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At least 19 recordsLinked to original sources

PubMed2006

S. pombe linear elements: the modest cousins of synaptonemal complexes.

Synaptonemal complexes (SCs) are not formed during meiotic prophase in the fission yeast, Schizosaccharomyces pombe. Instead, so-called linear elements (LinEs) are formed at the corresponding stages. LinEs are remarkable in that their number does not correspond to the number of chromosomes or bivalents and that the changes in their organisation during prophase do not evidently reflect the pairing of chromosomes. Yet, LinEs are necessary for full meiotic pairing levels and for meiotic recombination. In this review, the composition of LinEs, their evolutionary relationship to SCs and their possible functions are discussed.

Cell Cycle Proteins↗

PubMed1989

Immunocytogenetics. II. Human autoantibodies to synaptonemal complexes.

Synaptonemal complex (SC) autoantibodies are spontaneously produced by patients with various autoimmune diseases. Immunofluorescence staining of pachytene cells localized the antigen to the central element or transverse filaments of the SC but not to the lateral elements. Specific antibody labeling was confined to the SC at synapsis. Cytochemical tests showed that the SC autoantigen is a basic protein possibly bound to DNA. An unusual characteristic of the SC autoantigen is its species specificity. Patients were found whose sera selectively labeled the SCs of other humans, mice, or newts. The combining of anti SC and anti-kinetochore antibodies provides a new immunocytochemical method for the analysis of SC karyotypes. The optimum conditions for preparation of pachytene cells for visualization by indirect immunofluorescence were determined. The nature and functions of the SC antigen, as well as possible applications of SC-specific autoantibodies in cytogenetics and cell biology, are discussed.

Animals↗

PubMed1992

Identification of a structural protein component of rat synaptonemal complexes.

Synaptonemal complexes (SCs) are evolutionarily conserved nuclear structures of meiotic cells which form during the zygotene stage of the first meiotic prophase and are responsible for the pairing of homologous chromosomes. Their formation appears to be a prerequisite for crossing-over events and proper chromosome segregation during the first meiotic division. Despite knowledge of their central role in genetic recombination processes very little is known about the molecular composition and the mechanisms governing the assembly of the SCs. In the present study we report on the characterization of a monoclonal antibody (SC14f10) which enabled us to identify a novel SC protein termed SC48. Protein SC48 has a Mr of 48,000 and migrates in two-dimensional gels with a pH value of 6.9. By means of immunogold EM we localized this protein to the central region of the SC. In cell fractionation experiments we recovered protein SC48 together with SC-residual structures in a karyoskeletal fraction of pachytene spermatocytes. Our results indicate that SC48 is a meiosis-specific structural protein component of the SC probably involved in the pairing of homologous chromosomes.

Animals↗

PubMed2005

Loss of synaptonemal complex protein-1, a synaptonemal complex protein, contributes to the initiation of follicular assembly in the developing rat ovary.

In the rat ovary, germ and somatic cells become organized into primordial follicles 48-72 h after birth. Although several genes have been implicated in the control of early follicular growth, less is known about the factors involved in the formation of primordial follicles. Using the method of differential display of mRNAs, we found several genes differentially expressed at the time of follicular assembly. One of them encodes synaptonemal complex protein-1 (SCP1), a core component of the protein complex that maintains recombining chromosomes together during prophase I of the first meiotic division in germ cells. This association, evident during the pachytene stage, ends when chromosomal desynapsis begins in the diplotene stage at the end of prophase I. Oocytes become arrested in the diplotene/dictate stage before becoming enclosed into primordial follicles, suggesting that oocytes must complete meiotic prophase I before becoming competent to direct follicle assembly. We now show that attainment of the diplotene stage results in follicular formation. In developing rat ovaries, SCP1 mRNA expression is confined to oocytes and decreases precipitously within 24 h after birth, preceding the organization of primordial follicles. The premature loss of SCP1, achieved via treatment with an antisense oligodeoxynucleotide targeting SCP1 mRNA, resulted in more oocytes reaching the diplotene stage, as evidenced by a decrease in the number of oocytes containing germ cell nuclear antigen-1 (a nuclear protein whose expression ceases in diplotene) and an increase in the number of oocytes expressing MSY2 (a cytoplasmic Y box protein expressed in oocytes that have become arrested in diplotene). SCP1-deficient ovaries exhibited an increased number of newly formed follicles, suggesting that completion of meiotic prophase I endows oocytes with the ability to orchestrate follicular assembly.

Animals↗

PubMed1989

Synaptonemal complex proteins.

Synaptonemal complexes were isolated from rate spermatocytes for the purpose of biochemical and morphological analysis. Several monoclonal antibodies were elicited against purified synaptonemal complexes to study the composition and assembly of these structures. Four classes of antibodies could be discriminated according to the polypeptides that they recognize on Western blots of purified synaptonemal complexes, namely antibodies recognizing (i) a 190-kDa polypeptide; (ii) a 30- and a 33-kDa polypeptide; (iii) two polypeptides with molecular weights of about 120 kDa; and (iv) polypeptides with molecular weights of 66-55 kDa. The localization of these antigens within spermatocytes was analyzed light microscopically, by means of the immunoperoxidase technique and ultrastructurally, by immunogold labelling of surface-spread spermatocytes. The 66- to 55-kDa polypeptides are not confined to synaptonemal complexes; rather, these polypeptides appear to be chromosomal components. The 190-, 30-, and 33-kDa polypeptides make part of the lateral elements of paired as well as unpaired segments of synaptonemal complexes. The 120-kDa polypeptides were localized on the inner edge of the lateral elements, specifically in paired segments of synaptonemal complexes. The distribution of the 190-, 120-, 30-, and 33-kDa polypeptides within the testis was analyzed by immunofluorescence staining of cryostat sections. All these polypeptides turned out to be specific for nuclei of zygotene up to and including diplotene spermatocytes. Only in some early spermatids could the 190-, 30-, and 33-kDa polypeptides be detected, presumably in remnants of synaptonemal complexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Cryogenic preservation of mammalian testicular material for synaptonemal complex analysis.

Synaptonemal complex (SC) analyses have been used in mammalian cytogenetics to investigate the effects of chromosome heterozygosity on meiotic processes. To date, these analyses have been limited largely to the study of humans, livestock, or species which are easily maintained in the laboratory. The development of a method for the cryogenic preservation of testicular tissue for SC analyses allows for the application of this approach to field-oriented biological problems. This new method is described and data are presented which demonstrate its utility to mammalian cytogenetic studies.

Animals↗

PubMed2005

Juxtaposition of C(2)M and the transverse filament protein C(3)G within the central region of Drosophila synaptonemal complex.

The synaptonemal complex (SC) is intimately involved in the process of meiotic recombination in most organisms, but its exact role remains enigmatic. One reason for this uncertainty is that the overall structure of the SC is evolutionarily conserved, but many SC proteins are not. Two putative SC proteins have been identified in Drosophila: C(3)G and C(2)M. Mutations in either gene cause defects in SC structure and meiotic recombination. Although neither gene is well conserved at the amino acid level, the predicted secondary structure of C(3)G is similar to that of transversefilament proteins, and C(2)M is a distantly related member of the alpha-kleisin family that includes Rec8, a meiosis-specific cohesin protein. Here, we use immunogold labeling of SCs in Drosophila ovaries to localize C(3)G and C(2)M at the EM level. We show that both C(3)G and C(2)M are components of the SC, that the orientation of C(3)G within the SC is similar to other transverse-filament proteins, and that the N terminus of C(2)M is located in the central region adjacent to the lateral elements (LEs). Based on our data and the known phenotypes of C(2)M and C(3)G mutants, we propose a model of SC structure in which C(2)M links C(3)G to the LEs.

Animals↗

PubMed2004

The genetics and molecular biology of the synaptonemal complex.

The synaptonemal complex (SC) is a protein lattice that resembles railroad tracks and connects paired homologous chromosomes in most meiotic systems. The two side rails of the SC, known as lateral elements (LEs), are connected by proteins known as transverse filaments. The LEs are derived from the axial elements of the chromosomes and play important roles in chromosome condensation, pairing, transverse filament assembly, and prohibiting double-strand breaks (DSBs) from entering into recombination pathways that involve sister chromatids. The proteins that make up the transverse filaments of the SC also play a much earlier role in committing a subset of DSBs into a recombination pathway, which results in the production of reciprocal meiotic crossovers. Sites of crossover commitment can be observed as locations where the SC initiates and as immunostaining foci for a set of proteins required for the processing of DSBs to mature crossovers. In most (but not all) organisms it is the establishment of sites marking such crossover-committed DSBs that facilitates completion of synapsis (full-length extension of the SC). The function of the mature full-length SC may involve both the completion of meiotic recombination at the DNA level and the exchange of the axial elements of the two chromatids involved in the crossover. However, the demonstration that the sites of crossover formation are designated prior to SC formation, and the finding that these sites display interference, argues against a role of the mature SC in mediating the process of interference. Finally, in at least some organisms, modifications of the SC alone are sufficient to ensure meiotic chromosome segregation in the complete absence of meiotic recombination.

Animals↗

PubMedDate not supplied

[Synaptonemal complexes in vaccinated mice].

Synaptonemal complexes of spermatocytes I obtained from C57BL/6j male mice treated with inactivated bacterial vaccines were spread over the hypotonic phase and then were investigated using light microscope. The slides of synaptonemal complexes of mice treated with cyclophosphamide were used as positive control. It is shown possible in principle to reveal synaptonemal complex abnormalities by means of light microscopy. These abnormalities were not more frequent in vaccinated animals than in intact ones. Cyclophosphamide at doses of 100-200 mg/kg induced synaptonemal complex damage practically in 100% of cells 96 hours after the injection.

Animals↗

PubMed1988

The effect of bovine serum albumin and cytohelicase on surface-spread synaptonemal complexes of rye (Secale cereale).

Synaptonemal complexes of rye meiocytes were spread on plastic coated slides for electron microscopic observation. Two proteins generally used in synaptonemal complex spreading techniques, bovine serum albumin and cytohelicase, were applied separately or in combination in an isotonic protoplast medium at concentrations of 0.1-5%. At high concentrations these proteins proved to enhance notably the ultimate number of cells with synaptonemal complexes in the preparations. Also under this condition, centromere structures became stainable with silver nitrate in both the synaptonemal complexes of pollen mother cells and in interphase nuclei of other cell types. Since the true action of cytohelicase under appropriate spreading conditions was uncertain, the putative enzymatic digestion of cell walls was determined in a series of experiments using the fluorochrome calcofluor white as a stain of callose walls. Obvious breakdown of the cell walls was not observed before 8 min of treatment under standard conditions. This made it plausible that the prime effect of cytohelicase is that of a nonspecific protein interacting with the chromatin and improving the adhesion of synaptonemal complexes to the hydrophobic plastic film. The differential staining of the centromere structures in the presence of bovine serum albumin and cytohelicase probably reflects a reduced spreading of these structures due to preferential binding between these proteins and centromeric proteins.

Animals↗

PubMed1988

Presence of abnormal synaptonemal complexes in heterothallic species of Neurospora.

Synaptonemal complex abnormalities are frequent in reconstructed meiotic prophase nuclei of Neurospora crassa and Neurospora intermedia. Three kinds of synaptonemal complex anomalies were seen: lateral component splits, lateral component junctions, and multiple complexes. The anomalies apparently are formed during or after the pairing process, as they were not seen in the largely unpaired early zygotene chromosomes. Their presence at all the other substages from mid-zygotene to late pachytene indicates that they are not eliminated before the synaptonemal complex decomposes at diplotene. Abnormal synaptonemal complexes were seen in all 19 crosses of N. crassa and N. intermedia that were examined, including matings between standard laboratory strains, inversions, Spore killers, and strains collected from nature. The frequency of affected nuclei and degree of abnormality within a nucleus varied in different matings. No abnormalities were present in the homothallic species Neurospora africana and Neurospora terricola. Structural chromosome aberrations, introgression, and heterozygosity have been eliminated as causes for pairing disorder. The abnormal synaptonemal complexes seemingly do not interfere with normal ascus development and ascospore formation. The affected nuclei are not aborted during meiotic prophase, nor are they eliminated by abortion of mature asci. The abnormal meiocytes do not lead to aneuploidy, as judged by the low frequency of white ascospores in crosses between wild type strains that have many abnormalities. Thus, the abnormal synatonemal complexes do not appear to prevent chiasma formation between homologues.

Cell Nucleus↗

PubMed1987

Immunocytochemical labelling of the kinetochore of human synaptonemal complexes, and the extent of pairing of the X and Y chromosomes.

An immunocytochemical method was used to label the kinetochores on human synaptonemal complexes. Synaptonemal complex spreads were labelled with autoimmune CREST serum, followed by a second antibody labelled with colloidal gold, and examined by electron microscopy. Clusters of gold particles were found at discrete sites which were identified as kinetochores on the autosomal synaptonemal complexes, as well as on the XY pair. This method was used to investigate the extent of pairing of the human X and Y chromosomes at pachytene. Our observations confirm earlier work, based purely on measurements, that the pairing of the sex chromosomes sometimes extends beyond the centromere of the Y chromosome into the long arm. At the same time we showed that the centromeric indices of the X and Y at pachytene are highly variable, so that measurements alone are not sufficient to estimate the degree of pairing of the sex chromosomes.

Centromere↗

PubMed1991

Coming to grips with a complex matter. A multidisciplinary approach to the synaptonemal complex.

Research into the synaptonemal complex (SC) is currently finding renewed interest. This is because the primarily cytological knowledge of the SC has been increasingly supplemented by immunochemical characterization and genetical studies over recent years. Moreover, yeast, offering one of the most handy and rewarding experimental systems, has joined the group of organisms in which the SC can be studied cytologically. In this essay I shall present aspects concerning the SC and its role in meiotic pairing that have emerged over the past few years, parts of which were discussed at a recent meeting in Obertraun, Austria.

Meiosis↗

PubMed1977

Some morphological aspects of the synaptonemal complex in higher plants.

The synaptonemal complex is illustrated in electron micrographs from pollen mother cells (p.m.cs) of the following plants: Fritillaria lanceolata, Allium fistulosum, Tulbaghia violacea, Luzula purpurea, Phaedranassa viridiflora and the tulip cultivar Keiserkroon. The possibility that the lateral elements in synaptonemal complexes of plants are tubiform structures is discussed in relation to their fine structure and in the light of a deformity seen in them. An assessment of the evidence suggesting that both lateral and central elements in the complex are ribonucleoprotein structures is made. The effect of brief water treatment on the chromatin and synaptonemal complex at zygotene in p.m.cs of the Phaedranassa is discussed, particularly with reference to two precisely oriented axial strands then seen running between the lateral elements. Examination of stages of premeiotic interphase and early leptotene in p.m.cs of the Fritillaria, revealed that the axial cores laid down at leptotene are formed first in heterochromatic regions, which in this species are locked in chromocentres that persist until pachytene. Further, at leptotene the chromatin in these parts was singularly more decondensed (diffuse) than at any other period, including the premeiotic interphase, subsequent stages of meiosis and mitotic cycle in meristems. It is suggested that the diffuse state of the chromatin in chromocentres at the onset of leptotene, allows the necessary freedom of movement required to promote homologous pairing of the heterochromatic segments. Evidence of such a movement was indicated by a change in position of the nucleoli, which moved from a more central position at early premeiotic interphase to a peripheral one at the onset of leptotene, when they are seen adpressed to the nuclear envelope.

Cell Nucleus↗

PubMed1984

The synaptonemal complex and genetic segregation.

The assembly, rearrangement and disassembly of the synaptonemal complex during the stages from leptotene to anaphase I of meiosis are described. The assembly of the lateral component of the synaptonemal complex between the sister chromatids of the leptotene chromosome causes the undivided appearance of the leptotene chromosome in the light microscope. During zygotene the lateral component mediates the assembly of the synaptonemal complex between homologous segments of homologous as well as homoeologous chromosomes. Chromosome and bivalent interlockings are a regular feature during chromosome pairing at zygotene. They are resolved by breakage and precise repair of the chromosomes. The phase of synaptonemal complex formation between homologous chromosome segments is succeeded by a phase of rearrangements. In this phase, chromosome homology is no longer required for synaptonemal complex assembly. This reduces the number of univalent chromosome sections. Rearrangement of chromosome pairing with the synaptonemal complex is not expected to take place at positions where a crossover has occurred. Disassembly of the synaptonemal complex at diplotene is initiated at specific regions along the bivalent arms. Chiasmata are formed from retained pieces of the synaptonemal complex in which a recombination nodule is or had been present. A limit to the number of available recombination nodules and a mechanism which ensures that at least one nodule is placed in each bivalent arm are sources for the positive interference observed in linkage studies employing three-point tests. The time of crossing over relative to the zygotene assembly and pachytene rearrangement phases of the synaptonemal complex determines if multivalents or exclusively bivalents are found at metaphase I in amphidiploids and autotetraploids. The synaptonemal complex provides both the structural basis for the regular disjunction of chromosomes at meiosis and gene recombination between homologous or homoeologous chromosome arms.

Animals↗

PubMed1993

Zygotene-pachytene substaging and synaptonemal complex karyotyping of boar spermatocytes.

Synaptonemal complex analysis, by electron microscopy of spread spermatocytes after phosphotungstic acid staining, made possible description of the chromosomal synaptic patterns and the synaptonemal complex karyotype of the pig (Sus scrofa domestica). The autosomal synaptic pattern in conjunction with the sex chromosome morphology and pairing behaviour can serve as a reference for the meiotic cell progression from the zygotene stage to the pachytene. The autosomes started terminal synapsis at early zygotene (Z1) and at mid-zygotene (Z2) some of the small bivalents were completely paired. The extension of pairing between the X and the Y chromosome, and the differentiation of their axes, disclosed seven types of sex bivalent (Types 0-VI). The Type 0 sex bivalent occurred in late zygotene (Z3), at which the X and Y axes began terminal synapsis by their short arms. Each one of the pachytene substages, early, mid-, and late, included two sex bivalent types. By early pachytene (P1-P2) the entire Y chromosome was paired with the X axis. Subsequently, progressive desynapsis and differentiation of the sex chromosome axes defined the mid- (P3-P4) and late pachytene substages (P5-P6). At mid-pachytene, the unpaired XY segments were associated end-to-end and showed differing degrees of complexity (thickening, splitting, despiralization and strandedness). These axial complexities were replaced at late pachytene by fine excrescences along the sex chromosome axes, which still formed a short SC stretch. Additionally, an attempt to construct an SC karyotype for the pig is presented. There was general agreement between the autosomal SC karyotype and the autosomal somatic karyotype when comparisons were made, considering the relative lengths and arm ratios of individual chromosome pairs.

Animals↗

PubMedDate not supplied

[The dynamics of the formation of spontaneous autoantibodies to the synaptonemal complex in male mice].

Time-related changes in formation of spontaneous autoantibodies against the synaptonemal complex were studied by indirect immunofluorescence in male mice. Appearance of the spontaneous autoantibodies against the synaptonemal complex coincided with that of the cells containing synaptonemal complexes. The mouse synaptonemal complexes were binding spontaneous autoantibodies of the rabbit and human sera. The synaptonemal complexes of the equine spermatocytes were binding spontaneous autoantibodies of the mouse serum. There was no fluorescence of synaptonemal complexes on preparations of spread rye meiocytes treated with the mouse serum. Antigenic similarity was shown for the synaptonemal complex components in representatives of the different mammalian orders: rodents, odd-toed ungulates, and primates.

Aging↗

PubMed1975

Electron microscopy of meiosis in Drosophila melanogaster females. I. Structure, arrangement, and temporal change of the synaptonemal complex in wild-type.

Complete reconstruction of the synaptonemal complex in 12 pachytene (defined here as that stage in which the synaptonemal complex is continuous throughout the bivalents) nuclei from one wild-type germarium has permitted the following observations. 1) Drosophila melanogaster bivalents at pachytene exhibit a chromocentral arrangement; the pericentric heterochromatin of all bivalents lies in one region of the nucleus, the chromocenter. Telomeric ends do not appear to abutt the nuclear envelope. 2) Synaptonemal complex is present in the pericentric heterochromatin; however, it is morphologically distinct from that present in the euchromatic portion of thesynaptonemal complex of the bivalent arms is greatest at early pachytene; the synaptonemal complex then becomes progressively shorter. Minimum length is approximately one-half of the maximum. 4) Decrease in length of synaptonemal complex is accompanied by an increase in thickness. Reconstruction of 20 pachytene nuclei from an additional 8 germaria suggests that these observations are typical. Correlations between these cytological observations and genetic observations (e.g., patterns of crossing-over) are discussed.

Animals↗