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PubMed1989

Ki-67 detects a nuclear matrix-associated proliferation-related antigen. II. Localization in mitotic cells and association with chromosomes.

In interphase cells the proliferation-associated antigen recognized by monoclonal antibody Ki-67 is almost exclusively located in the nucleoli. When cells at several stages of mitosis were examined for the localization of the Ki-67 antigen, a striking redistribution could be observed. During prophase the distinct nucleolar Ki-67 fluorescence changed to a bright irregular meshwork throughout the nucleoplasm. At metaphase the antigen appeared to be distributed in a reticulate structure surrounding the condensed chromosomes, while at late telophase a punctated staining of the entire nucleoplasm was observed, which preceded the typical nucleolar localization pattern in each of the two daughter cells. Immunolabelling with Ki-67 of metaphase chromosome spreads revealed a circumferential staining of the individual chromosomes. The Ki-67 antigen is preserved in nuclear matrix preparations obtained after in situ fractionation of interphase cells. When mitotic cells were exposed to such treatments, the obtained fluorescence data suggested that the antigen may be part of the chromosome scaffold. Quantification of the Ki-67 fluorescence signal using flow cytometry revealed the highest staining intensities in mitotic cells. Furthermore, it was shown that nutritionally deprived cells became negative for Ki-67.

Antibodies, Monoclonal↗
PubMed1989

A somatic cell-derived system for studying both early and late mitotic events in vitro.

We describe a cell-free system for studying mitotic reorganization of nuclear structure. The system utilizes soluble extracts prepared from metaphase-arrested somatic chicken cells and supports both the disassembly and subsequent partial reassembly of exogenous nuclei. By fluorescence microscopy, biochemical fractionation, protein phosphorylation assays and electron microscopy, we show that chicken embryonic nuclei incubated in extracts prepared from metaphase-arrested chicken hepatoma cells undergo nuclear envelope breakdown, lamina depolymerization and chromatin condensation. These prophase-like events are strictly dependent on ATP and do not occur when nuclei are incubated in interphase extracts. Compared to interphase extracts, metaphase extracts show increased kinase activities toward a number of nuclear protein substrates, including lamins and histone H1; moreover, they specifically contain four soluble phosphoproteins of Mr 38,000, 75,000, 95,000 and 165,000. Following disassembly of exogenous nuclei in metaphase extracts, telophase-like reassembly of a nuclear lamina and re-formation of nuclear membranes around condensed chromatin can be induced by depletion of ATP from the extract. We anticipate that this reversible cell-free system will contribute to the identification and characterization of factors involved in regulatory and mechanistic aspects of mitosis.

Adenosine Triphosphate↗
PubMed1981

The fate of germ cells in the testis of fetal Sex-reversed mice.

XX germ cells in the fetal testes of XX Sex-reverse male mice were observed mostly to develop in the same manner as do XY germ cells in a normal fetal testis; but some, in the vicinity of the mesonephric rete region, entered the prophase of meiosis at the same time as do XX germ cells in a normal fetal ovary. No germ cells in meiosis were found in the fetal testes of XY males, nor of XO Sex-reversed males. It is suggested that a second X chromosome renders a germ cell more susceptible to the meiosis-inducing influence of the mesonephric rete.

Animals↗
PubMed2005

The program of sex chromosome pairing in meiosis is highly conserved across marsupial species: implications for sex chromosome evolution.

Marsupials present a series of genetic and chromosomal features that are highly conserved in very distant species. One of these features is the absence of a homologous region between X and Y chromosomes. According to this genetic differentiation, sex chromosomes do not synapse during the first meiotic prophase in males, and a special structure, the dense plate, maintains sex chromosome association. In this report we present results on the process of meiotic sex chromosome pairing obtained from three different species, Thylamys elegans, Dromiciops gliroides, and Rhyncholestes raphanurus, representing the three orders of American marsupials. We have investigated the relationships between the axial structures organized along sex chromosomes and the formation of the dense plate. We found that in the three species the dense plate arises as a modification of sex chromosomal axial elements, but without the involvement of other meiotic axial structures, such as the cohesin axes. Considering the phylogenetic relationships among the marsupials studied here, our data reinforce the idea that the dense plate emerged early in marsupial evolution as an efficient mechanism to ensure the association of the nonhomologous sex chromosomes. This situation could have influenced the further evolution of sex chromosomes in marsupials.

Animals↗
PubMed2006

Analysis of close stable homolog juxtaposition during meiosis in mutants of Saccharomyces cerevisiae.

A unique aspect of meiosis is the segregation of homologous chromosomes at the meiosis I division. The pairing of homologous chromosomes is a critical aspect of meiotic prophase I that aids proper disjunction at anaphase I. We have used a site-specific recombination assay in Saccharomyces cerevisiae to examine allelic interaction levels during meiosis in a series of mutants defective in recombination, chromatin structure, or intracellular movement. Red1, a component of the chromosome axis, and Mnd1, a chromosome-binding protein that facilitates interhomolog interaction, are critical for achieving high levels of allelic interaction. Homologous recombination factors (Sae2, Rdh54, Rad54, Rad55, Rad51, Sgs1) aid in varying degrees in promoting allelic interactions, while the Srs2 helicase appears to play no appreciable role. Ris1 (a SWI2/SNF2 related protein) and Dot1 (a histone methyltransferase) appear to play minor roles. Surprisingly, factors involved in microtubule-mediated intracellular movement (Tub3, Dhc1, and Mlp2) appear to play no appreciable role in homolog juxtaposition, unlike their counterparts in fission yeast. Taken together, these results support the notion that meiotic recombination plays a major role in the high levels of homolog interaction observed during budding yeast meiosis.

Alleles↗
PubMed1979

Side-by-side pairing of the XY bivalent in spermatocytes and the ubiquity of the H-Y locus.

The pairing mechanism of the XY bivalent, the possibility of crossing-over between X and Y chromosomes during meiotic prophase, and the location of the H-Y locus are of interest with regard to genetic control mechanisms, male gametogenesis, and testicular organization. A whole-mount electron microscope technique has permitted the study of a large number of mouse and hamster spermatocytes to evaluate the spatial relationship of sex chromosomes and autosomes. X and Y chromosomes showed a transient, extensive side-by-side pairing segment along most of the length of the Y chromosome. This extensive pairing segment may cause genetic exchange between X and Y chromosomes. The finding of a small unpaired paracentromeric region of the Y chromosome could be related to a locus of totally sex-linked gene(s) that determine the development of the testis from the undifferentiated embryonic gonad.

Animals↗
PubMed1979

Combined cycloheximide and 8-hydroxyquinoline pretreatment for study of plant chromosomes.

The actions of cycloheximide and 8-hydroxyquinoline on dividing cells of root meristems of Zea mays L. have been studied during the development of a new cytological technique for sugar cane (Saccharum) root tips. The determination of mitotic phase indices revealed that combined treatment with cycloheximide (70 ppm) plus 8-hydroxyquinoline (250 ppm) was superior to treatments with either chemical separately. After the combined treatment, the preparations contained nearly ten times more cells in prophase and metaphase that were suitable for chromosome counting than those given a single pretreatment with 8-hydroxyquinoline. This new pretreatment has been developed especially for chromosome studies in tropical grasses with a large number of small chromosomes. However, both chemicals are active in a wide range of plant species.

Chromosomes↗
PubMed1984

Expression of ribosomal cistrons of human chromosomes at high resolution.

The expression of ribosomal cistrons in the nucleolar organizer regions (NORs) has been studied with high resolution banding in the acrocentric chromosomes of 10 normal individuals. It was found that if a particular chromosome did not stain with silver nitrate at metaphase, then it did not stain at prophase either. Therefore, it is concluded that some of the acrocentric chromosomes have variable expression of NORs.

Adult↗
PubMed2005

The abnormal spindle-like, microcephaly-associated (ASPM) gene encodes a centrosomal protein.

Homozygous mutations in the abnormal spindle-like, microcephaly-associated ASPM gene are the leading cause of autosomal recessive primary microcephaly. ASPM is the putative human ortholog of the Drosophila melanogaster abnormal spindles gene (asp), which is essential for mitotic spindle function. Here, we report that downregulation of endogenous ASPM by siRNA decreases protein levels of endogenous BRCA1. ASPM localizes to the centrosome in interphase and to the spindle poles from prophase through telophase. These findings indicate that ASPM may be involved in mitotic spindle function, possibly, through regulation of BRCA1.

Animals↗
PubMed2006

Preventing fatal destruction: inhibitors of the anaphase-promoting complex in meiosis.

The anaphase-promoting complex/cyclosome (APC/C) is a multi-subunit ubiquitin-ligase whose major functions in the cell cycle are the initiation of sister chromatid separation and the inactivation of cyclin-dependent kinases. This complex is also essential for meiosis, a specialized form of the cell cycle characterized by two consecutive rounds of chromosome segregation. To ensure a proper meiotic cell cycle, the activity of APC/C needs to be tightly controlled. It is now evident that inhibitors of APC/C play pivotal roles to avert its untimely activation. During prophase I, this ubiquitin-ligase must be kept inactive to prevent precocious sister chromatid separation. Studies in yeast showed that this inhibition is mediated by a specific subunit of the complex. Accurate chromosome segregation in meiosis I depends on spindle checkpoint proteins such as Mad2 which delay APC/C activation in response to an erroneous spindle attachment of chromosomes. Additional APC/C antagonists are known to block complete cyclin destruction between meiosis I and II, thereby ensuring that cyclin dependent kinases remain active and that DNA replication does not occur. Inhibitors of APC/C also mediate the cytostatic factor induced metaphase II arrest of oocytes. This review highlights the current knowledge about the role and relevance of these diverse regulators of the meiotic APC/C.

Anaphase-Promoting Complex-Cyclosome↗
PubMed1999

The ins and outs of meiosis.

During oogenesis the oocyte is arrested in meiosis twice. First at prophase I, then a second time at metaphase I in many invertebrates and in metaphase II in the vast majority of vertebrates. Meiosis resumption is triggered by the sperm. This article examines mechanisms that cause oocytes' arrest in meiosis and how spermatozoa help the oocyte to get out of this cellular predicament. J. Exp. Zool. (Mol. Dev. Evol.) 285:226-236, 1999.

Animals↗
PubMedDate not supplied

Calcium oscillations in Xenopus egg cycling extracts.

Cell cycle in various types of cells and in early embryos is often accompanied by transient changes in the concentration of free cytosolic calcium. In the present study, using fluorescent indicator fura-2, we demonstrate that Ca(2+) oscillates cyclically with an amplitude of about 100 nM and a period of mitotic cycle in cell-free Xenopus egg cycling extracts. It peaks in early metaphase just preceding mitotic reactivation of Cdc2 kinase and MAPK and reaches a minimum in interphase. The source of Ca(2+) in the extracts is a particulate fraction containing egg intracellular Ca(2+) stores, since the addition of a calcium-mobilizing second messenger, inositol 1,4,5-trisphosphate (IP3), induced a transient increase in Ca(2+). The inclusion of heparin, an IP3 receptor antagonist, or ultrafiltration of the extracts prevented Ca(2+)-releasing activity of IP3. The depletion of Ca(2+) in the extracts by the calcium chelator BAPTA resulted in the blockade of cell cycle at different stages, depending on the time of drug administration. The addition of BAPTA late in interphase blocked cell cycle at mitotic entry in prophase, whereas its application in anaphase or telophase blocked the extracts in early interphase. BAPTA administration in metaphase before transition to anaphase brought about a metaphase-like arrest in the cycling extracts. Inhibition of IP3-induced calcium release by heparin also arrested cell cycle progression in the cycling extracts.

Anaphase↗
PubMed2000

Chromosome activities in cleaving mouse embryos to construct prenucleolar bodies orienting an intranuclear chromosome-chromosome configuration.

Most chromosomes of cleaving mouse embryos formed spherical structures called as prenucleolar bodies. Embryos stained with fluorescing dyes selective for AT-rich regions of DNA indicated that chromosome centromeres were organized by prenucleolar bodies and that chromosomes at pre-prophase of the cleavage division started to condense with their centromere regions aligned towards the peripheries of spheres. Embryo chromosomes as well as prenucleolar bodies were shown to bind a monoclonal antibody to spliceosomal snRNAs, which are contrasted to the nucleoli or chromosomes of somatic cells. More than 10 prenucleolar bodies were found in the pronuclei at the earliest stage after fertilization and 40 of them at most, diploid number of chromosomes of the mouse, in the nuclei of the 2-cell embryos. The number was decreased later in the cell cycles and at the 4-cell stage. Hence, every chromosome of cleaving mouse embryos is highly active in constructing prenucleolar bodies and behaves during the interphase until mitosis as a unit of the body; either as a single unit or as a member of the units fused. In other words, the prenucleolar bodies function as centers orienting chromosome-chromosome configuration in the fertilized eggs.

Adenine↗
PubMed1992

Effect of caffeine and isobutyl-methyl-xanthine on production of binucleate cells and on post-replicative repair.

Caffeine (CAF) but not 3-isobutyl 1-methyl-xanthine (IBMX) displayed a strong DNA anti-repair effect in G2 prophase, as estimated by the frequency of abnormal chromosomes in anaphase-telophase found shortly after treatment. IBMX is more effective than CAF in inhibiting cytokinesis, while the binucleate cells formed by a short treatment with any of these two xanthines have similar cycle kinetics.

1-Methyl-3-isobutylxanthine↗
PubMed1960

Demonstration of canonic gonial mitosis and meiosis in Parascaris equorum.

It is shown that, contrary to what has been held, separate canonic chromosomes, without fusion into a chromatin mass, occur in the meiotic prophase of Parascaris equorum. In mitosis no club-shaped chromosome ends are visible. These results, obtained with a modified fixation procedure, which is described, have been checked by supravital observation.

Ascaridoidea↗
PubMed2003

[Dynamics of cytoskeleton microtubules in higher plant meiosis. I. The perinuclear band of microtubules and the meiotic spindle formation].

A planar meridional perinuclear band of microtubules was observed at the late meiotic prophase I in a range of higher plant species. A distinct high-organized structure and a long time of existence allow to consider it as a new class of MTs dependent on the cell cycle in plant meiosis. MTs of the perinuclear band convert into meiotic spindle through a complex process of spatial rearrangements.

Cell Nucleus↗
PubMedDate not supplied

[Characteristics of microsporogenesis in the Siberian larch growing under the conditions of technogenic load].

Studies of microsporogenesis in the Siberian larch growing in Krasnoyarsk and its suburbs have shown that meiosis starts in October. Microsporocytes winter at prophase I (leptoneme, diploneme). Reduction divisions in male generative buds are resumed and terminated in spring, in March. However, in the case of thaws during the autumn-winter period, meiotic division proceeds in the larch buds and this leads to the formation of degrading tetrads and pollen. Hence, the organic quiescence is absent in the larch in winter. It was shown that in the larch growing in the city, meiosis proceed more asynchronously than in the background tree stands. An increase of chromosomal aberrations during the reduction division was noted under the conditions of technogenic pollution.

Air Pollutants↗