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PubMed2002

Cytochemical study of the distribution of RNA and DNA in the synaptonemal complex of guinea-pig and rat spermatocytes.

The distribution of DNA and RNA in the synaptonemal complex and related structures, was studied using high resolution cytochemical methods and in situ hybridization, in guinea pig and rat testis. Serial sectioning demonstrates that frequently the formation of the synaptonemal complex (SC) occurs without a previous development of isolated chromosomal axes. The lateral elements of the forming SC are in continuity with pairs of DNA-containing thin filaments. These chromatin filaments fold in numerous short loops just before incorporating to the lateral elements. Some of these loops are included in the ribbon-like structure of the lateral elements of the mature SC. We propose that these short loops contain the DNA attachment sequences associated with the proteins of the LE. During the formation of the SC one of the two chromatin filaments incorporates at the central surface of the forming lateral element (LE) and the other is located at the external side of the LE. This unexpected distribution does not correspond to the pair of thick filaments previously discerned in structure of the LE. The presence of RNA associated with the DNA-containing thin filaments, as well as with the axial chromatin elements of the forming SC, may be related with the transcription occurring during meiotic prophase, specially during zygotene stage. We propose that RNA is involved in a still uncharacterized process essential for pairing.

Animals↗

PubMedDate not supplied

[Localization of DNA sequences tightly associated with synaptonemal complex in compositional fractions of golden hamster].

The synaptonemal complex isolated from the spermatocyte nuclei by exhaustive hydrolysis of the latter by DNase II contains tightly associated DNA sequences (SCAR DNA). Here we studied the compositional properties of a cloned family of SCAR DNA of golden hamster, namely we performed the localization of 27 SCAR DNA clones on compositionally fractionated genomic DNA from golden hamster. We observed that sequences of the SCAR DNA family are mainly localized in the GC-poor isochore families L1 and L2, that showed 63% hybridization signals. This means that 37% of signals is referred to the GC-rich isochores, indicating the presence of SCAR DNA overall the genome, even if each isochore family presents differences in density and sequence type. Moreover, the SCAR DNA sequences containing regions of homology with LINE/SINE repeats were observed in all the isochore families. The compositional localization of SCAR DNA is in agreement with the hypothesis that SC and SCAR DNA participate in the chromatin organization during the meiosis prophase I, which should result in the attachment of chromatin loops to lateral elements of SC along the whole length of the latter.

Animals↗

PubMed2006

Identification of all pachytene bivalents in the common shrew using DAPI-staining of synaptonemal complex spreads.

A major problem in studies of synaptonemal complexes (SC) is the difficulty in distinguishing individual chromosomes. This problem can be solved combining SC immunostaining with FISH of chromosome-specific sequences. However, this procedure is expensive, time-consuming and applicable only to a very limited number of species. In this paper we show how a combination of SC immunostaining and DAPI staining can allow identification of all chromosome arms in surface-spreads of the SC of the common shrew (Sorex araneus L.). Enhancement of brightness and contrast of the images with photo editing software allowed us to reveal clear DAPI-positive and negative bands with relative sizes and positions similar to DAPI landmarks on mitotic metaphase chromosomes. Using FISH with DNA probes prepared from chromosome arms m and n we demonstrated correct recognition of the chromosomes mp and hn on the basis of their DAPI pattern. We show that the approach we describe here may be applied to other species and can provide an important tool for identification of individual bivalents in pachytene surface-spreads.

Animals↗

PubMed2006

Involvement of synaptonemal complex proteins in sex chromosome segregation during marsupial male meiosis.

Marsupial sex chromosomes break the rule that recombination during first meiotic prophase is necessary to ensure reductional segregation during first meiotic division. It is widely accepted that in marsupials X and Y chromosomes do not share homologous regions, and during male first meiotic prophase the synaptonemal complex is absent between them. Although these sex chromosomes do not recombine, they segregate reductionally in anaphase I. We have investigated the nature of sex chromosome association in spermatocytes of the marsupial Thylamys elegans, in order to discern the mechanisms involved in ensuring their proper segregation. We focused on the localization of the axial/lateral element protein SCP3 and the cohesin subunit STAG3. Our results show that X and Y chromosomes never appear as univalents in metaphase I, but they remain associated until they orientate and segregate to opposite poles. However, they must not be tied by a chiasma since their separation precedes the release of the sister chromatid cohesion. Instead, we show they are associated by the dense plate, a SCP3-rich structure that is organized during the first meiotic prophase and that is still present at metaphase I. Surprisingly, the dense plate incorporates SCP1, the main protein of the central element of the synaptonemal complex, from diplotene until telophase I. Once sex chromosomes are under spindle tension, they move to opposite poles losing contact with the dense plate and undergoing early segregation. Thus, the segregation of the achiasmatic T. elegans sex chromosomes seems to be ensured by the presence in metaphase I of a synaptonemal complex-derived structure. This feature, unique among vertebrates, indicates that synaptonemal complex elements may play a role in chromosome segregation.

Animals↗

PubMed2003

Loss of HR6B ubiquitin-conjugating activity results in damaged synaptonemal complex structure and increased crossing-over frequency during the male meiotic prophase.

The ubiquitin-conjugating enzymes HR6A and HR6B are the two mammalian homologs of Saccharomyces cerevisiae RAD6. In yeast, RAD6 plays an important role in postreplication DNA repair and in sporulation. HR6B knockout mice are viable, but spermatogenesis is markedly affected during postmeiotic steps, leading to male infertility. In the present study, increased apoptosis of HR6B knockout primary spermatocytes was detected during the first wave of spermatogenesis, indicating that HR6B performs a primary role during the meiotic prophase. Detailed analysis of HR6B knockout pachytene nuclei showed major changes in the synaptonemal complexes. These complexes were found to be longer. In addition, we often found depletion of synaptonemal complex proteins from near telomeric regions in the HR6B knockout pachytene nuclei. Finally, we detected an increased number of foci containing the mismatch DNA repair protein MLH1 in these nuclei, reflecting a remarkable and consistent increase (20 to 25%) in crossing-over frequency. The present findings reveal a specific requirement for the ubiquitin-conjugating activity of HR6B in relation to dynamic aspects of the synaptonemal complex and meiotic recombination in spermatocytes.

Adaptor Proteins, Signal Transducing↗

PubMed1984

Meiotic studies and synaptonemal complex analysis in two infertile males with a 13/14 balanced translocation.

Meiotic and synaptonemal complex studies by light and electron microscopy have been carried out in two infertile males with a balanced 13/14 translocation. As expected, all metaphase I figures in conventional meiotic preparations contained a chain trivalent. Synaptonemal complex studies showed typical trivalent images with incomplete pairing of the acrocentric elements in the cis configuration. A review of the literature shows that the fertility of these patients is quite variable. All of them show a slightly reduced number of chiasmata (mean 46.6). Pairing in cis, as detected by electron microscopic studies, does not seem to have a prognostic value.

Adult↗

PubMed2006

Characterization of a novel meiosis-specific protein within the central element of the synaptonemal complex.

During the first meiotic prophase, alignment and synapsis of the homologous chromosomes are mediated by the synaptonemal complex. Incorrect assembly of this complex results in cell death, impaired meiotic recombination and formation of aneuploid germ cells. We have identified a novel mouse meiosis-specific protein, TEX12, and shown it to be a component of the central element structure of the synaptonemal complex at synapsed homologous chromosomes. Only two other central element proteins, SYCE1 and SYCE2, have been identified to date and, using several mouse knockout models, we show that these proteins and TEX12 specifically depend on the synaptonemal transverse filament protein SYCP1 for localization to the meiotic chromosomes. Additionally, we show that TEX12 exactly co-localized with SYCE2, having the same, often punctate, localization pattern. SYCE1, on the other hand, co-localized with SYCP1 and these proteins displayed the same more continuous expression pattern. These co-localization studies were confirmed by co-immunoprecipitation experiments that showed that TEX12 specifically co-precipitated with SYCE2. Our results suggest a molecular network within the central elements, in which TEX12 and SYCE2 form a complex that interacts with SYCE1. SYCE1 interacts more directly with SYCP1 and could thus anchor the central element proteins to the transverse filaments.

Animals↗

PubMed1976

Synaptonemal complexes during premeiotic DNA synthesis in oocytes of Drosophila melanogaster.

Well-synchronized populations of oocytes obtained by means of the "pupal system" (Grell, 1973a) have been examined to determine the time of appearance of the synaptonemal complex. The complex first appears in the most advanced oocytes between 132 and 138 hr of female development. Between 138 and 156 hr the complex apparently undergoes a fourfold increase in length. At 150 and 156 hr the complex system is extensive and present in virtually all oocytes. Previous studies using the pupal system have placed the period of premeiotic DNA synthesis between 132 and 162 hr. Thus, indirect evidence indicates that a significant portion of synaptonemal complex formation is coextensive with the main DNA replication in the oocyte. Direct evidence that DNA synthesis and complex formation occur simultaneously in oocytes has been obtained by electron microscope autoradiography. By definition, then, the stage of synaptonemal complex formation in Drosophila must include premeiotic interphase.

Animals↗

PubMed2001

Germ cell differentiation and synaptonemal complex formation are disrupted in CPEB knockout mice.

CPEB is a sequence-specific RNA binding protein that regulates translation during vertebrate oocyte maturation. Adult female CPEB knockout mice contained vestigial ovaries that were devoid of oocytes; ovaries from mid-gestation embryos contained oocytes that were arrested at the pachytene stage. Male CPEB null mice also contained germ cells arrested at pachytene. The germ cells from the knockout mice harbored fragmented chromatin, suggesting a possible defect in homologous chromosome adhesion or synapsis. Two CPE-containing synaptonemal complex protein mRNAs, which interact with CPEB in vitro and in vivo, contained shortened poly(A) tails and mostly failed to sediment with polysomes in the null mice. Synaptonemal complexes were not detected in these animals. CPEB therefore controls germ cell differentiation by regulating the formation of the synaptonemal complex.

Age Factors↗

PubMed1994

The gene encoding a major component of the lateral elements of synaptonemal complexes of the rat is related to X-linked lymphocyte-regulated genes.

The lateral elements of synaptonemal complexes (SCs) of the rat contain major components with relative electrophoretic mobilities (M(r)S) of 30,000 and 33,000. After one-dimensional separation of SC proteins on polyacrylamide-sodium dodecyl sulfate gels, these components show up as two broad bands. These bands contain closely related proteins, as judged from their peptide maps and immunological reactivity. Using affinity-purified polyclonal anti-30,000- and anti-33,000-M(r) component antibodies, we isolated a cDNA encoding at least one of the 30,000- or 33,000-M(r) SC components. The protein predicted from the nucleotide sequence of the cDNA, called SCP3 (for synaptonemal complex protein 3), has a molecular mass of 29.7 kDa and a pI value of 9.4. It has a potential nucleotide binding site and contains stretches that are predicted to be capable of forming coiled-coil structures. In the male rat, the gene encoding SCP3 is transcribed exclusively in the testis. SCP3 has significant amino acid similarity to the pM1 protein, which is one of the predicted products of an X-linked lymphocyte-regulated gene family of the mouse: there are 63% amino acid sequence similarity and 35% amino acid identity between the SCP3 and pM1 proteins. However, SCP3 differs from pM1 in several respects, and whether the proteins fulfill related functions is still an open question.

Amino Acid Sequence↗

PubMed1983

A simple method of staining the synaptonemal complex with Coomassie brilliant blue for light microscopy.

A simple technique for staining synaptonemal complexes with Coomassie brilliant blue for light microscopy has been described. The testis cells were exposed to prolonged hypotonic treatment and dropped on Formvar-coated slides. Following fixation with paraformaldehyde the slides were stained with Coomassie brilliant blue for 15 min to 1 h at room temperature and rinsed in distilled water. For its simplicity and rapidity this technique may serve as an effective alternative to silver staining for light microscopic observation of synaptonemal complexes.

Animals↗

PubMed2000

The meiotic specific synaptonemal complex protein SCP3 is expressed by female and male primordial germ cells of the mouse embryo.

The synaptonemal complex proteins SCP3 and SCP1 are components of the synaptonemal complex, a meiosis-specific protein structure essential for synapsis of homologous chromosomes. Using polyclonal antibodies raised against SCPs of rat testis, we have studied the expression of these proteins in embryonic germ cells of the mouse embryo using immunohistochemistry and immunoblotting. This investigation provided the first description of the sequential appearance of SCP3 and SCP1 during the different stages of the female meiosis in the mouse. Most importantly, we found that also male primordial germ cells express SCP3 for a short time before undergoing G1 arrest. This strongly supports the hypothesis that primordial germ cells are programmed to enter meiosis unrespective of the sex and that foetal testis produces a factor that inhibits such programme.

Animals↗

PubMed1986

Synaptonemal complexes in Gerbillidae: probable role of intercalated heterochromatin in gonosome-autosome translocations.

A study of sex chromosomes and synaptonemal complexes in male specimens of Gerbillus chiesmani, G. nigeriae, G. hoogstrali, and Taterillus pygargus is reported. In each of these Gerbillidae species there are two or three translocations of autosomes with X and Y chromosomes. Analysis of mitotic chromosomes consistently shows the presence of constitutive heterochromatin on the der t(X;autosome) at the X-autosome junction and on the der t(Y;autosome). Analysis of the synaptonemal complexes shows the existence of an unusual structure, lightly stained, at the X-autosome junction and at the Y-autosome junction, which is probably heterochromatic in nature, thus corresponding to the mitotic patterns. This heterochromatin separates the autosomal and gonosomal segments, which behave independently and normally. By analogy with findings from humans and other mammals, a general hypothesis is proposed on the role of intercalated heterochromatin between translocated gonosomes and autosomes. This hypothesis explains why the pathological consequences of these translocations may be very different in males and females. The role of intercalated heterochromatin would be to avoid the pathological consequences of gonosome-autosome translocations resulting from inactivation of the sex chromosomes in female somatic cells and male germinal cells.

Animals↗

PubMed1988

Synaptonemal complex damage induced by clastogenic and anti-mitotic chemicals: implications for non-disjunction and aneuploidy.

Mice were treated with mitomycin C, cyclophosphamide, amsacrine, colchicine, or vinblastine sulfate, and meiotic prophase cells analyzed for synaptonemal complex (SC) damage. All test agents caused synaptonemal complex breakage and synapsis irregularities, although propensities for inducing specific types of damage at S-phase or prophase stages varied among the chemicals. The data indicate that SC analysis can reveal chemical-specific alterations to meiotic homologue pairing/synapsis which have not generally been recognized, and which theoretically may be implicated in non-disjunction.

Aneuploidy↗

PubMed1991

In situ hybridization of Lilium whole mount synaptonemal complex chromosomal preparations.

Whole mount meiotic preparations of the synaptonemal complex complement of Lilium have been used for in situ hybridization experiments. A probe of the maize ribosomal DNA gene cluster has been successfully hybridized to the lily preparations. Three strong signals, corresponding to the three known lily nucleolus organizer regions, have been seen in most of the chromosome preparations. In situ hybridization experiments using meiotic preparations should be useful for identifying specific chromosomes, and for investigating the role of particular DNA molecules important to meiotic function.

Histological Techniques↗

PubMed1993

[A preparative method for isolating the synaptonemal complexes from mammalian spermatocytes].

A method of isolation of synaptonemal complexes (SC) from mouse, rat and Syrian hamster spermatocytes is described. A fraction of pachytene spermatocyte nuclei was obtained by centrifugation of the testis homogenate in stepwise sucrose gradient and then lysed. The resulting chromatine was hydrolysed with DNAse II, and a fraction of isolated SCs was obtained by ultracentrifugation of the hydrolysate. The method can be applied for obtaining the SC fraction from spermatocytes sufficient for cytological, biochemical and molecular biology studies.

Animals↗

PubMed2006

Shaping meiotic prophase chromosomes: cohesins and synaptonemal complex proteins.

Recent progress in elucidating the function of synaptonemal complex (SC) proteins and of cohesins in meiocytes made possible, in particular, through the analysis of mice deficient in SC or cohesin proteins has significantly enriched our understanding of how meiotic chromosome architecture is determined. Cohesins and the SC proteins act together in generating the characteristic axis-loop structure of meiotic chromosomes, their pairing into bivalents, their ability to recombine, and to be properly segregated. This minireview attempts to summarize the current knowledge with a focus on higher eukaryotic systems and to ask questions that ought to be addressed in the future.

Animals↗

PubMed2006

[Synaptonemal complex--an essential role in etiology of idiopathic azoospermia].

Synaptonemal complex (SC) which is a meiosis-specific supramolecular proteinaceous structure plays a crucial role in condensation, pairing, recombination and disjunction of homologous chromosomes at meiosis I. In recent years,a series of new developments on SC has been made, including new findings in both component and function of SC. Abnormalities of SC resulting from genetic mutation can directly induce arrest of spermatogenesis in rat model. More importantly, in human male patients with non-obstructive infertility the fact that genetic variation of SC (e.g. SCP3) is the causative factor of idiopathic azoospermia had been confirmed, and the investigation of SCP1 is under way.

Animals↗