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 577 records · Page 32Linked to original sources

PubMed2005

Meiotic transverse filament proteins: essential for crossing over.

Meiosis is a specialized set of two nuclear divisions, meiosis I and II, by which a diploid cell produces four haploid daughters. After premeiotic DNA replication, homologous chromosomes pair and recombine, and then disjoin at meiosis I. Subsequently, at meiosis II, the sister chromatids of each chromosome segregate. In nearly all eukaryotes, meiotic chromosome pairing culminates in the formation of a ladder-like supramolecular protein structure, the synaptonemal complex (SC) (Page and Hawley, 2004). The rungs of the ladder are known as transverse filaments (TFs). Genes encoding TF proteins have been identified in a limited number of organisms, and their function has been studied by mutational analysis. Although TF proteins show little amino acid sequence conservation, their structure and function are largely conserved. In all analyzed species, TF proteins are required for meiotic reciprocal recombination (crossing over).

Animals↗

PubMed1991

Staining plant cells with silver. I. The salt-nylon technique.

A technique is described for selectively silver staining nucleoli, active nucleolus organizers, nucleolar material attached to chromosomes, kinetochores, synaptonemal complexes, and chromosome cores in plant cells. The technique, called salt-nylon silver staining, involves spreading cells on glass slides, treating the cells with a solution of saline sodium citrate, and incubating the cells in a silver nitrate solution covered with nylon screen. Selected variables important for achieving reliable silver staining are considered.

Allium↗

PubMed2000

Predator odour and its impact on male fertility and reproduction in Phodopus campbelli hamsters.

This study investigated the influence of cat urine odour in suppressing development and fertility in Campbell's hamster males. Exposure to this odour from postnatal day 11 until day 45 (sexual maturation) resulted in reduced sex organ weights, reduced testosterone levels and in an increase in abnormalities of the synaptonemal complex in both sex chromosomes and autosomes. Subsequent breeding experiments revealed a significant decrease in litter size. All these data indicate a severe effect of predator odour on the breeding success of potential prey species. It is assumed that these effects are caused by the sulphurous compounds in the urine; however, the underlying mechanisms are not yet known.

Animals↗

PubMed1994

Homologous pairing is reduced but not abolished in asynaptic mutants of yeast.

In situ hybridization was used to examine chromosome behavior at meiotic prophase in the rad50S, hop1, rad50, and spo11 mutants of Saccharomyces cerevisiae, which are defective in chromosome synapsis and meiotic recombination. Painting of chromosomes I and III revealed that chromosome condensation and pairing are reduced in these mutants. However, there is some residual pairing in meiosis, suggesting that homologue recognition is independent of synaptonemal complex formation and recombination. Association of homologues was observed in the rad50, rad50S, and spo11 mutants, which are defective in the formation or processing of meiotic double-strand breaks. This indicates that double-strand breaks are not an essential component of the meiotic homology searching mechanism or that there exist additional or alternative mechanisms for locating homologues.

Cell Nucleus↗

PubMed1998

Meiotic synapsis in the absence of recombination.

Although in Saccharomyces cerevisiae the initiation of meiotic recombination, as indicated by double-strand break formation, appears to be functionally linked to the initiation of synapsis, meiotic chromosome synapsis in Drosophila females occurs in the absence of meiotic exchange. Electron microscopy of oocytes from females homozygous for either of two meiotic mutants (mei-W68 and mei-P22), which eliminate both meiotic crossing over and gene conversion, revealed normal synaptonemal complex formation. Thus, synapsis in Drosophila is independent of meiotic recombination, consistent with a model in which synapsis is required for the initiation of meiotic recombination. Furthermore, the basic processes of early meiosis may have different functional or temporal relations, or both, in yeast and Drosophila.

Animals↗

PubMed1994

Synapsis and chiasma formation in four meiotic mutants of tomato (Lycopersicon esculentum).

Synapsis and chiasma formation were studied in pollen mother cells of four meiotic mutants of tomato. The four mutants displayed defects in the assembly of the synaptonemal complex (SC) covering the whole range from almost complete absence of synapsis to complete synapsis at pachytene. In three mutants, we found a good correlation between the number of bivalents connected by at least one tripartite SC segment at pachytene and the number of chiasmatic bivalents at metaphase I. We suggest that in tomato functional chiasmata are only formed in the context of the tripartite SC.

Cell Nucleus↗

PubMed1997

The yeast motor protein, Kar3p, is essential for meiosis I.

The recognition and alignment of homologous chromosomes early in meiosis is essential for their subsequent segregation at anaphase I; however, the mechanism by which this occurs is unknown. We demonstrate here that, in the absence of the molecular motor, Kar3p, meiotic cells are blocked with prophase monopolar microtubule arrays and incomplete synaptonemal complex (SC) formation. kar3 mutants exhibit very low levels of heteroallelic recombination. kar3 mutants do produce double-strand breaks that act as initiation sites for meiotic recombination in yeast, but at levels severalfold reduced from wild-type. These data are consistent with a meiotic role for Kar3p in the events that culminate in synapsis of homologues.

Cell Nucleus↗

PubMed1992

The rec102 mutant of yeast is defective in meiotic recombination and chromosome synapsis.

A mutation at the REC102 locus was identified in a screen for yeast mutants that produce inviable spores. rec102 spore lethality is rescued by a spo13 mutation, which causes cells to bypass the meiosis I division. The rec102 mutation completely eliminates meiotically induced gene conversion and crossing over but has no effect on mitotic recombination frequencies. Cytological studies indicate that the rec102 mutant makes axial elements (precursors to the synaptonemal complex), but homologous chromosomes fail to synapse. In addition, meiotic chromosome segregation is significantly delayed in rec102 strains. Studies of double and triple mutants indicate that the REC102 protein acts before the RAD52 gene product in the meiotic recombination pathway. The REC102 gene was cloned based on complementation of the mutant defect and the gene was mapped to chromosome XII between CDC25 and STE11.

Chromosome Mapping↗

PubMed2006

Selective binding of meiosis-specific yeast Hop1 protein to the holliday junctions distorts the DNA structure and its implications for junction migration and resolution.

Saccharomyces cerevisiae HOP1, which encodes a component of synaptonemal complex (SC), plays an important role in both gene conversion and crossing over between homologs, as well as enforces meiotic recombination checkpoint control over the progression of recombination intermediates. In hop1Delta mutants, meiosis-specific double-strand breaks (DSBs) are reduced to 10% of the wild-type level, and at aberrantly late times, these DSBs are processed into inter-sister recombination intermediates. However, the underlying mechanism by which Hop1 protein regulates these nuclear events remains obscure. Here we show that Hop1 protein interacts selectively with the Holliday junction, changes its global conformation and blocks the dissolution of the junction by a RecQ helicase. The Holliday junction-Hop1 protein complexes are significantly more stable at higher ionic strengths and molar excess of unlabeled competitor DNA than complexes containing other recombination intermediates. Structural analysis of the Holliday junction using 2-aminopurine fluorescence emission, DNase I footprinting and KMnO4 probing provide compelling evidence that Hop1 protein binding induces significant distortion at the center of the Holliday junction. We propose that Hop1 protein might coordinate the physical monitoring of meiotic recombination intermediates with the process of branch migration of Holliday junction.

Crossing Over, Genetic↗

PubMed2000

Effects of ionizing radiation on oocytes of prepubertally irradiated rats.

PURPOSE: To characterize the effects of ionizing radiation on the immature oocytes of prepubertal rats aged 16-20 days old. MATERIALS AND METHODS: The abdomen of Sprague Dawley (SD) female rats was exposed to 0, 1 and 2 Gy of X-rays. The effects were analysed when the animals became adults (80 days old) using as parameters the number of implantation sites, embryonic loss, dominant lethality and the synaptonemal complex (SC) analysis of F1 female foetuses. RESULTS: A statistically significant decrease in the fertility of the 2 Gy irradiated rats was observed. However, the SC analysis of F1 female foetuses showed no cytogenetic damage that could be attributed to radiation. CONCLUSIONS: A reproductive effect was demonstrated but no inherited genetic damage was detected by SC analysis in female foetuses of irradiated mothers.

Animals↗

PubMed1998

Extraordinary chromosomal polymorphism with 28 different karyotypes in the neotropical species Akodon cursor (Muridae, Sigmodontinae), one of the smallest diploid number in rodents (2n = 16, 15 and 14).

All available published cytogenetic data show the presence of 28 different karyotypes in 311 specimens of A. cursor as an exceptional example of high karyotype variability in a single species. Our present sample of 116 animals collected in the rain forest of the Atlantic coast of the states of São Paulo and Bahia, Brazil, show 25 karyotype constitutions. The diploid number (2n) ranged from 16 to 14, and the number of autosomal arms (NF) from 26 to 18, because of centric fusion and pericentric inversions involving two autosome pairs, pericentric inversions in three other chromosome pairs, trisomy in the pair 7 and the presence of two XO females. Synaptonemal complex analysis, associated with data from experimental cross-breeding, suggested that heterozygous individuals for pericentric inversions have normal fertility. In this paper, we have reviewed the chromosomal data of this species, and have thus standardized the karyotype description and chromosome numbering. We discuss about karyotype evolution of Akodon cursor based on the frequency and constitution of karyotypes of all different geographical samples described so far in the literature.

Animals↗

PubMed1985

Effects of the male contraceptive agent gossypol on meiotic chromosomes of the male rat.

Synaptonemal complexes (SCs) of rat spermatocytes were analyzed in silver-stained meiotic preparations 10-24 days after treatment with gossypol acetic acid, 30 mg/kg/day, for 70 days. Gossypol did not affect SC formation or function, as judged by the absence of pairing anomalies, SC fragmentation, or presynaptic arrest. The unpaired lateral axes could be seen at zygotene, and at pachytene normal SCs could be observed. The behavior of the XY axes also appeared to be normal.

Animals↗

PubMed1994

The meiotic pairing behaviour in human spermatocytes carrier of chromosome anomalies and their repercussions on reproductive fitness. I: Inversions and insertions. A European collaborative study.

The synaptic behavior of pachytene chromosomes was studied in men heterozygous for inversions and one inversion-insertion by analysis of synaptonemal complexes at the electron microscopy level. The human meiotic data were collected from European laboratories in order to test the current theories and to link the arrest of spermatogenesis and the risk of chromosome imbalance to the mode of pairing and their consequences. The breakpoint location would allow to predict the synaptic and recombinational behavior of chromosome aberrations and particularly the risk of aneusomie de recombinaison in the progeny of inversion carriers.

Aneuploidy↗

PubMed1995

Stable chromosome fission associated with rDNA mobility.

A spontaneous chromosome fission in the plant Hypochoeris radicata has been characterized by Feulgen staining, in situ hybridization of the rDNA probe pTA71 and silver staining for active nucleolus organizing regions. The parental acrocentric chromosome has no detectable ribosomal genes at the centromere, but both fission derivatives possess active NORs at their centric ends. In fission heterozygotes, pachytene configurations studied by synaptonemal complex spreading show that the ribosomal cistrons form short arms on each telocentric which pair together to form a triradial. The paired short arms are associated with the single nucleolus at pachytene. It is proposed that the origin and stabilization of the fission rearrangement involved transposition of rDNA from the nucleolus organizing region of chromosome 3 into the centromeric region of chromosome 1.

Chromosome Aberrations↗

PubMed1994

Chromosome pairing via multiple interstitial interactions before and during meiosis in yeast.

Fluorescence in situ hybridization analysis reveals that homologous chromosomes are paired in yeast cells about to enter meiosis. Pairing involves multiple interstitial interactions, one per approximately 65 kb. These observations exclude several classes of models for somatic/premeiotic pairing. The number of t = 0 pairing interactions is about the same as the number of subsequent meiotic recombination events. As cells enter meiosis, pairing disappears concomitant with DNA replication and then reappears, independent of synaptonemal complex. Mutant phenotypes suggest that formation of an individual meiotic pairing connection does not require a meiosis-specific double-stranded break (DSB). Mutants defective in recombination before or after DSBs exhibit pairing defects. These and other observations can be united by a model in which premeiotic pairing and early meiotic pairing occur by closely related paranemic DNA-DNA interactions between intact duplexes, with early meiotic interactions subsequently converted directly to plectonemic recombination intermediates via DSBs.

Cell Nucleus↗

PubMed1995

Male sterility and double heterozygosity for chromosomal inversion.

A meiotic analysis has been carried out on male mice heterozygous for one of two inversions in Chromosome 2, In(2)5Rk and In(2)2H, as well as on double heterozygotes for these two overlapping inversions. Electron microscopic observation of synaptonemal complexes revealed that heterosynapsis had occurred in a large number of spermatocytes, producing a small number of cells with an inversion loop. Heterozygous carriers of a single inversion loop reproduced quite normally, whereas doubly heterozygous carriers of a double loop showed a reduction in spermatogenesis. These data shed new light on the role of inversions in speciation.

Animals↗

PubMed1998

Effects on female fertility and germinal cells in prepubertal and adult rats (Rattus norvegicus) after X-ray irradiation.

In this work we analyse the effects of ionizing radiation in prepubertal and adult female rats, using as parameters, implantation sites, embryonic loss, and synaptonemal complex (SC) analysis of the female F1 of the pregnant rats. Our preliminary results show a decrease statistically significant in fertility of irradiated groups, but cytogenetic analysis did not shown any inherited damage attributed to radiation. At the same time, our results seem to indicate a higher resistance of oocytes from prepubertal rats and support the possible use of GnRH agonists as oestrus cycle suppressors to turn adult rats into gonadal quiescence.

Aging↗

PubMed1991

A meiosis-specific protein kinase homolog required for chromosome synapsis and recombination.

The mek1 (meiotic kinase) mutant of Saccharomyces cerevisiae was isolated in a screen for sporulation-proficient, meiotic-lethal mutants. Diploids homozygous for a mek1 null mutation produce only 13% viable spores. mek1 spore inviability is rescued by a spo13 mutation, which causes cells to bypass the meiosis I division. In a mek1 null mutant, meiotic recombination is reduced but not completely eliminated. Nuclear spreads of meiotic chromosomes from mek1 diploids reveal numerous stretches of synaptonemal complex (SC) that are shorter than wild-type SCs. Analysis of a mek1::lacZ fusion gene and Northern blot hybridization demonstrate that the MEK1 transcript is present only in meiosis. The sequence of the MEK1 gene predicts a 56.8-kD protein with homology to serine-threonine protein kinases. The MEK1 gene maps to chromosome XV, 13 cM proximal to CDC64. Models for the function of the MEK1 gene product are proposed.

Amino Acid Sequence↗