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Results for “Synaptonemal Complex”

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PubMed2001

Comparative study and prediction of DNA fragments associated with various elements of the nuclear matrix.

Scaffold/matrix-associated region (S/MAR) sequences are DNA regions that are attached to the nuclear matrix, and participate in many cellular processes. The nuclear matrix is a complex structure consisting of various elements. In this paper we compared frequencies of simple nucleotide motifs in S/MAR sequences and in sequences extracted directly from various nuclear matrix elements, such as nuclear lamina, cores of rosette-like structures, synaptonemal complex. Multivariate linear discriminant analysis revealed significant differences between these sequences. Based on this result we have developed a program, ChrClass (Win/NT version, ftp.bionet.nsc.ru/pub/biology/chrclass/chrclass.zip), for the prediction of the regions associated with various elements of the nuclear matrix in a query sequence. Subsequently, several test samples were analyzed by using two S/MAR prediction programs (a ChrClass and MAR-Finder) and a simple MRS criterion (S/MAR recognition signature) indicating the presence of S/MARs. Some overlap between the predictions of all MAR prediction tools has been found. Simultaneous use of the ChrClass, MRS criterion and MAR-Finder programs may help to obtain a more clearcut picture of S/MAR distribution in a query sequence. In general, our results suggest that the proportion of missed S/MARs is lower for ChrClass, whereas the proportion of wrong S/MARs is lower for MAR-Finder and MRS.

Animals↗

PubMed1978

Multiple complexes in human spermatocytes.

Multiple complexes develop during metaphase I in normal human spermatocytes. Usually they form two separate bodies about 1 micron in diameter, composed of tripartite units and a denser matrix. The tripartite units are structurally identical to the components of the central space of synaptonemal complexes (SCs). Formation of the multiple complexes occurs by shedding of SC fragments from a few chromosomal regions at prometaphase I. The combined total length of central elements in each multiple complex is 1 to 3 micron. Multiple complexes remain as cytoplasmic, perinuclear bodies during telophase I and interphase of spermatocytes II, but they were not observed during or after the second meiotic division. Although multiple complexes are initially located in the spindle, they do not show microtubular attachments and seem to be passively moved towards the periphery.

Chromosomes, Human↗

PubMed1998

Dynamics of meiotic prophase I during spermatogenesis: from pairing to division.

This review focuses on recent developments in our understanding of meiotic chromosome behavior in mammalian spermatogenesis, with a special emphasis on prophase I events in the best characterized organism, the laboratory mouse. The dynamics of chromosome movement prior to pairing and synapsis of chromosomes are complex and implicate function for both centromeres and telomeres in getting homologous chromosomes together in intimate synapsis. Likely candidates for mediating pairing and recombination include a host of proteins implicated in DNA repair and recombination, which have been shown to localize to the synaptonemal complex during meiotic prophase I. Precocious induction of meiotic metaphase in cultured pachytene spermatocytes has led to new information about requirements for MPF and topoisomerase II activity during the transition from meiotic prophase to metaphase. Together, the studies reviewed here increase our understanding of how chromosomes get together with their homologous partners and how these partners subsequently come apart.

Animals↗

PubMed2001

Fanconi anemia and DNA repair.

Fanconi anemia (FA) is an autosomal recessive disorder caused by defects in at least eight distinct genes FANCA, B, C, D1, D2, E, F and G. The clinical phenotype of all FA complementation groups is similar and is characterized by progressive bone marrow failure, cancer proneness and typical birth defects. The principal cellular phenotype is hypersensitivity to DNA damage, particularly interstrand DNA crosslinks. The FA proteins constitute a multiprotein pathway whose precise biochemical function(s) remain unknown. Five of the FA proteins (FANCA, C, E, F and G) interact in a nuclear complex upstream of FANCD2. FANCB and FANCD1 have not yet been cloned, but it is likely that FANCB is part of the nuclear complex and that FANCD1 acts downstream of FANCD2. The FA nuclear complex regulates the mono-ubiquitination of FANCD2 in response to DNA damage, resulting in targeting of this protein into nuclear foci. These foci also contain BRCA1 and other DNA damage response proteins. In male meiosis, FANCD2 also co-localizes with BRCA1 at synaptonemal complexes. Together, these data suggest that the FA pathway functions primarily as a DNA damage response system, although its exact role (direct involvement in DNA repair versus indirect, facilitating role) has not yet been defined.

DNA Repair↗

PubMed1991

Indium (III)-hematoxylin as a staining and contrasting agent for light and electron microscopy.

A deeply violet indium (III)-hematoxylin complex is formed when indium trichloride is added to an aqueous solution of oxidized hematoxylin. Treatment of glutaraldehyde fixed and Araldite embedded sections of rat seminiferous tubules with indium-hematoxylin revealed a definite staining and contrasting pattern. Semithin sections showed chromatin and nucleoli in violet-blue. Under the electron microscope, chromatin, nucleoli, ribosomes, synaptonemal complexes, chromatoid bodies, membranous components, and microtubules from sperm tails presented high electron opacity, while the acrosome and basement membrane appeared with a lower contrast. This performed indium-hematoxylin complex, which shows an absorption peak at lambda = 560 nm with shoulders at about lambda = 440 and 400 nm, could be valuable as a new staining and electron contrasting agent.

Animals↗

PubMed1985

Ultrastructure of the testis of Pekin ducks fed methyl mercury chloride: seminiferous epithelium.

Testicular cells of Pekin ducks (Anas platyrhynchos) fed with 0 (control), 0.5 (group 1), 5 (group 2), or 15 (group 3) mg of methyl mercury chloride (CH3HgCl)/kg of basal feed for 12 weeks were examined by electron microscope. Sertoli's cells from ducks in group 2 had dilated smooth endoplasm reticulum, increased lysosomes, and large vacuoles, some with lipid droplets. Degenerative changes were more advanced in group 3 ducks. There were increases in lysosomes, myelinoid figures, vacuolations, cytoplasmic and nuclear debris, cristolyses of mitochondria, and distended Golgi's complexes, and a reduction in smooth endoplasm reticulum and microtubules when compared with those of the controls. Spermatogonia were resistant to CH3HgCl exposure, except in 2 ducks from group 3 which had cells that showed electron-lucent cytoplasm, abnormal mitochondria, and membrane-bound vacuoles. In primary spermatocytes, degenerative changes were evident in ducks fed the larger dose levels. In nuclei, synaptonemal complexes showed unpaired elements. In cytoplasm, cellular debris and vacuoles predominated. There was an increase in synchronized meiosis and apparent incomplete cell division. In ducks from group 3, the cellular damage was more severe and was present throughout the germinal epithelium. Spermatids differentiation was affected variably in groups 2 and 3. Severity of damage increased with the increased dosage of mercury. Where there was spermiogenic activity, the electron-dense acrosome granules, manchette, and midpiece were rarely found. Since the seminiferous tubules from 2 ducks in group 3 had severe destruction of spermatocytes and spermatids, the spermiogenic activity was negligible. Ingestion of CH3HgCl caused toxic injury to seminiferous tubules in groups 2 and 3 ducks. The degree of damage was related to the dietary amount of mercury.

Administration, Oral↗

PubMed2005

All paired up with no place to go: pairing, synapsis, and DSB formation in a balancer heterozygote.

The multiply inverted X chromosome balancer FM7 strongly suppresses, or eliminates, the occurrence of crossing over when heterozygous with a normal sequence homolog. We have utilized the LacI-GFP: lacO system to visualize the effects of FM7 on meiotic pairing, synapsis, and double-strand break formation in Drosophila oocytes. Surprisingly, the analysis of meiotic pairing and synapsis for three lacO reporter couplets in FM7/X heterozygotes revealed they are paired and synapsed during zygotene/pachytene in 70%-80% of oocytes. Moreover, the regions defined by these lacO couplets undergo double-strand break formation at normal frequency. Thus, even complex aberration heterozygotes usually allow high frequencies of meiotic pairing, synapsis, and double-strand break formation in Drosophila oocytes. However, the frequencies of failed pairing and synapsis were still 1.5- to 2-fold higher than were observed for corresponding regions in oocytes with two normal sequence X chromosomes, and this effect was greatest near a breakpoint. We propose that heterozygosity for breakpoints creates a local alteration in synaptonemal complex structure that is propagated across long regions of the bivalent in a fashion analogous to chiasma interference, which also acts to suppress crossing over.

Animals↗

PubMed1995

Electron microscopy of the seminiferous epithelium in the triploid (ZZZ and ZZW) fowl, Gallus domesticus.

The ultrastructure of cells of the seminiferous epithelium is described in both triploid ZZZ and ZZW fowls, especially cytological aberrations influencing the development of morphologically abnormal spermatids and spermatozoa. Mitotic divisions in triploid fowls are similar to those in diploid fowls, but meiosis in both the ZZZ and ZZW triploid fowl is abnormal and many defective gametes are produced. The majority of spermatids have structural abnormalities and this is attributed to the aneuploidy expected from meiotic chromosome pairing in a triploid. Some spermatids were observed to possess an irregularly shaped head, 2 centriolar complexes, 2 acrosomes and 2 tails and this type differentiated into large-headed spermatoza. Such spermatids and spermatozoa are suggested to be near diploid due to their large nuclear size and 2 sets of organelles. Other spermatids, observed with only 1 centriolar complex, 1 acrosome and 1 tail, are suggested to be near haploid. Differentiation of these spermatids is similar to the process observed in diploid fowls except that there is a high percentage of abnormally shaped heads. The fact that morphologically normal spermatozoa were rare is consistent with the expectation that very few spermatozoa would be exactly haploid. In both ZZZ and ZZW triploid fowls, triple pairing of chromosomes is observed in synaptonemal complexes (SC) during meiosis and recombination nodules are distributed at random in the central regions of the triple pairing SC. In ZZW triploid fowls gamete formation is more severely affected than in ZZZ triploid fowls and it is suggested that many of the degenerative changes occurring in ZZW fowls could be attributed to those spermatids that possess a W sex chromosome, since normal male fowls are the homogametic sex (ZZ) and normal spermatids and spermatozoa contain only a Z sex chromosome.

Animals↗

PubMed1995

[The formation of the karyosphere in the oogenesis of insects and amphibians].

This review deals with the authors' own and literary data on the ultrastructural and cytochemical organization of insect and amphibian oocyte nuclei, with special attention being paid to the karyosphere and its capsule. The evidence provided is supplemented with data on isolated karyospheres in Rana temporaria oocytes. A conclusion is made that the karyosphere is a complex structure which contains all chromosomes in the limited space of the oocyte nucleus, and that these chromosomes are, as a rule, in the process of inactivation. It is inferred that the karyosphere capsule commonly appears in gigantic oocyte nuclei (more than 100 micron in diameter) containing extrachromosomal DNA. The analogy of capsule organization in different invertebrate and vertebrate species is discussed, in addition to the involvement of presumably homologous nuclear structures (e.g. derivatives of synaptonemal complexes and nuclear envelope) in capsule formation. It is assumed that the karyosphere capsule is a specially organized part of the nuclear matrix. The capsule provides nuclear compartmentalization and chromosome localization in the germinal vesicle. Studies of this sort open up new possibilities to further investigation of intranuclear morphogenesis.

Amphibians↗

PubMed1992

Meiotic and sperm chromosome analysis in a male carrier of an inverted insertion (3;10)(q13.2;p14p13).

A phenotypically normal male who fathered a son with the karyotype 46,XY,del(10)(p13) was found to be a balanced carrier of an inverted insertion (3;10) (q13.2;p14p13). Karyotyping five later pregnancies showed four to be unbalanced with respect to the insertion, one of which was also trisomic for chromosome 18. The latest pregnancy was balanced with respect to insertion but had the additional complexity of 47,XXY. In the light of six out of six chromosomally abnormal pregnancies, two of which potentially exhibit an interchromosomal effect, it was decided to investigate the gametic output of the father. Testicular biopsy and semen samples were obtained permitting both meiotic and sperm chromosome analysis. Information was thus obtained at three levels of gamete production, that is, prophase I pairing, chiasma frequency distribution at metaphase I, and sperm karyotypes. Electron microscope studies of synaptonemal complexes showed the rearranged chromosomes to pair fully in meiotic prophase I with no indication of the presence of an insertion. This non-homologous pairing of the inserted region was accompanied by an abnormal frequency distribution of pachytene substages. There was also a reduction in chiasma frequency throughout the genome. However, this did not lead to detectable autosomal univalence or abnormally high X/Y univalence. Thus, the trisomy 18 and XXY pregnancies are unlikely to reflect increased non-disjunctional rates either before or during the first meiotic division. Sperm karyotyping showed that the proportion of chromosomally balanced:unbalanced gametes did not differ from the theoretically expected 1:1. There was no evidence of any increase of unrelated abnormalities in the sperm, further indicating that the overall rate of meiotic non-disjunction was not increased above normal.

Adult↗

PubMed2006

From skin cells to ovarian follicles?

Generating oocytes from cells derived from skin in vitro may provide a valuable model for identifying factors involved in germ cell formation and oocyte differentiation. In addition, the "oocytes" produced could potentially be useful for therapeutic cloning, and thus offer new possibilities for tissue therapy. We recently reported the differentiation of cells derived from porcine fetal skin into cells resembling germ cells and oocytes. A subpopulation of these cells expressed germ cell markers and formed aggregate like oocyte-cumulus complexes that secreted ovarian steroid hormones and responded to gonadotropin stimulation. Some of these aggregates extruded large oocyte-like cells that expressed markers appropriate to oocytes. We now show further evidence of germ cell marker expression during differentiation. We have also compared the oocyte-like cells with natural oocytes for their expression levels of Oct4, growth differentiation factor-9b (GDF9b), the deleted in azoospermia -like (DAZL) gene, vasa, zona pellucida (ZP), and the meiosis marker synaptonemal complex protein 3 (SCP3), and have revealed interesting similarities and differences.

Animals↗

PubMed1977

Meiosis in a temperature-sensitive DNA-synthesis mutant and in an apomictic yeast strain (Saccharomyces cerevisiae).

It is shown that in the temperature-sensitive yeast mutant (Saccharomyces cerevisiae) spo 11 at the restrictive temperature of 34 degrees C. (1) premeiotic DNA synthesis is nearly completely blocked; (2) the nucleus enters meiotic prophase indicated by the formation of axial cores and polysynaptonemal complexes; (3) the kinetic apparatus functions normally at meiosis I and II; (4) early spore formation occurs in nearly all cells but it is variable and all spores eventually degenerate. It is concluded that chromosome replication is not a prerequisite for the functions listed above. The apomictic yeast strain 4117 produces 2 diploid spores. It is shown that a diploid which produces 2-spored asci, synthesized from 4117, no. 5, and an adenine requiring strain (1) has a normal meiotic prophase with abundant synaptonemal complexes; (2) has only one meiotic spindle; (3) has spores which form red clones more frequently than normal or u.v.-treated vegetative cells form ade/ade red sectors through mitotic recombination. It is concluded that this apomictic yeast has maintained meiotic prophase, but that one of the two meiotic divisions is suppressed.

Chromosomes↗

PubMed2001

Synapsis in Robertsonian heterozygotes and homozygotes of Dichroplus pratensis (Melanoplinae, Acrididae) and its relationship with chiasma patterns.

Dichroplus pratensis has a complex system of Robertsonian rearrangements with central-marginal distribution; marginal populations are standard telocentric. Standard bivalents show a proximal-distal chiasma pattern in both sexes. In Robertsonian individuals a redistribution of chiasmata occurs: proximal chiasmata are suppressed in fusion trivalents and bivalents which usually display a single distal chiasma per chromosome arm. In this paper we studied the synaptic patterns of homologous chromosomes at prophase I of different Robertsonian status in order to find a mechanistic explanation for the observed phenomenon of redistribution of chiasmata. Synaptonemal complexes of males with different karyotypes were analysed by transmission electron microscopy in surface-spread preparations. The study of zygotene and early pachytene nuclei revealed that in the former, pericentromeric regions are the last to synapse in Robertsonian trivalents and bivalents and normally remain asynaptic at pachytene in the case of trivalents, but complete pairing in bivalents. Telocentric (standard) bivalents usually show complete synapsis at pachytene, but different degrees of interstitial asynapsis during zygotene, suggesting that synapsis starts in opposite (centromeric and distal) ends. The sequential nature of synapsis in the three types of configuration is directly related to their patterns of chiasma localisation at diplotene-metaphase I, and strongly supports our previous idea that Rb fusions instantly produce a redistribution of chiasmata towards chromosome ends by reducing the early pairing regions (which pair first, remain paired longer and thus would have a higher probability of forming chiasmata) from four to two (independently of the heterozygous or homozygous status of the fusion). Pericentromeric regions would pair the last, thus chiasma formation is strongly reduced in these areas contrary to what occurs in telocentric bivalents.

Animals↗

PubMed2001

The Saccharomyces cerevisiae MUM2 gene interacts with the DNA replication machinery and is required for meiotic levels of double strand breaks.

The Saccharomyces cerevisiae MUM2 gene is essential for meiotic, but not mitotic, DNA replication and thus sporulation. Genetic interactions between MUM2 and a component of the origin recognition complex and polymerase alpha-primase suggest that MUM2 influences the function of the DNA replication machinery. Early meiotic gene expression is induced to a much greater extent in mum2 cells than in meiotic cells treated with the DNA synthesis inhibitor hydroxyurea. This result indicates that the mum2 meiotic arrest is downstream of the arrest induced by hydroxyurea and suggests that DNA synthesis is initiated in the mutant. Genetic analyses indicate that the recombination that occurs in mum2 mutants is dependent on the normal recombination machinery and on synaptonemal complex components and therefore is not a consequence of lesions created by incompletely replicated DNA. Both meiotic ectopic and allelic recombination are similarly reduced in the mum2 mutant, and the levels are consistent with the levels of meiosis-specific DSBs that are generated. Cytological analyses of mum2 mutants show that chromosome pairing and synapsis occur, although at reduced levels compared to wild type. Given the near-wild-type levels of meiotic gene expression, pairing, and synapsis, we suggest that the reduction in DNA replication is directly responsible for the reduced level of DSBs and meiotic recombination.

Alleles↗

PubMed1999

Complex, compound inversion/translocation polymorphism in an ape: presumptive intermediate stage in the karyotypic evolution of the agile gibbon Hylobates agilis.

Karyotypic variation in five gibbon species of the subgenus Hylobates (2n = 44) was assessed in 63 animals, 23 of them wild born. Acquisition of key specimens of Hylobates agilis (agile gibbon), whose karyotype had been problematic due to unresolved structural polymorphisms, led to disclosure of a compound inversion/translocation polymorphism. A polymorphic region of chromosome 8 harboring two pericentric inversions, one nested within the other, was in turn bissected by one breakpoint of a reciprocal translocation. In double-inversion + translocation heterozygotes, the theoretical meiotic pairing configuration is a double inversion loop, with four arms of a translocation quadrivalent radiating from the loop. Electron-microscopic analysis of synaptonemal complex configurations consistently revealed translocation quadrivalents but no inversion loops. Rather, nonhomologous pairing was evident in the inverted region, a condition that should preclude crossing over and the subsequent production of duplication-deficiency gametes. This is corroborated by the existence of normal offspring of compound heterozygotes, indicating that fertility may not be reduced despite the topological complexity of this polymorphic system. The distribution of inversion and translocation morphs in these taxa suggests application of cytogenetics in identifying gibbon specimens and avoiding undesirable hybridization in captive breeding efforts.

Animals↗

PubMed1994

Physical mapping of 5S rDNA reveals a new locus on 3R and unexpected complexity in a rye translocation used in chromosome mapping.

Using fluorescence in situ hybridization (FISH) with probe pScT7, three different 5S rDNA loci were detected in the satellite of rye chromosome 1R (5SDna-R1) and in the short arms of chromosomes 3R (5SDna-R3) and 5R (5SDna-R2) respectively. All three loci showed polymorphism for the hybridization signal intensity. In order to determine the localization of these rye 5S rDNA multigene loci with higher precision within the corresponding chromosome arms, the probe pScT7 was physically mapped by FISH in relation to the following five translocations (Wageningen Tester Set): T850W (1RS/4RL), T248W (1RS/6RS), T273W (1RS/5RL), T305W (2RS/5RS) and T240W (3RS/5RL). Accurate physical maps of the translocation breakpoints had previously been made using electron microscope analysis of spread pachytene synaptonemal complexes of heterozygotes for the different translocations. The results indicate that locus 5SDna-R3 is located between the breakpoint of translocation T240W and the telomere, whereas locus 5SDna-R2 is located between the breakpoint of translocation T305W and the centromere, the hybridization of probe pScT7 on T305W translocated chromosomes demonstrating the complex nature of this translocation. On the other hand, the simultaneous detection of probes pScT7 and pTA71 (18S-5.8S-26S rDNA) with two different fluorochromes, indicated that the breakpoints of translocations T850W and T248W are located between loci Nor-R1 and 5SDna-R1.

Chromosome Mapping↗

PubMed2000

Replication-dependent early meiotic requirement for Spo11 and Rad50.

Spo11 and the Rad50-Mre11 complex have been indirectly implicated in processes associated with DNA replication. These proteins also have been shown to have early meiotic roles essential for the formation of a programmed DNA double-strand break known in Saccharomyces cerevisiae to initiate meiotic recombination. In both S. cerevisiae and the basidiomycete Coprinus cinereus, spo11 and rad50 mutants are defective in chromosome synapsis during meiosis. Here we demonstrate that a partial restoration of synapsis occurs in C. cinereus spo11 and rad50 mutants if premeiotic DNA replication is prevented. Double mutants were constructed with spo11-1 or rad50-4 and another mutant, spo22-1, which does not undergo premeiotic DNA replication. In both cases, we observed an increase in the percentage of nuclei containing synaptonemal complex (SC) structures, with concomitant decreases in the percentage of nuclei containing axial elements (AE) only or no structures. Both types of double mutants demonstrated significant increases in the average numbers of AE and SC, although SC-containing nuclei did not on average contain more AE than did nuclei showing no synapsis. Our results show that Spo11-induced recombination is not absolutely required for synapsis in C. cinereus, and that the early meiotic role of both Spo11 and Rad50 in SC formation partially depends on premeiotic S phase. This dependency likely reflects either a requirement for these proteins imposed by the premeiotic replication process itself or a requirement for these proteins in synapsis when a sister chromatid (the outcome of DNA replication) is present.

Coprinus↗

PubMed1994

Dynamics of chromosome organization and pairing during meiotic prophase in fission yeast.

Interactions between homologous chromosomes (pairing, recombination) are of central importance for meiosis. We studied entire chromosomes and defined chromosomal subregions in synchronous meiotic cultures of Schizosaccharomyces pombe by fluorescence in situ hybridization. Probes of different complexity were applied to spread nuclei, to delineate whole chromosomes, to visualize repeated sequences of centromeres, telomeres, and ribosomal DNA, and to study unique sequences of different chromosomal regions. In diploid nuclei, homologous chromosomes share a joint territory even before entry into meiosis. The centromeres of all chromosomes are clustered in vegetative and meiotic prophase cells, whereas the telomeres cluster near the nucleolus early in meiosis and maintain this configuration throughout meiotic prophase. Telomeres and centromeres appear to play crucial roles for chromosome organization and pairing, both in vegetative cells and during meiosis. Homologous pairing of unique sequences shows regional differences and is most frequent near centromeres and telomeres. Multiple homologous interactions are formed independently of each other. Pairing increases during meiosis, but not all chromosomal regions become closely paired in every meiosis. There is no detectable axial compaction of chromosomes in meiotic prophase. S. pombe does not form mature synaptonemal complexes, but axial element-like structures (linear elements), which were analyzed in parallel. Their appearance coincides with pairing of interstitial chromosomal regions. Axial elements may define minimal structures required for efficient pairing and recombination of meiotic chromosomes.

Cell Nucleus↗