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 523 records · Page 29Linked to original sources
PubMed1992

Expression of testis-specific histone genes during the development of rat spermatogenic cells in vitro.

We have used two radiolabeled oligonucleotide probes (TH2B and H1t), Northern blotting, two-dimensional gel electrophoresis, and autoradiography to study the temporal expression of TH2B and H1t testis-specific histone genes during the development of rat spermatogenic cells in vitro. These studies were carried out to determine whether meiotic prophase spermatocytes, known to synthesize in vivo TH2B and H1t histones among other histones, are capable of expressing these testis-specific genes in vitro during an extended period of time. We have found abundant TH2B and H1t mRNA steady state levels as well as newly-synthesized TH2B and H1t histones after 5 days of coculture. Northern blots reprobed with H1t-specific oligonucleotide showed that H1t mRNA remained prominent when TH2B mRNA started to decline after 8-12 days of coculture. Phase-contrast and transmission electron microscopy studies carried out throughout the course of the experiments demonstrated that the number of viable spermatogonia and meiotic prophase spermatocytes was relatively constant during 12 days of coculture. Spermatocytes, in a clone-like arrangement, remained attached to Sertoli cell surfaces and displayed subcellular features consistent with those observed in the intact seminiferous epithelium. Spermatogonia formed long, branching chains of interconnected cells. Results of this study indicate that spermatogenic cells in coculture with Sertoli cells express testis-specific histone genes for an extended period of time. Testis-specific histone gene expression in vitro should facilitate further studies for understanding the role of these histones in chromatin structure, transcription, and genetic recombination during male meiotic prophase.

Animals↗
PubMed1990

Cdc2 H1 kinase is negatively regulated by a type 2A phosphatase in the Xenopus early embryonic cell cycle: evidence from the effects of okadaic acid.

In Xenopus embryos, the cell cycle is abbreviated to a rapid alternation between interphase and mitosis. The onset of each M phase is induced by the periodic activation of the cdc2 kinase which is triggered by a threshold level of cyclins and apparently involves dephosphorylation of p34cdc2. We have prepared post-ribosomal supernatants from eggs sampled during interphase (interphase extracts) and just before the first mitosis of the early embryonic cell cycle (prophase extracts). In 'interphase extracts', the cdc2 kinase never activates spontaneously upon incubation at room temperature whereas in 'prophase extracts' it does. We show here that in 'interphase extracts', specific inhibition of type 2A phosphatase by okadaic acid induces cdc2 kinase activation. This requires a subthreshold level of cyclin and the presence of a particulate factor in the extract. Inhibition of type 1 phosphatases by inhibitor 1 and inhibitor 2 never results in cdc2 kinase activation. These results demonstrate that during the period of cyclin accumulation, cdc2 kinase activation is inhibited by a type 2A phosphatase. In 'prophase extracts', spontaneous activation of the cdc2 kinase is inhibited by beta-glycerophosphate and NaF, but not by okadaic acid, inhibitor 1 and inhibitor 2 or divalent cation chelation. This demonstrates that when enough cyclin has accumulated, cdc2 kinase activation involves a protein phosphatase which must be distinct from the type 1 and 2A phosphatases, and from the calcium-dependent (type 2B) and magnesium-dependent (type 2C) phosphatases.

Animals↗
PubMed1989

Regulation of mitosis onset and thymidine kinase activity during the cell cycle of Physarum polycephalum plasmodia: effect of fluorodeoxyuridine.

The effects of fluorodeoxyuridine were investigated during three events of the cell cycle: S-phase, mitosis, and the cyclic synthesis of thymidine kinase in the synchronous plasmodium of the myxomycete Physarum. DNA synthesis was inhibited, and there was limited action on other macromolecular syntheses. When DNA synthesis was slowed down, onset of the following increase of thymidine kinase synthesis occurred at approximately the same time as in the control, but mitosis was blocked in a very early prophase stage and metaphase was never observed. These effects were suppressed when the action of fluorodeoxyuridine was prevented by the addition of thymidine to the medium. In agreement with the action of aphidicolin and hydroxyurea, these observations show that: 1) perturbation of the S-phase does not prevent the nuclei from entering a very early prophase stage, but it does prevent them from proceeding through metaphase; 2) blockage of DNA synthesis does not perturb the normal timing of the triggering of thymidine kinase synthesis; and 3) the signal that triggers the arrest of thymidine kinase synthesis is postmitotic and does not require extensive DNA synthesis. In contrast with hydroxyurea and aphidicolin, in the presence of fluorodeoxyuridine metaphase was not observed. Thus, the triggering of thymidine kinase synthesis is unambiguously dissociated from metaphase and postmitotic events. Because synthesis of thymidine kinase remains under the control of temperature shifts from 22 to 32 degrees C, a simple model of the cell cycle involving two regulatory pathways could account for the triggering of thymidine kinase synthesis, early prophase stage, and metaphase.

Cell Cycle↗
PubMed1995

Induced premature G2/M-phase transition in pachytene spermatocytes includes events unique to meiosis.

Little is known about the control of events ending the lengthy prophase of meiosis I and leading to the G2/M-phase transition in mammalian spermatocytes, primarily because the relevant late pachytene, diplotene, and MI cells are present in low numbers in the testis and it is not possible to isolate them in significant numbers. We have utilized short-term cultures of pachytene spermatocytes from the mouse to study events of the G2/M cell-cycle transition induced by the protein phosphatase inhibitor okadaic acid (OA). Treatment of cultured pachytene spermatocytes with OA induced a rapid and premature onset of events leading to the M phase, visualized cytologically by nuclear envelope breakdown and chromosome condensation. After OA treatment, condensed chromosomes were seen as bivalents, not as univalents. Treatment with OA induced disassembly of synaptonemal complexes and resolution of crossovers as cytologically visible chiasmata. Chiasmata counts were similar in treated cells and control cells. Thus, surprisingly, even though the treated cells were in the pachytene substage of meiotic prophase, events of recombination were apparently completed to the point of chiasma formation in the majority of these cells. The sex chromosomes, forming the sex body of the pachytene spermatocyte, lagged behind the autosomal chromosomes in their condensation and progression toward the M phase. Treatment with OA induced an increase in histone H1 kinase activity, generally used as an indicator of metaphase-promoting factor (MPF) activity; furthermore, the OA-induced cell-cycle transition does not require new protein synthesis. These results suggest that OA treatment overrides a cell-cycle checkpoint control that normally keeps pachytene spermatocytes in a lengthy prophase and that this control may be exerted by regulation of protein phosphorylation status.

Animals↗
PubMed1997

Entry of mouse embryonic germ cells into meiosis.

Germ cells harvested from mouse embryonic genital ridges were mixed with disaggregated embryonic lung cells, and the reaggregates were cultured for 4-7 days. Germ cells derived from female embryos 10.5-13.5 days postcoitum (dpc) entered and progressed through meiotic prophase in vitro as in vivo, although with a 12- to 24-hr delay. If the cultures were maintained for 2-3 weeks, the germ cells developed into growing oocytes. When germ cells were taken from male embryos 10.5 and 11.5 dpc, they too entered and progressed through meiotic prophase, but germ cells from later embryos (12.5 and 13.5 dpc) developed as prospermatogonia, as in male genital ridges in vivo. When 11.5 dpc male genital ridges were disaggregated, reaggregated, and cultured in the same way as the lung reaggregates, the germ cells again entered meiotic prophase. We conclude that the male genital ridge at about 12 dpc produces a factor that inhibits entry of germ cells into meiosis, and that production of this factor is disrupted by prior disaggregation of the genital ridge. If a meiotic inducing substance is required for entry of germ cells into meiosis, it must be present in the male genital ridge as well as in the female genital ridge, and probably also in the lung.

Animals↗
PubMed1997

Characterization and physiological importance of a novel cell cycle regulated protein kinase in Xenopus laevis oocytes that phosphorylates cyclin B2.

We have partially purified a specific cyclin B2 kinase (cyk) from prophase oocytes of Xenopus laevis after an ATP-gamma-S activation step. Phosphopeptide analysis identified Ser53 as the major in vitro phosphorylation site for cyk in cyclin B2. Using a synthetic peptide derived from cyclin B2 encompassing Ser53 (cyktide) as a substrate, cyk was shown to be activated during progesterone-induced maturation, with a peak of activity between 40 and 50% maturation. A sustained high cyk activity was observed in oscillating egg extracts. Microinjection of cyk-phosphorylated cyclin B2 into prophase oocytes accelerated progesterone-induced maturation by about 2 h, indicating that cyclin B2 is a relevant substrate for cyk and that the function of cyk is situated upstream of cdc2-cyclin B activation. Microinjection of cyk-phosphorylated cyktide or a combination of cyk and cyclin B1 into G2 fibroblasts induced significant changes in cell morphology, reminiscent of a premature prophase-like phenotype. Similarly, addition of cyk-phosphorylated cyktide in cyclin B1-dependent interphase extracts resulted in histone H1 kinase activation.

Adenosine Triphosphate↗
PubMed2002

Dynamics of chromosome compaction during mitosis.

We have quantitatively studied the space-time dynamics of mitotic chromosome compaction in cultured amphibian cells. After collecting digital phase-contrast images we have done digital image analysis to study spatial correlations in density. We find a characteristic distance at which the strongest correlations occur, which provides a quantitative measure of the size of patches of dense chromatin during interphase and early prophase. Later in mitosis, this length corresponds to the thickness of prophase and metaphase chromosomes. We find that during interphase strong correlations exist at a few-micrometer length; during prophase this correlation length progressively drops as the chromosomes are compacted. Our data are explained by a model based on assembly of chromatin loops onto already fiberlike interphase chromosomes. To test this model we have microinjected cobalt hexamine trichloride into interphase nuclei and have observed the rapid condensation of the interphase chromatin into thick fibers with a spacing similar to the native-state interphase correlation length determined from our image analysis.

Animals↗
PubMed2001

Isolation and characterization of sexual sporulation mutants of Aspergillus nidulans.

For the genetic dissection of sexual sporulation in Aspergillus nidulans, we started a collection of ascosporeless mutants. After mutagenization of conidiospores with high doses of UV, we isolated 20 mutants with defects in ascospore formation. We crossed these mutants in two successive rounds with the wild-type strain. Eighteen of the 20 isolated mutants produced progeny with the original mutant phenotype in these crosses, and these mutants were further analyzed. All 18 analyzed mutations were recessive to wild type. We assigned them to 15 complementation groups, based on crosses between mutants. The mutants could be classified as follows according to their cytological phenotype: (1) no croziers, (2) arrest at prekaryogamy, (3) arrest in early meiotic prophase, (4) arrest in late meiotic prophase, (5) arrest in meiotic metaphase I, (6) defective postmeiotic mitosis and/or deliniation of ascospores, and (7) slow progression through the postmeiotic stages of ascospore formation. A large proportion of the mutants, namely 11 of 18, arrested in meiotic prophase or metaphase I. We discuss a possible approach for isolating the wild-type alleles of the genes that carry the sexual sporulation mutations.

Aspergillus nidulans↗
PubMed1985

Gene expression during oogenesis and oocyte development in mammals.

Mouse oocytes progress through early meiotic prophase during fetal life and reach the diplotene stage by birth. During prepubertal and reproductive life, oocytes are continuously selected to grow from the pool of small primordial oocytes. Growing oocytes reach full size in 2 weeks, and full-grown oocytes are present in rapidly enlarging follicles for about 5 days before meiotic maturation and ovulation. RNA synthesis during early meiotic prophase, as estimated from [3H]uridine incorporation followed by autoradiography and from electron microscopic analysis of nuclear components, proceeds at a moderate rate throughout except for a brief period in early pachytene when synthesis is low or absent. RNA synthesis continues in primordial oocytes at a moderate rate. Incorporation studies, electron microscopic analyses, and particularly measurements of ongoing RNA polymerase activity (completion of initiated chains as analysed in tissue sections) indicate a distinctly increased rate of synthesis during oocyte growth over that of primordial oocytes, followed by a decline in full-grown oocytes. During growth, this rate increases severalfold. The absolute rate of synthesis of heterogeneous nuclear RNA (using rRNA as a standard) during mid-growth is very rapid, but nevertheless still much lower than that in typical lampbrush chromosomes. Most of the hnRNA turns over with a half-life of about 20 min, as is typical in somatic cells. Newly synthesized mRNA-like RNA enters the cytoplasm at about one-half the rate of rRNA, and about one-third of the ribosomes and one-fourth of the mRNA appear in polysomes. In full-grown oocytes, the rate of synthesis falls distinctly, but a significant level of synthesis continues until it essentially ceases at breakdown of the germinal vesicle. During meiotic prophase, chromosomes are most compact at pachytene and unfold lateral projections as RNA synthesis increases in late pachytene-early diplotene. In primordial oocytes, the diplotene state of chromosomes is obvious in most mammals, but in rodents the chromosomes are more evenly dispersed and are said to be in a dictyate state, although they are still presumably in a diplotene configuration. The chromosome core, which is present in leptotene through early diplotene stages, apparently disappears in the dictyate stage.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1977

Germ cell proliferations in the fetal horse ovary.

During the 340 day pregnancy of the horse, the germ cells in the fetal ovary showed a meiotic prophase which began in days 60-70 and might be prolonged after day 200. Three or four successive oogonial mitotic proliferations passed into the meiotic prophase but the great majority of the oocytes first involved degenerated, and no appreciable numbers of primordial follicles were left behind. At 150 days of pregnancy and again at 197 days, oocytes in early meiotic stages filled the ovarian cortex. Primordial follicles were present, but rare. As the prophase gradually came to an end, groups of oocytes became enclosed by small 'boundary' cells which formed in the stroma. Coalescence of these groups led to the appearance of coiled and branching formations containing small and large oocytes. Many of the original groups, however, contracted and became narrow strands and these persisted until the end of pregnancy, many oocytes disappearing from them, while others eventually developed in primordial follicles.

Animals↗
PubMed1981

Chromosome organization during male meiosis in Bombyx mori.

Chromatin organization during male meiosis in Bombyx mori has been investigated utilizing the Miller spreading procedure. During meiotic prophase, the linear 200-300 A chromatin fibers evident at interphase are folded into tandem arrays of approximately 7,000 loops per haploid genome. Adjacent loops visualized during early prophase are separated by 0.15-0.2 nm of nucleosomal DNA. Meiotic metaphase chromosomes display numerous loops which project radially from the central region of the chromosome suggesting that the loop conformation of prophase is maintained throughout meiosis. Spread preparations of spermatogenic stages through pachytene allow the visualization of actively transcribed ribosomal DNA. Throughout this period, these transcription units appear to be organized into loops in such a way that one active transcription unit exists on a single loop. Furthermore, there are various levels of transcription on different ribosomal loops, although the number of loops displaying active transcription remains constant throughout this period.

Animals↗
PubMed1980

Ultrastructural characterization of the sex chromosomes during spermatogenesis of spiders having holocentric chromosomes and a long diffuse stage.

An ultrastructural study has been made of spermatogenesis in two species of primitive spiders having holocentric chromosomes (Dysdera crocata, male X0 and Sergestria florentia X1X2O). Analysis of the meiotic prophase shows a scarcity or absence of typical leptotene to pachytene stages. Only in D. crocata have synaptonemal complex (SC) remnants been seen, and these occurred in nuclei with an extreme chromatin decondensation. In both species typical early prophase stages have been replaced by nuclei lacking SC and with their chromatin almost completely decondensed, constituting a long and well-defined diffuse stage. Only nucleoli and the condensed sex chromosomes can be identified. - In S. florentina paired non-homologous sex chromosomes lack a junction lamina and thus clearly differ from the sex chromosomes of more evolved spiders with an X1X20 male sex determination mechanism. In the same species, sex chromosomes can be recognized during metaphase I due to their special structural details, while in D. crocata the X chromosome is not distinguishable from the autosomes at this stage. - The diffuse stage and particularly the structural characteristics of the sex chromosomes during meiotic prophase are reviewed and discussed in relation to the meiotic process in other arachnid goups.

Animals↗
PubMed1995

A change in the phosphorylation pattern of the 30000-33000 Mr synaptonemal complex proteins of the rat between early and mid-pachytene.

The lateral elements (LEs) of synaptonemal complexes (SCs) of the rat contain major components with relative electrophoretic mobilities (Mr s) of 30000-33000, which are the products of a single gene. After one-dimensional separation of SC proteins on polyacrylamide-SDS gels, these components show up as two major bands, whereas upon two-dimensional electrophoresis they are resolved in at least 24 spots, which focus at pH 6.5 to 9.5. In this paper we show that these spots represent phosphorylation variants. For the analysis of the phosphorylation of the 30000- to 33000-Mr SC components during progression through meiotic prophase, we developed a procedure for isolation of fractions of testicular cells of the rat that are enriched in separate stages of meiotic prophase. Analysis of the 30000- to 33000-Mr SC components in these fractions by two-dimensional electrophoresis and immunoblotting showed that phosphorylated variants of the 30000- to 33000-Mr SC proteins occur throughout meiotic prophase. However, the extent of phosphorylation changes between early and mid-pachytene, when one phosphate group is probably added to each of the variants.

Animals↗
PubMed1991

Chromosome banding in Amphibia. XVI. High-resolution replication banding patterns in Xenopus laevis.

High-resolution replication banding patterns were induced in prometaphase and prophase chromosomes of Xenopus laevis by treating kidney cell lines with 5-bromodeoxyuridine (BrdU) and deoxythymidine (dT) in succession. Up to 650 early and late replicating bands per haploid karyotype were demonstrated in the very long prophase chromosomes. This permits an exact identification of all chromosome pairs of X. laevis. Late replicating heterochromatin was located by analysing the time sequence of replication throughout the second half of S-phase. Neither heteromorphic sex chromosomes nor sex chromosome-specific replication bands were demonstrated in the heterogametic ZW females of X. laevis. A detailed examination of the BrdU/dT-labelled prometaphases and prophases revealed that the X. laevis chromosomes can be arranged in groups of four (quartets), most of which show conspicuous similarities in length, centromere position, and replication pattern. This is interpreted as further evidence for an ancient allotetraploid origin of X. laevis.

Animals↗
PubMed1979

G-banding patterns of high-resolution human chromosomes 6--22, X, and Y.

A precise schematic representation of the number, height, position, and staining intensity of the Giemsa bands of late prophase, prometaphase, early metaphase, and mid-metaphase chromosomes 6--22, X, and Y is presented. Late prophase chromosomes were found to have 2--2 1/2 times the length and 3--3 1/2 times the number of bands previously observed in mid-metaphase, whereas prometaphases and early metaphases were intermediate in length and number of bands. In this work, the maximum number of bands observed per haploid set in late prophase was 1353, while more than 350 were generally found in mid-metaphase.

Azure Stains↗
PubMed1996

Differences in hydration state of nucleus and cytoplasm of the amphibian oocyte.

Nuclear magnetic resonance (NMR) microimaging and proton relaxation times were used to monitor differences between the hydration state of the nucleus and cytoplasm in the Rana pipiens oocyte. Individual isolated ovarian oocytes were imaged in a drop of Ringer's solution with an in-plane resolution of 80 microm. Proton spin echo images of oocytes arrested in prophase I indicated a marked difference in contrast between nucleoplasm and cytoplasm with additional intensity gradations between the yolk platelet-rich region of the cytoplasm and regions with little yolk. Neither shortening taue (spin echo time) to 9 msec (from 18 msec) nor lengthening taur (spin recovery time) to 2 sec (from 0.5 sec) reduced the observed contrast between nucleus and cytoplasm. Water proton T1 (spin-lattice) relaxation times of oocyte suspensions indicated three water compartments that corresponded to extracellular medium (T1 = 3.0 sec), cytoplasm (T1 = 0.8 sec) and nucleoplasm (T1 = 1.6 sec). The 1.6 sec compartment disappeared at the time of nuclear breakdown. Measurements of plasma and nuclear membrane potentials with KCl-filled glass microelectrodes demonstrated that the prophase I oocyte nucleus was about 25 mV inside positive relative to the extracellular medium. A model for the prophase-arrested oocyte is proposed in which a high concentration of large impermeant ions together with small counter ions set up a Donnan-type equilibrium that results in an increased distribution of water within the nucleus in comparison with the cytosol. This study indicates: (i) a slow exchange between two or more intracellular water compartments on the NMR time-scale, (ii) an increased rotational correlation time for water molecules in both the cytoplasmic and nuclear compartments compared to bulk water, and (iii) a higher water content (per unit dry mass) of the nucleus compared to the cytoplasm, and (iv) the existence of a large (about 75 mV positive) electropotential difference between the nuclear and cytoplasmic compartments.

Animals↗
PubMed2001

Mitotic arrest of female germ cells during prenatal oogenesis. A colcemid-like, non-apoptotic cell death.

The sequence of events and a possible reason for germ cell death during oogenesis in the prenatal ovary were studied in rat and mouse embryos. ED 14-22 rat and ED 14-16 mouse embryos were studied using semithin sections for light microscopy and serial ultrathin sections for electron microscopy. In addition, the rat material was 3H-thymidine labelled for historadioautography and cytospin preparations of freshly obtained gonads were immunohistochemically analysed. During the transition from the proliferating oogonial stage to the meiotic prophase about 16% of the postmitotic oocytes do not pass the initial meiotic checkpoint on ED 18/19 in the rat (ED 15/16 in the mouse). These germ cells first show structural signs of mitosis; the diploid number of 'super-condensed' chromosomes are globally formed and are concentrated in the center of the cell. Although the germ cells show all morphological signs of living cells they never have mitotic spindles; the micro-tubulus-organisation-centres (MTOCs) are found peripherally and become concentrated, forming a single centrosomal body (acentriolar MTOC) as detected by immunohistochemistry for the centrosomal protein MPM2 and gamma-tubulin. EM studies show 25 nm tubule-like profiles within the MTOC bodies. The centrioles frequently lie separate from the MTOC material or are not present at all; the germ cells are apparently arrested in a prophase- or metaphase-like stage when they have reached the postmitotic G2/preleptotenal transition and are unable to enter meiosis. Forty-eight to 72 h after the first mitotically arrested germ cells are found, degeneration is seen in these germ cells. This second event, the germ cell death proper, shows neither criteria of apoptosis (cell shrinkage, marginal condensation of chromatin, DNA fragmentation) nor signs of necrosis (cell swelling, pycnosis, inflammation). Both arrested pro- and metaphase-like stages are found with signs of cell death and phagocytosis. The morphological signs of phagocytosis are found in neighbouring pregranulosa cells. The final heterocytotic bodies contain the remnants of the centrosomal (MTOC) material and DAPI-positive DNA material. The pregranulosa cells are mitotically silent during the phase when mitotic arrest and germ cell degeneration is found. The results suggest the presence of a hypothetical 'anti-spindle' factor, which under normal conditions is necessary for induction of meiotic prophase. The structural events of 'arrested mitosis' is reminiscent of those induced by the antimitotic, tubule-degrading drug colcemid. This type of arrest may inhibit meiosis of more than 33% prenatal germ cells and induce their cell death.

Animals↗
PubMed2005

Caspase-independent apoptosis is activated by diazepam-induced mitotic failure in HeLa cells, but not in human primary fibroblasts.

DZ, a benzodiazepine known to affect centrosome separation at prophase, leads to a higher degree of mitotic arrest in HeLa cells than in primary human fibroblasts. In fact, differently from fibroblasts, which undergo a transient block in prophase-to-prometaphase transition, a high proportion of tumor cells attempt to escape from the DZ-imposed mitotic block, fail to undergo complete mitosis and die by mitotic failure. DZ-treated samples showed certain biochemical hallmarks of apoptosis, such as induction of the proapototic Bax protein, mitochondrial alterations assessed by JC-1 staining and TEM analysis, PARP cleavage, and DNA fragmentation. However, in DZ-treated cells, we observed a very low or absent caspase activation as shown by immunofluorescence and immunoblot experiments with antibodies directed to activated caspases and by staining with the pancaspase inhibitor FITC-VAD-FMK. Experiments on mitochondrial depolymerization and apoptosis induction carried out in the presence of specific inhibitors of caspase-2 and caspase-3/7 indicated a caspase-independent apoptotic process induced by DZ. Accordingly, TEM analysis of treated cells revealed ultrastructural features resembling those reported for caspase-independent apoptosis. In conclusion, we hypothesize that HeLa cells override the prophase block imposed by DZ, producing a high rate of aberrant pro-metaphases, which, in turn, activates caspase-independent, apoptosis-like mitotic catastrophe.

Apoptosis↗