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PubMed1987

Effect of inhibition of the catalytic activity of cyclic AMP-dependent protein kinase on mitosis in PtK1 cells.

Evidence has suggested that cyclic AMP, acting through activation of the type II cyclic AMP-dependent protein kinase, may play a role in the regulation of interphase and mitotic microtubules. In order to examine the potential role of the type II cAMP-dependent kinase during mitosis, dividing PtK1 cells were microinjected with two specific inhibitors of the catalytic activity of the type II kinase. These inhibitors were a specific protein inhibitor of cAMP-dependent protein kinase (PKI) and an affinity-purified polyclonal antiserum (anti-C) directed against the catalytic subunit of the kinase. Both have been shown previously to inhibit kinase activity in vitro. Microinjection of PKI during early- to mid-prophase significantly delayed the progression of the cells through mitosis, with the greatest delay occurring in metaphase. PKI injected during prometaphase also delayed progression through mitosis but to a lesser extent. Microinjection of anti-C during early- to mid-prophase also caused a significant delay in the completion of mitosis, with many cells becoming "hung up" in prometaphase. Anti-C injected during prometaphase had little effect on subsequent progression through mitosis. Microinjection of either anti-C or PKI during metaphase had no discernible effect. No effect on anaphase movement of chromosomes was observed with any treatment. These results provide further evidence that cAMP-dependent phosphorylation may be involved in the regulation of mitosis, although whether it acts directly through regulation of mitotic spindle microtubules is unclear.

Animals↗
PubMed1989

Actomyosin organization during cytokinesis: reversible translocation and differential redistribution in Dictyostelium.

Synchronized cultures of Dictyostelium discoideum were used to study organizational changes of the cytoskeleton during mitotic cell division. The agar-overlay technique (Yumura et al.: J. Cell Biol. 99:894-899, 1984) was employed for immunofluorescence localization and video microscopic observation of living mitotic cells. The mitotic phase was defined by changes in chromosome configuration by using a double stain with the fluorescent dye DAPI. This study showed that the actin- and myosin-containing cytoskeleton was reversibly redistributed between the cortical ectoplasm and the endoplasm during prophase and telophase. Both actin and myosin filaments were dissociated from the cell cortex in prophase. Most of the actin and myosin was filamentous and remained in the endoplasm until telophase. Saltatory movements of organelles stopped suddenly, coincident with the breakdown of the cytoplasmic microtubule network. This change in the microtubule system was temporally coupled with the disappearance of actomyosin from the cortex. At the same time, the local vibrating movement of particles almost stopped, suggesting that the viscoelastic nature of the endoplasm was altered. In the late anaphase, actin and myosin relocalized to the cortical ectoplasm. Early in this phase, myosin filaments were localized specifically at the anticipated cleavage furrow region of the cleavage furrow, whereas actin filaments were redistributed more uniformly in the cell cortex, with an extremely large accumulation in the polar pseudopods. Subsequently the actin formed an orderly parallel array of cables along with myosin filaments in the contractile ring. The spatial segregation of actin and myosin in late anaphase was clearly demonstrated by multipolar cell division of artificially induced giant cells. Actin was relocalized in both the polar and the proximal constricting regions whereas myosin was only localized in the center of each pair of daughter microtubule networks where the cleavage furrow was formed. This study demonstrates that actin and myosin are reorganized by a temporally coordinated but spatially different mechanism during cytokinesis of Dictyostelium.

Actins↗
PubMed1995

Antibody against phosphorylated proteins (MPM-2) recognizes mitotic microtubules in endosperm cells of higher plant Haemanthus.

In diverse cell types, monoclonal antibody MPM-2 recognizes a class of phosphorylated proteins related to microtubule organizing centers and abundant during mitosis. We have used this antibody in an attempt to identify the spatial and temporal localization of putative microtubule organizing centers in endosperm cells of the higher plant Haemanthus. Our results show that MPM-2 recognized epitope is present in interphase cells and enriched in mitotic cells. In interphase the antibody usually stains cytoplasmic granules. During the interphase-prophase transition immunoreactive material appears in the nucleus, at the nuclear envelope, and in association with microtubules. Concomitantly, we observed an increase of immunoreactivity of the cytoplasm. During mitosis the phosphorproteins recognized by MPM-2 are detected in the cytoplasm, in association with microtubules of the spindle, the phragmoplast, and in the newly-formed cell plate. After completion of mitosis, only the cell plate and cytoplasmic granules are MPM-2 positive. Extraction of the cells with Triton X-100 prior to fixation removes staining of the cytoplasm by MPM-2. The detergent resistant immunoreactive material remains associated with surrounding the nucleus microtubules of the prophase spindle, the core of kinetochore fibers, and the phragmoplast. In the phragmoplast, however, segments of microtubules which are distal to the cell plate are depleted of MPM-2. These data demonstrate that microtubule arrays of endosperm cells are phosphorylated during mitosis. Thus, similar to animal cells, interphase and mitotic microtubules of higher plants have different properties. Additionally, the localization of detergent resistant MPM-2 antigen points to the difference in microtubule nucleation/organization between higher plant and animal cells.

Antibodies, Monoclonal↗
PubMedDate not supplied

Electron microscopic and time lapse studies of mitosis in cultured rat hepatocytes.

Primary cultures of adult rat hepatocytes in a serum-free medium were observed by time lapse cinematography to proceed through mitotis and cytokinesis. An ultrastructural study of these cultures is presented with electron micrographs of each stage of mitosis and cytokinesis. The cultured hepatocytes begin to enter prophase about 48 hr after plating and proceed through mitosis in approximately 70 min not including cytokinesis. During this time, they remain somewhat flattened and joined to neighboring cells rather than rounding up. Both mononucleate and binucleate hepatocytes proceed through mitosis. Some mononucleate cells do not undergo cytokinesis, resulting in the formation of binucleate cells. In binucleate hepatocytes, both nuclei proceed through prophase simultaneously. Usually a single mitotic spindle with a large metaphase plate containing chromosomes from both nuclei is observed. Cytokinesis frequently occurs in binucleate hepatocytes which have a single mitotic spindle. Some binucleate cells form tripolar or 4-polar metaphase plates. In tripolar metaphases, some cells do not divide, resulting in multinucleate cells, whereas others undergo cytokinesis yielding three mononucleate cells or one binucleate and one mononucleate cell. Two mitotic spindles located perpendicularly to each other with microtubules intertwining have been observed in 4-polar metaphases. In this latter case, no cytokinesis has been observed. This study shows that both mononucleate and binucleate adult rat hepatocytes cultured in a serum-free medium in the presence of epidermal growth factor not only synthesize DNA, but progress through mitosis and often cytokinesis.

Animals↗
PubMed2005

The first missense alteration in the MCPH1 gene causes autosomal recessive microcephaly with an extremely mild cellular and clinical phenotype.

Autosomal recessive primary microcephaly (MCPH) is a rare neurodevelopmental disorder characterized by mental retardation and congenital microcephaly with a head circumference at least 4 SD below age and sex means, in the absence of other significant malformations or neurological deficits. Truncating alterations in the MCPH1 gene have previously been shown to exhibit a distinct cellular phenotype, with a high proportion of prophase-like cells (>10%) due to premature chromosome condensation in early G2- and delayed decondensation in early G1-phase of the cell cycle. We report here the first patient with a homozygous substitution of a highly conserved threonine residue by an arginine (c.80C>G, Thr27Arg) localized in the N-terminal BRCT domain of MCPH1. The cellular and clinical phenotype of this patient is much less pronounced than that of previously described patients with truncating alterations in the MCPH1 gene. Firstly, the fraction of prophase-like cells accounts for just 3-4% of the cell population. Secondly, clinically, he has only a very mild mental retardation with predominantly delayed motor skills but normal verbal IQ attainment. Additionally, head circumference was less severely affected, being -2.4 SD at birth and -3 SD at the age of six years. This justifies reconsideration and widening of the clinical phenotype definition of MCPH1.

Amino Acid Sequence↗
PubMed2006

Morphodynamics of ovarian follicles during oogenesis in mice.

In the mouse, oogonia enter the prophase of the first meiotic division and differentiate into oocyte while developing in the fetal ovary. Shortly after birth, all oocytes are arrested in the dictyate stage of late prophase in the developing follicles; a small number of follicles reach the ovulatory stage; the rest are lost by apoptosis. The resumption of meiotic division and nuclear progression to metaphase II (oocyte maturation) occur in the ovulatory follicles. In this article we review recent morphological data that have clarified how cytokines and glycosaminoglycans (GAGs) are involved in mouse follicular development, atresia, and maturation during oogenesis, as exogenous/endogenous factors. (1) Microvascular networks and angiogenic factors (epidermal growth factor; GAGs) are deeply involved in selective mouse oocyte growth beyond approximately 20-30 microm in diameter. (2) Gonadotropin-inducible neuronal apoptosis inhibitory protein may indirectly affect oocyte survival as a result of the inhibition of apoptotic granulosa-cell death during folliculogenesis. (3) The pattern of oocyte degeneration depends on follicle and oocyte developmental stages, and follicle stimulating hormone accelerates the process of degeneration of oocytes. (4) The process of degeneration of mouse oocytes/eggs is modulated by tumor necrosis factor-alpha that is accumulated in the expanded cumulus during oocyte maturation. (5) A colloidal iron-positive substance was detected in the intercellular spaces of follicular tissue, especially in the cumulus mass. Cells located where the cumulus mass and granulosa cell layer interwound became enlarged during the resumption of oocyte meiosis. Colloidal iron-positive substances accumulated extensively within the intercellular spaces of the enlarged cells.

Animals↗
PubMed2001

Maturation and fertilization in Lottia gigantea oocytes: intracellular pH, Ca(2+), and electrophysiology.

Intracellular pH and Ca(2+) were measured with BCECF- and Calcium Green-dextran during maturation and fertilization of oocytes of the limpet Lottia gigantea. Maturation of oocytes from prophase to metaphase I of meiosis was induced in seawater adjusted to pH 9 with NH(4)OH. Intracellular pH rose during maturation induction, and maturation was also induced by microinjecting pH 8, but not pH 7, HEPES buffer. Intracellular Ca(2+) rose during NH(4)OH-induced maturation, but maturation was not inhibited when the increase was blocked by microinjection of BAPTA. When the metaphase I oocytes were fertilized(), there was an abrupt increase in intracellular Ca(2+), and activation (polar body formation) failed to occur in BAPTA-injected oocytes. Intracellular pH did not rise during fertilization. These observations show that maturation from prophase to metaphase I of meiosis is pH-dependent and activation of the metaphase I oocytes is Ca(2+)-dependent. A Ca(2+) action potential was present in both immature and mature oocytes but was more prominent in mature oocytes whose input resistance was higher. Fertilization produced a long-lasting (17-20 min) Na(+)-dependent fertilization potential with superimposed oscillations resembling Ca(2+) action potentials.

Action Potentials↗
PubMed1987

Effect of ouabain on the meiotic maturation of stage IV-V Xenopus laevis oocytes.

Full-grown stage VI Xenopus laevis oocytes (1,200 to 1,300 micron) respond to progesterone stimulation by undergoing a series of physiological and morphological changes that are referred to as meiotic maturation. Oocytes in earlier stages of oogenesis (I through V) do not undergo these changes and remain in prophase arrest when exposed to this steroid. We have found that oocytes ranging from 850 micron (stage IV) to 1,000 micron (stage V) are capable of responding to progesterone under the appropriate conditions. Oocytes greater than or equal to 850 micron in diameter underwent germinal vesicle breakdown (GVBD) after 10-12 hr of exposure to progesterone when ouabain was added to the medium at a concentration greater than 2.5 X 10(-6) M. Under this culture condition, progesterone was now able to induce a 0.3- to 0.4-unit increase in the intracellular pH of stage IV-V oocytes, a 4- to 5-fold increase in 40s ribosomal protein S-6 phosphorylation, and a 2.3-fold increase in their rate of protein synthesis. All of these physiological changes are characteristic of full-grown stage VI oocytes undergoing meiotic maturation. In addition, we have found that oocytes greater than or equal to 750 micron are capable of amplifying maturation promoting factor (MPF) in their cytoplasm leading to GVBD. Therefore, stage IV-V Xenopus oocytes have the potential for undergoing meiotic maturation, but they are blocked at a point in prophase that appears to be alleviated by the combination of progesterone and ouabain.

Animals↗
PubMed2005

Calcium currents correlate with oocyte maturation during the reproductive cycle in Octopus vulgaris.

Using the whole-cell voltage clamp technique, we have studied the Ca2+ currents and the steady-state conductance during different oocyte growth stages and during the reproductive cycle of the female of Octopus vulgaris. Evidence is presented that L-type Ca2+ currents are high in small pre-vitellogenic oocytes (80-150 microm diameter) and significantly lower in early vitellogenic oocytes (180-300 microm diameter). Similarly, a significant decrease of the steady-state conductance occurred from the pre to early- vitellogenic oocytes. Octopus oocytes showed larger Ca2+ currents in the reproductive rather than non-reproductive periods. These data indicates that ion and L-type Ca2+ currents play a role in oocyte growth and cytoplasmic maturation, and possibly in preparing the plasma membrane to the interaction with the spermatozoon. By using fluorescent microscopy, we show that oocytes from 80 to 400 microm diameter have the large germinal vesicle characteristic of the immature oocytes. In subsequent stages of growth (up to 1000 microm diameter) the nucleus is no more visible and the metaphase spindle appears. These data demonstrate that Octopus vulgaris oocytes are arrested in the first meiotic prophase up to the early-vitellogenic stage and resume meiosis at this stage up to a second block presumably in metaphase I. We discuss a possible role for progesterone as the hormonal stimulus for the first prophase-metaphase meiotic transition.

Animals↗
PubMed1988

A quantitative analysis of mitochondria during fetal mouse oogenesis.

A quantitative analysis of mitochondrial populations during the meiotic prophase of mouse oogenesis was carried out. The mean absolute area occupied by mitochondria and the mean number of mitochondria per cell increases in a linear fashion from pachytene through dictyate. The mean area occupied by mitochondria increases at pachytene and thereafter. Both small and large aggregations of mitochondria are seen, particularly during the later stages of prophase. Vacuolated mitochondria are present from preleptotene through pachytene. Mitochondria show major dynamic changes throughout fetal mouse oogenesis, which may suggest significant functional activities yet to be elucidated.

Animals↗
PubMed2002

Pyruvate utilization by mouse oocytes is influenced by meiotic status and the cumulus oophorus.

In this study, the effects of meiotic status on the energy substrate dynamics of mouse oocyte-cumulus cell complexes (OCCs) and denuded oocytes (DOs) have been examined. In the first series of experiments, OCCs from PMSG-primed, immature mice were cultured in minimum essential medium in 8-microl microdrops under a variety of conditions, and the medium and oocytes were sampled for pyruvate and glucose concentration and for meiotic status. Oocytes in control medium underwent germinal vesicle breakdown within 3 hr and the OCCs displayed a time-dependent increase in pyruvate consumption, but the glucose concentration changed very little. Treatment with IBMX or dbcAMP, which maintained complete meiotic arrest, suppressed pyruvate consumption, but slightly more glucose was consumed than in controls. Hypoxanthine (HX) allowed up to 10% of the oocytes to resume maturation, and pyruvate and glucose consumption resembled that of control OCCs. FSH added to HX-containing medium stimulated significant glucose consumption and pyruvate production. In general, a reciprocal relationship was observed between glucose and pyruvate consumption. When the energy substrate dynamics were compared with meiotic status of the oocytes, pyruvate consumption was associated with the maturation process. Although HX maintained oocytes in the germinal vesicle stage, the meiotic arrest was "leaky," allowing increased pyruvate consumption. Additional experiments showed that DOs at either the prophase I or metaphase II stages consumed less pyruvate than oocytes actively engaged in meiotic maturation. DOs oxidized significantly more pyruvate than OCCs, and glycolytic metabolism of glucose lowered the oxidation rate in OCCs. Furthermore, while 5-6.2 times more pyruvate was consumed by OCCs than by DOs in the absence of glucose, oxidation did not mediate the meiosis-inducing effect of pyruvate, since less of this substrate was oxidized by OCCs than by DOs. We conclude that meiotically active oocytes have a greater requirement for pyruvate than prophase I- or metaphase II-arrested oocytes and that meiotic status can influence the metabolism not only of oocytes, but also of the OCCs.

1-Methyl-3-isobutylxanthine↗
PubMed2002

Ultrastructure of oocyte maturation, fertilization, and early embryo development in vitro in the Siberian tiger (Panthera tigris altaica).

The application of assisted reproduction techniques to wild cats has been stalled by a lack of basic knowledge of the reproductive biology in these species. In this study, the ultrastructure of Siberian tiger (Panthera tigris altaica) cumulus-oocyte-complexes (COCs), as well as in vitro produced (IVP) zygotes and embryos were investigated, to estimate the normality of the manipulated reproduction processes. Adult female tigers were subjected to a purified porcine pFSH/pLH stimulation treatment followed by oocyte aspiration. According to morphological appearance at the stereomicroscopical level, COCs were classified as mature, immature, or degenerated, and then allocated into the following groups: presumptively immature COCs, which were in vitro matured (IVM-group) before fixation; presumptively mature COCs, which were either fixed after retrieval (pre-IVF-group), following in vitro insemination (IVF-group) or following in vitro insemination and subsequent in vitro culture (IVC-group). All specimens were processed for light and transmission electron microscopy (TEM). Both the IVM- and pre-IVF-group included oocytes in meiotic stages ranging from prophase I to metaphase II, and some prophase I oocytes in the IVM-group were apparently in their growth phase. The IVF-group presented features of presumptive normal fertilization, but aberrations such as polynucleation were also noted. The IVC-group included cleavage stage embryos of which, however, many were polynucleated. In conclusion, the procedures used for stimulation, aspiration, and classification of COCs resulted in retrieval of a heterogeneous population of oocytes which, following IVF and IVC, displayed a high rate of developmental deviations.

Animals↗
PubMed2003

Meiotic state of bovine oocytes is regulated by interactions between cAMP, cumulus, and granulosa.

Bovine oocytes are arrested at the prophase of first meiotic cell cycle. Meiosis resumes in oocytes of pre-ovulatory follicles upon LH surge. However, oocytes from secondary follicles spontaneously resume meiosis in the absence of hormones if removed from the follicle and cultured in vitro. The nature of meiotic arrestor in bovine follicles is poorly understood. In this study we investigated the role of cell-cell interactions between granulosa and cumulus cells and the oocyte in mediating maintenance of meiotic arrest by cAMP. We sorted oocytes as granulosa-cumulus oocyte complexes (GCOC) if surrounded with cumulus cells attached to a large granulosa investment or cumulus oocytes complexes (COC) if surrounded with cumulus cells only and investigated the role cAMP in maintenance of meiotic arrest in these oocytes under various conditions. In hormone- and serum-free medium both GCOC and COC enclosed oocytes resumed meiosis. When [cAMP](i) was elevated with addition of invasive adenylate cyclase (iAC) GCOC enclosed oocytes were maintained in the prophase with intact germinal vesicle (GV) while COC enclosed oocytes underwent GV breakdown (GVBD). iAC elevated [cAMP](i) in both types of oocytes to the same level. If oocytes were liberated from the cumulus and granulosa cells, they re-initiated meiosis in serum and hormone free medium, but remained in the GV stage if iAC was added to the medium. Untreated GCOC and COC enclosed oocytes extruded first polar body at the same frequency in hormone-supplemented media. GCOC and COC enclosed oocytes but not denuded oocytes (DO) cultured without somatic cells acquired developmental competence if cultured in hormone-containing medium. It is concluded that maintenance of meiotic arrest is regulated by the interplay of [cAMP](i), and cumulus and granulosa cells.

Animals↗
PubMed1993

Cellular localization of the mRNAs of the somatic and testis-specific cytochromes c during spermatogenesis in the rat.

During mammalian spermatogenesis, two forms of cytochrome c, cytochromes cs and ct, are present in male germ cells. During meiosis, cytochrome ct begins to replace cytochrome cs. At least four size classes of cytochrome cs mRNA are expressed in all somatic cells and in early stages of male germ cells. In addition, a cytochrome cs transcript of 1.7 kB has been detected in rodent testes and is abundant in post meiotic male germ cells. Here we utilize "in situ" hybridization to define the cellular sites where the four ubiquitous cytochrome cs transcripts, the 1.7 kB cytochrome cs transcripts, and the testis-specific cytochrome ct transcripts are expressed in the rat. Low levels of cytochrome cs mRNAs are detected in Leydig cells, myoepithelial cells, Sertoli cells, all types of spermatogonia, and during meiotic prophase. The 1.7 kB cytochrome cs mRNA is first detected in late stages of meiotic prophase and reaches its highest levels in steps 1 to 9 spermatids. No cytochrome cs mRNAs are detected in spermatids between steps 10 to 19. Low levels of cytochrome ct mRNAs, initially detected in zygotene spermatocytes, reach maximal levels in round spermatids. For all three probes the majority of the silver grains are localized randomly throughout the cytoplasm, suggesting that neither the translating nor non-translating (the 1.7 kB mRNA) forms of cytochrome cs mRNA nor the cytochrome ct mRNAs are sequestered during spermatogenesis. The absence of cytochrome cs or ct mRNAs in steps 10-19 spermatids suggest that the cytochrome ct protein does not turn over rapidly in late stage male germ cells.

Animals↗
PubMed2005

XY chromosomal bivalent: nucleolar attraction.

Nucleolar organization by autosomal bivalents occurs during male meiotic prophase in mammalian species. During late leptotene-early zygotene stages, several autosomal bivalents are engaged in ribosomal RNA synthesis. At pachytene stage, nucleolar masses detach from the sites of primary autosomal origin, relocate close to the XY chromosomal pair, and nucleolar components become segregated. In early pachytene, an extensive synaptonemal complex at the pseudoautosomal region, links X and Y chromosomes in close juxtaposition along most of the length of the Y chromosome, except for a terminal region of the Y that diverges from the pairing region. As meiotic prophase advances, X and Y chromosomes progressively desynapse and, at diplotene, the XY pair is associated end-to-end. Xmr (Xlr-related, meiosis regulated) is a protein component of the nucleolus associated to the XY pair and of the asynapsed portions of the X and Y axial cores. Xmr, like SCP3, is a component of the lateral element of the synaptonemal complex. Both share structural homology in their C-terminal region. This region contains several putative coiled-coil domains known to mediate heterodimeric protein-protein interactions and to provide binding sites to regulatory proteins. Like Xmr, the tumor repressor protein BRCA1 is present along the unsynapsed cores of the XY bivalent. Both Xmr and BRCA1 have been implicated in a mechanism leading to chromatin condensation and transcription inactivation of the XY bivalent. The BRCA1-ATR kinase complex, as recent research suggests, triggers the phosphorylation of histone H2AX, which predominates in the condensed chromatin of the XY chromosomal pair. Xmr is not present in the XY bivalent when the expression of histone H2AX is deficient. The role of Xmr in chromatin condensation of the XY bivalent has not been determined. The partial structural homology of SCP3 and Xmr, their distribution along the unsynapsed axial cores of the X and Y chromosomes, and the presence of Xmr in the XY pair-associated nucleolus raises the possibility that Xmr, and other proteins including protein kinases, may be recruited to the nucleolus to perform functions related to chromosomal synapsis, chromatin condensation and recombination processes, as well as cell cycle progression.

Animals↗
PubMed2006

Spermatocyte responses in vitro to induced DNA damage.

Spermatocytes normally sustain many meiotically induced double-strand DNA breaks (DSBs) early in meiotic prophase; in autosomal chromatin, these are repaired by initiation of meiotic homologous-recombination processes. Little is known about how spermatocytes respond to environmentally induced DNA damage after recombination-related DSBs have been repaired. The experiments described here tested the hypothesis that, even though actively completing meiotic recombination, pachytene spermatocytes cultured in the absence of testicular somatic cells initiate appropriate chromatin remodeling and cell-cycle responses to environmentally induced DNA damage. Two DNA-damaging agents were employed for in vitro treatment of pachytene spermatocytes: gamma-irradiation and etoposide, a topoisomerase II (TOP2) inhibitor that results in persistent unligated DSBs. Chromatin modifications associated with DSBs were monitored after exposure by labeling surface-spread chromatin with antibodies against RAD51 (which recognizes DSBs) and the phosphorylated variant of histone H2AFX (herein designated by its commonly used symbol, H2AX), gammaH2AX (which modifies chromatin associated with DSBs). Both gammaH2AX and RAD51 were rapidly recruited to irradiation- or etoposide-damaged chromatin. These chromatin modifications imply that spermatocytes recruit active DNA damage responses, even after recombination is substantially completed. Furthermore, irradiation-induced DNA damage inhibited okadaic acid-induced progression of spermatocytes from meiotic prophase to metaphase I (MI), implying efficacy of DNA damage checkpoint mechanisms. Apoptotic responses of spermatocytes with DNA damage differed, with an increase in frequency of early apoptotic spermatocytes after etoposide treatment, but not following irradiation. Taken together, these results demonstrate modification of pachytene spermatocyte chromatin and inhibition of meiotic progress after DNA damage by mechanisms that may ensure gametic genetic integrity.

Animals↗
PubMed2006

Homologous chromosome pairing in Schizosaccharomyces pombe.

Homologous chromosome pairing is a central feature of meiosis I, contributing to the correct segregation of chromosomes during meiosis. The fission yeast, Schizosaccharomyces pombe, has been widely used to study meiotic chromosome dynamics, partly because studies in this yeast are simplified due to the lack of post-pairing synaptic structures. Chromosome pairing in Sz. pombe occurs differentially throughout the genome. Telomeres cluster at the spindle pole body (SPB) at the onset of meiosis, imposing a spatial restriction on pairing events. Subsequently, centromeres dissociate from the SPB and pair in a recombination- and heterochromatin (Swi6)-independent fashion. Pairing of telomere distal regions occurs during meiotic prophase, concomitant with a dynamic association/dissociation of homologous regions, with interhomologue associations becoming increasingly stable. The stabilization of paired regions is enhanced by factors required for the initiation of meiotic recombination, suggesting that recombination stabilizes paired regions. However, substantial pairing is initiated in the absence of recombination; this is dependent upon another factor, the conserved Meu13 protein, demonstrating that recombination is not required for initial pairing interactions. During meiotic prophase Sz. pombe exhibits a pronounced dynein-dependent nuclear oscillation, which drives the pairing of centromeric and interstitial regions. Dynein is also required for the significant levels of achiasmate reductional segregation observed in Sz. pombe, possibly implicating the centromere-associated pairing with achiasmate homologue segregation. Whilst Sz. pombe does not form discernable synaptic structures continuously along the meiotic chromosomes, it does form proteinacious, meiosis-specific, linear structures (linear elements). However, the role, if any, of these structures in mediating homologue pairing is unknown.

Cell Cycle Proteins↗
PubMed1993

Localization of MPM-2 recognized phosphoproteins and tubulin during cell cycle progression in synchronized Vicia faba root meristem cells.

MPM-2 antibody reacts with a subset of mitotic phosphoproteins. We followed localization of MPM-2 immunoreactive material and localization of microtubules during cell cycle progression in a highly synchronous population of Vicia faba root meristem cells and isolated nuclei. The MPM-2 antibody labelling showed significant cell cycle dependence. MPM-2 nuclear reactivity was weak and homogeneous in G1 and S phase of the cell cycle and became stronger and heterogeneous during G2, resembling staining of the nuclear matrix, with maximum staining at the G2/M interface. Similarly the staining intensity of nucleoli increased from late G1 phase to nucleoli dispersion in early prophase. During mitosis MPM-2 immunoreactivity was associated with spindle configurations and the brightest signal was localized in kinetochores from prophase to metaphase.

Antibodies, Monoclonal↗