse during meiotic prophase. Five new mutant alleles (three conditional, two nonconditional) of HOP1 were identified by screening EMS-mutagenized cells for a failure to complement the spore viability defect of a hop1 null allele. Two high copy plasmids were found that partially suppress the temperature-sensitive spore inviability phenotype of one of these alleles, hop1-628. The suppression is allele-specific; no effect of the plasmids is observed in hop1 null diploids. Mutation of either of the two suppressor genes results in recessive spore lethality, indicating that these genes play important roles during meiosis. The DNA sequence of one high copy suppressor gene matched that of RED1, a previously identified meiosis-specific gene. Our data strongly support the idea that RED1 protein is also a component of the synaptonemal complex and further suggest that the RED1 and HOP1 gene products may interact. The second suppressor maps to the right arm of chromosome VIII distal to CDC12 and is REC104, a meiosis-specific gene believed to act early in meiosis.

Alleles↗

PubMed2000

The dicentric nature of the metacentric B chromosome of Metaleptea brevicornis adspersa (Acridinae, acrididae).

The meiotic behaviour of a large B isochromosome of Metaleptea brevicornis adspersa (Acridinae, Acrididae) was studied in both sexes using conventional preparations and in males by silver staining of surface-spread synaptonemal complexes and kinetochores. In males, both arms of the B chromosome synapse at zygotene-early pachytene suggesting its isochromosomal nature. Both arms separate precociously at late pachytene and remain joined only through the formation of a single distal chiasma in 92.5% and 91.7% of male and female meiocytes, respectively. In both sexes, the B chromosome tends to migrate precociously to one of the spindle poles, auto-orientating at the equator in 19.2% and 16.6% of metaphase I cells of males and females, respectively. In males, this produces a high frequency of anaphase I/telophase I lagging with the consequent inhibition of cytokinesis and the formation of second division restitution nuclei. For a better understanding of the synaptic and segregation behaviour of the B chromosome in males, pachytene synaptonemal complex (SC) formation was studied. In 0B males, pachytene nuclei invariably showed 11 fully paired SCs, each one with a densely stained pair of terminal kinetochores, and a single axis with a single kinetochore corresponding to the X univalent. In 1B males, both arms of the B chromosome appeared fully paired in 93. 8% of the nuclei, showing complete asynapsis in the rest. This frequency is almost exactly the same as distal chiasma formation in diplotene. The centric region of the SC of the B chromosome had two kinetochores connected by a single axial filament of variable length. The dicentric nature of the B was confirmed by silver staining of kinetochores at metaphase I and anaphase II stages. This is the first time that a dicentric B isochromosome has been described. Based on these results, two alternative models for the origin of isochromosomes are postulated.

Animals↗

PubMed1995

Microtubule-driven nuclear movements and linear elements as meiosis-specific characteristics of the fission yeasts Schizosaccharomyces versatilis and Schizosaccharomyces pombe.

Meiotic prophase in Schizosaccharomyces pombe is characterized by striking nuclear movements and the formation of linear elements along chromosomes instead of tripartite synaptonemal complexes. We analysed the organization of nuclei and microtubules in cells of fission yeasts undergoing sexual differentiation. S. japonicus var. versatilis and S. pombe cells were studied in parallel, taking advantage of the better cytology in S. versatilis. During conjugation, microtubules were directed towards the mating projection. These microtubules seem to lead the haploid nuclei together in the zygote by interaction with the spindle pole bodies at the nuclear periphery. After karyogamy, arrays of microtubules emanating from the spindle pole body of the diploid nucleus extended to both cell poles. The same differentiated microtubule configuration was elaborated upon induction of azygotic meiosis in S. pombe. The cyclic movements of the elongated nuclei between the cell poles is reflected by a dynamic and coordinated shortening and lengthening of the two microtubule arrays. When the nucleus was at a cell end, one array was short while the other bridged the whole cell length. Experiments with inhibitors showed that microtubules are required for karyogamy and for the elongated shape and movement of nuclei during meiotic prophase. In both fission yeasts the SPBs and nucleoli are at the leading ends of the moving nuclei. Astral and cytoplasmic microtubules were also prominent during meiotic divisions and sporulation. We further show that in S. versatilis the linear elements formed during meiotic prophase are similar to those in S. pombe. Tripartite synaptonemal complexes were never detected. Taken together, these findings suggest that S. pombe and S. versatilis share basic characteristics in the organization of microtubules and the structure and behaviour of nuclei during their meiotic cell cycle. The prominent differentiations of microtubules and nuclei may be involved in the pairing, recombination, and segregation of meiotic chromosomes.

Benomyl↗

PubMedDate not supplied

XY-quadrivalent association and sterility in a man carrier of a reciprocal autosomal translocation involving the whole arm of an acrocentric chromosome t(2;15)(q21.3;cen).

Meiotic and synaptonemal complex studies using electron microscopy were carried out on an infertile man with a 46,XY t(2q;15p). Synaptonemal complex analysis showed terminal asynapsis in the totality of quadrivalents and a high and significant frequency of association with the XY vesicle (80%), possibly related to the high amount of satellite DNA of the acrocentric chromosome 15. In this translocation carrier, the XY quadrivalent association at pachytene stage is positively correlated with the degree of spermatogenic breakdown after pachytene stage. Whether association with the non-paired segment represents the causative factor or only a secondary effect has still to be clarified.

Adult↗

PubMed1991

[Synapsis and chiasma distribution in mice heterozygous for translocations in chromosomes 16 and 17].

Electron microscopic analysis of synaptonemal complexes and analysis of chiasmata distribution in male mice heterozygous for Robertsonian translocation T(16; 17)7Bnr - (Rb7), for synaptonemal reciprocal translocation T(16;17)43H - (T43), in double heterozygotes for these translocations and in males with partial trisomy of the proximal region of chromosome 17 was carried out. Synaptic disturbances around the breakpoints of the translocations, such as asynapsis of homologous regions of partners and non-homologous synapsis of centromeric regions of acrocentric chromosomes, were revealed. Synaptic regularity in the proximal part of the chromosome 17 appeared to be affected by no t12 haplotype. Good coincidence between sizes of mitotic chromosomes and corresponding lateral elements of synaptonemal complexes was found for all chromosomes, with the exception of Rb7 in trisomics. In the latter karyotype, the proximal part of chromosome 17 involved in Robertsonian fusion seems to be shortened in the course of zygotene and never synapted with homologous segment of neither the acrocentric chromosome 17 nor large product of reciprocal translocation. Drastic increase in chiasmata frequency in the proximal part of chromosome 17 was revealed in heterozygotes for T43H and in trisomics, as compared with the double heterozygotes Rb7/T43. The latter finding was explained by the existence of two independent pairing segments in the former karyotypes.

Animals↗

PubMed2001

Mammalian STAG3 is a cohesin specific to sister chromatid arms in meiosis I.

Cohesins, which have been characterized in budding yeast and Xenopus, are multisubunit protein complexes involved in sister chromatid cohesion. Regulation of the interactions among different cohesin subunits and the assembly/disassembly of the cohesin complex to chromatin are key steps in chromosome segregation. We previously characterized the mammalian STAG3 protein as a component of the synaptonemal complex that is specifically expressed in germinal cells, although its function in meiosis remains unknown. Here we show that STAG3 has a role in sister chromatid arm cohesion during mammalian meiosis I. Immunofluorescence results in prophase I cells suggest that STAG3 is a component of the axial/lateral element of the synaptonemal complex. In metaphase I, STAG3 is located at the interchromatid domain and is absent from the chiasma region. In late anaphase I and the later stages of meiosis, STAG3 is not detected. STAG3 interacts with the structural maintenance chromosome proteins SMC1 and SMC3, which have been reported to be subunits of the mitotic cohesin complex. We propose that STAG3 is a sister chromatid arm cohesin that is specific to mammalian meiosis I.

Animals↗

PubMed2005

Mutations in the chromosome pairing gene FKBP6 are not a common cause of non-obstructive azoospermia.

Although it is generally thought that spermatogenic failure has a genetic background, to date only a limited percentage of men with non-obstructive azoospermia (NOA) are diagnosed with a genetic defect. The only common and well-established genetic causes of NOA in humans are numerical and structural chromosomal abnormalities and Y-chromosome deletions. In addition, some infrequent mutations have been identified in the ubiquitin-specific protease 9, Y-linked (USP9Y) and the synaptonemal complex protein 3 (SYCP3) gene that cause azoospermia. FK506-binding protein 6 (Fkbp6) is a newly discovered component of the synaptonemal complex (SC), which is essential for proper chromosome pairing and meiotic division. A null mutation of the Fkbp6 gene causes azoospermia in mice as well as in rats. We tested the hypothesis whether mutations in this gene can also cause azoospermia in humans. We performed a mutation screen in 51 men with NOA through direct sequencing methods. No homozygous mutations were identified. Two heterozygous mutations (T173T and R183C) were identified, which are likely to disrupt FKBP6 protein function. However, both mutations were also found in a group of 218 normospermic controls indicating that one FKBP6 allele appears to be sufficient for normal spermatogenesis. In conclusion, our results suggest that genetic defects in FKBP6 can be excluded as a common cause of azoospermia in humans.

Azoospermia↗

PubMed1979

Karyotype analysis of the plant-parasitic nematode Heterodera glycines by electron microscopy. 1. The diploid.

Heterodera glycines is a diploid amphimictic nematode with n = 9 chromosomes. Nine normal synaptonemal complexes (SC) were detected following 3-dimensional reconstruction of pachytene nuclei from electron microscopy of serial sections. Regions of unique 'modified synaptonemal complexes' (MSC) were observed along 2 SCs. These consist of a heterochromatic knob within which the SC appears either disorganized or stacked in layers of lateral elements. Its function is not known. Recombination nodules and 'cylindrical granular complexes', were not observed in H. glycines.

Animals↗

PubMed1980

Light microscopic observations on the behavior of silver-stained trivalents in pachytene cells of Sigmodon fulviventer (Rodentia, Muridae) heterozygous for centric fusion.

Silver-stained pachytene cells of male cotton rats, Sigmodon fulviventer, heterozygous for a naturally occurring Robertsonian fusion, were examined by light microscopy. Silver staining clearly revealed synaptonemal complexes of all autosomal bivalents and of the translocation trivalent, as well as X-Y conformations within the sex vesicle. The synaptonemal complex of the trivalent conforms closely in morphology to that observed by electron microscopy in hybrids of other species. In all cases, the proximal telomeric knobs of the two acrocentric elements were paired and projected in the same direction from the metacentric element. The geometry of trivalent pairing in pachytene may predispose to normal disjunction and, therefore, account for the high fertility observed in S. fulviventer heterozygotes.

Animal Population Groups↗

PubMed1986

Recombination nodules in the oocytes of the chicken, Gallus domesticus.

Chicken oocytes at pachytene were processed with the microspreading technique (Moses, 1977), and their synaptonemal complex (SC) complements were analyzed by electron microscopy. Ellipsoidal nodules, 140 X 120 nm in diameter, were associated with the central space of synaptonemal complexes. The average number of nodules per pachytene oocyte was 57.5. The number of nodules per bivalent showed a clear linear relationship with SC length, except for the microchromosomes, which showed a single obligatory nodule. The distribution of nodules along the 10 longest SCs was nonrandom, with low frequencies in the vicinity of kinetochores and high frequencies near the telomeres. The microchromosomes showed a single nodule whose average location was 1.21 micron from the kinetochore. In the ZW pair there was a single nodule whose average location was 0.31 micron from the paired telomeres and not more than 0.65 micron from them. The total number of nodules per cell and the number of nodules in each of the five major bivalents showed good agreement with the total number of chiasmata and the number of chiasmata of the major bivalents of roosters. Thus, these nodules share the characteristics of recombination nodules described in other organisms. The single, obligatory, strictly localized recombination nodule found in the pairing end of the ZW pair strongly suggests that recombination between the Z and W chromosomes in the female chicken is a regular process that may be similar to the obligatory recombination between the pairing ends of the human X and Y chromosomes that was recently described in studies using DNA probes.

Animals↗

PubMed1979

Silver-stained structures in mammalian meiotic prophase.

Silver staining of mammalian spermatocytes revealed, in light microscopy, synaptonemal complex and structures within the sex vesicle. It is feasible to follow the chromosome pairing phenomenon from zygotene to pachytene by examining the behavior of synaptonemal complexes. Nucleolus organizer regions take heavy silver stain in pachytene but are no longer detectable in later stages of meiosis.

Animals↗

PubMed2006

Dysfunction of the mitotic:meiotic switch as a potential cause of neoplastic conversion of primordial germ cells.

Germ cell tumours (GCT) are thought to arise as the result of a defect in early development, probably shortly after arrival of the migrating primordial germ cells (PGC) in the genital ridge when, if in a male genital ridge, the germ cells arrest in mitosis, but in a female genital ridge they enter meiosis. We suggest that dysfunction of the mitotic:meiotic switch, with cells aberrantly co-expressing functions pertinent to both states, might provide the genetic instability that could initiate tumour development. If this hypothesis is correct, GCT could arise because of disruption in the function of any one of a number of different genes involved in controlling mitosis and meiosis, rather than being dependent upon a single prominent susceptibility gene. The Notch signalling system is one candidate system for controlling the switch and we have identified expression of Notch2 and Notch4 in seminomas and carcinoma in situ. Thus those two members of the Notch family are candidates for proto-oncogenes that could play a role in GCT development. We have also identified a human homologue of the synaptonemal complex protein, SCP3, and have found its apparently aberrant expression in some established EC cell lines. One possibility is that abnormal regulation of such proteins involved in the synaptonemal complex could also lead to genetic instability in PGC and so also initiate tumour development.

Cell Cycle Proteins↗

PubMed2006

Linear element-independent meiotic recombination in Schizosaccharomyces pombe.

Most organisms form protein-rich, linear, ladder-like structures associated with chromosomes during early meiosis, the synaptonemal complex. In Schizosaccharomyces pombe, linear elements (LinEs) are thread-like, proteinacious chromosome-associated structures that form during early meiosis. LinEs are related to axial elements, the synaptonemal complex precursors of other organisms. Previous studies have led to the suggestion that axial structures are essential to mediate meiotic recombination. Rec10 protein is a major component of S. pombe LinEs and is required for their development. In this report we study recombination in a number of rec10 mutants, one of which (rec10-155) does not form LinEs, but is predicted to encode a truncated Rec10 protein. This mutant has levels of crossing over and gene conversion substantially higher than a rec10 null mutant (rec10-175) and forms cytologically detectable Rad51 foci indicative of meiotic recombination intermediates. These data demonstrate that while Rec10 is required for meiotic recombination, substantial meiotic recombination can occur in rec10 mutants that do not form LinEs, indicating that LinEs per se are not essential for all meiotic recombination.

Cell Nucleus Structures↗

PubMed1996

The rad9 gene of Coprinus cinereus encodes a proline-rich protein required for meiotic chromosome condensation and synapsis.

The rad9 gene of Coprinus cinereus is essential for the normal completion of meiosis. We examined surface-spread preparations of wild-type and rad9-1 nuclei from the meiotic stages of karyogamy through metaphase I, and we determined the primary sequence, structure, and meiotic expression of the rad9 gene. In wild-type C. cinereus, karyogamy is followed by condensation and alignment of homologous chromosomes. Condensation and axial core development largely precede synapsis, which often initiates at telomeres. A diffuse diplotene phase coincides with dissolution of the synaptonemal complex, and subsequently chromosomes further condense as the cells progress into metaphase I. In contrast, although karyogamy and nucleolar fusion are apparently normal in rad9-1 basidia, only short stretches of synaptonemal complex form. These correlate with stretches of condensed chromatin, mostly at apparent chromosome ends, and regions of presumptive triple synapsis are numerous. rad9-1 basidia enter the diffuse stage of early diplotene, and then 50% of these cells enter metaphase I by the criteria of nucleolar elimination and at least some chromatin condensation. rad9 gene expression is induced after gamma irradiation and during meiosis. The gene has 27 exons and encodes a predicted protein of 2157 amino acids, with a proline-rich amino terminus.

Amino Acid Sequence↗