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At least 307 records · Page 17Linked to original sources
PubMed2006

Alleles of afd1 dissect REC8 functions during meiotic prophase I.

REC8 is a master regulator of chromatin structure and function during meiosis. Here, we dissected the functions of absence of first division (afd1), a maize rec8/alpha-kleisin homolog, using a unique afd1 allelic series. The first observable defect in afd1 mutants is the inability to make a leptotene chromosome. AFD1 protein is required for elongation of axial elements but not for their initial recruitment, thus showing that AFD1 acts downstream of ASY1/HOP1. AFD1 is associated with the axial and later the lateral elements of the synaptonemal complex. Rescuing 50% of axial element elongation in the weakest afd1 allele restored bouquet formation demonstrating that extent of telomere clustering depends on axial element elongation. However, rescuing bouquet formation was not sufficient for either proper RAD51 distribution or homologous pairing. It provides the basis for a model in which AFD1/REC8 controls homologous pairing through its role in axial element elongation and the subsequent distribution of the recombination machinery independent of bouquet formation.

Alleles↗
PubMed1998

Aspects of three-dimensional chromosome reorganization during the onset of human male meiotic prophase.

The three-dimensional morphology and distribution of human chromosomes 3 were studied in nuclei of spermatogonia and spermatocytes I from formaldehyde-fixed human testis sections. Chromosome arms, pericentromeres and telomeric regions were painted by a three-color, five-probe fluorescence in situ hybridization protocol. Light optical serial sections of premeiotic and meiotic nuclei obtained by confocal laser scanning microscopy revealed that premeiotic chromosomes 3 are separate from each other and occupy variably shaped territories, which are sectored in distinct 3 p- and q-arm domains. Three-dimensional reconstructions of the painted chromosome domains by a Voronoi tessellation approach showed that mean chromosome volumes did not differ significantly among the premeiotic and meiotic stages investigated. A significant increase in surface area and reduction of dimensionless 'roundness factor' estimates of arm domains indicated that the restructuring of spatially separate chromosome territories initiates during preleptotene. Telomeric regions, which in meiotic stem cells located predominantly in arm-domain chromatin, showed a redistribution towards the domain surface during this stage. At leptotene homologues were generally misaligned and displayed intimate intermingling of non-homologous chromatin. Pairing initiated at the ends of bent zygotene chromosomes, which displayed a complex surface structure with discernible sister chromatids. The results indicate that, in mammals, homology search is executed during leptotene, after remodeling of chromosome territories.

Chromatin↗
PubMed1978

Ultrastructure and activity of the nucleolar organizer in the mouse oocyte during meiotic prophase.

The mouse oocyte is the site of nucleolar synthesis during pachytene. The chromosomes containing a nucleolar organizer are attached to the nuclear envelope by their paracentromeric heterochromatin, either alone or by taking part in the formation of a chromocentre. The nucleolus appears at the junction of the paracentromeric heterochromatin with the euchromatic portion of the bivalent. In this zone, 5.0-nm-diameter fibres, thinner than those of the rest of the chromosome (10.0 nm), extend from the lateral element of the synaptonemal complex up to the nucleolar fibrillar centre in which they penetrate. At the onset of its synthesis, the nucleolus only contains the fibrillar centre and an electron-dense fibrillar component in continuity with the latter. Growth of the nucleolus often takes place in the form of a strand whose proximal end, in contact with the fibrillar centre, is formed by preribosomal fibrils and whose distal end is at first fibrillo-granular then granular. Following brief incorporation of tritiated uridine, nucleolar labelling is active in oogonia. No ribosomal RNA-synthetic activity is revealed during leptotene and zygotene. Incorporation resumes at mid-pachytene, with labelling located over the electron-dense fibrillar component adjacent to the fibrillar centre. These observations suggest that the rDNA is located in both the fibrillar centre and its associated electron-dense fibrillar component and that the rDNA transcription occurs in the latter.

Animals↗
PubMed1979

Fine structure of meiotic prophase chromosomes and modified synaptonemal complexes in diploid and triploid Rhoeo spathacea.

The synaptonemal complex (SC) in the diploid Rhoeo consists of 2 amorphous lateral elements, each about 46.0 nm thick, and one amorphous central element about 30.0 nm thick. The central region is about 115.0 nm wide. SC in the triploid have essentially the same dimensions as those of the diploid; both lateral (46.0 nm) and central (30.0 nm) elements are amorphous, and the central region is about 117.5 nm wide. The coil, observed in both diploid and triploid, is a modified short segment of SC with several twists at the end of a synapsed bivalent that is attached to the nuclear membrane. Serial sections in a diploid cell reveal that a coil extends inwards about 3.5 micron from the nuclear membrane and makes a complete turn at a distance of every 0.5 micron. There is a correlation between the modified ends of SC and terminal chiasmata in Rhoeo. The coils might have a positive role in the process of crossing over, or alternatively might be involved in ring formation by holding chromosome ends together while chiasmata are not involved. SC are present in chromocentres of both diploid and triploid. Chromocentres in diploid and triploid are indistinguishable, and appear to be formed from the aggregation of pericentromeric heterochromatin as a result of translocations which occured close to the centromeres. 3-dimensional hypothetical pachytene configuration of the diploid is presented.

Chromosomes↗
PubMed2003

Efficient repair of DNA damage induced by heavy ion particles in meiotic prophase I nuclei of Caenorhabditis elegans.

The effects of heavy ion particle irradiation on meiosis and reproductive development in the nematode Caenorhabditis elegans were studied. Meiotic pachytene nuclei are significantly resistant to particle irradiation by the heavy ions carbon and argon, as well as to X-rays, but not UV, whereas diplotene to diakinesis stage oocytes and early embryonic cells are not. Chromosomal abnormalities appear in mitotic cells and in maturing oocytes irradiated with heavy ion particles during the diplotene to the early diakinesis stages, but not in oocytes irradiated during the pachytene stage. The pachytene nuclei of ced-3 mutants, which are defective in apoptosis, are similarly resistant to ionizing radiation, but pachytene nuclei depleted for Ce-atl-1 (ataxia-telangiectasia like 1) or Ce-rdh-1/rad-51 are more sensitive. Pachytene nuclei thus appear to effectively repair heavy ion-induced DNA damage by the meiotic homologous recombination system.

Animals↗
PubMed1995

Maintenance of bovine oocytes in prophase of meiosis I by high [cAMP]i.

The effects of high intracellular cAMP concentrations ([cAMP]i) on germinal vesicle maintenance of bovine cumulus-oocyte complexes were investigated, using 8-bromo-3',5'-cAMP (8-Br-cAMP) or an invasive adenylate cyclase from Bordetella pertussis to increase the [cAMP]i. The effects of interactions of these agents with macromolecular supplements in culture medium (fetal calf serum, FCS; polyvinylpyrrolidone, PVP; BSA), and different methods of processing complexes before culture, on subsequent germinal vesicle maintenance by invasive adenylate cyclase were studied. While 8-Br-cAMP was unable to maintain germinal vesicle arrest in the majority of oocytes for 20 h (36% with FCS, 24% with BSA, 18% with PVP), it maintained germinal vesicle arrest in a high proportion of cumulus-enclosed oocytes when BSA or PVP was used (37% with FCS, 52% with BSA, 53% with PVP). The difference in frequency of germinal vesicle maintenance between macromolecular supplements was not related to [cAMP]i when assayed after culture for 2 h with invasive adenylate cyclase. Complexes processed in whole follicular fluid were not maintained in meiotic arrest (26%) when cultured with invasive adenylate cyclase and PVP. Complexes processed in follicular fluid with 3-isobutyl 1-methylxanthine (IBMX) plus invasive adenylate cyclase were arrested at the germinal vesicle stage at high frequencies (65%), while those processed in IBMX or IBMX plus 8-Br-cAMP-supplemented follicular fluid had intermediate (43% and 49%, respectively) frequencies of intact germinal vesicles. Oocyte complexes processed in follicular fluid supplemented with IBMX and invasive adenylate cyclase formed morulae and blastocysts (27.2%), as did oocytes processed in follicular fluid alone (26%). Phosphoprotein profiles showed that control oocytes and 8-Br-cAMP-treated oocytes share a profile that is different from that of oocytes treated with invasive adenylate cyclase. These results show that increased [cAMP]i reversibly maintains bovine oocytes in meiotic arrest for an extended period without the occurrence of the post-translational protein modifications observed during meiotic resumption or transient arrest.

1-Methyl-3-isobutylxanthine↗
PubMed2006

Gene expression profiles of Spo11-/- mouse testes with spermatocytes arrested in meiotic prophase I.

Spo11, a meiosis-specific protein, introduces double-strand breaks on chromosomal DNA and initiates meiotic recombination in a wide variety of organisms. Mouse null Spo11 spermatocytes fail to synapse chromosomes and progress beyond the zygotene stage of meiosis. We analyzed gene expression profiles in Spo11(-/ -)adult and juvenile wild-type testis to describe genes expressed before and after the meiotic arrest resulting from the knocking out of Spo11. These genes were characterized using the Gene Ontology data base. To focus on genes involved in meiosis, we performed comparative gene expression analysis of Spo11(-/ -)and wild-type testes from 15-day mice, when spermatocytes have just entered pachytene. We found that the knockout of Spo11 causes dramatic changes in the level of expression of genes that participate in meiotic recombination (Hop2, Brca2, Mnd1, FancG) and in the meiotic checkpoint (cyclin B2, Cks2), but does not affect genes encoding protein components of the synaptonemal complex. Finally, we discovered unknown genes that are affected by the disruption of the Spo11 gene and therefore may be specifically involved in meiosis and spermatogenesis.

Animals↗