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PubMed1987

[Reaction of the ovaries of 1- and 4-day-old rat pups to transplantation].

Morphofunctional peculiarities of ovarian development in 1- and 4-day-old rats have been studied under conditions of their transplantation into mature female rats. In 30 days in transplants of both series of the experiments atretic process develops. Better preservation of the general pool of the germ cells and follicles is obtained at transplantation of the ovaries from the 4-day-old donors; their ovocytes at the operation time are at the stationary state of meiosis prophase. Ovocytes of 1-day-old animals, being at the stages of early prophase, are more vulnerable at homotransplantation.

Aging↗
PubMedDate not supplied

Meiosis-inducing and meiosis-preventing effects of sex steroid hormones on hamster fetal ovaries in organ culture.

Day 11 to day 15 p.c. female gonads were cultured for 6-8 days in chemically-defined media. In day 11 and day 12 p.c. ovaries grown in a non-hormonal medium, the germ cells were unable to enter meiosis; they were retained at a stage of oogonia or more frequently at a preleptotene stage. Ovaries of the same ages cultured in an estradiol-containing medium showed germ cells progressing through meiotic prophase in a way close to that in ovaries of equivalent age in vivo. That was the case of the germ cells in day 13 to day 15 p.c. ovaries maintained in a non-hormonal medium. In a testosterone-containing medium, the germ cells in day 13 and day 14 p.c. ovaries were prevented from entering meiosis; by contrast, those in day 15 p.c. ovaries underwent meiotic prophase normally. These results indicated that each of both hormones was able to exert its corresponding (meiosis-inducing or meiosis-preventing) effect before a definite critical time of ovarian development. The possibility is suggested that the germ cell differentiation in the female and male gonads in vivo would also depend on estrogens or androgens precociously synthesized in the gonads or supplied from other organs via the fetal blood.

Animals↗
PubMed1985

Phosphorylation of histone H1 through the cell cycle of Physarum polycephalum. 24 sites of phosphorylation at metaphase.

H1 phosphorylation has been studied through the precise nuclear division cycle of Physarum polycephalum. The number of sites of phosphorylation of Physarum H1 is very much larger than the number of sites reported for mammalian H1 molecules which is consistent with the larger molecular weight of Physarum H1. At metaphase all of the Physarum H1 molecules contain 20-24 phosphates. Immediately following metaphase, these metaphase-phosphorylated H1 molecules undergo rapid dephosphorylation to give an intermediate S phase set of phosphorylated H1 molecules containing 9-16 phosphates. Progressing into S phase newly synthesized H1 is phosphorylated and eventually merges with the old dephosphorylated H1 to give a ladder of bands 1-20. By the end of S phase or early G2 phase, there is a ladder of bands 1-16 all of which undergo phosphate turnover. Further into G2 phase the bands move to higher states of phosphorylation, and by prophase all of the H1 molecules contain 15-24 phosphates which increases to 20-24 phosphates at metaphase. These results support the proposals that H1 phosphorylation is an important factor in the process of chromosome condensation through G2 phase, prophase to metaphase.

Alkaline Phosphatase↗
PubMed1984

Dynamics of the nuclear envelope and of nuclear pore complexes during mitosis in the Drosophila embryo.

Early embryonic development in Drosophila melanogaster is marked by a series of thirteen very rapid (10-15 min) and highly synchronous nuclear divisions, the last four of which occur just beneath the embryo surface. A total of some 6000 blastoderm nuclei result, which are subsequently enclosed by furrow membranes to form the cellular blastoderm. We have examined the fine structure of nuclear division in late syncytial embryos. The mitotic spindle forms adjacent to the nuclear envelope on the side facing the embryo surface. During prophase, astral microtubules deform the nuclear envelope which then ruptures at the poles at the onset of prometaphase. The nuclear envelope remains essentially intact elsewhere throughout mitosis. A second envelope begins to form around the nuclear envelope in prometaphase and is completed by metaphase; the entire double layered structure, referred to as the spindle envelope, persists through early in the ensuing interphase. Pole cell spindles are enclosed by identical spindle envelopes. Interphase and prophase nuclei contain nuclear pore complexes (PCs) of standard dimensions and morphology. In prometaphase PCs become much less electron-dense, although they retain their former size and shape. By metaphase, no semblance of PC structure remains, and instead, both layers of the spindle envelope are interrupted by numerous irregular fenestrae. PCs are presumably disassembled into their component parts during mitosis, and reassembled subsequently. Yolk nuclei remain among the central yolk mass when most nuclei migrate to the surface, cease to divide, yet become polyploid. These nuclei nonetheless lose and regain PCs in synchrony with the dividing blastoderm nuclei. In addition, they gain and lose a second fenestrated membrane layer with the same timing. Cytoplasmic membranes containing PCs (annulate lamellae) also lose and regain pores in synchrony with the two classes of nuclear envelopes. The factors that affect the integrity of PCs in dividing blastoderm nuclei appear to affect those in other membrane systems to an equivalent degree and with identical timing.

Animals↗
PubMed1984

Nuclear asynchrony in multinucleate rat kangaroo cells.

Multinucleate (MN) cells were induced in PtK1 cells by colcemid treatment. A large percentage of cells developed nuclear asynchrony both in relation to DNA synthesis and mitosis within one cell cycle. Asynchrony could be traced even in metaphase and anaphase cells in which interphase nuclei, PCC of S-phase nuclei and less condensed prophase-like chromosomes could be observed along with normally condensed chromosomes. The occurrence of such abnormalities in these large MN cells may be explained on the basis of an uneven distribution of inducer molecules of DNA synthesis and mitosis due to cytoplasmic compartmentation. The less condensed form of all the chromosomes except chromosome 4 could be traced in asynchronous metaphase. The failure of the less condensed chromosomes to undergo complete condensation does not always appear to result from late entry of nuclei containing these chromosomes into G2 phase. It is likely that chromosome 4 carries gene(s) for chromosome condensation, as this chromosome itself never appears in a less condensed form. The inducers for chromosome condensation may not always be available at equal concentrations to all chromosomes located in separate nuclei, thus they may sometimes fail to undergo complete condensation before other nuclei reach the end of prophase, when the nuclear envelopes of all nuclei present in the cell break down simultaneously.

Animals↗
PubMed1983

Effect of stypoldione on cell cycle progression, DNA and protein synthesis, and cell division in cultured sea urchin embryos.

We have found that stypoldione, a bright red o-quinone isolated from the brown alga Stypopodium zonale, inhibits the division of sea urchin embryos in a concentration-dependent manner (IC50 approximately 2.5 X 10(-6) M). Although previous studies have shown this marine natural product to inhibit beef brain microtubule assembly in vitro [Fed. Proc. 39:26-29 (1980); Mol. Pharmacol. 24:493-499 (1983)], we have found that stypoldione does not accumulate sea urchin embryos in mitosis and hence does not act like a mitotic spindle poison. We have also shown this marine natural product to inhibit both amino acid and nucleoside uptake. By preloading sea urchin embryos with nucleoside (i.e., [3H]thymidine) in order to dissociate effects on uptake from those on incorporation, we found that stypoldione in fact produces no significant inhibition of the M phase-independent S1 period of DNA synthesis, a result which suggests that stypoldione has no direct effect on DNA synthesis. In contrast, stypoldione did reduce the extent of amino acid incorporation in embryos preloaded with [3H]leucine. An inhibition of incorporation was apparent as early as 20 min after fertilization, and incorporation was reduced to 50% of control by 40 min postfertilization. This result suggests that stypoldione might inhibit cleavage via an inhibition of translation, although the existence of other inhibitory mechanisms cannot yet be ruled out. Cytological examination revealed that sea urchin embryos did not progress beyond-interphase or very early prophase when incubated in the presence of 1.0 X 10(-5) M stypoldione. The nuclear membranes remained intact, and chromatin did not condense into chromosomes in these arrested embryos. These results indicate that embryos exposed to stypoldione early in the cell cycle initiate and complete the M phase-independent S1 period of DNA synthesis, but stop cell cycle progression prior to the start of prophase of mitosis. The period between S phase and mitosis is referred to, by definition, as the "G2" phase of the cell cycle. The result therefore suggest that stypoldione blocks cell cycle progression (and, ultimately, cell division) by inhibiting progression through G2. This compound may represent a new class of G2-accumulating agents.

Animals↗
PubMed1983

[Possible mechanisms of the origination of chromosomal restructurings. III. The role of chromosome association and isolation].

The kinetics of early appearance of chromosome breaks and exchanges (5-60 min after ionizing irradiation) in pea roots, in primary culture of embryonal fibroblasts of BALB mice and in chinese hamster cells BIId-ii-FAF-28 has been studied. It was found that chromosome resistance to irradiation increases during mitosis as fast as the process of chromosome isolation is advanced (the latter prevents the interchromosome and interchromatid contacts). From the outset of activation of sister chromatids isolation (i.e. from the end of prophase in pea and mouse cells, and from the beginning of prophase in hamster cells), the chromosomes "cease" to respond to irradiation. The prolongation of the period of isolation of sister chromatids in mouse cells by means of colchicine results in prolongation of the "insensitivity" period. A causal relationship between the chromosome isolation phenomenon and the increase in their radiosensitivity is supposed to exist. The importance of chromosome association and isolation in formation of chromosome breaks and exchanges is discussed.

Animals↗
PubMed1978

[Changes in the mitotic activity of corneal epithelial cells under the influence of pyruvic acid].

92 specimens of rat's corneal epithelium were studied to estimate the effect of pyruvic acid on cell division characteristics. 0.1 M solution of pyruvic acid decreases the mitotic activity of rat corneal epithelium, the portion of prophase increasing the number of metaphase decreasing. These results support a hypothesis on the possible role of low molecular acceptors in the cell division regulation "in vivo", and suggests the effect of pyruvic acid both during the period prior to cell division, and the prophase-metaphase stage.

Animals↗
PubMed1982

[Incorporation at [3H]thymidine into the repetitive and unique nucleotide sequences in DNA of the sea urchin Strongylocentrotus droebachiensis at the stage of synchronous cleavage divisions].

The DNA synthesis in the sea urchin Strongylocentrotus droebachiensis at the stage of 4-8 blastomers starts in the telophase and is completed in the prophase. The highest [3H]thymidine incorporation was observed in telophase chromosomes. The changes in the relative rate of [3H] thymidine incorporation during DNA replication are not the same for the repetitive and unique nucleotide sequences. Highly repetitive nucleotide sequences incorporate [3H]thymidine mainly at the beginning and at the end of DNA synthesis. Moderately repetitive nucleotide sequences do not demonstrate any significant changes in the rate of [3H]thymidine incorporation during DNA replication. The unique nucleotide sequences have the lowest rate of [3H]thymidine incorporation at the beginning (telophase) and at the end (prophase) of DNA synthesis and the highest rate--in the middle of the interphase. The data obtained suggest that there exists some temporal organization of replication process of repetitive and unique nucleotide sequences in the sea urchin genome at the stage of the synchronous cleavage divisions.

Animals↗
PubMed1980

Mitosis in Oedogonium: spindle microfilaments and the origin of the kinetochore fiber.

New ultrastructural observations of mitosis in the closed spindle of Oedogonium cardiacum have been made using cells fixed with glutaraldehyde and tannic acid. Fine filaments 5 to 8 nm in diameter are attached to kinetochores from prophase through anaphase. Some are free in the early division nucleus while others emanate from forming kinetochores at prophase when few if any microtubules (MTs) are inside the nucleus. During prometaphase, MTs invade the nucleus from the poles and appear to interact with the microfilaments. Early in prometaphase, numerous MTs are laterally associated with kinetochores, and the kinetochore fiber is often formed first at one kinetochore of a pair. During metaphase and anaphase, the microfilaments are interspersed among the MTs of these kinetochore fibers. There also is an ill-defined matrix concentrated in the kinetochore fiber, and MTs are often coated irregularly with osmiophilic material. Live mitotic cells of Oedogonium were studied using time lapse cinematography, and we correlate these observations with the above results. We conclude that these microfilaments may constitute one structural component of the traction apparatus that moves chromosomes during metakinesis and anaphase, and that at least some (and possibly many) of the MTs of the kinetochore fiber are derived from those entering the nucleus at prometaphase.

Centromere↗
PubMed1978

[Ultrastructure of human chromosomes].

The structural elements of chromosomes are chromatin fibrils of about 100 A diameter (see the preceeding paper by NOLL). The chromosomes of most eukaryontic species are single stranded. Each chromatid consists of only one chromatin fibril and thus only of one DNA-double helix. In interphase the chromatin fibril is loosely and irregularly folded. With the onset of mitosis it becomes more densely but still irregularly packed to form the long and thin prophase chromosome. Metaphase chromosomes are formed by a coiling of the thin prophase chromatids (major coils). Chromosome banding can be produced with the aid of specific fluorescent dyes or by special pretreatments before staining. The banding is due to many factors but an important one is the different AT- ad GC-content of bandlike regions. In very thin chromosomes such as premature condensed chromosomes the bands are very fine and can be correlated in size to the chromomeres of polytene giant chromosomes.

Chromatin↗
PubMed1980

Role of SS bridges in mitotic condensation of chromatin.

The effects of beta-mercaptoethanol on the mitotic index, phase index, condensation of chromatin in late G2 phase and in metaphase chromosomes, and on the content of protein -SH groups in successive developmental stages of antheridial filaments of Chara vulgaris L. were investigated. It has been shown earlier that as the development of antheridial filaments proceeds, the content of condensed chromatin in the late G2 phase increases, prophase duration shortens and metaphase chromosomes become more condensed. As cytophotometric measurements have shown, the concentration of the protein -SH groups is similar in all developmental stages, their total content, however, decreases in parallel with the shortening of cell length in successive generations. The more advanced developmental stage of antheridial filaments, the higher increase in the concentration of the protein -SH groups is induced by 2 h incubation with beta-mercaptoethanol. After 2 h incubation with beta-mercaptoethanol, the surface area of condensed chromatin decreases in late G2 phase, but the number of chromocenters remains unchanged, beta-mercaptoethanol does not modify the mitotic index but, beginning from the 4-celled stage, it increases the prophase index. In 1-,2-,4- and 8-celled antheridial filaments after 2 h incubation with beta-mercaptoethanol the chromosomes show a lower degree of condensation in about 30% of metaphases.

Cell Cycle↗
PubMed1980

Temporal analysis of the nuclear cycle by serial section electron microscopy of the fungus, Saprolegnia ferax.

Data on the dynamics of the nuclear cycle in the coenocytic fungus, Saprolegnia ferax, were obtained by a combination of serial-section electron microscopy, DNA measurements and nuclear counts of vegetative hyphae and germinating spores. These methods are the only ones capable of giving the timing of the stages of division at the level of resolution of thin-section electron microscopy. All nuclei observed contained various arrays of kinetochore microtubules and were thus defined as being in mitosis. Among this population the mean percentage (corrected for age gradient) of each stage was as follows: prophase with one pair of centrioles, 28.5; prophase with two pairs of centrioles, 41.9; metaphase, 23.8, anaphase, 0.8 and telophase, 4.4. The total duration of the nuclear cycle was calculated as a mean of 76 min and a minimum of 30 min from which the duration of each phase was calculated. Based on these figures and observed spindle lengths, rates of spindle elongation up to 31 micron/min, chromosome-to-pole movements up to 8.5 micron/min and microtubule polymerization up to 30.8 micron/min were deduced. Because transitions between the pre-metaphase stages were rare, it is concluded that mitosis progresses initially as a series of rapid steps with intervening morphologically quiescent stages.

Cell Cycle↗
PubMed1995

4-aminopyridine acts as a weak base and a Ca2+ mobilizing agent in triggering oocyte meiosis reinitiation and activation in the Japanese clam Ruditapes philippinarum.

Ovarian oocytes of the prosobranch mollusc Patella vulgata and the pelecypod Ruditapes philippinarum are arrested during prophase of the first maturation division. Release from this blockade, which is revealed by germinal vesicle breakdown, drives these oocytes to a second arrest in metaphase I, at which time the oocytes become fertilizable. The respective roles of Ca2+ and H+ ion movements during this early step in meiosis reinitiation has not been fully established yet. In this work we reveal the presence of acidic vesicles and report that bafilomycin A1 and N,N'-dicyclohexylcarbodiimide, two inhibitors of the vacuolar-type H(+)-ATPase, applied to Ruditapes oocytes, produce a significant inhibition of their response to the natural neurohormone serotonin. Since sodium deprivation did not affect this response, this suggests that a v-type ATPase pump, possibly located in the membrane of these acidic vesicles, may play a subtle role in the cascade of events that releases oocytes from their prophase block. We then describe how 4-aminopyridine, a drug reputed to be a K+ channel antagonist, triggers both meiosis reinitiation and activation of Patella and Ruditapes oocytes. This agent acts as a weak base, its effect depending on external pH. Moreover, using the fluorescent probes BCECF and Fluo-3/AM, we observe that this drug both alkalinizes the endoplasm and promotes an intracellular Ca2+ surge. This dual effect may explain why Ruditapes oocytes no longer stop in metaphase under these conditions and behave like other bivalve species which are directly fertilizable at the germinal vesicle stage.

4-Aminopyridine↗
PubMed1995

Thimerosal triggers meiosis reinitiation in oocytes of the Japanese clam Ruditapes philippinarum by eliciting an intracellular Ca2+ surge.

Ovarian oocytes of the bivalve mollusc Ruditapes philippinarum are arrested during first meiotic prophase. Release from this blockade is triggered by the neurohormone serotonin (5HT or 5-hydroxytryptamine), which promotes germinal vesicle breakdown and drives these oocytes to a second arrest in metaphase I. 5HT action involves binding to a specific G protein-coupled receptor which results in a transient rise in IP3 and in the intracellular free Ca2+ concentration. Here we analyze the cytological effects and mode of action of the sulphydryl reagent thimerosal which could also trigger meiosis reinitiation in Ruditapes. No metaphase I spindle formed under these conditions since thimerosal was found to be able to preclude or reverse tubulin polymerization when applied to prophase- or to metaphase-arrested oocytes, respectively. Our results strongly suggest that the common final target for 5HT and thimerosal actions consists in a transient rise in internal free Ca2+ level that we could follow using Fluo3/AM as a probe. The effect of thimerosal in promoting oocyte maturation and increasing intracellular free Ca2+ concentration was improved by excess KCI. In addition, thimerosal, but not KCI, was found to facilitate 5HT-induced maturation at subthreshold hormone concentrations which, by themselves, did not produce an intracellular Ca2+ surge. These data suggest that thimerosal may inhibit Ca2+ pumps of the endoplasmic reticulum and unmask the plasma membrane voltage-sensitive Ca2+ channels which also appear after 5HT-induced GVBD.

Aniline Compounds↗
PubMed1994

Expression of proliferating cell nuclear antigen in the mouse germ line and surrounding somatic cells suggests both proliferation-dependent and -independent modes of function.

The distribution of proliferating cell nuclear antigen (PCNA) in specific somatic and germ cells of the adult mouse ovary and testis was assessed using immunocytochemical staining and immunoblot analysis and was correlated with cellular proliferation and differentiation. In the adult ovary, immunocytochemical staining for PCNA within follicular cells varied depending on the stage of follicular growth. Since PCNA staining has proven to be a useful indicator of cells involved in DNA synthesis and repair, the pattern of PCNA staining in the ovary was compared to previous studies which used tritiated thymidine labeling as a marker for DNA synthesis. In the testis, PCNA was detected in the mitotically proliferating spermatogonia, but not in spermatocytes which had just entered meiosis. PCNA staining was again observed in spermatogenic cells in later stages of meiotic prophase, in particular zygotene and pachytene spermatocytes. As these cells are undergoing meiotic recombination, the presence of PCNA in these meiotic prophase cells could reflect a second function of PCNA, that of DNA excision repair.

Animals↗
PubMed1994

cdc2 kinase sets a memory phosphorylation signal on elongation factor EF-1 delta during meiotic cell division, which perdures in early development.

EF-1 delta is a physiological substrate for cdc2 protein kinase in Xenopus oocytes. The protein is part of the nucleotide exchange factor EF-1 beta gamma delta, involved in the elongation step of protein synthesis. We show that EF-1 delta exists under four isoforms in the prophase oocyte, all phosphorylable by casein kinase II. Each of the prophase isoforms was further separated into a 36 and a 38 kDa form upon phosphorylation by cdc2 kinase which therefore reveals the existence of eight different isoforms. Phosphorylation by cdc2 kinase can be monitored as the electrophoretic mobility dedoublement 36/38 kDa. Developmental regulation of EF-1 delta was analyzed. The cdc2 kinase-induced change occures at meiotic division, after complete oogenesis and perdures during early development. It is therefore a phosphorylation memory signal for early development.

Animals↗
PubMed1995

Calcium-cell cycle regulator, differentiator, killer, chemopreventor, and maybe, tumor promoter.

Ca2+ and Ca(2+)-binding proteins are involved in running the cell cycle. Ca2+ spikes and signals from integrin-activated focal adhesion complexes and Ca2+ receptors on the cell surface along with cyclic AMP begin the cycle of cyclin-dependent protein kinases (PKs). These transiently expressed PKs stimulate the coordinate expression of DNA-replicating enzymes, activate replication enzymes, inactivate replication suppressors (e.g., retinoblastoma susceptibility protein), activate the replicator complexes at the end of the G1 build-up, and when replication is complete they and a Ca2+ spike trigger mitotic prophase. Another Ca2+ surge at the end of metaphase triggers the destruction of the prophase-stimulating PKs and starts anaphase. Ca2+ finally stimulates cytoplasmic division (cytokinesis). However, Ca2+ does more than this in epithelial cells, such as those lining the colon, and skin keratinocytes. These cells also need Ca2+, integrin signals, and only a small amount (e.g., 0.05-0.1 mM) of external Ca2+ to start DNA replication. Signals from their surface Ca2+ receptors trigger a combination of differentiation and apoptosis ("diffpoptosis") when external Ca2+ concentration reaches their setpoints. The skin's steep, upwardly directed, Ca2+ gradient has a low concentration in the basal layer to allow stem and precursor keratinocytes to proliferate, and higher concentrations in the suprabasal layers to trigger the differentiation-apoptosis ("diffpoptosis") mechanism that converts granular cells into protective, hard-shelled, dead corneocytes. A similar Ca2+ gradient may exist in the colon crypt allowing the stem cell and its amplifying transit or precursor offspring to cycle in the lower parts of the crypt, while stopping proliferation and stimulating terminal differentiation in the upper crypt and flat mucosa. Raising the amount of Ca2+ in fecal water above a critical level reduces proliferation and thus colorectal carcinogenesis in normal rats and some high-risk humans. But during carcinogenesis the Ca2+ sensors malfunction or their signals become ineffective: high Ca2+ does not stop, and may even stimulate, the proliferation of initiated mutants. Therefore, Ca2+ may either not affect, or even promote, the growth of epithelial cells in carcinogen-initiated rat colon and human adenoma patients. Clearly, a much greater understanding of how Ca2+ controls the proliferation and differentiation of epithelial cells and why initiated cells lose their responsiveness to Ca2+ are needed to assess the drawbacks and advantages of using Ca2+ as a chemopreventor.

Animals↗