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At least 217 records · Page 12Linked to original sources
PubMed2005

Chimpanzee chromosomes: retrotransposable compound repeat DNA organization (RCRO) and its influence on meiotic prophase and crossing-over.

The terminal C-bands that are a specific feature of chimpanzee chromosomes were dissected using a molecular cytogenetic technique, PRINS, with primers for telomeric sequences, subterminal satellite, and retrotransposable elements (HERV-K and -W). These DNA elements jointly formed a large block of retrotransposable compound repeat DNA organization (RCRO) at the terminal C-band regions of 30 chromosomes, and are also located at the centromeric regions of some chromosomes. Additionally, a block consisting of all members of the RCRO has transposed to the middle (q31.1) of the long arm of chromosome 6, and three members, the subterminal satellite and the two HERVs, have integrated into the proximal region (q14.4) of the long arm of chromosome 14. Terminal RCROs seem to induce and prolong the bouquet stage in meiotic prophase, and to affect chiasma formation, together with interstitial RCROs. It is also postulated that RCROs may cause a position effect to gene expression, resulting in gene silencing and/or late replication.

Animals↗
PubMed1988

Synaptonemal complex analysis of B-chromosome behavior in meiotic prophase I in the East-Asiatic mouse Apodemus peninsulae (Muridae, Rodentia).

The mitotic and meiotic chromosomes of four male East-Asiatic mice, Apodemus peninsulae, having three to seven chromosomes in addition to the standard karyotype (2n = 48), were investigated. B-chromosomes were represented by medium-sized metacentric and dotlike chromosomes. Mosaicism of bone marrow cells due to a numerical variation of accessory chromosomes was established for the males examined. Capacity of B-chromosomes to form axial elements and synaptonemal complexes in meiotic prophase I was revealed by electron microscopy. The occurrence of univalents of different morphology, bivalents, and multivalents, corresponding to B-chromosomes, was demonstrated. An increase in the number of B-chromosomes was found in spermatocytes at zygotene-pachytene relative to the number in bone marrow cells, which may be evidence of B-chromosome accumulation in the germ cell line of the East-Asiatic mouse.

Animals↗
PubMed1989

Trivalent behavior during prophase I in male mice heterozygous for three Robertsonian translocations: an electron-microscopic study.

A synaptonemal complex (SC) analysis was carried out in male mice heterozygous (CHT/+) for three Robertsonian translocations. All pachytene preparations studied showed the presence of three trivalents. At early pachytene, the nonhomologous centromeric regions of the acrocentric chromosomes were unpaired. Heterosynapsis subsequently took place with complete pairing of the trivalents. Association between one of the three trivalents and the sex vesicle was observed in 30.4% of the nuclei. Association between the unpaired regions of two trivalents was present in 14.4% of the cells, suggesting that the relationship between unpaired regions of structural rearrangements and the X-Y bivalent may simply reflect the tendency of unpaired regions to establish end-to-end associations or heterosynapses among them, which are usually resolved during the pachytene stage of prophase I. Since the sex bivalent always has unpaired regions, these associations often affect the sex chromosomes.

Animals↗
PubMed2000

Expression and nuclear localization of BLM, a chromosome stability protein mutated in Bloom's syndrome, suggest a role in recombination during meiotic prophase.

Bloom's syndrome (BS) is a recessive human genetic disorder characterized by short stature, immunodeficiency and elevated risk of malignancy. BS cells have genomic instability and an increased frequency of sister chromatid exchange. The gene mutated in BS, BLM, encodes a 3'-5' helicase (BLM) with homology to bacterial recombination factor, RecQ. Human males homozygous for BLM mutations are infertile and heterozygous individuals display increased frequencies of structural chromosome abnormalities in their spermatozoa. Also, mutations in the Saccharomyces cerevisiae homolog of BLM, Sgs1, cause a delay in meiotic nuclear division and a reduction in spore viability. These observations suggest that BLM may play a role during meiosis. Our antibodies raised against the C terminus of the human protein specifically recognize both mouse and human BLM in western blots of cell lines and in successive developmental stages of spermatocytes, but fail to detect BLM protein in a cell line with a C-terminally truncated protein. BLM protein expression and location are detected by immunofluorescence and immunoelectron microscopy as discrete foci that are sparsely present on early meiotic prophase chromosome cores, later found abundantly on synapsed cores, frequently in combination with the recombinases RAD51 and DMC1, and eventually as pure BLM foci. The colocalization of RAD51/DMC1 with BLM and the statistically significant excess of BLM signals in the synapsed pseudoautosomal region of the X-Y chromosomes, which is a recombinational hot spot, provide indications that BLM protein may function in the meiotic recombination process.

Adenosine Triphosphatases↗
PubMed2002

Increase of cAMP upon release from prophase arrest in surf clam oocytes.

Surf clam (Spisula solidissima) oocytes are spawned at the prophase I stage of meiosis, and they remain arrested at this stage until fertilization. Full oocyte meiosis reinitiation, first evidenced by germinal vesicle breakdown (GVBD), may be induced by artificial activators mimicking sperm, such as high K(+) or serotonin. Previous reports indicated that treatments thought to increase the level of oocyte cAMP inhibited sperm- or serotonin-induced, but not KCl-induced, GVBD in clam oocytes. These observations extend the well known requirement for a drop in oocyte cAMP levels in mammalian, amphibian or starfish oocytes and support the view that such a drop is universally important throughout the animal kingdom. We have re-examined the cAMP dependency of GVBD in clam oocytes and found that various treatments that raise oocyte cAMP levels did not, surprisingly, affect either KCl- or serotonin-induced GVBD. Such treatments, however, inhibited GVBD upon insemination of the oocytes, but this was due to the failure of sperm to fuse/penetrate the oocytes; thus, it was not an inhibition of oocyte activation as such. Direct measurements of oocyte cAMP levels after activation by serotonin, KCl or sperm showed that, contrary to expectations, there is a rise in cAMP levels before GVBD. Using SQ22536, an adenylyl cyclase inhibitor, the increase in oocyte cAMP level was partly prevented and GVBD proceeded, but with a significant retardation, indicating that the normal cAMP rise facilitates GVBD. Our work sheds light on the diversity of upstream pathways leading to activation of MPF and provides a unique model whereby the onset of meiosis reinitiation is associated with an increase, not a decrease, in oocyte cAMP levels.

1-Methyl-3-isobutylxanthine↗
PubMed1980

The nucleolus in telophase, interphase and prophase.

The ultrastructure of telophase to interphase has been followed in a green alga, Spirogyra submargaritata. A series of changes transitional between the late anaphase chromatid, the decondensing chromatid of telophase, and the 'pale fibrillar material' occupying channels in the nucleolus at interphase have been demonstrated. Early stages in the regeneration of the nucleolus are described. It has been shown that the pale fibrillar material in the nucleolus is attached to, and continuous with, the fully condensed (chromocentric) part of the nucleolar-organizing chromosome at interphase. It is also shown that in early prophase, the channels in the nucleolonema of the nucleolus are no longer occupied by pale fibrillar material, but instead a long section of condensed chromosome is present, traversing the nucleolonema. It is contended that these observations taken together constitute evidence that the pale fibrillar material of the nucleolus is the chromatin of the nucleolar-organizing region of the chromosome, expanded for transcription. A model of the nucleolus as it is seen in most electron-microscope sections, and as it can be interpreted in the light of present-day knowledge about it, is presented. A brief review of the relevant literature considers the views supporting the mode, and the contrary views, implicating the use of the term 'nucleolar organizer', that are still current at the present time.

Cell Nucleolus↗
PubMed1984

Morphological and temporal sequence of meiotic prophase development at puberty in the male mouse.

The correct sequence of meiotic prophase development in the male mouse has been established by the use of pubertal males. The first wave of spermatogenesis at this time provides a unique opportunity to study progressive meiotic development in a direct way. Air-dried and micro-spread analyses have been carried out. Temporal and morphological progression at this time is entirely consistent with that occurring in the later waves of meiosis of the adult male. Morphological detail shows delayed pairing of the X and Y chromosomes relative to the autosomes. The longest XY synaptonemal complex is seen in early pachytene cells, occupying up to 72% of the length of the Y and 22% of the length of the X axis. By late pachytene, end-to-end pairing in the XY bivalent is established, the autosomal axes remaining fully paired. Desynapsis of the autosomes commences at early diplotene. A 'diffuse' diplotene stage in the male, comparable to the dictyate stage of the female, could not be found. Marked lengthening of the XY and autosomal axes did, however, occur through the diplotene stage.

Animals↗
PubMed1986

Flow cytometry and sorting of meiotic prophase cells of female rabbits.

We present a new, flow cytometric method by which cells in various stages of the meiotic prophase can be quantitated and sorted in partly enriched fractions. Ovarian cells of 3-16-day-old rabbits were mechanically dispersed and fixed in ethanol and aldehydes. The cell suspension was stained with the DNA fluorochrome mithramycin and analysed and sorted in a FACS IV cell sorter according to the fluorescence and forward light scatter distribution. Cells sorted onto slides were stained with haematoxylin and eosin and differentially counted in the microscope. In the diploid fraction, preleptotene cells were more fluorescent than somatic cells. Leptotene cells were found throughout the S fraction and the tetraploid fraction. Zygotene and pachytene cells caused a major peak in the tetraploid region with 10-25% more fluorescence than somatic cells. Cells in diplotene had 5-15% more fluorescence than somatic cells. Mitotic cells were 20-40% more fluorescent than somatic cells and scattered the light more intensely than did meiotic cells with the same fluorescence.

Animals↗
PubMed2006

Fission yeast Num1p is a cortical factor anchoring dynein and is essential for the horse-tail nuclear movement during meiotic prophase.

During meiotic prophase in the fission yeast Schizosaccharomyces pombe, the nucleus oscillates between the two ends of a cell. This oscillatory nuclear movement is important to promote accurate pairing of homologous chromosomes and requires cytoplasmic dynein. Dynein accumulates at the points where microtubule plus ends contact the cell cortex and generate a force to drive nuclear oscillation. However, it remains poorly understood how dynein associates with the cell cortex. Here we show that S. pombe Num1p functions as a cortical-anchoring factor for dynein. Num1p is expressed in a meiosis-specific manner and localized to the cell cortex through its C-terminal PH domain. The num1 deletion mutant shows microtubule dynamics comparable to that in the wild type. However, it lacks cortical accumulation of dynein and is defective in the nuclear oscillation as is the case for the dynein mutant. We also show that Num1p can recruit dynein independently of the CLIP-170 homolog Tip1p.

Carrier Proteins↗
PubMed2004

[Advance of study on effects of Chfr gene of mitosis prophase checkpoint--review].

Chfr, a mitotic stress checkpoint gene, regulates a prophase delay in cells exposed to agents that disrupt microtubules, such as nocodazole and taxol. Chfr expression was ubiquitious in normal human tissues. It is very high conserved between human and mice. Preliminary sutdies indicated that Chfr expression was cell cycle regulated and it dependent on its ubiqitin ligase activity. The direct target of the Chfr pathway was Polo-like kinase 1 (Plk1). Ubiquitination of Plk1 by Chfr delayed the activation of the Cdc25C phosphatase and the inactivation of the Weel kinase, leading to a delay in Cdc 2 activation. The chfr gene was inactivated owing to lack of expression or by mutation in some human cancer cell lines examined. Normal primary cells and tumour cell lines that express wild-type chfr exhibited delayed entry into metaphase when centrosome separation was inhibited by mitotic stress. In contrast, the tumour cell lines that had lost chfr function entered metaphase without delay. Ecotopic expression of wild-type chfr restored the cell cycle delay and increased the ability of the cells to survive mitotic stress. Thus, chfr defines a checkpoint that delays entry into metaphase in response to mitotic stress. The progress of research on structure of Chfr gene and effects of Chfr protein was reviewed.

Cell Cycle↗
PubMed1983

[Autoradiographic and cytophotometric study of DNA synthesis in the oocytes of the domestic hen at the preleptotene prophase stage of meiosis].

3H-thymidine incorporation into the fowl oocytes was established radioautographically at the middle preleptotene, when chromosomes are condensed and associated in the complex chromocenters. According to the cytophotometry of Feulgen stained oocyte nuclei, their DNA value increases during preleptotene from 2 to 4c. So, the DNA synthesis observed is characteristic of chromosome reduplication, rather than of nuclear organizer amplification. The preleptotene should be considered as the initial stage of meiotic prophase because it involves spiralization and individualization of chromosomal threads. Both the analysis of literary data and of our own results enable us to conclude that in different species the meiotic chromosome reduplication may proceed in different periods between telophase of last gonial mitosis and the beginning of homologous chromosome conjugation.

Animals↗
PubMed1995

[Patterns in the condensation of bovine chromosomes in the prophase-late metaphase of mitosis].

A comparative analysis of Bos taurus L. cytogenetic maps of different resolution levels was used to study principles of fusion R(G)-bands during chromosome condensation from prophase to the late metaphase. Three different types of fusion have been demonstrated, differing in quantity of interacting bands and fusion mechanism. Preferential condensation zones with constant localization was found. By means of the fusion index, faster condensation of R-bands than that of G-bands was revealed. Relevant data on B. taurus and Homo sapiens were compared. The obtained results are discussed in terms of common problems of mitotic chromosome R(G)-banding nature in warm-blooded animals.

Animals↗
PubMed2002

Definitive expression of c-mos in late meiotic prophase leads to phosphorylation of a 34 kda protein in cultured rat spermatocytes.

To investigate the role of c-mos in rat spermatogenesis, expression of c-mos, MAP kinase kinase (MAPKK), MAP kinase (MAPK), cdc2 and protein kinase A (PKA) by spermatogenic cell culture of 14 day-old rats was examined. MAPKK and PKA expressions were constitutive, whereas the expression of MAPK and cdc2 in spermatogonia initially decreased, but later increased on meiotic maturation of spermatocytes. c-mos expression was definitive of late meiotic prophase. c-mos immunoprecipitates prepared from the c-mos-enriched fraction (pI9.0-9.6) could form complex(es) in the cultured spermatogenic cell lysates. In vitro phosphorylation of the c-mos immune complexes revealed a 34 kDa protein that was phosphorylated at serine and threonine residues as a target of the c-mos signal. Its pI value was 4.4-4.5, and cdc2 was not detected, making it different from cdc2 (p34). These results suggest that the phosphorylation of the 34 kDa protein by the c-mos signal may play a crucial role in the meiotic division of rat spermatocytes.

Animals↗
PubMed1983

Relationship of meiotic prophase and ornithine decarboxylase in the neonatal rabbit ovary.

Ornithine decarboxylase (ODC) activity was measured in homogenates of neonatal rabbit ovaries from the day of birth to day 22, an interval that corresponds to the progressing stages of the meiotic prophase from oogonia to diplotene and follicle formation. The ODC-activity was high on days 1 and 3 when most germ cells start the phase of pre-meiotic DNA-synthesis. A peak of ODC-activity appeared on day 12, simultaneously with a small increase in mitotic activity of the intraovarian rete cells. It is suggested that ODC and therefore polyamine synthesis may be related to the regulation of the onset of meiosis and the mitotic activity of the intraovarian rete cells.

Animals↗
PubMed1975

The G-banded prophase chromosomes of man.

Using a simple G-banding technique developed in our laboratory, analysis of late prophases enables the visualization of approximately 1000 bands in the haploid set of human chromosomes. These bands have been classified according to the recommendations of the Paris Conference. The increased resolution offered by this technique is likely to be useful in the study of the structure and molecular organization of chromosomes and in identifying minute chromosome defects in birth defects and neoplasia.

Acetates↗
PubMed1978

Patterns of RNA synthesis in early meiotic prophase oocytes from fetal mouse ovaries.

In a study of the early meiotic prophase stages of mouse oogenesis from d12 of gestation to 10d post-partum the patterns of RNA synthesis during these stages of oogenesis using H3-uridine incorporation as visualized by light microscope autoradiography are reported. We find that chromosomal RNA synthesis occurs in all stages except early to mid-pachytene, the time of maximum chromosome condensation. Diplotene and dictyate nuclei are the most heavily labelled stages. Nucleolar labelling ceases before leptotene and reappears in late pachytene or early diplotene, even though nucleoli can be identified in all stages except early to mid-pachytene.

Animals↗