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PubMed1993

Immunocytochemical localization of DNA in synaptonemal complexes of rat and mouse spermatocytes, and of chick oocytes.

The distribution of DNA in synaptonemal complexes of rat and mouse spermatocytes, and of chick oocytes was investigated by immunogold electron microscopy. Except for a few specific sites, DNA was not immunolocalized in the space between lateral elements of the complex. Some labeled fibrils connecting the lateral elements with the central element were observed associated with recombination nodules or near them. However, other labeled fibrils in the space between lateral elements did not appear to present any relationship to recombination nodules. The immunocytochemical approaches used here confirmed the presence of significant amounts of DNA in the lateral elements as previously indicated by preferential DNA staining methods. Furthermore, our findings support the view that recombination nodules are the site of chiasma formation.

Animals↗
PubMed1992

Synaptonemal complex alterations in X-irradiated and in oestrogen-treated mice: a comparative study.

Synaptonemal complexes (SCs) were analysed in male NMRI mice either X-irradiated or treated with oestradiol benzoate (E2B). Animals 30 days old underwent a single X-ray exposure of either 5, 7.5 or 10 Gy and were killed at different times after exposure, i.e., 24 h, 1, 4, 12 and 16 weeks. E2B was injected daily to adult mice from day 30 to day 60 or up to day 90 of age. Oestradiol was also administered during the neonatal period and animals were examined on days 28, 60 and 90 of age. Different SC alterations were found in X-irradiated and in E2B-treated mice. SC lesions were rare in oestrogen-treated adult mice. Among SC anomalies, asynapsis and fragmentation of SC were common lesions. However, the former was more frequent in E2B-treated mice, whereas the latter was more frequent in X-irradiated mice. Quadri- or multi-valents, bridges between bivalents, rings and loops were exclusively encountered in the latter, whereas heterotelomeric associations seemed to be specific in E2B-treated animals. The mechanisms of the different SC lesions are discussed.

Animals↗
PubMed2006

An analysis of univalent segregation in meiotic mutants of Arabidopsis thaliana: a possible role for synaptonemal complex.

During first meiotic prophase, homologous chromosomes are normally kept together by both crossovers and synaptonemal complexes (SC). In most eukaryotes, the SC disassembles at diplotene, leaving chromosomes joined by chiasmata. The correct co-orientation of bivalents at metaphase I and the reductional segregation at anaphase I are facilitated by chiasmata and sister-chromatid cohesion. In the absence of meiotic reciprocal recombination, homologs are expected to segregate randomly at anaphase I. Here, we have analyzed the segregation of homologous chromosomes at anaphase I in four meiotic mutants of Arabidopsis thaliana, spo11-1-3, dsy1, mpa1, and asy1, which show a high frequency of univalents at diplotene. The segregation pattern of chromosomes 2, 4, and 5 was different in each mutant. Homologous univalents segregated randomly in spo11-1-3, whereas they did not in dsy1 and mpa1. An intermediate situation was observed in asy1. Also, we have found a parallelism between this behavior and the synaptic pattern displayed by each mutant. Thus, whereas spo11-1-3 and asy1 showed low amounts of SC stretches, dsy1 and mpa1 showed full synapsis. These findings suggest that in Arabidopsis there is a system, depending on the SC formation, that would facilitate regular disjunction of homologous univalents to opposite poles at anaphase I.

Arabidopsis↗
PubMedDate not supplied

Electron microscopy of synaptonemal complexes in semithin sections.

The technique of osmium tetroxide fixation followed by a treatment with p-phenylenediamine was applied to mouse testes in order to analyze pachytene nuclei. Observation of Epon semithin sections (0.25--0.5 micrometer) in conventional electron microscopy revealed the presence of positively stained synaptonemal complexes surrounded by unstained chromatin. The present results show that by using this method a suitable contrast and resolution can be achieved for semithin sections, which facilitates the topographical study of synaptonemal complexes.

Animals↗
PubMed1993

Scanning electron microscopy of synaptonemal complexes.

The novel application of scanning electron microscopy to study whole-mount surface-spread synaptonemal complex complements of rye (Secale cereale) and rat (Rattus norvegicus) is described. Scanning electron microscopy is able to resolve the third dimension in such preparations and improve the tracing of the continuity of lateral elements without losing information that could be obtained by conventional transmission electron microscopy. This improvement is likely to benefit detailed studies of chromosome synapsis and karyology, and may provide a means of circumventing technical obstacles inhibiting the use of surface-spreads as substrates for in situ hybridization under the electron microscope.

Animals↗
PubMed1986

[Analysis of chromosome aberrations on the basis of synaptonemal complexes in the offspring of mice irradiated with gamma-rays].

Electron-microscopic analysis of synaptonemal complexes (SC) spread on the surface of hypophase was carried out to study chromosome rearrangements in sterile and semisterile F1 offsprings of mice exposed to gamma-radiation at a dose of 5 Gy. Chromosome rearrangements were microscopically scored at diakinesis - metaphase I in the same animals. SC analysis at pachytene revealed chromosome rearrangements in 63% spermatocytes. Analysis of chromosomes at diakinesis - metaphase I in the same animals only revealed chromosome rearrangements in 32% cells. SC analysis permits detecting chromosome rearrangements undetectable at diakinesis - metaphase I.

Animals↗
PubMed1998

The synaptic process in Locusta migratoria spermatocytes by synaptonemal complex analysis.

We describe the synaptic process during meiotic prophase in spermatocytes from Locusta migratoria, using synaptonemal complex (SC) spreads analyzed by light (LM) and electron (EM) microscopy. At leptotene, a stage of short duration, unpaired axial elements begin to be assembled. Synapsis starts at zygotene, beginning usually at the terminal regions of the bivalents, either at the proximal, centromeric end or at the distal, non-centromeric end; interstitial initiation of synapsis was only occasionally observed in the longer chromosomes. Pairing is asynchronous, and shorter chromosomes are the first to complete synapsis. At pachytene all bivalents are fully synapsed. Diplotene is characterized by the progressive fragmentation of SCs; fragmentation is asynchronous, and affects mainly the longer chromosomes, while the shorter ones maintain their morphology up to late diplotene.

Animals↗
PubMed1996

The synaptonemal complex--the chaperone of crossing over.

During meiosis homologous chromosomes pair and exchange homologous chromosome segments. The synaptonemal complex (SC) forms between paired chromosomes. The role of the SC in the process of reciprocal exchange of flanking markers is a matter of debate. I propose a dual pathway for reciprocal exchange of flanking markers (REFM). In the first, SC-independent, path, two 'half-nodules' and an independent REFM protein combine to form a functional recombination nodule (RN). The RN binds to paired chromosomes and accomplishes reciprocal exchange of flanking markers. In the other, SC-dependent, pathway 'half-nodules' occur at pairing initiation sites. 'Half-nodules' move along the SC as it forms. Assisted by an SC-bound REFM protein, 'half-nodules' combine to form functional RNs. I propose that different organisms rely to different extents on the two pathways, and hence rely to different extents on the SC.

Aspergillus↗
PubMed2001

Synaptonemal complex analysis in spermatocytes and oocytes of turbot, Scophthalmus maximus (Pisces, Scophthalmidae).

A surface-spreading synaptonemal complex (SC) technique was used to analyze spermatocytes and oocytes of turbot (Scophthalmus maximus) to visualize the process of chromosome synapsis. The total SC length was 205 +/- 12 microm in males and 172 +/- 29 microm in the only female analyzed. A representative SC karyotype of turbot was obtained. Each SC showed lateral elements of equal length. No bivalent exhibiting atypical synaptic behaviour that could be associated with heteromorphic sex chromosomes was observed, either in males or in the female. The DNA content of turbot was evaluated in eight individuals of both sexes by flow cytometry analysis. The 2C mean DNA content of turbot (1.308 +/- 0.009 pg/cell) was among the lowest observed within fishes. No statistical differences in DNA content were revealed between the sexes [Wilcoxon/Mann-Whitney test; P(W(x) = 0.243)]. The SC/DNA content ratio observed in turbot was the highest reported to date in bony fishes (Osteichthyes).

Animals↗
PubMed1991

[Control of genetic consequences of vaccinations: electron microscopic analysis of murine synaptonemal complexes].

The ability of two inactivated bacterial vaccines, from Proteus vulgaris and Klebsiella pneumoniae, to injure synaptonemal complexes (SCs) was studied by means of electron microscopy. The preparations were given intraperitoneally to C57BL/6J male mice during five successive days and testes were fixed 24 h after the last injection. Cyclophosphamide was used for positive control. The vaccine from Klebsiella given at subtoxic dose, which was about 200 times higher that that given to people during vaccinations, induced the 10-fold rise in the frequency of SC abnormalities in murine 1-storger spermatocytes. Breaks of SCs and of single lateral elements of SCs predominated over other types of vaccine-induced anomalies. According to the preliminary data, vaccine from Proteus at subtoxic dose showed no damaging SC activity. The results of the given study are discussed in connection with the negative data obtained earlier when genotoxicity of these two vaccines had been studied in the Ames test, in routine investigations of bone marrow metaphases of vaccinated mice as well as under light microscopy of their SCs.

Animals↗
PubMed2001

Synaptonemal complex analysis of the Holstein-Friesian, Piemontese and Simmental breeds of Bos taurus taurus.

The synaptonemal complex (SC) of specimens of Bos taurus taurus from the Holstein-Friesian, Piemontese, and Simmental breeds, was analysed. The analysis included quantification of the frequency of various types of abnormalities in the SC, and the frequency of cells with SC abnormalities. All animals had 29 autosomal bivalents and one sexual bivalent and the most frequently recorded abnormality was pairing failure. The number of cells with abnormalities in the Holstein-Friesian breed was 29.41%, in the Piemontese breed was 30.00% and in the Simmental breed it was 29.54%. The subspecies Bos taurus taurus had 29.63% of cells showing abnormalities with 57.33% of these abnormalities occurring in zygotene and 42.67% occurring in pachytene. Statistical analyses showed that there were no significant differences in the number of cells with SC abnormalities among the breeds studied. The frequency of cells with abnormalities, and the efect on the fertility of the Holstein-Friesian, Piemontese and Simmental breeds are discussed.

Animals↗
PubMed2006

Chromosome synapsis in Arabidopsis: analysis of the transverse filament protein ZYP1 reveals novel functions for the synaptonemal complex.

With respect to history, plants have provided an ideal system for cytogenetical analysis of the synaptonemal complex (SC). However, until recently, the identification of the genes that encode the SC in plants has proved elusive. In recent years, Arabidopsis thaliana was developed as a model system for plant meiosis research. As a result, there was substantial progress in the isolation of meiotic genes and this has recently led to the isolation of the first plant SC gene, ZYP1. The ZYP1 gene encodes a transverse filament (TF) protein that is predicted to have structural similarity to TF proteins found in other organisms. Analysis of plants deficient in ZYP1 expression has provided important insights into the function of the SC in plants. Loss of ZYP1 has only a limited effect on the overall level of recombination. However, it is associated with extensive nonhomologous recombination leading to multivalent formation at metaphase I. This phenomenon was not previously reported in other organisms. It is important to note that cytological analysis of the ZYP1 deficient lines indicates that SC formation is not required for the imposition of crossover interference.

Arabidopsis↗
PubMed1995

A change in the phosphorylation pattern of the 30000-33000 Mr synaptonemal complex proteins of the rat between early and mid-pachytene.

The lateral elements (LEs) of synaptonemal complexes (SCs) of the rat contain major components with relative electrophoretic mobilities (Mr s) of 30000-33000, which are the products of a single gene. After one-dimensional separation of SC proteins on polyacrylamide-SDS gels, these components show up as two major bands, whereas upon two-dimensional electrophoresis they are resolved in at least 24 spots, which focus at pH 6.5 to 9.5. In this paper we show that these spots represent phosphorylation variants. For the analysis of the phosphorylation of the 30000- to 33000-Mr SC components during progression through meiotic prophase, we developed a procedure for isolation of fractions of testicular cells of the rat that are enriched in separate stages of meiotic prophase. Analysis of the 30000- to 33000-Mr SC components in these fractions by two-dimensional electrophoresis and immunoblotting showed that phosphorylated variants of the 30000- to 33000-Mr SC proteins occur throughout meiotic prophase. However, the extent of phosphorylation changes between early and mid-pachytene, when one phosphate group is probably added to each of the variants.

Animals↗
PubMed2001

c(3)G encodes a Drosophila synaptonemal complex protein.

The meiotic mutant c(3)G (crossover suppressor on 3 of Gowen) abolishes both synaptonemal complex (SC) formation and meiotic recombination, whereas mutations in the mei-W68 and mei-P22 genes prevent recombination but allow normal SC to form. These data, as well as a century of cytogenetic studies, support the argument that meiotic recombination between homologous chromosomes in Drosophila females requires synapsis and SC formation. We have cloned the c(3)G gene and shown that it encodes a protein that is structurally similar to SC proteins from yeast and mammals. Immunolocalization of the C(3)G protein, as well as the analysis of a C(3)G-eGFP expression construct, reveals that C(3)G is present in a thread-like pattern along the lengths of chromosomes in meiotic prophase, consistent with a role as an SC protein present on meiotic bivalents. The availability of a marker for SC in Drosophila allowed the investigation of the extent of synapsis in exchange-defective mutants. These studies indicate that SC formation is impaired in certain meiotic mutants and that the synaptic defect correlates with the exchange defects. Moreover, the observation of interference among the residual exchanges in these mutant oocytes implies that complete SC formation is not required for crossover interference in Drosophila.

Animals↗
PubMed1980

Silver-stained synaptonemal complexes of human pachytene bivalents studied by light microscopy.

The synaptonemal complex (SC), a part of the ultrastructure of the pachytene bivalent of eukaryotic organisms, is intimately connected with the pairing of homologous chromosomes. Its development, structure, and function have been studied extensively with the electron microscope during the past 20 years. A simple method of staining with silver nitrate has made it possible for us to visualize human SCs with the light microscope.

Cell Cycle↗
PubMed1983

Synaptonemal complexes and the chromosome complement of domestic fowl, Gallus domesticus.

Synaptonemal complexes (SC's) were compared to their chromosomes by transmission electron microscopy (TEM) of whole-mount spreads from 42 male chickens. Individual macrochromosomal SC's were first identified in heterokaryotypes and later by their centromere index. For all nine macrochromosomes (eight autosomes and the Z sex chromosome), the relative length (rl) of each SC corresponded to that of its mitotic and meiotic chromosome, and the centromere position along each SC corresponded to that of its mitotic chromosome. An idiogram was constructed which included the 30 microchromosomes. The idiogram revealed a graded series of SC lengths with a 30-fold difference between the longest and the shortest SC. Microchromosomal SC's comprised 35% of the genome length.

Animals↗
PubMed1978

Mitotic recombination in the absence of synaptonemal complexes in Saccharomyces cerevisiae.

Mitotic cells of a diploid strain of Saccharomyces cerevisiae with appropriate markers for the detection of mitotic crossing-over and mitotic gene conversion were irradiated with X-rays. Induction of these recombinational events was strong. After irradiation, cells were incubated in a rich growth medium and samples were removed for studying the possible formation of synaptonemal complexes up to a time when most cells had completed the first post-irradiation cell division. No complexes were found during the entire period of sampling, during which mitotic recombination in G1 (mitotic gene conversion), DNA replication and G2 (mitotic crossing-over) had occurred. These results are interpreted to mean that synaptonemal complexes are not required for mitotic recombination.

Alleles↗