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PubMed1996

Localization of the N-terminus of SCP1 to the central element of the synaptonemal complex and evidence for direct interactions between the N-termini of SCP1 molecules organized head-to-head.

The synaptonemal complex (SC) is a meiosis-specific, tripartite structure essential for synapsis of homologous chromosomes; it contains a central element positioned between two lateral elements and transversal filaments connecting the lateral elements. In mammals, a major constituent of the transversal filament is known: the SCP1 protein. It contains a long central coiled-coil motif and the molecules are probably organized as dimers, each forming a coiled-coil fiber. We have now developed a new sensitive procedure for immunoelectron microscopy of synaptonemal complex proteins and determined the exact localization of the two nonhelical ends of the SCP1 protein within the mouse synaptonemal complex. We found that the N-terminal end of the SCP1 protein is located within the central element of the synaptonemal complex, whereas the C-terminal end is close to or within the lateral element of the synaptonemal complex. This result supports the notion that SCP1 is an extended filamentous protein and that the two molecules of the putative SCP1 dimer are likely to have the same polarity. The observation that the N-termini are confined to the central element indicated that SCP1 dimers, anchored in opposite lateral elements, could establish contact with each other in the central element via their N-termini. To test this possibility we used the yeast two-hybrid system and found that the N-terminal end of the SCP1 protein indeed strongly interacted with itself, but not with other protein domains tested. We therefore suggest that a transversal filament consists of one or more pairs of SCP1 dimers, each pair being organized in a head-to-head arrangement with the C-termini anchored in the lateral elements and the two N-termini being joined in the central element.

Animals↗

PubMed1997

Presence of synaptonemal complex protein 1 transversal filament-like protein in human primary spermatocytes.

The synaptonemal complex (SC) is involved in the pairing of chromosomes during meiosis. We found that antibodies raised against a protein component (P1) of the mouse synaptonemal complex, mouse SCP1, also identified the SC in human primary spermatocytes. Biopsies from 18 men presented with infertility were evaluated by light-field microscopy and grouped into five categories: normal spermatogenesis, Sertoli cell-only syndrome, meiotic disturbances, spermiogenic (i.e. differentiation) disturbances, and other combined disturbances. In all the normal subjects the SCP1 antibody distinctly stained the synaptonemal complexes of primary spermatocytes, whereas Sertoli cells, spermatogonia or spermatids were never stained. In three of the groups, which had germ cells but showed spermatogenic disturbances, the staining was similar to that seen in normal subjects. In sharp contrast to this, in sections from men with Sertoli cell-only syndrome no specific staining was seen. This study demonstrates that a SCP1-related protein is also conserved in the synaptonemal complex in meiotic cells from man. Further studies will reveal to what extent the absence or the non-functionality of SCP1 contributes to male infertility.

Animals↗

PubMed1986

Sequential analysis of synaptonemal complexes in the repopulating spermatocytes of Rattus norvegicus after restricting the germ cell population to spermatogonia by gossypol treatment.

Synaptonemal complexes of the repopulating spermatocytes of male rats were analyzed day by day using silver-stained surface spread nuclei between 8 and 25 days after restricting the germ cell population to spermatogonia by treatment of gossypol acetic acid at 30 mg/kg body weight/day for 70 days. The method allowed sequential analysis of male meiotic prophase on successive days after the last day of treatment. The leptotene cells appeared on day 11 and were characterized by a network of lateral elements and large nucleolar bodies in a diffuse mass. On day 13 the unpaired lateral elements and short stretches of synaptonemal complexes characteristic for zygotene could be seen. Pachytene nuclei showing 20 autosomal synaptonemal complexes and XY axes appeared on day 15. The diplotene cells were defined on day 22 by the loss of a complete synaptonemal complex set and by the appearance of disjoined lateral elements and persistent segments of synaptonemal complexes.

Animals↗

PubMed1983

Isolation and preliminary characterization of the synaptonemal complex from rat pachytene spermatocytes.

A method for preparation of the morphologically intact synaptonemal complex from rat pachytene spermatocytes is described. Pachytene spermatocytes were fractionated from rat testicular cells by centrifugal elutriation. Nuclei from fractionated pachytene cells were prepared and extensively digested with micrococcal nuclease. The digested nuclei were sedimented through 20% (w/v) sucrose containing 2 M NaCl by centrifugation. About 10% of total nuclear proteins and 1-2% of total genomic DNA was found to be associated with the residual structure. The residual structure, which contains mainly the synaptonemal complex, but may be still contaminated with other nuclear components including membrane and matrix, was stained with silver and examined under light microscopy. It was found that a silver-staining component of the synaptonemal complex is not grossly different from that in pachytene nuclei not subjected to digestion and extraction. Sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis revealed that virtually all the proteins in the residual structure are non-histones. The DNA isolated from the residual structure was about 135 base pairs (bp), long. The DNA was end-labeled and hybridized with a large excess of sonicated rat genomic DNA. The hybridization displayed a kinetics virtually identical to that of total nuclear DNA. We also prepared restricted DNA fragments associated with the residual structure. Southern blot analyses using a probe made from a recombinant DNA clone containing the albumin gene revealed that the DNA associated with the residual structure was not enriched (or depleted) in this gene sequence. Our results strongly suggest that (1) the synaptomenal complex may play a structural role to support the chromatin domains inside pachytene nucleus; and (2) a simple common DNA sequence in the chromatin domain is not required for association with the residual structure which contains morphologically intact synaptonemal complex in rat spermatocytes.

Albumins↗

PubMed2024

Diffusion within the synaptonemal complex can account for signal transduction along meiotic chromosomes.

Meiotic chromosomes efficiently transduce information along their length to regulate the distribution of genetic exchanges (crossovers). However, the mode of signal transduction remains unknown. A conserved protein interface called the synaptonemal complex forms between the parental chromosomes. The synaptonemal complex exhibits liquid-like behaviors, suggesting that the diffusion of signaling molecules along its length could coordinate crossover formation. Here, we directly test the feasibility of such a mechanism by tracking a component of the synaptonemal complex (SYP-3) and a conserved regulator of exchanges (ZHP-3) in live Caenorhabditis elegans gonads. While we find that both proteins diffuse within the synaptonemal complex, ZHP-3 diffuses 4- and 9-fold faster than SYP-3 before and after crossover designation, respectively. We use these measurements to parameterize a physical model for signal transduction. We find that ZHP-3, but not SYP-3, can explore the lengths of chromosomes on the time scale of crossover designation, consistent with a role in the spatial regulation of exchanges. Given the conservation of ZHP-3 paralogues across eukaryotes, we propose that diffusion along the synaptonemal complex may be a conserved mechanism of meiotic regulation. More broadly, our work explores how diffusion compartmentalized by condensates could regulate crucial chromosomal functions.

Synaptonemal Complex↗

PubMedDate not supplied

Isolation and characterization of a cDNA encoding a synaptonemal complex protein.

A gene encoding a 65-kilodalton antigen of the rat synaptonemal complex, SC65, has been cloned by screening rat testis lambda gt11 and lambda ZAPII cDNA expression libraries using polyclonal antibodies against rat synaptonemal complex proteins. The longest open reading frame, initiating at an ATG codon in the cDNA, encodes a protein of 431 amino acids, with a relative molecular mass of 50,000. Immunological analysis locates the SC65 gene product on the synaptonemal complex between the pairing faces of the parallel aligned cores of homologous chromosomes in spermatocytes. Of the rat tissues examined, the SC65 gene is transcribed in testis, brain, and heart at similar levels, and in the liver at a much lower level. The DNA sequence extending about 80 base pairs downstream of the translation termination codon has 93% similarity to the identifier sequence present in the rat genome in 1 x 10(5)-1.5 x 10(5) copies and in cDNA clones of precursors of brain-specific mRNAs. The amino acid sequence encoded by the SC65 gene contains an acidic region in the C-terminal domain of the protein, potential glycosylation sites, and at least one possible phosphorylation site. The protein shows no overall similarity to proteins of known function, nor is there similarity to protein sequences present in GenBank or EMBL data bases.

Amino Acid Sequence↗

PubMed1989

Histone electrophoretic pattern in the characterization of synaptonemal complexes.

The presence of a stoechiometric electrophoresis pattern of histones in carefully isolated synaptonemal complexes is reported. The use of this pattern is suggested as an internal standard of synaptonemal complex purification, in addition to the more generally used electron micrographs. This is especially useful in experiments leading to the characterization of the protein components of SCs. The use of mice of an age at which pachytenes predominate (90%) in the prophase-cell population is also advantageous to improve the final yield in synaptonemal complexes.

Animals↗

PubMed1981

The staining of the synaptonemal complex for light microscopic study in the mouse.

Demonstration of the synaptonemal complex for light microscopy has until now been based on staining with silver. After fixation at pH 9-10 it is also possible to visualize synaptonemal complexes with several nonspecific protein stains such as Coomassie brilliant blue, Giemsa, fast green, light green and Stains All. Although staining with silver gives the best contrast between synaptonemal complexes and the background, the other dyes have a number of advantages, such as more even staining, easy extractability, and lower cost than silver.

Animals↗

PubMed1996

HSP70-2 is part of the synaptonemal complex in mouse and hamster spermatocytes.

Mouse spermatogenic cells are known to express HSP70-2, a member of the HSP70 family of heat-shock proteins. The purpose of the present study was to characterize further the expression and localization of HSP70-2 in meiotic cells of mice and hamsters. After separating mouse spermatogenic cells into cytoplasmic and nuclear fractions, proteins were separated by two-dimensional gel electrophoresis and detected with HSP-specific antibodies. Of several HSP70 proteins identified in the cytoplasm, only HSC70 and HSP70-2 were also detected in the nucleus. Immunocytological analyses of spermatocyte prophase cells revealed that HSP70-2 was associated with the synaptonemal complex. Surface-spread synaptonemal complexes at pachytene and diplotene stages labeled distinctly with the antiserum to HSP70-2. Synaptonemal complexes from fetal mouse oocytes failed to show any evidence of HSP70-2. Reverse-transcriptase-polymerase chain reaction (RT-PCR) analyses of gene expression confirmed this sex specificity; Hsp70-2 mRNA was detected in mouse testes, but not ovaries. These findings are suggestive of a previously unsuspected sexual dimorphism in structure and/or function of the synaptonemal complex.

Animals↗

PubMed1996

The perinuclear microtubule-organizing center and the synaptonemal complex of higher plants share a common antigen: its putative transfer and role in meiotic chromosomal ordering.

Recognition of homologous chromosomes during meiotic prophase is associated in most cases with the formation of the synaptonemal complex along the length of the chromosome. Telomeres, located at the nuclear periphery, are preferential initiation sites for the assembly of the synaptonemal complex. In most eukaryotic cells, telomeres cluster in a restricted area, leading to the "bouquet" configuration in leptotene-zygotene, while this typical organization progressively disappears in late zygotene-pachytene. We wondered whether such striking changes in the intranuclear ordering and pairing of meiotic chromosomes during the progression of prophase I could be correlated with activity of the centrosome and/or microtubule-organizing center (MTOC). Plant cells may be used as a model of special interest for this study as the whole nuclear surface acts as an MTOC, unlike other cell types where MTOCs are restricted to centrosomes or spindle pole bodies. Using a monoclonal antibody (mAb 6C6) raised against isolated calf centrosomes we found that the 6C6 antigen is present over the entire surface of the plant meiotic nucleus, in early prophase I, before chromosomal pairing. At zygotene, short fragments of chromosomes become stained near the nuclear envelope and within the nucleus. At pachytene, after complete synapsis, the labeling specifically concentrates within the synaptonemal complexes, although the nuclear surface is no longer reactive. Ultrastructural localization using immunogold labeling indicates that the 6C6 antigen is colocalized with the synaptonemal complex structures. Later in metaphase I, the antigen is found at the kinetochores. Our data favor the idea that the 6C6 antigen may function as a particular "chromosomal passenger-like" protein. These observations shed new light on the molecular organization of the plant synaptonemal complex and on the redistribution of cytoskeleton-related antigens during initiation of meiosis. They suggest that antigens of MTOCs are relocated to chromosomes during the synapsis process starting at telomeres and contribute to the spatial arrangement of meiotic chromosomes. Such cytoskeleton-related antigens may acquire different functions depending on their localization, which is cell-cycle regulated.

Antibodies, Monoclonal↗

PubMed1988

Synaptonemal complex damage as a measure of genotoxicity at meiosis.

Synaptonemal complex aberrations can provide a sensitive measure of chemical-specific alterations to meiotic chromosomes. Mitomycin C, cyclophosphamide, amsacrine, ellipticine, colchicine, vinblastine sulfate, and cis-platin exposures in mice have been shown to cause various patterns of synaptonemal complex structural damage and synaptic irregularity. These effects are suggestive of abnormal homologue pairing/synapsis/recombination effects which, theoretically, could be implicated in mechanisms leading to aneuploidy and other potentially heritable chromosomal disorders.

Alkaloids↗

PubMed1998

SCP2: a major protein component of the axial elements of synaptonemal complexes of the rat.

In the axial elements of synaptonemal complexes (SCs) of the rat, major protein components have been identified, with relative electrophoretic mobilities (M rs) of 30 000-33 000 and 190 000. Using monoclonal anti-SC antibodies, we isolated cDNA fragments which encode the 190 000 M r component of rat SCs. The translation product predicted from the nucleotide sequence of the cDNA, called SCP2 (for synaptonemal complex protein 2), is a basic protein (pI = 8.0) with a molecular mass of 173 kDa. At the C-terminus, a stretch of approximately 50 amino acid residues is predicted to be capable of forming coiled-coil structures. SCP2 contains two clusters of S/T-P motifs, which are common in DNA-binding proteins. These clusters flank the central, most basic part of the protein (pI = 9.5). Three of the S/T-P motifs are potential target sites for p34(cdc2) protein kinase. In addition, SCP2 has eight potential cAMP/cGMP-dependent protein kinase target sites. The gene encoding SCP2 is transcribed specifically in the testis, in meiotic prophase cells. At the amino acid sequence and secondary structural level, SCP2 shows some similarity to the Red1 protein, which is involved in meiotic recombination and the assembly of axial elements of SCs in yeast. We speculate that SCP2 is a DNA-binding protein involved in the structural organization of meiotic prophase chromosomes.

Amino Acid Sequence↗

PubMed1994

Synaptonemal complex proteins: occurrence, epitope mapping and chromosome disjunction.

We have used polyclonal antibodies against fusion proteins produced from cDNA fragments of a meiotic chromosome core protein, Cor1, and a protein present only in the synapsed portions of the cores, Syn1, to detect the occurrence and the locations of these proteins in rodent meiotic prophase chromosomes. The 234 amino acid Cor1 protein is present in early unpaired cores, in the lateral domains of the synaptonemal complex and in the chromosome cores when they separate at diplotene. A novel observation showed the presence of Cor1 axial to the metaphase I chromosomes and substantial amounts of Cor1 in association with pairs of sister centromeres. The centromere-associated Cor1 protein becomes dissociated from the centromeres at anaphase II and it is not found in mitotic metaphase centromeres. The extended presence of Cor1 suggests that it may have a role in chromosome disjunction by fastening chiasmata at metaphase I and by joining sister kinetochores, which ensures co-segregation at anaphase I. Two-colour immunofluorescence of Cor1 and Syn1 demonstrates that synapsis between homologous cores is initiated at few sites but advances rapidly relative to the establishment of new initiation sites. If the rapid advance of synapsis deters additional initiation sites between pairs of homologues, it may provide a mechanism for positive recombination interference. Immunogold epitope mapping of antibodies to four Syn1 fusion proteins places the amino terminus of Syn1 towards the centre of the synaptonemal complex while the carboxyl terminus extends well into the lateral domain of the synaptonemal complex. The Syn1 fusion proteins have a non-specific DNA binding capacity. Immunogold labelling of Cor1 antigens indicates that the lateral domain of the synaptonemal complex is about twice as wide as the apparent width of lateral elements when stained with electron-dense metal ions. Electron microscopy of shadow-cast surface-spread SCs confirms the greater width of the lateral domain. The implication of these dimensions is that the proteins that comprise the synaptic domain overlap with the protein constituents of the lateral domains of the synaptonemal complex more than was apparent from earlier observations. This arrangement suggests that direct interactions might be expected between some of the synaptonemal complex proteins.

Amino Acid Sequence↗

PubMedDate not supplied

Studies of synaptonemal complexes in farm mammals--a review.

For the last 10 years extensive studies of synaptonemal complexes in farm mammals were carried out. In this article a survey of the obtained results is presented. Studies on synaptic behavior of chromosomes at pachytene substage of meiotic prophase I in carriers of centric fusions (cattle, sheep, goat, pig, and blue fox) showed that the trivalent is rarely involved in an association with the sex bivalent. In carriers of reciprocal translocations (pig and cattle) a wide range of synaptic configurations were found. Besides the expected cross-shaped quadrivalent, the following configurations were observed: open quadrivalent, trivalent plus univalent, and two heteromorphic bivalents. The latter configurations were quite frequently involved in the association with XY bivalent. Studies of synaptonemal complexes in interspecies hybrids (cattle x zebu, river x swamp buffalo, blue fox x silver fox) revealed a wide range of synaptic disturbances. Cases of pericentric inversions, aneuploidy, and chromosomal polymorphisms are also reviewed. This survey shows that synaptonemal complex analysis is a very useful tool in studies on causes of altered fertility in carriers of abnormal chromosome complement.

Aneuploidy↗

PubMed1982

Two-dimensional spreads of synaptonemal complexes from solanaceous plants. I. The technique.

Using beta-glucuronidase the cell walls of tomato and potato primary microsporocytes can be digested. When the resulting protoplasts are exposed to distilled water, they burst, and complete sets of synaptonemal complexes are released to settle on plastic coated slides. After drying and formalin fixation, the synaptonemal complexes can be stained with silver or phosphotungstic acid and observed in the light and/or electron microscope. Silver staining gives better contrast for both light and electron microscopy but stains only lateral elements and kinetochores. Phosphotungstic acid staining gives little or no contrast for light microscopy, but stains both the lateral and central elements of the synaptonemal complex, kinetochores, and structures that are probably recombination nodules for electron microscopy. This technique offers a powerful tool for genome analysis by allowing (1) the determination of relative and absolute lengths of synaptonemal complexes and chromosome arm ratios at pachytene, (2) the analysis of complex patterns of synapsis, and (3) the location of what are probably recombination nodules along the length of synaptonemal complexes.

Chromosomes↗

PubMed1987

Identification of two major components of the lateral elements of synaptonemal complexes of the rat.

This paper describes the identification of two major components of the lateral elements of synaptonemal complexes of the rat by immunocytochemical techniques. We prepared monoclonal antibodies against synaptonemal complexes (SCs) by immunization of mice with purified SCs. One of these antibodies, II52F10, reacts with a 30 and a 33 kDa polypeptide, which are major components of purified SCs. Using this antibody, we studied the localization of its antigens light microscopically, by means of the indirect immunoperoxidase technique, as well as ultrastructurally, by means of the immunogold labeling technique. The immunolocalization was carried out on whole-mount preparations of lysed spermatocytes. The antibody reacts with paired as well as unpaired segments of zygotene, pachytene and diplotene SCs. In light microscopic preparations, the attachment plaques, particularly those of late pachytene and diplotene SCs, also appear to react strongly. In electron micrographs the lateral elements in paired as well as unpaired segments could be seen to react. No reaction was observed in the attachment plaques; however, in late pachytene and diplotene SCs the swollen terminal segments of the lateral elements did react with the antibody. Thus, we conclude that a 30 and a 33 kDa polypeptide make part of the lateral elements of synaptonemal complexes of the rat.

Animals↗

PubMedDate not supplied

Spermatogenesis and synaptonemal complexes of hybrid Petrogale (Marsupialia).

Fertility, synaptonemal complexes (SCs) and spermiogenesis were examined in hybrids bred from four chromosomally different species of rock wallaby. Each of the four male hybrids had different forms of chromosomal heterozygosity (i.e., a trivalent, a quadrivalent, a pentavalent, and a trivalent plus two centric shifts). Testes and seminiferous tubules of each hybrid were smaller than those of full-bloods, and no hybrid produced young when paired with parous females. The degree of chromosomal heterozygosity in the hybrids was associated with the degrees of asynapsis, XY-autosome associations, and disruption of spermatogenesis. In only one hybrid were all stages of spermiogenesis commonly seen, and in this animal, sperm abnormalities were common. SC formation was consistent with that expected from the G-banded karyotypes, except that in one hybrid the chromosomes involved in the presumed centric shifts did not pair as expected but instead formed heteropycnotic masses. In addition, the studies demonstrated the links between the nonpairing X and Y chromosome and revealed an array of patterns of abnormalities at the ultrastructural level in spermiogenesis of hybrid marsupials.

Animals↗

PubMed1994

A monoclonal antibody to lateral element proteins in synaptonemal complexes of Lilium longiflorum.

To identify synaptonemal complex (SC) proteins in Lilium longiflorum (lily), monoclonal antibodies were generated using mice immunized with isolated pachytene nuclei. While most of the resulting monoclonal antibodies recognized nucleolar or chromatin proteins, one monoclonal antibody (anti-LE) was found that binds to lateral elements. Anti-LE bound more to lateral elements of SCs digested with DNase than to lateral elements that had not been digested with DNase. The opposite pattern of labeling was observed using monoclonal antibodies to lily chromatin and nucleolar proteins. These results indicate that anti-LE is specifically recognizing lateral element proteins and not chromatin or nucleolar proteins surrounding the lateral elements. On immunoblots, anti-LE binds to three pachytene nuclear proteins (Mr 60000, 66000 and 70000), two tetrad (early microspore) nuclear proteins (Mr 60000 and 70000), and two root tip nuclear proteins (Mr 52000 and 60000). However, anti-LE does not bind to proteins from leaf nuclei. Of these four tissues, leaf is the only one that does not have actively dividing cells. This observation suggests that at least some SC proteins are related to nuclear proteins from mitotically active cells.

Animals↗