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At least 793 records · Page 44Linked to original sources
PubMed1994

The spindle apparatus in early embryonic divisions of Ephestia kuehniella Z. (Pyralidae, Lepidoptera) is formed by alignment of minispindles.

Spindles were isolated from deposited eggs of the Mediterranean mealmoth, Ephestia kuehniella. Their structure and development were studied using anti-tubulin immunofluorescence. The microtubules were labelled with three different monoclonal antibodies. These were directed against beta-tubulin, tyrosinated alpha-tubulin and acetylated alpha-tubulin. Significant differences in the staining behaviour were not detected with the three antibodies. An unusual mode of spindle formation was observed during the first mitotic division after fusion of the pronuclei. Several of the ensuing embryonic divisions may show the same phenomenon. Prophase of these divisions was characterised by an irregular arrangement of microtubules in the nuclear area. The microtubular mass in the nuclear area increased concomitantly with chromosome condensation. Microtubular foci, comparable to the forming asters of canonical spindles, were not detected. The formation of an orderly pattern in the microtubule mass was signalled by the appearance of minispindles apparently developing around individual chromosomes. Several minispindles subsequently aligned and formed metaphase-like entities within the nuclear area. The metaphase-like entities, in turn, aligned with one another and gave rise to a conventional bipolar metaphase spindle with small asters. The further development of the spindle was conventional. The chromosomes migrated towards the spindle poles and finally daughter nuclei formed. The anaphase and telophase spindles possessed both a prominent array of interzone microtubules and asters. The events in prophase of early embryonic mitosis of E. kuehniella may represent a rare case of chromosome-induced spindle formation.

Animals↗
PubMed1997

Sperm nuclear envelope: breakdown of intrinsic envelope and de novo formation in hamster oocytes or eggs.

During fertilisation of a fully mature oocyte, the sperm intrinsic nuclear envelope (SINE) disappears soon after sperm-oocyte fusion. A new nuclear envelope appears around the decondensed sperm chromatin when the oocyte reaches telophase II. Whether the SINE persists or rapidly disappears after sperm entry into immature oocytes or fertilised eggs has been controversial. Nuclear envelopes have been demonstrated around the sperm chromatin, which cannot be decondensed within the ooplasm of these oocytes or eggs, but whether these envelopes are persisting SINEs or newly formed envelopes has been a point of dispute. To resolve this issue, the fate of the SINEs of hamster sperm nuclei was traced after incorporation into immature oocytes at the germinal vesicle stage (GV oocytes) or fertilised eggs at the pronuclear stage (PN eggs). The SINEs disappeared quickly within these oocytes or eggs, like those within maturing or mature oocytes, suggesting that the envelopes around the sperm chromatin must be newly formed after SINE breakdown. To obtain further evidence, a detergent-treated, SINE-free sperm nucleus was injected into a PN egg. A new envelope appeared around the still-condensed or partially decondensed sperm chromatin within 3 h after injection. Thus, disassembly of the SINE within ooplasm, unlike that of nuclear envelopes of other cells at prophase, is independent of the cell cycle stage of the oocyte or egg, whereas the ability of the ooplasm to assemble the new envelope is restricted to certain periods of the cycle, i.e. early prophase and telophase during meiosis and interphase, periods when active M-phase promoting factor (MPF) is absent from the ooplasm.

Animals↗
PubMed2002

Banding techniques on tardigrade chromosomes: the karyotype of Macrobiotus richtersi (Eutardigrada, Macrobiotidae).

This work represents the first attempt to define tardigrade chromosomes using banding techniques. Macrobiotus richtersi, a eutardigrade morphospecies with amphimictic diploid and thelytokous triploid cytotypes, was used as a model. Prime consideration was given to oocyte chromosomes because they are larger than those of spermatocytes and of mitotic chromosomes. With Giemsa staining, the chromatids of the 6 bivalents of the diploid cytotypes and those of the 17-18 univalents of the triploid cytotypes were very similar to each other and appeared rod- or flame-shaped. In the amphimictic strain, a chiasma was generally present in each bivalent at diplotene, whereas there were no chiasmata in the oocyte prophase chromosomes of the triploid strain. Both in diploid and triploid cytotypes, C-banding and fluorescence showed a heterochromatic centromeric band on the telomere of each chromosome oriented towards the spindle pole, indicating that all of them were acrocentric. Silver staining showed the presence of a NOR in only a pair of chromosomes, close to the centromeric C-banded site. NOR was particularly evident in the oocyte prophases. Other silver positive regions, corresponding to the kinetochore, were located on all other chromosomes on the telomeres towards the spindle pole.

Animals↗
PubMed2003

Dynamics of the apical plasma membrane recycling system during cell division.

The members of the family of Rab11 small GTPases are critical regulators of the plasma membrane vesicle recycling system. While previous studies have determined that the Golgi apparatus disperses during mitosis and reorganizes after cytokinesis, the fate of the recycling system during the cell cycle is more obscure. We have now studied in MDCK cells the fate during mitosis of an apical recycling system cargo, the polymeric IgA receptor (pIgAR), and regulators of the recycling system, Rab11a and its interacting proteins myosin Vb, Rab11-FIP1, Rab11-FIP2 and pp75/Rip11. Rab11a, pIgAR and myosin Vb containing vesicles dispersed into diffuse puncta in the cytosol during prophase and then became clustered near the spindle poles after metaphase, increasing in intensity throughout telophase. A similar pattern was observed for Rab11-FIP1 and Rab11-FIP2. However, Rab11-FIP1 lost colocalization with other recycling system markers during late prophase, relocating to the pericentriolar material. During telophase, Rab11-FIP1 returned to recycling system vesicles. Western blot analysis indicated that both Rab11a and pIgAR remained associated with membrane vesicles throughout the cell cycle. This behavior of the Rab11a-containing apical recycling endosome system during division was distinct from that of the Golgi apparatus. These results indicate that critical components of the apical recycling system remain associated on vesicles throughout the cell cycle and may provide a means for rapid re-establishment of plasma membrane components after mitosis.

Animals↗
PubMed1989

Focal points for chromosome condensation and decondensation revealed by three-dimensional in vivo time-lapse microscopy.

Although the dynamic behaviour of chromosomes has been extensively studied in their condensed state during mitosis, chromosome behaviour during the transition to and from interphase has not been well documented. Previous electron microscopic studies suggest that chromosomes condense in a non-uniform fashion at the nuclear periphery. But chromosome condensation is a complicated and dynamic process and requires continuous observation in living tissues to be fully understood. Using a recently developed three-dimensional time-lapse fluorescence microscopy technique, we have observed chromosomes as they relax from telophase, through interphase, until their condensation at the next prophase. This technique has been improved to produce higher-resolution images by implementing new stereographic projection and computational processing protocols. These studies have revealed that chromosomal regions on the nuclear envelope, distinct from the centromeres and telomeres, serve as foci for the decondensation and condensation of diploid chromosomes. The relative positions of the late decondensation sites at the beginning of interphase appear to correspond to the early condensation sites at the subsequent prophase.

Animals↗
PubMed1999

Cell cycle perturbations and apoptosis induced by isohomohalichondrin B (IHB), a natural marine compound.

Isohomohalichondrin B (IHB), a novel marine compound with anti-tumoral activity, extracted from the Lissodendorix sponge, inhibits GTP binding to tubulin, preventing microtubule assembly. Cell cycle perturbations and apoptosis induced by IHB were investigated on selected human cancer cell lines by using flow cytometric and biochemical techniques. Monoparameter flow cytometric analysis showed that 1 h IHB exposure caused a delayed progression through S-phase, a dramatic block in G2M phase of the cell cycle and the appearance of tetraploid cell population in LoVo, LoVo/DX, MOLT-4 and K562 cells. At 24 h after IHB exposure, the majority of cells blocked in G2M were in prophase as assessed by morphological analysis and by the fact that they expressed high levels of cyclin A/cdc2 and cyclin B1/cdc2. At 48 h, all cells were tetraploid as assessed by biparameter cyclin A/DNA and cyclin B1/DNA content analysis. Apoptotic death was detected in both leukaemic MOLT-4 and K562 cells, which express wild-type and mutated p53 respectively, when the cells were blocked in mitotic prophase. In conclusion, IHB is a novel potent anti-tumour drug that causes delayed S-phase progression, mitotic block, tetraploidy and apoptosis in cancer cell lines.

Antineoplastic Agents↗
PubMed1999

Bcl-2 and Bax regulation of apoptosis in germ cells during prenatal oogenesis in the mouse embryo.

Apoptosis is the main cause of primordial germ cell and oocyte degeneration in the developing fetal ovary. In this study we examined by immunohistochemistry and immunoblotting the expression of the anti- and pro-apoptotic proteins Bcl-2 and Bax in primordial germ cells and fetal oocytes during pre natal oogenesis in the mouse embryo. While Bcl-2 and Bax were not detectable in primordial germ cells in vivo, both proteins were upregulated when they undergo apoptosis in culture. Treatment with the stem cell factor (SCF), a growth factor known to partially reduce primordial germ cell apoptosis, resulted in decreased Bax expression. Bcl-2 was barely detectable in oocytes entering into meiosis and its expression did not change during the stage of meiotic prophase I examined. On the contrary, high levels of Bax was expressed in degenerating oocytes while low levels of the protein was present in many apparently healthy oocytes between 15.5 days post coitum (d.p.c.) and birth, when Bax was downregulated. Oocytes isolated from 15.5 days post coitum (d.p.c.) ovaries that progress through prophase I and undergo a wave of apoptosis at the stage of pachytene/diplotene in vitro, showed a pattern of Bax expression similar to the in vivo condition. Although the addition of SCF to the culture medium reduced significantly apoptosis in oocytes at the pachytene/diplotene stages, it was not possible to directly correlate this effect with the downregulation of Bax in the surviving oocytes. These findings indicate that whereas a balance between Bcl-2 and Bax might regulate apoptosis of proliferating primordial germ cells under a partial control by SCF, Bax-mediated apoptosis in meiotic oocytes may be due to intrinsic meiotic checkpoints which act to monitor aberrant DNA recombination rather than to a growth factor-dependent process. Elimination of supernumerary oocytes might be a subsequent apoptotic phenomenon controlled by the availability of growth factors such as SCF within the ovary.

Animals↗
PubMed2005

Dynamic distribution of Ser-10 phosphorylated histone H3 in cytoplasm of MCF-7 and CHO cells during mitosis.

The dynamic distribution of phosphorylated Histone H3 on Ser10 (phospho-H3) in cells was investigated to determine its function during mitosis. Human breast adenocarcinoma cells MCF-7, and Chinese hamster cells CHO were analyzed by indirect immunofluorescence staining with an antibody against phospho-H3. We found that the phosphorylation begins at early prophase, and spreads throughout the chromosomes at late prophase. At metaphase, most of the phospho-H3 aggregates at the end of the condensed entity of chromosomes at equatorial plate. During anaphase and telophase, the fluorescent signal of phospho-H3 is detached from chromosomes into cytoplasm. At early anaphase, phospho-H3 shows ladder bands between two sets of separated chromosome, and forms "sandwich-like structure" when the chromosomes condensed. With the cleavage progressing, the "ladders" of the histone contract into a bigger bright dot. Then the histone aggregates and some of compacted microtubules in the midbody region are composed into a "bar-like" complex to separate daughter cells. The daughter cells seal their plasma membrane along with the ends of the "bar", inside which locates microtubules and modified histones, to finish the cytokinesis and keep the "bar complex" out of the cells. The specific distribution and kinetics of phospho-H3 in cytoplasm suggest that the modified histones may take part in the formation of midbody and play a crucial role in cytokinesis.

Animals↗
PubMed2006

Double-stranded DNA breaks and gene functions in recombination and meiosis.

Meiotic prophase I is a long and complex phase. Homologous recombination is an important process that occurs between homologous chromosomes during meiotic prophase I. Formation of chiasmata, which hold homologous chromosomes together until the metaphase I to anaphase I transition, is critical for proper chromosome segregation. Recent studies have suggested that the SPO11 proteins have conserved functions in a number of organisms in generating sites of double-stranded DNA breaks (DSBs) that are thought to be the starting points of homologous recombination. Processing of these sites of DSBs requires the function of RecA homologs, such as RAD51, DMC1, and others, as suggested by mutant studies; thus the failure to repair these meiotic DSBs results in abnormal chromosomal alternations, leading to disrupted meiosis. Recent discoveries on the functions of these RecA homologs have improved the understanding of the mechanisms underlying meiotic homologous recombination.

Animals↗
PubMed1999

High copy number suppression of the meiotic arrest caused by a dmc1 mutation: REC114 imposes an early recombination block and RAD54 promotes a DMC1-independent DSB repair pathway.

BACKGROUND: DMC1, the meiosis-specific eukaryotic homologue of bacterial recA, is required for completion of meiotic recombination and cell cycle progression past prophase. In a dmc1 mutant, double strand break recombination intermediates accumulate and cells arrest in prophase. We isolated genes which, when present at high copy numbers, suppress the meiotic arrest phenotype conferred by dmc1 mutations. RESULTS: Among the genes isolated were two which suppress arrest by altering the recombination process. REC114 suppresses formation of double strand break (DSB) recombination intermediates. The low viability of spores produced by dmc1 mutants carrying high copy numbers of REC114 is rescued when reductional segregation is bypassed by mutation of spo13. High copy numbers of RAD54 suppress dmc1 arrest, promote DSB repair, and allow formation of viable spores following reductional segregation. Analysis of the combined effects of a null mutation in RED1, a gene required for meiotic chromosome structure, with null mutations in RAD54 and DMC1 shows that RAD54, while not normally important for repair of DSBs during meiosis, is required for efficient repair of breaks by the intersister recombination pathway that operates in red1 dmc1 double mutants. CONCLUSIONS: Over-expression of REC114 suppresses meiotic arrest by preventing formation of DSBs. High copy numbers of RAD54 activate a DMC1-independent mechanism that promotes repair of DSBs by homology-mediated recombination. The ability of RAD54 to promote DMC1-independent recombination is proposed to involve suppression of a constraint that normally promotes recombination between homologous chromatids rather than sisters.

Cell Cycle Proteins↗
PubMed2000

Inhibition of serine/threonine-specific protein phosphatases causes premature activation of cdc2MsF kinase at G2/M transition and early mitotic microtubule organisation in alfalfa.

Reversible phosphorylation of serine/threonine residues of cell cycle-regulatory proteins is one of the key molecular mechanisms controlling eukaryotic cell division. In plants, the protein kinase partners (i.e. p34cdc2/CDC28-related kinases) have been extensively studied, while the role of counter-acting protein phosphatases is less well understood. We used endothall (ET) as a cell-permeable inhibitor of serine/threonine-specific protein phosphatases to alter cytological and biochemical characteristics of cell division in cultured alfalfa cells. A high concentration of ET (10 and 50 microM) inhibited both protein phosphatases 1 and 2 (PP1 and PP2A), while a low concentration (1 microM) of ET-treatment primarily reduced the PP2A activity. High concentrations of the inhibitor increased the frequency of hypercondensed early and late prophase chromosomes that could not enter metaphase. In contrast, a low concentration of ET did not interfere with chromosomal events but caused significant alterations in the organisation of microtubules. Exposure of cells to 1 microM ET resulted in disturbance of preprophase band formation, increase in the number of nuclei with prophase microtubule assembly, premature polarisation of the spindle, and abnormal phragmoplast maturation. Under the same conditions, the ET-treated cells exhibited an early increase in cdc2MsF kinase activity. These results suggest that PP2A contributes to the control of mitotic kinase activities and microtubule organisation. Normal chromosome condensation and mitotic progression are dependent on both PP1 and PP2A activities. The presented data support the functional role of protein phosphatases in the co-ordination of chromosomal and microtubule events in dividing plant cells.

Chromosomes↗
PubMed2002

Development of the blood-testis barrier in the mouse is delayed by neonatally administered diethylstilbestrol but not by beta-estradiol 3-benzoate.

A group of newborn mice were treated with 1 micro g dose-1 individual-1 of diethylstilbestrol (DES) on alternate days, from days 1 to 11 postnatally. Another group of mice were treated similarly with 125 ng dose-1 individual-1 of beta-estradiol 3-benzoate (E2B). The testes were sequentially examined up to 84 days of age using light and electron microscopy. Spermatogenic cells in the DES-treated mice differentiated normally from birth until 17 days of age, when they differentiated into pachytene spermatocytes and remained at this meiotic prophase for the next 10 days approximately. The cells then began to differentiate further, ultimately forming spermatozoa by 49 days of age. Confocal and electron microscopy showed that the blood-testis barrier did not form until 28 days of age in the DES-treated mice, and a delay in the functional maturation of this structure, as the blood-testis barrier, was confirmed by intercellular tracer experiments. The arrest of spermatogenesis at the meiotic prophase may have been attributable to the DES-induced defective formation of the blood-testis barrier. No delay of the blood-testis barrier formation was detected in the E2B-treated mice. Thus, DES and E2B, both of which are known as potent oestrogenic compounds, had different effects on the Sertoli cells.

Animals↗
PubMed1982

Changes in the number of germ cells in the gonads of the rainbow trout (Salmo gairdneri) during the first 10 post-hatching weeks.

The number of germ cells in fry gonads was determined from histological sections sampled periodically over a 10-week post-hatching period. Several successive types of germ cells were identified: primordial germ cells (PGC), two kinds of gonocytes (G1 and G2) and all the stages of female meiotic prophase. The mean diameters are shown in table 1. The number of germ cells increased regularly from 47 +/- 35 (SD) after hatching (PGC) to 166 +/- 25 at 2 post-hatching weeks (G1). At 5 post-hatching weeks, two groups of fish could be distinguished by the number of their germ cells (G2) - one group had less than 926 cells and the other more than 1 577 - and by their gonadal morphology (Filiform or with an enlarged anterior part due to germ cell concentration). At 6 post-hatching weeks, the ovary differentiated with organization of the ovarian lamellae and the appearance of oocytes in meiotic prophase (4 out of 10 trout). The gonads of the other fish stayed at the indifferent stage. The number of germ cells was significantly higher in female-type gonads (6 335 +/- 3 558) than in indifferent gonads (1 696 +/- 467). The situation was the same at 8 to 10 weeks.

Animals↗
PubMed1994

Spermatogenic cells and stages of the seminiferous epithelial cycle in the Indian gerbil field rat, Tatera indica.

Four types of spermatogonia (A0, A, In, B) are distinguished in T. indica. Four generations of A type, a single generation of intermediate (In) and two generations of B type spermatogonia are identified. Seven divisions of spermatogonia have been observed, in Stages 1b, 2b, 3b, 4b, 5, 6 and 7 respectively. Spermatocytes have been observed in prophase, metaphase, anaphase and telophase; in terms of size and morphology, the phases of prophase could be further divided. Pre-leptotene and leptotene appear in Stage 8 and Stage 1 respectively. Round spermatids become asymmetrical in Stage 1b. For the first time in rodents, Stages 1, 2, 3, 4 and 8 have been subdivided. The percentage frequencies of Stages 1-8 are 12.93, 10.69, 17.54, 10.33, 3.76, 11.20, 7.88 and 25.67 respectively. Although the morphology of the spermatogenic cells and associations of these cell types are basically similar to those in albino rats, T. indica markedly differs from all other rodents studied in having two generations of B spermatogonia and subdivisions of Stages 1, 2, 3, 4 and 8; in addition, the relative frequencies of the stages distinctly differ from those recorded in previous studies of rats. Hence, the durations of different cell types in T. indica may differ markedly from those in other rodents.

Animals↗
PubMed2003

Localization and roles of Ski8p protein in Sordaria meiosis and delineation of three mechanistically distinct steps of meiotic homolog juxtaposition.

Ski8p is implicated in degradation of non-poly(A) and double-stranded RNA, and in meiotic DNA recombination. We have identified the Sordaria macrospora SKI8 gene. Ski8p is cytoplasmically localized in all vegetative and sexual cycle cells, and is nuclear localized, specifically in early-mid-meiotic prophase, in temporal correlation with Spo11p, the meiotic double-strand break (DSB) transesterase. Localizations of Ski8p and Spo11p are mutually interdependent. ski8 mutants exhibit defects in vegetative growth, entry into the sexual program, and sporulation. Diverse meiotic defects, also seen in spo11 mutants, are diagnostic of DSB absence, and they are restored by exogenous DSBs. These results suggest that Ski8p promotes meiotic DSB formation by acting directly within meiotic prophase chromosomes. Mutant phenotypes also divide meiotic homolog juxtaposition into three successive, mechanistically distinct steps; recognition, presynaptic alignment, and synapsis, which are distinguished by their differential dependence on DSBs.

Chromosome Mapping↗
PubMed1972

Cytogenetic analysis of the first cleavage division in mouse embryos (fertilization-pronuclei-T163H translocation).

Chromosome counts of 338 mouse zygotes at late prophase and metaphase of the first cleavage division revealed 96.4% diploidy, 1.8% hypodiploidy, 1.2% triploidy, and 0.3% tetraploidy. One additional anomaly might have given rise to an embryo mosaic for maternal but not paternal genes. In zygotes collected without colchicine administration to the mother, one of ten anaphases had a lagging chromosome. Reciprocal crosses with the translation T163H as a marker chromosome at late prophase, when the male- and female-derived chromosome groups have not yet combined, demonstrate that the group derived from the larger pronucleus and having less condensed chromosomes is of paternal origin. T163H undergoes Mendelian segregation in female heterozygotes.

Animals↗
PubMed1981

X chromosome reactivation in oocytes of Mus caroli.

Mature mammalian oocytes have both of their X chromosomes active, while somatic cells from the same individual have one of their X chromosomes in an inactive state. We asked whether the X chromosomes of the germ cells never undergo inactivation in their ontogeny or whether inactivation of an X chromosome does occur but is followed by a subsequent reactivation event. Our approach has used an electrophoretic polymorphism for the X-linked enzyme glucose-6-phosphate dehydrogenase (G6PD) in the mouse species Mus caroli. G6PD is dimeric, and a heterodimer is produced in cells from heterozygous females if and only if both X chromosomes are active. Ovaries from heterozygous fetuses at different gestational ages were dissected and either studied cytologically or pressed between microscopy slides to obtain germ cell-rich and germ cell-poor preparations. No heterodimer band was detected on the 10th day of development in germ cell-rich preparations. On subsequent days, an increasingly intense heterodimer band was detected, which, by the 13th day, was approximately twice as intense as the corresponding homodimer bands. Consideration of (i) the G6PD activity per germ cell and per somatic cell and (ii) the percentage of germ cells in the germ cell-rich preparations indicated that a heterodimer band should have been visible on the 10th day had both X chromosomes been active. Cytological examinations showed that the earliest germ cells enter meiotic prophase on the eleventh day. These results demonstrate that oogonia have a single active X chromosome and that the inactive X chromosome is reactivated at or, more likely, shortly before entry into meiotic prophase.

Alleles↗
PubMed1984

Phosphoproteins are components of mitotic microtubule organizing centers.

Protein phosphorylation has been suggested as an important control mechanism for the events leading toward the initiation and completion of mitosis. Using a monoclonal antibody recognizing a class of phosphoproteins abundant in mitotic cells, we demonstrated the localization of a subset of these phosphoproteins to several discrete mitotic structures. Patchy immunofluorescence was present in the interphase nuclei, but a significant increase in nuclear immunofluorescence was apparent at prophase. Subsequent mitotic stages demonstrated that immunoreactive material was particularly apparent at microtubule organizing centers, namely, centrosomes, kinetochores, and midbodies. Intense centrosomal localization occurred at the prophase-prometaphase transition and persisted until the reformation of the nuclear membrane in early G1. The cytoplasm of mitotic cells also contained immunoreactive material in sharp contrast to interphase cells that exhibited no cytoplasmic fluorescent staining. Much of the diffuse immunofluorescent cytoplasmic material was removed by a brief lysis of the cells with 0.15% Triton X-100 prior to fixation. The localization of the remaining immunoreactive material after detergent lysis to mitotic microtubule organizing centers suggests that they contain phosphoprotein structural components important, perhaps, in the mitotic phase-interphase transition.

Animals↗