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Results for “Synaptonemal Complex”

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PubMed2005

Effects of a low dose of bentazon on spermatogenesis of mice exposed during foetal, postnatal and adult life.

Bentazon is a herbicide used to control many broadleaf weeds and sedges. Its use has improved rice production in paddy fields in Northern Italy, but as a negative consequence it is found in groundwater, the major source of drinking water. To determine whether low doses of bentazon affect spermatogenesis, it was dissolved in water at the concentration of 30 microg/L. Bentazon was administered through drinking water to: (1) adult mice for 100 days and (2) mice exposed in utero, during lactation and for 100 days after birth. The histopathological analysis of testes of treated animals showed that the frequency of defective tubules was comparable to that found in control groups. The cell associations of the 12 stages of the seminiferous epithelium were correct as well as the architecture of the epithelium. The spermatocytes/spermatids ratio was the same as in controls. However, the frequency of stages VII, IX and XII of the cycle of the seminiferous epithelium of adult mice and of stages I, III and VII of mice exposed in utero and for 100 days after birth was different when compared to that of control mice. Sperm number and morphology were not affected by the treatment. The potential genotoxic effects were evaluated on spermatozoa (Comet assay), in pachytene spermatocytes (analysis of the synaptonemal complex) and in bone marrow cells (frequency of micronuclei). None of these analyses evidenced genotoxic effects of bentazon. Although our results show that the administration of a low dose of bentazon does not impair spermatogenesis, we found alterations of the frequency of some stages of the cycle of the seminiferous epithelium in both experimental groups.

Animals↗

PubMed2006

The Arabidopsis thaliana PARTING DANCERS gene encoding a novel protein is required for normal meiotic homologous recombination.

Recent studies of meiotic recombination in the budding yeast and the model plant Arabidopsis thaliana indicate that meiotic crossovers (COs) occur through two genetic pathways: the interference-sensitive pathway and the interference-insensitive pathway. However, few genes have been identified in either pathway. Here, we describe the identification of the PARTING DANCERS (PTD) gene, as a gene with an elevated expression level in meiocytes. Analysis of two independently generated transferred DNA insertional lines in PTD showed that the mutants had reduced fertility. Further cytological analysis of male meiosis in the ptd mutants revealed defects in meiosis, including reduced formation of chiasmata, the cytological appearance of COs. The residual chiasmata in the mutants were distributed randomly, indicating that the ptd mutants are defective for CO formation in the interference-sensitive pathway. In addition, transmission electron microscopic analysis of the mutants detected no obvious abnormality of synaptonemal complexes and apparently normal late recombination nodules at the pachytene stage, suggesting that the mutant's defects in bivalent formation were postsynaptic. Comparison to other genes with limited sequence similarity raises the possibility that PTD may present a previously unknown function conserved in divergent eukaryotic organisms.

Amino Acid Sequence↗

PubMed2001

Synaptic behaviour of some structural and numerical chromosome anomalies in female and male rats (Rattus norvegicus).

The processes of synapsis and synaptic adjustment have been detected in some structural and numerical anomalies in two female rat foetuses and in one male rat in the course of a study on X-ray genotoxicity. The synaptic characteristics and adjustment of one pericentric inversion and a deletion have been analysed by electron microscopy in synaptonemal complex spreads from two female foetuses, and the synaptic behaviour of a trisomy has been studied in a testicular biopsy from an adult male. In a large proportion (from 50% to 90%) of the analysed cells, the abnormal meiotic configuration could not be detected either because the anomaly was present in mosaic from trisomy or because synaptic adjustment had already taken place (inversion) or as result of a combination of two of the above (deletion).

Animals↗

PubMed2001

The genomic structure of SYCP3, a meiosis-specific gene encoding a protein of the chromosome core.

SYCP3 localizes to the lateral elements of the synaptonemal complex and is essential for male meiosis. The genomic structure of SYCP3 consists of nine exons spanning approximately 14 kb. In mouse and rat, but not in hamster, the putative translation start of SYCP3 is present in the first exon. The putative promoter of SYCP3 was also cloned and shown to drive transcription of a reporter gene in somatic cells.

3T3 Cells↗

PubMed2006

Identification and physical mapping of induced translocation breakpoints involving chromosome 1R in rye.

To obtain translocations involving specific chromosomes in rye, pollen of a line in which chromosome 1R has large C-bands on its two telomeres, but which lacks C-bands (or has very small ones) on the telomeres of the remaining chromosomes, was X-irradiated. All translocations involving the labelled chromosome (1R) could be easily recognized in C-banded mitotic metaphases. The non-labelled chromosome involved in each translocation was identified either from mitotic C-banding analysis or from the meiotic configurations observed in some specific progenies. A physical map including 40 translocation breakpoints has been developed by means of synaptonemal complex (SC) analysis of well-paired pachytene quadrivalents. The results agree with the hypothesis of chromosomes 2R to 7R having similar probabilities of participating in translocations with chromosome 1R. However, the locations of the breakpoints are not entirely random: an excess of translocation breakpoints located on the short arm of chromosome 1R was obtained, and the two acentric translocated segments of each translocation show a trend towards having similar sizes. The possible reasons for these two non-random situations are discussed.

Chromosome Banding↗

PubMed2003

Essential role of Fkbp6 in male fertility and homologous chromosome pairing in meiosis.

Meiosis is a critical stage of gametogenesis in which alignment and synapsis of chromosomal pairs occur, allowing for the recombination of maternal and paternal genomes. Here we show that FK506 binding protein (Fkbp6) localizes to meiotic chromosome cores and regions of homologous chromosome synapsis. Targeted inactivation of Fkbp6 in mice results in aspermic males and the absence of normal pachytene spermatocytes. Moreover, we identified the deletion of Fkbp6 exon 8 as the causative mutation in spontaneously male sterile as/as mutant rats. Loss of Fkbp6 results in abnormal pairing and misalignments between homologous chromosomes, nonhomologous partner switches, and autosynapsis of X chromosome cores in meiotic spermatocytes. Fertility and meiosis are normal in Fkbp6 mutant females. Thus, Fkbp6 is a component of the synaptonemal complex essential for sex-specific fertility and for the fidelity of homologous chromosome pairing in meiosis.

Amino Acid Sequence↗

PubMed1998

Analysis of meiotic chromosome pairing in the female mouse using a novel minichromosome.

Analysis of a radiation-induced minichromosome using classical cytogenetic techniques and fluorescence in situ hybridization (FISH) has shown this element to be composed primarily, if not entirely, of repeat sequence DNAs that are common to the ends of all chromosomes in the mouse genome. This novel chromosome has been used to examine further the role of centromeric and telomeric DNA sequences in the initiation of homologous chromosome pairing and synapsis in female germ cells. In pachytene oocytes of a fetus carrying two copies of the minichromosome, it was found that these elements were collocalized, but had not undergone synapsis, in half of the cells analysed. The minichromosomes formed a synaptonemal complex in approximately 14% of oocytes. Overall, therefore, the minichromosomes showed a surprising ability to achieve the first phase of homologous chromosome pairing, i.e. collocalization, despite their dearth of chromosome-specific DNA sequences. It is suggested that this collocalization largely results from the tendency of mouse chromosome ends to form centromeric and telomeric clusters at zygotene. The observations here provide support for the proposition that clustering of chromosome ends in early meiosis fosters pairing interactions and synapsis.

Animals↗

PubMed1996

Meiotic behavior of the X1X2Y1Y2 quadrivalent of the primate Alouatta caraya.

A multiple sex chromosome system was found in three unrelated individuals of the primate Alouatta caraya. This mechanism is originated by a translocation between the Y chromosome and one of the autosomes (A7). Mitotic karyotypes show two small, acrocentric chromosomes (AY and YA), which are the translocation products. In metaphase I of male meiosis, there is a very long chain quadrivalent in which the order of the element is: X-YA-A7-AY. Segregation in the quadrivalent is alternate and gives balanced products. Synaptonemal complex karyotypes at pachytene show the structure of the quadrivalent made by the four axes. There is a slight difference in the relative length of AY and YA and the kinetochore of A7 aligns with that of AY. The synaptic pattern and changes in the quadrivalent during pachytene are described. Thin sections of the quadrivalent body show that the chromatin packing in the sex chromosome region is different from that of the autosomal region. This X1X2Y1Y2/X1X1XX2 sex chromosome system may be extended among other members of the genus Alouatta.

Alouatta↗

PubMed1992

Unusual heteromorphic bivalents in the common vole (Microtus arvalis) from Belorussia.

Electron microscopic analysis was carried out on the synaptonemal complexes of 10 male common voles (Microtus arvalis) caught in 1990 in Belorussia. In the early pachytene stage of spermatocytes of four males, a heteromorphic bivalent has been found in one of five large autosomes. In the central region of the bivalent one of the lateral elements is in the form of a D-loop, characteristic of insertion/deletion heterozygotes. However, high-resolution G-band staining of mitotic chromosomes from fibroblasts shows no significant differences in the G-band pattern between homologs.

Animals↗

PubMed1998

Pachytene chromosomes in trisomy 19 male mice with Robertsonian translocations.

Three male mice with trisomy 19 induced by a Robertsonian translocation system were used for the study of meiotic prophase cells and germ cell differentiation. Present in these males were two Robertsonian chromosomes each with a chromosome 19 arm in common, two acrocentric chromosomes corresponding to the second arms of the two Rbs and one acrocentric chromosome 19. These five chromosomes showed a wide range of meiotic pairing configurations. One particular observation was the formation of a true double synaptonemal complex (SC) with three lateral axes and two central elements, which joined the three chromosomes 19 together. Integration of the acrocentric chromosome 19 in a complex pentavalent configuration was seen in 45% of the pachytene nuclei. The proportion of spermatocytes showing association between a quadrivalent and the acrocentric no. 19 was 26%. In 29% of the nuclei, the acrocentric no. 19 was free, integrated or associated with the XY complex, paired with the X chromosome or associated with a bivalent. Finally, in 57% of pachytene cells, the meiotic multivalents or the free univalent 19 were associated with the proximal part of the X chromosome or integrated in the sex chromatin. Therefore, the question arises with regard to the fate of these spermatocytes. The testicular histology shows an arrest of germ cell development at the spermatocyte stage. Several mechanisms seem to be the cause of germ cell depletion in a sequence of different, impaired developmental processes.

Animals↗

PubMed2005

Meiotic and epigenetic defects in Dnmt3L-knockout mouse spermatogenesis.

The production of mature germ cells capable of generating totipotent zygotes is a highly specialized and sexually dimorphic process. The transition from diploid primordial germ cell to haploid spermatozoa requires genome-wide reprogramming of DNA methylation, stage- and testis-specific gene expression, mitotic and meiotic division, and the histone-protamine transition, all requiring unique epigenetic control. Dnmt3L, a DNA methyltransferase regulator, is expressed during gametogenesis, and its deletion results in sterility. We found that during spermatogenesis, Dnmt3L contributes to the acquisition of DNA methylation at paternally imprinted regions, unique nonpericentric heterochromatic sequences, and interspersed repeats, including autonomous transposable elements. We observed retrotransposition of an LTR-ERV1 element in the DNA from Dnmt3L-/- germ cells, presumably as a result of hypomethylation. Later in development, in Dnmt3L-/- meiotic spermatocytes, we detected abnormalities in the status of biochemical markers of heterochromatin, implying aberrant chromatin packaging. Coincidentally, homologous chromosomes fail to align and form synaptonemal complexes, spermatogenesis arrests, and spermatocytes are lost by apoptosis and sloughing. Because Dnmt3L expression is restricted to gonocytes, the presence of defects in later stages reveals a mechanism whereby early genome reprogramming is linked inextricably to changes in chromatin structure required for completion of spermatogenesis.

Animals↗

PubMed2005

A histone code in meiosis: the histone kinase, NHK-1, is required for proper chromosomal architecture in Drosophila oocytes.

To promote faithful propagation of the genetic material during sexual reproduction, meiotic chromosomes undergo specialized morphological changes that ensure accurate segregation of homologous chromosomes. The molecular mechanisms that establish the meiotic chromosomal structures are largely unknown. We describe a mutation in a recently identified Histone H2A kinase, nhk-1, in Drosophila that leads to female sterility due to defects in the formation of the meiotic chromosomal structures. The metaphase I arrest and the karyosome, a critical prophase I chromosomal structure, require nucleosomal histone kinase-1 (NHK-1) function. The defects are a result of failure to disassemble the synaptonemal complex and to load condensin onto the mutant chromosomes. Embryos laid by nhk-1-/- mutant females arrest with aberrant polar bodies and mitotic spindles, revealing that mitosis is affected as well. We analyzed the role of Histone H2A phosphorylation with respect to the histone code hypothesis and found that it is required for acetylation of Histone H3 and Histone H4 in meiosis. These studies reveal a critical role for histone modifications in chromosome dynamics in meiosis and mitosis.

Animals↗

PubMed2005

Fine structure and meiotic behaviour of the male multiple sex chromosomes in the genus Alouatta.

The meiotic cytology and fine structure of the sex multiples in males from two species of the genus Alouatta are presented and compared with descriptions from other species of this genus. As shown in pachytene by synaptonemal complex analysis and in metaphase I by spreading, there is a quadrivalent in male meiosis in A. caraya, which is formed by an X(1)X(2)Y(1)Y(2) complex, while in A. palliata there is a trivalent formed by an X(1)X(2)Y(1) complex. Chromosome painting with human probes shows that A. caraya sex multiples share the same components as those of A. seniculus sara and A. seniculus arctoidea. However, as shown here for A. palliata and by others in A. fusca, there are differences among the multiples of some species. It is shown that in this genus there are several varieties of sex multiples that share some features, and that the origin of these multiples is most probably a primitive development in the genus Alouatta.

Alouatta↗

PubMed1993

The effect of 13;14 Robertsonian translocations on germ-cell differentiation in infertile males.

Two infertile men heterozygous for a 13;14 Robertsonian (Rb) translocation were investigated by means of synaptonemal complex studies, testicular histology, and semen analysis. In both individuals interaction between the Rb trivalent and the XY pair was observed. Twenty percent of pachytene cells analyzed in one patient showed XY-trivalent association which correlated with malformed spermatids; the higher rate of XY-trivalent association (approximately 47%) in the second proband corresponded with complete spermatogenic arrest. The data presented indicate a positive correlation between increased frequency of XY trivalent association and the degree of germ-cell impairment.

Adult↗

PubMed1993

Seasonal changes of the blood-testis barrier in viscacha (Lagostomus maximus maximus): a freeze-fracture and lanthanum tracer study.

Adult male viscachas (Lagostomus maximus maximus) were gathered from their natural habitat during the period of complete spermatogenesis (June) and during the month of maximum testicular regression (August). The testes were processed by conventional electron microscopic technique using lanthanum nitrate (electron-dense intercellular tracer) to define the intercellular spaces below the inter-Sertoli tight junctions and by freeze-fracture techniques. During complete spermatogenesis the tracer surrounds spermatogonia, preleptotene, and leptotene spermatocytes and stops at the level of the inter-Sertoli tight junctions below all germ cells displaying synaptonemal complexes (zygotene-pachytene spermatocytes) and germ cells in more advanced stages of differentiation. Conversely, during testicular regression the tracer percolates all intercellular spaces between Sertoli cells and the remaining germ cells (spermatogonia and few preleptotene and leptotene spermatocytes). During complete spermatogenesis, freeze-fracture replicas exhibit numerous inter-Sertoli tight junction strands parallel to each other and to the basal lamina. During spermatogenesis decay, the inter-Sertoli tight junctions are found to be short, tortuous, frequently interrupted, and often associated with extented membranous areas of gap junctions.

Animals↗

PubMed2000

MSH4 acts in conjunction with MLH1 during mammalian meiosis.

MSH4 is a meiosis-specific MutS homolog. In yeast, it is required for reciprocal recombination and proper segregation of homologous chromosomes at meiosis I. MLH1 (MutL homolog 1) facilitates both mismatch repair and crossing over during meiosis in yeast. Germ-line mutations in the MLH1 human gene are responsible for hereditary nonpolyposis cancer, but the analysis of MLH1-deficient mice has revealed that MLH1 is also required for reciprocal recombination in mammals. Here we show that hMSH4 interacts with hMLH1. The two proteins are coimmunoprecipitated regardless of the presence of DNA or ATP, suggesting that the interaction does not require the binding of MSH4 to DNA. The domain of hMSH4 responsible for the interaction is in the amino-terminal part of the protein whereas the region that contains the ATP binding site and helix-turn-helix motif does not bind to hMLH1. Immunolocalization analysis shows that MSH4 is present at sites along the synaptonemal complex as soon as homologous chromosomes synapse. The number of MSH4 foci decreases gradually as pachynema progresses. During this transition, MLH1 foci begin to appear and colocalize with MSH4. These results suggest that MSH4 is first required for chromosome synapsis and that this MutS homologue is involved later with MLH1 in meiotic reciprocal recombination.

Adaptor Proteins, Signal Transducing↗

PubMed2006

Reproductive isolation due to the genetic incompatibilities between Thrichomys pachyurus and two subspecies of Thrichomys apereoides (Rodentia, Echimyidae).

We tested intrinsic reproductive isolation between 3 taxa of the South American caviomorph rodent Thrichomys (Rodentia, Echimyidae): T. pachyurus, T. apereoides subsp. apereoides and T. apereoides subsp. laurentius. They were mated in captivity and produced viable progeny. Some F1 hybrid females were fertile, whereas all F1 males were sterile. Histological examination revealed meiotic arrest at the primary spermatocyte stage. No sperm was detected in testes or epididymes. Electron microscopic analysis of surface spread synaptonemal complexes revealed a complete failure of chromosome pairing in F1 hybrids of T. pachyurus with T. apereoides subsp. laurentius and T. apereoides subsp. apereoides. In the male hybrids between T. apereoides subsp. apereoides and T. apereoides subsp. laurentius, meiosis did not proceed beyond diplotene, although all of the chromosomes, including heteromorphic ones, paired in an orderly fashion. Backcross males with homomorphic karyotypes showed segregation in meiosis progression. This indicates that male hybrid sterility is due to genetic, but not chromosomal, incompatibility of the parental taxa.

Animals↗

PubMed2006

Zebrafish: chiasmata and interference.

With immunofluorescence microscopy, the positions of centromeres and MLH1 (MutL homolog) foci representing the sites of presumptive chiasmata are shown for zebrafish (Danio rerio Hamilton 1822) synaptonemal complexes (SCs) in spermatocyte nuclei at meiotic prophase. Most SCs have a single focus and a few (7 of 140) have 2 chiasmata. MLH1 foci tend to be in the distal regions of SCs, with progressively fewer occurring towards the middle of the SCs. This non-random distribution suggests chiasma interference. Synaptic initiation, as well as replication protein A (RPA) foci at the chromosome ends, correlates with the distal localization of MLH1 foci. These observations may provide the physical basis for the reported limited genetic recombination in the centromeric region of androgenetic offspring of a male.

Animals↗