Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Prophase”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 595 records · Page 33Linked to original sources
PubMed1990

sn-1,2-diacylglycerol levels increase in progesterone-stimulated Xenopus laevis oocytes.

Full-grown Xenopus laevis oocytes resume meiosis from prophase arrest in response to progesterone stimulation. Recent studies have shown that the tumor promoter, 12-O-tetradecanoylphorbol 13-acetate (TPA), a very potent activator of protein kinase C, can also induce the resumption of meiosis in amphibian oocytes. We have investigated the possibility that sn-1,2-diacylglycerol (DAG), the intracellular activator of protein kinase C, may be involved in the pathway normally used by progesterone. We have found that full-grown oocytes arrested in meiotic prophase contain 48 +/- 5 pmoles DAG/oocyte. This level increases within the first 5 minutes following the addition of progesterone and reaches a maximum of 75 +/- 10 pmoles following 60 minutes of steroid stimulation. Progesterone induces the up-regulation of a Na+/H+ antiport in the plasma membrane of the oocyte causing an increase in pHi following 60 minutes of steroid stimulation. We have found that the addition of 200 microM DAG (1,2-dioctanoylglycerol, diC8) to the culture medium can cause a partial up-regulation of this Na+/H+ pump in the absence of hormonal stimulation. These results suggest that DAG and protein kinase C may be involved in regulating certain aspects of meiotic maturation in progesterone-stimulated Xenopus oocytes.

Animals↗
PubMed1995

Reorganization of the endoplasmic reticulum during meiotic maturation of the mouse oocyte.

The endoplasmic reticulum (ER) of live metaphase II mouse eggs and prophase I-arrested oocytes was compared using the fluorescent, lipophilic dicarbocyanine dye, DiI. DiL, dissolved in soybean oil, was microinjected into oocytes and eggs; the dye diffused throughout the cytoplasm to label the ER, which was imaged by confocal microscopy. The mature egg had a fine reticular network of ER throughout the cell and numerous dense accumulations of membrane in the cortex. These ER accumulations, 1-2 microns in diameter, were generally absent deeper in the cytoplasm. A similar staining pattern was observed when the eggs were fixed within 1 min of injection, providing evidence that the cortical accumulations of membrane are part of a continuous ER membrane system, since membrane trafficking could not occur in a fixed egg. Cortical ER accumulations were localized to the same region of the egg as the cortical granules and were not observed in the cortical granule-free region adjacent to the meiotic spindle. In contrast, ER accumulations were rarely found in the cortex of the immature, prophase I-arrested oocyte, but larger and less well-defined membrane clusters were found throughout the deeper cytoplasm of the oocyte. The appearance of ER clusters in the egg cortex following oocyte maturation correlates with an increased ability of the mature egg to release calcium at fertilization. Since the ER is a calcium store, structural reorganization of the ER may be necessary to permit the large release of calcium and resulting cortical granule exocytosis at fertilization.

Animals↗
PubMed2000

Induction of DNA replication in the germinal vesicle of the growing mouse oocyte.

Growing mouse oocytes are physiologically arrested in the G2 phase of prophase of the first meiotic division. Growing oocytes were isolated from ovaries of 9- to 12-day-old mice and fused with parthenogenetic one-cell eggs or two-cell embryos derived from fertilized eggs. Resulting hybrids were injected with Dig-11-dUTP and examined for DNA replication using immunofluorescence. Parthenogenetic one-cell eggs fused at telophase II, G1, and middle-to-late S phase, and also S-phase two-cell blastomeres, were able to trigger DNA synthesis in oocyte germinal vesicle (GV) in the majority of hybrids cultured to the end of the first cell cycle. Activation of replication in the GV occurred within 2-3 h after fusion of growing oocytes with S-phase eggs. We show indirectly that the reactivation of replication in GVs was not dependent on the breakdown of the GV envelope. Although GVs had the ability to renew DNA replication after fusion, the G2 blastomere nuclei were incapable of reinitiating DNA replication under the influence of S-phase one-cell eggs. We hypothesize that the nuclei of growing oocytes arrested in meiotic prophase are in a physiological state that is equivalent to replication-competent G1, and not G2, nuclei.

Adenine↗
PubMed1998

Meiotic maturation in mollusc oocytes.

Molluscs, annelids and other lower invertebrates belonging to the protostome group exhibit special features in their ionic regulation of meiotic maturation and in their molecular control of metaphase arrest. These oocytes proceed from prophase I upon fertilization or hormonal stimulation and then either complete meiotic maturation or secondarily arrest in metaphase I until fertilization. We review here the recent progress on identifying the initial trigger in prophase I-arrested oocytes, emphasizing the crucial role of an early Ca2+ influx through specific Ca2+ channels. Metaphase I arrest, a unique feature of protostome animals, appears to rely on a subtle equilibrium between protein synthesis rate and destruction of regulating proteins. Some well-known components of MPF (M-phase-promoting factor) play their regular roles in protostome animals, albeit in a different environment which has not been fully characterized yet.

Animals↗
PubMed1998

Cell cycle arrest and release in starfish oocytes and eggs.

Immature starfish oocytes are arrested at the prophase of meiosis I. Once released from this arrest, meiotic maturation proceeds to the completion of meiosis II in the absence of fertilization, resulting in a second arrest at the female pronucleus stage. This article discusses how Cdc2 kinase is activated in response to the hormone 1-methyladenine at the release from the meiotic prophase arrest, and how MAP kinase is involved in the arrest at the female pronucleus stage. The experimental findings reveal both generality and divergence in the initial Cdc2 kinase activation pathway and in the role of MAP kinase signaling.

Adenine↗
PubMed1987

Cytogenetic studies on Cervus elaphus. II. Synaptonemal complexes and NOR activity during spermatogenesis.

The activity of the nucleolus organizer regions (NORs) in various stages of spermatogenesis of the red deer was studied with the silver staining technique. The Ag-stainability of the NORs, an indicator of the transcriptional activity of the r-RNA genes, is present during the meiotic prophase until pachytene and is absent during the remainder of the meiotic prophase, to reappear during the first stages of spermiogenesis and then disappear again during the elongation phase of the spermatids. The development and behaviour of synaptonemal complexes (SCs) of primary spermatocytes were also studied with the silver staining technique under the light microscope. The organization of SC is similar to that of other mammalian species. The pairing behaviour of the axes of the sex chromosomes is described.

Animals↗
PubMed1988

Sequential study of the synaptonemal complex in rat (Rattus norvegicus) oocytes by light and electron microscopy.

The progression of first meiotic prophase and synaptonemal complex (SC) formation in female rats, Rattus norvegicus S.D., is described through the analysis of the different stages of the first meiotic prophase, and confirms the high synchrony of the process in this species. Leptotene is a stage of very short duration and since pairing of the homologues begins very early, only a leptotene-zygotene stage can be distinguished. The progression of pairing during zygotene is asynchronous. The morphology of the SCs is similar to that described in other species. During diplotene and before disintegration of the lateral elements, desynapsis takes place. In some oocytes a double or even multiple nature of lateral elements was seen. Associations between SCs and nucleoli or nucleolar filaments are frequent. The presence of fragmented SCs can be interpreted as a technical artifact.

Animals↗
PubMed1995

Further insights on chromosomal pairing of autopolyploids: a triploid and tetraploids of rye.

Chromosomal pairing of one triploid and three tetraploid plants of rye, Secale cereale, was analyzed by electron microscopy in surface-spread prophase I nuclei and compared with light microscopic observations of metaphase I cells. Prophase I is characterized by: (i) the weak alignment showed by the three or four unsynapsed or partially homologous synapsed axes; (ii) the low number of pairing partner switches (PPSs) displayed by both trivalents and quadrivalents; and (iii) the existence of complex multivalents in which up to 13 chromosomes in the triploid and 22 chromosomes in the tetraploids were involved. However, only few heterologous chromosomal associations were maintained at metaphase I. The results obtained are discussed under the assumptions of the random end pairing model with some modifications.

Chromosome Banding↗
PubMed1994

Making first contacts between the spindle and the chromosomes in HeLa cells.

To guarantee an ordered bipartition of the genetic material during mitosis, the chromosomes must be incorporated into the mitotic spindle. In HeLa cells, this process starts early in prophase when the nuclear envelope is still nearly complete, but only a few small holes in the double membranes offer access to the chromosomes for individual microtubules growing out from the poles. Inside the nuclear domain, these microtubules make contact with the kinetochore/centromere complexes which can be found in the vicinity of the hole. These complexes seem to be distributed at random during early prophase until early prometaphase. Therefore, the chromosomes become incorporated in a sequential order. No accumulation of the complexes in the nucleus near the centrosomes can be recognized. The individual microtubules attach tangentially to the kinetochores. This contact can already take place before the kinetochore is fully developed.

Centromere↗
PubMed2004

TopBP1 localises to centrosomes in mitosis and to chromosome cores in meiosis.

Topoisomerase IIbeta binding protein 1 (TopBP1), previously shown to localise to sites of DNA damage and to stalled replication forks, has been implicated in DNA replication and in DNA damage response. In this work we showed that TopBP1 was localised in structures other than stalled replication forks. In late mitosis TopBP1 localises to centrosomes in a manner similar to other DNA damage response proteins such as BRCA1 and p53. Spindle checkpoint activation does not affect this centrosomal localisation. Moreover, in the testis, we detected high levels of TopBP1 associated with meiotic prophase chromosome cores and the X-Y pair. Together, these data suggest a direct role of TopBP1 during both mitosis and meiotic prophase I.

Anaphase↗
PubMed2000

Hanging on to your homolog: the roles of pairing, synapsis and recombination in the maintenance of homolog adhesion.

Homologous chromosomes initially undergo weak alignments that bring homologous sequences into register during meiosis. These alignments can be facilitated by two types of mechanisms: interstitial homology searches and telomere-telomere alignments. As prophase (and chromatin compaction) proceeds, these initial pairings or alignments need to be stabilized. In at least some organisms, such as Saccharomyces cerevisiae and S. pombe, these pairings can apparently be maintained by the creation of recombination intermediates. In contrast, synapsis during zygotene may be able to facilitate and/or maintain chromosome pairing even in the absence of exchange in several higher organisms. It thus seems possible that the synaptonemal complex plays a role both in maintaining homolog adhesion during meiotic prophase and, more speculatively, in facilitating meiotic exchange.

Animals↗
PubMed2004

Gamma-tubulin localization changes from discrete polar organizers to anastral spindles and phragmoplasts in mitosis of Marchantia polymorpha L.

Unlike the astral mitotic spindle that is organized at discrete centriolar centrosomes, the spindle of land plants is typically anastral and its origin has remained obscure. Gamma tubulin (gamma-tubulin), an important component of the centrosome, has been demonstrated at microtubule-nucleating sites in plant cells. Mitotic spindles of certain hepatics are initiated at distinct acentriolar polar organizers (POs) that appear de novo at the onset of mitosis. Data on the relationship of gamma-tubulin to POs and to microtubule arrays throughout the cell cycle were collected from rapidly dividing cells of Marchantia polymorpha (Bryophyta) that were triple-stained for gamma-tubulin, microtubules, and nuclei. POs at opposite ends of the elongated nucleus in early prophase stain brightly for gamma-tubulin and astral microtubules emanating from them initiate the spindle. As the spindle develops, however, the gamma-tubulin becomes dispersed from the highly concentrated spherical form of the POs to more diffusely organized cups at tips of the fusiform nucleus. By the end of prophase, all astral microtubules have disappeared and the gamma-tubulin is located in several minipoles along the now broad polar regions of the spindle. At metaphase, gamma-tubulin extends into the spindle itself. By telophase, the gamma-tubulin has migrated from distal to proximal surfaces of the sister nuclei and extends into the phragmoplast. Upon completion of cytokinesis, gamma-tubulin appears diminished and surrounds the nuclear envelopes. These data show that gamma-tubulin is only briefly concentrated in the PO, migrates in a cell-cycle-specific manner, and is consistently present at all putative sites of microtubule nucleation.

Cell Nucleus↗
PubMed1988

Synaptonemal complex damage in relation to meiotic chromosome aberrations after exposure of male mice to cyclophosphamide.

The genetic implications of induced synaptonemal complex (SC) damage are not known. However, on theoretical grounds, such aberrations could be involved in mechanisms leading to potentially heritable defects. Cyclophosphamide (CP), a chemical reported to cause structural and numerical chromosomal aberrations in the mouse, was used to determine if SC damage observed in meiotic prophase is related to subsequent metaphase chromosomal aberrations. Male mice were injected i.p. with CP. In some instances, mice were also injected simultaneously with tritiated thymidine to label DNA so that cells could be tracked autoradiographically through spermatogenesis. Prophase, primary metaphase (M1), and secondary metaphase (M2) samples were sequentially harvested at appropriate times from the same individual, and nuclei were examined for aberrations. Correlation coefficients between SC and metaphase chromosome aberrations were calculated. The inclusion of tritium labeling increased the number and significance of positive correlations. Positive correlations were found between (1) dose-dependent total SC damage and damage to M1, and to a lesser extent, M2 chromosomes; (2) SC breaks/fragments and M1 chains/rings as well as isochromatid breaks/fragments; (3) SC asynapsis and M1 chromatid breaks/fragments; (4) SC multi-axial configurations and M1 chains/rings as well as isochromatid and chromatid breaks/fragments; and (5) SC multi-axial configurations and M2 hyperploidy. These correlations do not define mechanistic or causal relationships between SC and chromosomal damage. However, taken together with the observation that induced SC damage is many times greater than ensuing metaphase chromosome damage, they substantiate SC analysis as a highly sensitive indicator of potentially heritable effects of this (and presumably other) genotoxic agents.

Aneuploidy↗
PubMed1986

Nuclear aberrations and loss of synaptonemal complexes in response to diethylstilbestrol (DES) in Caenorhabditis elegans hermaphrodites.

In Caenorhabditis elegans, loss of viability and fertility is observed after treatment with DES. The decrease in life span is associated with senescent morphology of meiotic prophase nuclei, such that nuclei from young and old specimens cannot be differentiated. Aging in oocytes at the pachytene stage of meiotic prophase is manifested by nucleo-cytoplasmic aberrations, increased density of the nucleoplasm and cytoplasm and decrease in numbers of mitochondria. Increasing concentrations of DES are characterized by concomitant decrease in fertility and increased production of abnormal gametes. At DES concentrations higher than 1.25 micrograms/ml, synaptonemal complexes (SC) are absent from the nuclei, thus, effective pairing and segregation of homologous chromosomes is not possible. The absence of SCs may be the result of: a premeiotic colchicine-like effect that influences pairing of chromosomes; changes in the structure of the DNA due to DES binding that results in changes in expression of the DNA; and changes in temporal DNA synthesis in response to DES. Since the SC is essential for regulating pairing and subsequent separation of bivalents, the lack of an SC explains the loss of fertility, due to the production of unbalanced gametes, observed in DES-treated specimens.

Animals↗
PubMed1984

The vesicular compartment of the mitotic apparatus in mammalian cells.

Intracellular membranes might play an eminent role in regulating several events during mitosis: In this paper the appearance and changing configurations of the vesicular compartment of the mitotic apparatus of HeLa cells was studied from anaphase to telophase. In early prophase electron opaque and transparent membranous vesicles are found in the pericentriolar region outside the nucleus. During prometaphase when the nuclear envelope opens and starts to disappear, an increasing number of these vesicles appears in the mitotic apparatus near the chromosomes. During metaphase vesicles are spread all over the mitotic apparatus, the number of electron opaque vesicles decreases while the total amount of vesicles does not change significantly. Anaphase shows the same pattern of distribution in the half-spindle and in the midbody. In telophase the amount of electron opaque vesicles increases again. They are now found around vacuoles and near the newly appearing Golgi-cisternae. We assume that the electron opaque vesicles are derived from the Golgi- apparatus which disintegrates during prophase and reappears in late telophase. The change in the appearance of the different types of vesicles during metaphase coincides with drastic changes in the ionic milieu in the mitotic apparatus (Wolniak et al., 1983).

Anaphase↗
PubMed1990

The nucleolar chromatin and the secondary constriction.

We have traced the nucleolar chromatin from early prophase to the metaphase stage. In prophase this chromatin begins to condense and in metaphase it is fully condensed. In mitotic chromosomes, this chromatin remains surrounded by achromatic materials resembling the fibrillar centre. As such this region of the chromosomes appears as a gap or constriction at the light microscope level. The possible role of this achromatic material in relation to nucleologenesis and satellite association has been discussed.

Animals↗
PubMed2004

C. elegans HIM-17 links chromatin modification and competence for initiation of meiotic recombination.

Initiation of meiotic recombination by double-strand breaks (DSBs) must occur in a controlled fashion to avoid jeopardizing genome integrity. Here, we identify chromatin-associated protein HIM-17 as a link between chromatin state and DSB formation during C. elegans meiosis. Dependencies of several meiotic prophase events on HIM-17 parallel those seen for DSB-generating enzyme SPO-11: HIM-17 is essential for DSB formation but dispensable for homolog synapsis. Crossovers and chiasmata are eliminated in him-17 null mutants but are restored by artificially induced DSBs, indicating that all components required to convert DSBs into chiasmata are present. Unlike SPO-11, HIM-17 is also required for proper accumulation of histone H3 methylation at lysine 9 on meiotic prophase chromosomes. HIM-17 shares structural features with three proteins that interact genetically with LIN-35/Rb, a known component of chromatin-modifying complexes. Furthermore, DSB levels and incidence of chiasmata can be modulated by loss of LIN-35/Rb. These and other data suggest that chromatin state governs the timing of DSB competence.

Alleles↗
PubMed2005

Formation of division spindles in higher plant meiosis.

Depolymerisation of the MT cytoskeleton during late prophase makes it impossible to follow the cytoskeleton cycle in centrosomeless plant meiocytes. This paper describes rearrangements of the MT cytoskeleton during plant meiotic spindle formation in normally dividing pollen mother cells in various higher plant species and forms in which the cytoskeleton does not depolymerise at prophase. In such variants of the wild-type, cytoskeleton rearrangements can be observed at late prophase/early prometaphase. Radial MT bundles coalesce in the meridian plane, reorientate tangentially, curve and give rise to a developed ring-shaped perinuclear cytoskeleton system at the meridian. During nuclear envelope breakdown this ring disintegrates and splits into a set of free MT bundles. Three sub-stages of prometaphase are indicated: early prometaphase (disintegration of perinuclear ring and invasion of MTs into the former nuclear area), middle prometaphase or chaotic stage (formation of bipolar spindle fibres), and late prometaphase (formation of bipolar spindle). Analysis of a range of abnormal phenotypes (disintegrated, multiple, polyarchal, chaotic spindles) reveals two previously unknown processes during late prometaphase: axial orientation and consolidation of the spindle fibres.

Cytoskeleton↗