PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Synaptonemal Complex”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 721 records · Page 40Linked to original sources
PubMed2005

[Genetic collection of meiotic mutants of rye Secale cereale L].

Genetic collection of meiotic mutants of winter rye Secale cereale L. (2n = 14) was created. Mutations were detected in inbred F2 generations after self-fertilization of the F1 hybrids, obtained by individual crossing of rye plants (cultivar Vyatka) or weedy rye with plants from autofertile lines. The mutations cause partial or complete plant sterility and are maintained in collection in a heterozygous state. Genetic analysis accompanied by cytogenetic study of meiosis has revealed six mutation types. (1) Nonallelic asynaptic mutations sy1 and sy9 caused the formation of only axial chromosome elements in prophase and anaphase. The synaptonemal complexes (SCs) were absent, the formation of the chromosome "bouquet" was impaired, and all chromosomes were univalent in meiotic metaphase I in 96% (sy1) and 67% (sy2) of cells. (2) Weak asynaptic mutation sy3, which hindered complete termination of synapsis in prophase II. Subterminal asynaptic segments were always observed in the SC, and at least one pair of univalents was present in metaphase I, but the number of cells with univalents did not exceed 2%. (3) Mutations sy2, sy6, sy7, sy8, sy10, and sy19, which caused partially nonhomologous synapsis: change in pairing partners and fold-back chromosome synapsis in prophase I. In metaphase I, the number of univalents varied and multivalents were observed. (4) Mutation mei6, which causes the formation of ultrastructural protrusions on the lateral SC elements, gaps and branching of these elements. (5) Allelic mutations mei8 and mei10, which caused irregular chromatin condensation along chromosomes in prophase I, sticking and fragmentation of chromosomes in metaphase I. (6) Allelic mutations mei5 and mei10, which caused chromosome hypercondensation, defects of the division spindle formation, and random arrest of cells at different meiotic stages. However, these mutations did not affect the formation of microspore envelopes even around the cells, whose development was blocked at prophase I. Analysis of cytological pictures of meiosis in double rye mutants reveled epistatic interaction in the mutation series sy9 > sy1 > sy3 > sy19, which reflects the order of switching these genes in the course of meiosis. The expression of genes sy2 and sy19 was shown to be controlled by modifier genes. Most meiotic mutations found in rye have analogs in other plant species.

Chromatin Assembly and Disassembly↗
PubMed1999

Colchicine effects on meiosis in the male mouse. II. Inhibition of synapsis and induction of nondisjunction.

This report follows from our earlier study using synaptonemal complex (SC) analysis in which colchicine administered to mouse spermatocytes specifically at leptotene/zygotene blocks synapsis, resulting in univalents at early pachytene. Despite loss of severely damaged cells from the prophase population, substantial numbers of cells with lesser damage progress to late pachytene on schedule. The present study tests whether the surviving cells would continue through meiotic divisions and if so, whether the univalents at MI result in hyperploidy at MII. At 7 days after treatment (late pachytene) 5.9% of the surviving population contains at most four autosomal axial univalents. In whole chromosome preparations 10 days post-colchicine the highest frequency of MIs with univalents is 5.2%. The maximum number of autosomal "chromosomal" univalents per cell is four. The percentage of cells with autosomal univalents at late pachytene, is not significantly different from the percentage of cells with chromosomal univalents at MI. We infer from these observations that the two kinds of univalents are equivalent. At days 11-12 post-colchicine, hyper (and hypo) ploidy at AI-MII is observed. We conclude that univalents produced by colchicine-induced asynapsis at leptotene/zygotene persist and lead to nondisjunction at division I and hyperploidy at division II. If the hyperploid spermatids mature, they would give rise to aneuploid sperm, thus constituting a mechanism for inducing aneuploid (e.g., trisomic) zygotes after fertilization. It is also observed that chiasma frequency (number of chiasmata per bivalent, univalents excluded) is reduced by about 15% of the control. Nondisjunction is known to be the endpoint of colchicine action when administered at prometaphase-MI, interfering with the segregation of homologues through effects on the MI-AI spindle. We show that nondisjunction is also the endpoint of colchicine's effect at early pachytene, in this case causing synaptic inhibition that creates univalents which are then distributed randomly at first division. These conclusions draw special attention to predivision meiotic events, particularly those affecting synapsis, and their sensitivity to induced and/or inherent effects that may have consequences later at meiotic divisions, creating risk to the chromosomal constitution of the gametes.

Animals↗
PubMed1992

A coiled-coil related protein specific for synapsed regions of meiotic prophase chromosomes.

Synaptonemal complexes (SCs) are structures that are formed between homologous chromosomes during meiotic prophase. They are probably involved in chromosome pairing and recombination. Using a monoclonal anti-SC antibody we isolated cDNAs encoding a major component of SCs which is localized specifically in synapsed segments of meiotic prophase chromosomes. The protein predicted from the nucleotide sequence of a full-length cDNA, named SCP1, consists of 946 amino acid residues and has a molecular weight of 111 kDa. It shares several features with nuclear lamins and some recently identified nuclear matrix proteins. The major part of SCP1 consists of long stretches capable of forming amphipathic alpha-helices. This region shows amino acid sequence similarity to the coiled-coil region of myosin heavy chain. A leucine zipper is included in this region. The carboxy-terminus has two small basic domains and several S/T-P-X-X motifs, which are characteristic of DNA-binding proteins. One of these motifs is a potential target site for p34cdc2 protein kinase. The amino-terminus is acidic and relatively proline-rich, but does not contain the S/T-P-X-X motif. The transcription of the gene encoding SCP1 is restricted to zygotene-diplotene spermatocytes. A polyclonal antiserum raised against the fusion protein of one of the cDNA clones recognizes a single protein on Western blots of isolated SCs, with an electrophoretic mobility identical to that of the antigen recognized by the original monoclonal antibody (mAb), IX5B2. From a detailed comparison of the immunogold labelling of rat SCs by mAb IX5B2 and the polyclonal anti-fusion protein antiserum respectively, we tentatively infer that the carboxy-terminus of SCP1 is orientated towards the lateral elements and that the other domains of the protein extend towards the central region between the lateral elements. We conclude that SCP1 is the major component of the transverse filaments of SCs, and speculate that it has evolved by specialization of a nuclear matrix protein.

Amino Acid Sequence↗
PubMed2001

The distribution of early recombination nodules on zygotene bivalents from plants.

Early recombination nodules (ENs) are protein complexes approximately 100 nm in diameter that are associated with forming synaptonemal complexes (SCs) during leptotene and zygotene of meiosis. Although their functions are not yet clear, ENs may have roles in synapsis and recombination. Here we report on the frequency and distribution of ENs in zygotene SC spreads from six plant species that include one lower vascular plant, two dicots, and three monocots. For each species, the number of ENs per unit length is higher for SC segments than for (asynapsed) axial elements (AEs). In addition, EN number is strongly correlated with SC segment length. There are statistically significant differences in EN frequencies on SCs between species, but these differences are not related to genome size, number of chromosomes, or phylogenetic class. There is no difference in the frequency of ENs per unit length of SC from early to late zygotene. The distribution of distances between adjacent ENs on SC segments is random for all six species, but ENs are found at synaptic forks more often than expected for a random distribution of ENs on SCs. From these observations, we conclude that in plants: (1) some ENs bind to AEs prior to synapsis, (2) most ENs bind to forming SCs at synaptic forks, and (3) ENs do not bind to already formed SCs.

Chromosomes↗
PubMed1998

Stable interaction between the products of the BRCA1 and BRCA2 tumor suppressor genes in mitotic and meiotic cells.

BRCA1 and BRCA2 account for most cases of familial, early onset breast and/or ovarian cancer and encode products that each interact with hRAD51. Results presented here show that BRCA1 and BRCA2 coexist in a biochemical complex and colocalize in subnuclear foci in somatic cells and on the axial elements of developing synaptonemal complexes. Like BRCA1 and RAD51, BRCA2 relocates to PCNA+ replication sites following exposure of S phase cells to hydroxyurea or UV irradiation. Thus, BRCA1 and BRCA2 participate, together, in a pathway(s) associated with the activation of double-strand break repair and/or homologous recombination. Dysfunction of this pathway may be a general phenomenon in the majority of cases of hereditary breast and/or ovarian cancer.

Antibodies, Monoclonal↗
PubMed1972

The temporal sequence of synaptic initiation, crossing over and synaptic completion.

Questions are raised as to the validity of arguments that crossover positions have been demonstrated to be normally established only during pachytene (after synapsis is maximal). An alternative and testable hypothesis is that crossover commitment can occur at events of synaptic initiation.-Measurements are presented of extents of pachytene synapsis and failure in and around a region of maize chromosome heterozygous for a short paracentric inversion, and these are compared to conjectured expectations from observations of crossover frequencies within the inversion. Various hypotheses consistent with the results are considered. It is pointed out that the hypothesis that increases in crossover frequency in the synapsed region of the inversion are compensatory to crossover inhibitions elsewhere requires complex assumptions: that the adjustment must take place among, not within cells and that the enhancement is preferentially expressed within the inversion instead of elsewhere in the genome. The hypothesis that the fixing and squashing procedure forces apart non-crossover regions previously synapsed but lacking a crossover also requires complex assumptions. The simplest hypothesis proposes that crossover commitment may determine synaptic expression. A role of the synaptonemal complex in the establishment of crossover sites is questioned or minimized.-Evidence is also presented with respect to conceivable function of the telomere in synaptic initiation. Restrictions on such a function, if it exists, seem to be required to account for the observations.

Chromosome Aberrations↗
PubMed2002

The Mnd1 protein forms a complex with hop2 to promote homologous chromosome pairing and meiotic double-strand break repair.

The hop2 mutant of Saccharomyces cerevisiae arrests in meiosis with extensive synaptonemal complex (SC) formation between nonhomologous chromosomes. A screen for multicopy suppressors of a hop2-ts allele identified the MND1 gene. The mnd1-null mutant arrests in meiotic prophase, with most double-strand breaks (DSBs) unrepaired. A low level of mature recombinants is produced, and the Rad51 protein accumulates at numerous foci along chromosomes. SC formation is incomplete, and homolog pairing is severely reduced. The Mnd1 protein localizes to chromatin throughout meiotic prophase, and this localization requires Hop2. Unlike recombination enzymes such as Rad51, Mnd1 localizes to chromosomes even in mutants that fail to initiate meiotic recombination. The Hop2 and Mnd1 proteins coimmunoprecipitate from meiotic cell extracts. These results suggest that Hop2 and Mnd1 work as a complex to promote meiotic chromosome pairing and DSB repair. The identification of Hop2 and Mnd1 homologs in other organisms suggests that the function of this complex is conserved among eukaryotes.

Alleles↗
PubMed1982

Sex chromosome pairing during male meiosis in marsupials.

The pairing of the sex chromosomes at pachytene has been examined in twenty-two species of Australian marsupials, including four with complex sex chromosome systems. The axial elements of the sex chromosomes associate in all but one species. However, no synaptonemal complex has been observed between the axes of the X and Y chromosome in any of the examined species. Both the type of association between the sex chromosome axes, and the structural modifications of these axes are conserved within taxonomic groupings. In three species with complex sex chromosome systems, the t(XA), Y, A trivalents do not have a favoured relative orientation of the axes of the Y and A chromosomes, whereas in a fourth species with a t(XA1), t(A2YA1), A2 system the t(XA1) and A2 axes are in a cis arrangement with each other.

Animals↗
PubMed2005

Absence of mouse REC8 cohesin promotes synapsis of sister chromatids in meiosis.

REC8 is a key component of the meiotic cohesin complex. During meiosis, cohesin is required for the establishment and maintenance of sister-chromatid cohesion, for the formation of the synaptonemal complex, and for recombination between homologous chromosomes. We show that REC8 has an essential role in mammalian meiosis, in that Rec8 null mice of both sexes have germ cell failure and are sterile. In the absence of REC8, early chromosome pairing events appear normal, but synapsis occurs in a novel fashion: between sister chromatids. This implies that a major role for REC8 in mammalian meiosis is to limit synapsis to between homologous chromosomes. In all other eukaryotic species studied to date, REC8 phenotypes have been restricted to meiosis. Unexpectedly, Rec8 null mice are born in sub-Mendelian frequencies and fail to thrive. These findings illuminate hitherto unknown REC8 functions in chromosome dynamics during mammalian meiosis and possibly in somatic development.

Acetaminophen↗
PubMed2004

A new role for the mitotic RAD21/SCC1 cohesin in meiotic chromosome cohesion and segregation in the mouse.

The evolutionarily conserved cohesin complex is required for the establishment and maintenance of sister chromatid cohesion, in turn essential for proper chromosome segregation. RAD21/SCC1 is a regulatory subunit of the mitotic cohesin complex, as it links together all other subunits of the complex. The destruction of RAD21/SCC1 along chromosomal arms and later at centromeres results in the dissociation of the cohesin complex, facilitating chromosome segregation. Here, we report for the first time that mammalian RAD21/SCC1 associates with the axial/lateral elements of the synaptonemal complex along chromosome arms and on centromeres of mouse spermatocytes. Importantly, RAD21/SCC1 is lost from chromosome arms in late prophase I but persists on centromeres. The loss of centromeric RAD21/SCC1 coincides with the separation of sister chromatids at anaphase II. These findings support a role for mammalian RAD21/SCC1 in maintaining sister chromatid cohesion in meiosis.

Anaphase↗
PubMed1999

BRCA1, BRCA2, and Rad51 operate in a common DNA damage response pathway.

The two major hereditary breast cancer susceptibility genes, BRCA1 and BRCA2, are associated with early-onset breast and/or ovarian cancer and encode products that each interact with the product of the eukaryotic RecA homologue, hRad51. We have recently found that BRCA1 and BRCA2 coexist in a common biochemical complex. The two proteins also colocalize in subnuclear foci in somatic cells as well as on the axial elements of developing synaptonemal complexes in meiotic cells. Thus, BRCA1 and BRCA2 participate in a common DNA damage response pathway associated with the activation of homologous recombination and double-strand break repair. Dysfunction of this pathway may be a general phenomenon in the majority of cases of hereditary breast and/or ovarian cancer. The BRCA1/BRCA2 complex may function in postreplicational repair processes activated during the DNA synthesis stage of the cell cycle.

BRCA2 Protein↗
PubMed1980

Synaptosomal complexes and associated structures in microspread human spermatocytes.

Human spermatocytes processed with a modified microspreading technique which involves the use of sodium dodecyl-sulphate (SDS) have been used to construct synaptonemal complex (SC) karyotypes. Twenty two pachytene spermatocytes were selected for length quantitation. The mean values of relative lengths and centromeric indexes of each SC agree closely with values obtained by three-dimensional reconstructions (Holm and Rasmussen, 1977), except for SCs #4--5, 6--7 and 19--20. Absolute lengths are consistently longer in spreads (10.7% longer than in sections, on average). The mean total length of the SC complement is 258.7 micrometer. Six morphological types of XY pairs have been described. On the basis of the relationships between the XY pair, nucleolar development and autosome behavior, these six XY types are assumed to develop in succession. Type O XY pairs occur during late zygotene, types I and II XY pairs occur during early to mid-pachytene, and types III, IV and V occur during later pachytene substages. Alignment of the X and Y axes is observed at late zygotene, and formation of the SC occurs in relation with type I XY pairs. Progressive desynapsis occurs in types II and III. Splitting and fusion of the X and Y axes attain a maximum in types IV and V. The breakdown of the dense bodies associated with the X and Y axes occurs during stage V. --Bar-like structures, having a mean length of 2,100 A are associated with SCs in all the pachytene substages defined by the XY types. The average number of bars per nucleus is 46.2 (SD = 8.4, N = 20), and the average SC length per bar is 5.57 micrometer. The distribution along the SCs of 923 bars shows that near-termini locations are preferred (SC length per bar, 2.98 micrometer) and centromere regions are avoided (SC length per bar, 16.9 micrometer). --On the basis of these data, bars are similar to recombination nodules described in other organisms. The availability of a standard SC karyotype for microspreads and a temporal sequence given by the XY pair provide a basis for rapid screening of chromosome aberrations in human testicular biopsies.

Adult↗
PubMed1981

Synaptosomal complex analysis of mouse chromosomal rearrangements. II. Synaptic adjustment in a tandem duplication.

Surface spread spermatocytes of mice heterozygous for a tandem duplication show nuclei in late zygotene-early pachytene in which the heteromorphic synaptonemal complex (SC) contains a lateral element that is buckled out into a unpaired loop as a consequence of the added length of the duplication (estimated in another study to be 21.7%, with breakpoints at 0.50 and 0.72 of the length of the chromosome). The ends of the buckle, marking the interstitial termini of synapsis proceeding from opposite directions, vary over a wide range of positions, but within limits: the proximal end of the loop does not exceed the distal end of the duplication segment, while the distal end of the loop does not lie closer to the kinetochore than the proximal end of the segment. Thus synapsis (SC formation) at zygotene is restricted to homologous regions (exclusive homosynapsis). --In the last half of pachytene, no buckles are found, only simple SCs with lateral elements of equal length, as a consequence of synaptic adjustment. Intermediate stages of adjustment are found throughout the first half of pachytene. Shortly after homosynapsis is complete, synaptic adjustment begins: the ends of the duplication loop separate (desynapsis of homosynapsed regions); the long axis shortens with respect to the short axis in both the unpaired loop and in the SC portions; asymmetrical twists take up inequalities; the loop is reduced to from 1 to 3 asymmetrical twists; the axes (lateral elements) equalize as the long axis shortens; and a simple SC is formed, indistinguishable from others in the complement, in which the region of the duplication and those adjacent to it have heterosynapsed, while the distal regions of the SC are presumably still homosynapsed. Synaptic adjustment evidently involves two sequential events: localized instability of the homosynapsed condition, leading to desynapsis, then restoration of the SC by heterosynapsis. Adjustment therefore represents the loss of strict homosynapsis. It is concluded that the asymmetry produced by the duplication loop constitutes an instability that triggers synaptic adjustment.

Animals↗
PubMed2001

Chromatin and chromosomal fine structure in spermatogenesis of some species of amphibians.

Spermatogenesis is a complex differentiation process which is characterised, among other features, by conspicuous stage-specific nuclear events such as the pairing of homologous chromosomes coupled with the formation of synaptonemal complexes, the replacement of histones with sperm-specific proteins during spermiogenesis and, as a result, chromatin condensation and its inactivation in sperm cells. The chromatin of spermatogenic cells undergoes dramatic conformational changes upon differentiation from spermatogonia to mature spermatozoa. During the haploid stage of spermatogenesis, histones are gradually replaced, firstly by transition proteins and later by sperm-specific proteins. As a result of the high degree of condensation and inactivation of spermatid and sperm chromatin, Sertoli cells are responsible for the nourishment of germ cells with ribosomal RNA and nutritive substances.

Amphibians↗
PubMed1997

Evolution of the black muntjac (Muntiacus crinifrons) karyotype revealed by comparative chromosome painting.

The black muntjac (Muntiacus crinifrons) has an unusual karyotype of 2n = 8 in females and 2n = 9 in males. We have studied the evolution of this karyotype by hybridising chromosome-specific paints derived from flow-sorted chromosomes of the Chinese muntjac (M. reevesi, 2n = 46) to chromosomes of the black muntjac. The hybridisation pattern allowed us to infer chromosomal homologies between these two species. Tandem and centromeric fusions, reciprocal translocations, and insertions are involved in the reduction of the diploid number from 2n = 46 to 2n = 8, 9. The painting patterns further show complex chromosomal rearrangements in the male black muntjac which involve more than half the karyotype, including both sex chromosomes. Since early meiosis is reported to be normal without any visible inversion loops of the synaptonemal complex, the observed chromosomal rearrangements would lead to heterosynapsis and, therefore, leave a large fraction of the male black muntjac karyotype balanced between the two sexes.

Animals↗
PubMed1998

Germ cell-specific enhancer activity of a repeated element in a variable region of the mouse genome.

We recently described a complex genetic structure on mouse chromosome 8, a region of the murine genome in which genetic rearrangements frequently occur. A large repeated element specific to this chromosome was found to overlap with one of the cadherin genes (Cad11). An additional degree of complexity became apparent with the identification, in a subset of laboratory strains of mice, of a retrogene integrated into one of the repeated units. Designated Sycp1-ps2, it originated from the early meiotic gene encoding Synaptonemal Complex Protein 1. We now report that, among wild Mus species in which the retrogene is not present, this region of Chr 8 shows a high degree of variability. Sequence analysis showed that integration of Sycp1-ps2 created a 5' transcription initiator element. Transcription of the pseudogene in the testis was directly demonstrated. A germ cell-specific enhancer activity was localized within a 1117 bp region of the repeat, which was sufficient to direct the expression of reporter genes in transgenic mice to late meiotic and post-meiotic spermatogenic cells.

Animals↗
PubMed1999

Meiotic chromosomes: integrating structure and function.

Meiotic chromosomes have been studied for many years, in part because of the fundamental life processes they represent, but also because meiosis involves the formation of homolog pairs, a feature which greatly facilitates the study of chromosome behavior. The complex events involved in homolog juxtaposition necessitate prolongation of prophase, thus permitting resolution of events that are temporally compressed in the mitotic cycle. Furthermore, once homologs are paired, the chromosomes are connected by a specific structure: the synaptonemal complex. Finally, interaction of homologs includes recombination at the DNA level, which is intimately linked to structural features of the chromosomes. In consequence, recombination-related events report on diverse aspects of chromosome morphogenesis, notably relationships between sisters, development of axial structure, and variations in chromatin status. The current article reviews recent information on these topics in an historical context. This juxtaposition has suggested new relationships between structure and function. Additional issues were addressed in a previous chapter (551).

Animals↗