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Results for “Synaptonemal Complex”

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PubMed1991

Meiotic chromosome synapsis in a haploid yeast.

An extensive synaptonemal complex (SC) is found at pachytene in whole mount spread preparations of a haploid yeast, Saccharomyces cerevisiae, strain. Whereas unsynapsed axial elements are present only in a few nuclei, in others non-homologous synapsis involves virtually the whole chromosome set. This suggests that homology is not an indispensable precondition for SC formation in yeast but that chromosomes engage in non-homologous synapsis if no homologous partner is available. Recent evidence that in the sporulation deficient yeast mutants rad50 and mer1 axial elements do form but remain unsynapsed in the majority of nuclei is discussed in the light of the above findings.

Chromosomes, Fungal↗

PubMed1993

[An unusual heteromorphic bivalent in the common vole (Microtus arvalis) from Byelarus].

Electron microscopic analysis was carried out on the synaptonemal complexes of ten male common voles (Microtus arvalis) caught of 1990 in Byelorussia. In the early pachytene stage of spermatocytes of four males heteromorphic bivalent has been found in one of five large autosomes. In the central region of the bivalent one of the lateral elements is in the form of a D-loop, characteristic of insertion/deletion heterozygotes. However, high-resolution G-band staining of mitotic chromosomes from fibroblasts showed no significant differences in the G-band patterns between homologues.

Animals↗

PubMed1994

The yeast med1 mutant undergoes both meiotic homolog nondisjunction and precocious separation of sister chromatids.

A mutant at the yeast MED1 locus was isolated in a screen for sporulation-proficient, meiotic-lethal mutants. Synaptonemal complex formation in the med1 mutant is apparently normal and med1 strains undergo meiotic crossing over at approximately 50% of the wild-type level. The med1 mutant undergoes homolog nondisjunction at meiosis I, presumably as a consequence of the decrease in crossing over. In addition, the mutant undergoes precocious separation of sister chromatids, resulting in chromosome missegregation at both meiotic divisions. We suggest that the med1 mutation perturbs chromosome structure, leading to a reduction in recombination and a defect in sister chromatid cohesion.

Cell Nucleus↗

PubMed1994

Synaptic patterns of rye B chromosomes. III. The deficient B.

Chromosomal pairing of a deficient B chromosome in rye has been studied by surface spreading of synaptonemal complexes in pollen mother cells from plants containing one deficient B (dB), one deficient B plus one standard B (dBstB) and one deficient B plus two standard Bs (dB2stB). Single dBs are often located peripherally in surface spread nuclei, and they undergo extensive non-homologous synapsis at pachytene. In the dBstB bivalents, homologous and non-homologous synapses occur simultaneously throughout pachytene without axial equalization. Competition for pairing between the dB and the two stBs results in a large predominance (80%) of stB bivalents. This finding is explained by the identical origin of the standard Bs and/or by the minor homology between the stB and the dB chromosomes.

Chromosomes↗

PubMed2000

Organization of highly repeated sequences in surface-spread pachytene chromosomes of rye.

A method of preparing two-dimensional surface spreads of plant synaptonemal complexes (SCs) associated with fluorescence in situ hybridization (FISH) has been applied to analyze the location and organization of five different highly repeated DNA sequences in rye. Our observations indicate that, depending on the type of sequence, the chromatin displays different types of organization. Telomeric sequences were seen tightly associated with the SC while other repetitive DNA sequences were found to form loops that are associated with SCs only at their bases. On the contrary, the FISH signal of a centromeric satellite had a granular appearance, reflecting that the hybridization occurs only with parts of the chromatin loops.

Chromosomes↗

PubMed1992

A reciprocal whole-arm translocation, rcp(1;6)(1p6p;1q6q) in a boar, localization of the breakpoints, and reassignment of the genes for glucose phosphate isomerase (GPI) and calcium release channel (CRC).

A reciprocal whole-arm translocation between chromosomes 1 and 6 in a Swiss Large White boar with reduced fertility was identified by the use of different staining techniques in mitotic metaphase cells, synaptonemal complex analyses, and meiotic chromosome preparations. The karyotype of this boar was demonstrated to be 38,XY,rcp(1;6)(1p6p;1q6q). To further localize the breakpoints more precisely and determine the precise gene locations, several in situ hybridization experiments were performed with a chromosome 1 centromere-specific probe and two other gene probes. The breakage and reunion points of both chromosomes were located in the centromeric regions. The genes for glucose phosphate isomerase and calcium release channel were mapped to 6cen----q12.

Animals↗

PubMed1995

Histones H1 and H4 of surface-spread meiotic chromosomes.

The chromatin conformation of somatic and meiotic chromosomes is, at least in part, a function of electrostatic nucleosome interactions that are mediated by transient acetylation of the histone H4 N-terminal domain and phosphorylation of histone H1. The distribution of those histones in the chromatin of meiotic chromosomes is reported here. Antibodies to testis-specific histone 1, H1t, detect H1t in the chromatin of mouse meiotic prophase chromosomes only after synapsis and synaptonemal complex (SC) assembly is completed and before core separation is initiated. The H1t protein is evenly distributed over euchromatin, heterochromatin and the SC. Antibodies to acetylated lysine residues 5, 12 or 16 of histone H4, indicate that the euchromatin is more acetylated than the centromeric heterochromatin. The pattern is most pronounced for acetylated residue 5 and least for 16. Antibodies to phosphorylated H1 epitopes do not react with chromatin but, instead, recognize the chromosome cores and SCs. Possibly these are not phosphorylated histone H1 epitopes, but SC proteins with similar potentially phosphorylatable sequences such as KTPTK of the synaptic protein Syn1.

Acetylation↗

PubMed1992

Silver staining two types of meiotic nodules.

We have developed a reliable method for silver staining nodules on synaptonemal complexes (SCs) of tomato (Lycopersicon esculentum). This technique involves hypotonically bursting primary microsporocytes, fixing SC spreads with paraformaldehyde, and incubating the spreads at 40 degrees C in a 33% aqueous silver nitrate solution covered with nylon mesh. When tomato SCs were stained by this method, nodules were observed with the same distribution and frequency as nodules stained with uranyl acetate and lead citrate. Incubation in silver nitrate at higher temperatures caused the loss of some or all nodules. The pattern of loss suggests that two types of nodules coexist during late zygonema and early pachynema and that one type becomes the late nodules of mid-pachynema through early diplonema.

Meiosis↗

PubMed1989

Meiosis in trisomic female mice with Robertsonian translocations. I. Prophase pairing.

The prophase oocytes of two murine Robertsonian translocation (Rb) trisomies of chromosomes 16 and 19 were investigated using electron microscopy and a whole-cell micro-spreading technique after silver staining. About 20% of fetuses of each type were trisomic. They were obtained by mating animals heterozygous for two Rb's, monobrachially homologous for either chromosome 16 or 19, to an entirely acrocentric stock. Because of the almost inevitable prenatal mortality of the trisomic embryos, their fetal ovaries were "rescued" by an in vitro method for prophase studies. Analysis of the recovered oocytes showed frequent, close pairing associations of the three trisomic axes and evidence suggesting that the closely apposed axes coincided with the side-by-side formation of parallel, complete, true synaptonemal complexes; hence, the cytogenetic dogma that pairing is always two-by-two was contradicted. The presence of two parallel complexes has implications for crossing-over recombination. Triple associations of axes were found in almost half the trisomy 19 (Ts19) and in about 70% of the trisomy 16 (Ts16) prophases. The extent of triple associations varied and was greater in Ts16 than in Ts19 oocytes. Other relevant observations concerned the proportions of univalents and of univalence of the trisomic axes (21% in Ts16 and 46% in Ts19) and the distinctive, thickened appearance of all univalent axes. The pairing behaviour observed in balanced heterozygotes confirms what appears to be nonhomologous pairing and synaptic adjustment within the short-arm axes of the Rb trivalents.

Animals↗

PubMed1988

Heterosynapsis in a heterozygous fertile boar carrier of a 3;7 translocation.

Silver-stained synaptonemal complexes (SCs) in surface-spread pachytene nuclei from a boar, heterozygous for a reciprocal translocation, were analysed by electron microscopy. In such heterozygotes, cross-shaped quadrivalent configurations are expected to form in order to maximize homologous pairing. Contrary to the classical, expected cross-shaped configuration, heterosynapsis was often observed, with asymmetrical association in the lateral elements of the non-homologous partners of the quadrivalents. This heterosynapsis is assumed to be a mechanism preventing spermatocyte loss, but inducing a secondary segregational type of impairment of fertility due to foetal wastage leading to reduced prolificacy.

Animals↗

PubMed2000

A homologue of the yeast HOP1 gene is inactivated in the Arabidopsis meiotic mutant asy1.

Synapsis of homologous chromosomes is a key event in meiosis as it is essential for normal chromosome segregation and is implicated in the regulation of crossover frequency. We have previously reported the identification and cytological characterisation of a T-DNA-tagged asynaptic mutant of Arabidopsis thaliana. We have demonstrated that this mutant, asy1, is defective in meiosis in both males and females. Cloning and nucleotide sequencing of the ASY1 gene has revealed that it encodes a polypeptide of 596 amino acids that exhibits similarity to the HOP1 gene of Saccharomyces cerevisiae, which is known to encode a protein essential for synaptonemal complex assembly and normal synapsis. Expression studies indicate that, in common with a number of other Arabidopsis meiotic genes, ASY1 exhibits low-level expression in a range of plant tissues. Southern analysis coupled with database searching has resulted in the identification of an ASY1 homologue, ASY2. Although asy1 exhibits a strong asynaptic phenotype, a residual low level of synapsis indicates that ASY1 and ASY2 may exhibit a low degree of functional redundancy.

Arabidopsis↗

PubMed1996

[Localization of RecA-like proteins in preparations of spread nuclei of mouse spermatocytes at meiotic prophase I].

Earlier, polyclonal antibodies to Escherichia coli RecA protein were used to identify immunologically related proteins in meiotic spermatocytes of different eukaryotes. At least one such protein proved to be a component of the synaptonemal complex (SC) [1]. Subsequent experiments on localization of RecA-like antigens in SCs of spermatocytes were performed by indirect immunocytochemical methods and electron microscopy, which showed that RecA-like protein(s) at early leptotene are largely associated with chromatin. During SC formation (at leptotene and zygotene), they are found in both lateral elements and the central space of SC. In some cases, RecA-like proteins are associated with SC substructures that resemble recombination nodules. When spermatocytes enter late diplotene, Rec-A-like proteins cease to be detected in SC structures.

Animals↗

PubMed2006

The many facets of SC function during C. elegans meiosis.

Sexually reproducing organisms rely on meiosis for the formation of haploid gametes. This is achieved through two consecutive rounds of cell division (meiosis I and II) after one round of DNA replication. During the meiotic divisions, chromosomes face several challenges to ultimately ensure proper chromosome segregation. Unique events unfold during meiosis I to overcome these challenges. Homologous chromosomes pair, synapse, and recombine. A remarkable feature throughout this process is the formation of an evolutionarily conserved tripartite proteinaceous structure known as the synaptonemal complex (SC). It is comprised of two lateral elements, assembled along each axis of a pair of homologous chromosomes, and a central region consisting of transverse filaments bridging the gap between lateral elements. While the presence of the SC during meiosis has been appreciated now for 50 years (Moses, Biophys Biochem Cytol 2:215-218, 1956; Fawcett, J Biophys Biochem Cytol 2:403-406, 1956), its role(s) remain a matter of intense investigation. This review concentrates on studies performed in Caenorhabditis elegans, a powerful system for investigating meiosis. Studies in this organism are contributing to the unraveling of the various processes leading to the formation of the SC and the various facets of the functions it exerts throughout meiosis.

Animals↗

PubMed2001

Asynchronous chromosome pairing in male meiosis of the rat (Rattus norvegicus).

Premeiotic and meiotic chromosome distribution was studied in rat testes suspensions by a triple-color fluorescent staining protocol which allows simultaneous visual inspection of two chromosomal targets highlighted by FISH together with immunostained SCP3 synaptonemal complex (SC) proteins which are marked by a third, composite color. Triple labeling with rat chromosome (RNO) 4q and 19p specific probes and SCP3 staining disclosed that homologs are separated in premeiotic and leptotene nuclei. Pairing of homologous chromosome regions commenced during early zygotene, with pairing of the small metacentric chromosomes 19 preceding that of the distal region of the long arm of RNO4. Our results show that homolog association occurs during zygotene of rat spermatogenesis, with small and large chromosomes showing a considerable asynchrony. Comparison with pairing progression in meiosis of other mammals suggests that asynchronous chromosome pairing reflects size differences within a complement.

Animals↗

PubMed1995

Reciprocal chromosome translocation, rcp(7;17)(q26;q11), in a boar giving reduced litter size and increased rate of piglets dying in the early life.

Cytogenetic investigations in a boar causing a 41% reduction in litter size and also producing piglets that died soon after birth revealed the presence of a reciprocal chromosome translocation, rcp(7;17)(q26;q11). The translocation resulted in one extremely small telocentric chromosome marker. Synaptonemal complex analysis of spread spermatocytes by electron microscopy revealed an unusual behaviour of the translocation. This formed not only different types of quadrivalents (78.1% of the cells), similar to those previously found in boars heterozygous for reciprocal exchanges, but also completely or incompletely paired trivalent configurations, plus univalent (21.9%). Association between the sex bivalent and the translocation configuration was observed (18.7%), but testicular histology was normal. Furthermore, the boar with the translocation was found to produce tertiary monosomy and trisomy in some of the liveborn piglets. Some of the tertiary monosomic offspring, which died in the early extra-uterine life, demonstrated ventricular septal defect and cleft palate.

Animals↗

PubMed1989

[Effect of heterozygosity for insertions of homogeneously stained regions in chromosome 1 of the house mouse on synapsis in meiotic prophase].

Electron microscope analysis of surface-spread synaptonemal complexes (SC) in oocytes and spermatocytes from double cis heterozygotes for Is(HSR; 1C5)1Icg and Is(HSR; 1E3)2Icg was carried out. Aberrant chromosomes were isolated from the feral population of Mus musculus musculus of Novosibirsk. They contain homogeneously stained regions of total length of about 30% of Chr 1 mitotic metaphase. Heteromorphic bivalents of Chr1 with different lengths of the lateral elements of SC and the loop in the intermedial position were revealed in 4.4% spermatocytes and 20% oocytes of heterozygous animals. The loop size depends on the stage of meiosis: it is maximal at late zygotene and decreases up to disappearance during pachytene.

Animals↗

PubMed1998

Zip2, a meiosis-specific protein required for the initiation of chromosome synapsis.

We describe the identification and characterization of the Saccharomyces cerevisiae ZIP2 gene, which encodes a novel meiosis-specific protein essential for synaptonemal complex formation. In the zip2 mutant, chromosomes are homologously paired but not synapsed. The Zip2 protein localizes to discrete foci on meiotic chromosomes; these foci correspond to sites of convergence between paired homologs that are believed to be sites of synapsis initiation. Localization of Zip2p requires the initiation of meiotic recombination. In a mutant defective in double-strand break repair, Zip2p colocalizes with proteins involved in double-strand break formation and processing. We propose that Zip2p promotes the initiation of chromosome synapsis and that localization of Zip2p to sites of interhomolog recombination ensures synapsis between homologous chromosomes.

Chromosomes, Fungal↗

PubMed2000

[Studies on the Robertsonian translocation of Microtus mandarinus].

The type of chromosome No. 1 and chromosome number from 53 individuals of Microtus mandarinus have been studied and compared in three sex types: XY, XX, XO. We found that the first pair of autosomes are very unstable, and there are three types: (1) M, M (With a double metacentric chromosome), (2) M, T, T, (With single metacentric chromosome). (3) T, T, T, T (Without metacentric chromosome). The chromosome number of the same sex individuals changes regularly with the type change of chromosome No. 1, that is, the increase of one chromosome in 2n number is always accompanied by the increase of two T and the decrease of one M, and vice versa. The synaptonemal complexes (SCs) of spermatocyte in pachytene nuclei from the males (2n = 51) were analysed by the electron microscopy. The SCs studies demonstrate that there are 23 fully paired autosomal bivalents, XY-bivalent and an autosomal trivalent. This trivalent is formed by one metacentric and two telocentric elements and characterized by the presence of two short side-arms. Meanwhile, all trivalents are in a cis configuration. The study of G-banding also demonstrates that the No. 1 autosome polymorphism is caused by Robertsonian translocation. Robertsonian fission is the main reason of the polymorphism of chromosome No. 1 and of variation of chromosome number in M. mandarinus.

Animals↗