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Results for “karyokinesis”

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At least 19 recordsLinked to original sources
PubMed2004

Participation of the adhesive disc during karyokinesis in Giardia lamblia.

Evidence is presented for a potential involvement of the adhesive disc on the nucleus division in Giardia lamblia. The trophozoite mitotic nucleus was studied by transmission electron microscopy, freeze-fracture, freeze-substitution and also by immunofluorescence microscopy using anti-tubulin antibodies specific to spindle microtubules and Panotic staining. Prior to cell division the nucleus elongated and a displaced disc fragment, established contact with the nucleus. A progressive nucleus indentation was coincident with the concomitant presence of a disc fragment at the constricted region. One nucleus each time progressively divided until the karyokinesis was finished and two daughter-nuclei were observed. After the first karyokinesis a second karyokinesis takes place following the same procedure. When Giardia gets the four nuclei, cytokinesis occurs. Duplicated basal bodies were seen in between the first and the second karyokinesis. Immunofluorescence microscopy, using a panel of anti-tubulin antibodies, and electron microscopy of cells processed using microtubule stabilizer buffers, or cells fast-frozen and freeze-substituted, did not reveal the presence of a typical spindle. We propose that Giardia lamblia presents an uncommon mitotic behavior where the adhesive disc, a microtubular structure, seems to participate in the karyokinesis process.

Animals↗
PubMed1999

Mitotic aberrations induced by carbaryl reflect tyrosine kinase inhibition with coincident up-regulation of serine/threonine protein phosphatase activity: implications for coordination of karyokinesis and cytokinesis.

The insecticide carbaryl and its metabolite 1-naphthol cause partial uncoupling of karyokinesis and cytokinesis in V79 Chinese hamster fibroblasts; karyokinesis is blocked in metaphase, the microtubules of the spindle depolymerize and the chromosomes and spindle remnants become displaced to the periphery of the cell. A high frequency of these disturbed cells elongate and a smaller fraction initiate a cleavage furrow. Here, we attempt to determine the potential targets for carbaryl and 1-naphthol in cytokinesis-specific signalling, led by the fact that the potential protein phosphatase inhibitor 1-naphthyl phosphate was previously identified in treated cells. We found that the typical cytological pattern induced by carbaryl and 1-naphthol could be obtained with tyrphostins, specific tyrosine kinase inhibitors, indicating that the carbaryl-induced effects could be due to tyrosine kinase inhibition. This was confirmed by tyrosine kinase assays showing that carbaryl, 1-naphthol and 2-naphthol were equally efficient at inhibiting tyrosine kinase activity as tyrphostin B44(-). As tyrosine kinases can act as regulatory factors in determining dephosphorylation rates, the activities of type-1 (PP1) and type-2A (PP2A) serine/threonine protein phosphatases were also determined. There was a clear up-regulation of the overall PP1/PP2A activities in cells treated with carbaryl, 1-naphthol or tyrphostin B44(-). This stimulation was shown to be indirect because these compounds had no effect on the activity of purified human PP1 in the test tube. 2-Naphthol, which has been found to be less efficient with regard to displacement of chromatin, did not cause up-regulation, but a significant decrease in PP1/PP2A activity. We suggest that a net decrease in tyrosine kinase activity in combination with a net increase in PP1/PP2A activity is a precondition for cell elongation and cytokinesis in mammalian cells and that the corresponding enzymes are targets in the network of activities serving to coordinate karyokinesis and cytokinesis.

Adenosine Triphosphate↗
PubMed2005

Involvement of Xtr (Xenopus tudor repeat) in microtubule assembly around nucleus and karyokinesis during cleavage in Xenopus laevis.

We have previously shown that the transcriptional product of the novel gene, Xenopus tudor repeat (Xtr), occurred exclusively in germline cells and early embryonic cells and that the putative Xtr contained plural tudor domains which are thought to play a role in the protein-protein interactions. To understand the role of Xtr, we produced an antibody against a polypeptide containing Xtr tudor domains as an antigen and investigated the distribution and the function of the Xtr. Immunoprecipitation/Western blot and immunohistochemical analyses indicated a similar occurrence of the Xtr to the mRNA except for a slightly different profile of its amount during spermatogenesis. In spite of a large amount of Xtr mRNA at late-secondary spermatogonial stage, the amount of Xtr was kept at a low level until this stage and increased after entering into the meiotic phase. Depletion of the Xtr function in the activated eggs by injection of the anti-Xtr antibody caused the inhibition both of microtubule assembly around nucleus and of karyokinesis progression after prophase, but not of the oscillation of H1 kinase activity. These results suggest that the karyokinesis of at least early embryonic cells are regulated by unique mechanisms in which the Xtr is involved.

Animals↗
PubMed2002

Post-karyokinesis centrosome movement leaves a trail of unanswered questions.

The centrosome is a complex structure composed of a large number of proteins (pericentriolar material, PCM) usually organized around a pair of centrioles (or a centriole duplex). This structure is capable of nucleating and organizing microtubules, duplication, and motility. In general, episodes of dramatic centrosome movement correlate with periods of cellular reorganization and nowhere is cellular reorganization more apparent, or more important, than in the periods before and after cell division. It is now clear that centrosome movement occurs not only prior to cell division but also at its completion, in concert with cytokinesis. The focus of this review is the newly emerging picture of centrosome activity during the post-karyokinesis period and the role that this activity might play in the transition of cells from mitosis to interphase.

Actins↗
PubMed1993

Centrosome repositioning immediately following karyokinesis and prior to cytokinesis.

The behaviour of the centrosome immediately following cell division in tissue culture cells has been investigated. We find that following karyokinesis, but preceding cytokinesis, sister centrosomes relocate from the spindle poles to a position adjacent to the intercellular bridge. This repositioning is accompanied by the appearance of a microtubule bundle that extends from the poleward region of the cell to the centrosome and increases in length as the centrosome approaches the intercellular bridge. Disruption of this bundle with colcemid interrupts centrosome repositioning. In contrast, centrosome repositioning persists in late mitotic cells grown in the presence of cytochalasin D. However, the position of the microtubule-centrosome complex within the cell is randomized suggesting that the path, but not the process, of centrosome repositioning is dependent on an intact actin filament network. This study points out, for the first time, that the complex migration of the centrosome preceding mitosis is paralleled by an equally complex set of events following cell division. We suggest that post-mitotic centrosome repositioning may play a role in ensuring that daughter cells have equal but opposite polarity and may reflect an interrelationship between the establishment of the interphase cytoskeleton and the completion of cytokinesis.

Anaphase↗
PubMed1998

Developmental consequences of karyokinesis without cytokinesis during the first mitotic cell cycle of bovine parthenotes.

Bovine parthenogenetic embryos and bovine embryos produced by in vitro fertilization were compared for chromosomal complement and developmental potential. Oocytes (n = 1885) were matured in vitro, fertilized (n = 1151) or activated (n = 734) by exposure to 5 microM ionomycin for 4 min, and then treated with 1.9 mM 6-dimethylaminopurine for 5 h to inhibit protein kinase functions and promote mitosis. Mean cleavage rates at 48 h were 76.3+/-4.7% for fertilization and 60.1+/-4.2% for activation (p < 0.05). A similar percentage of embryos had reached the blastocyst stage on Day 8 post fertilization/postactivation (16.4+/-3.3%) and (15.8+/-1.0%), respectively. Blastocysts (n = 53) produced by in vitro fertilization had higher total cell numbers (116.9+/-5.5) than parthenotes (n = 71, 67.2+/-3.5 cells, p < 0.05). Differential staining indicated a significant reduction in the number of blastomeres allocated to both the inner cell mass and trophectodermal lineages in parthenotes (p < 0.05). All parthenotes (n = 65) were polyploid or mixoploid, with observed karyotypes of 4n (61.53%), 2n/4n (30.76%), 2n/8n (4.61%), and 3n (3.07%). In contrast, only 9 control blastocysts (n = 53) revealed abnormal metaphases (16.9%). At 6 h postactivation (hpa), 70.7% of parthenotes (n = 65) demonstrated a fully formed pronucleus; and at 10 hpa (n = 86), 89% had completed pronuclear formation. Pronuclear DNA replication was observed by 6 hpa and resulted in the formation of a second pronucleus in 76.9% of activated oocytes (n = 104) by 24 hpa. These pronuclear kinetics lead to a high number of embryos with binucleate blastomeres upon cleavage. Thus, alterations in the DNA content (ploidy) of bovine parthenogenetic blastocysts reflect ongoing karyokinesis without cytokinesis during the first mitotic cell cycle after exposure to a protein kinase inhibitor.

Adenine↗
PubMed2000

Import of proteins into the trypanosome nucleus and their distribution at karyokinesis.

In all eukaryotic organisms proteins are targeted to the nucleus via a receptor-mediated mechanism that requires a specific nuclear localization sequence (NLS) in the protein. Little is known about this process in trypanosomatid protozoa that are considered amongst the earliest divergent eukaryotes. We have used the green fluorescent protein (gfp) and beta-galactosidase reporters to identify the NLS of two trypanosomal proteins, namely the Trypanosoma brucei La protein homologue and histone H2B of T. cruzi. A monopartite NLS was demonstrated at the C terminus of the La protein, whereas a bipartite NLS was identified within the first 40 amino acids of histone H2B. Treatment of live trypanosomes with poisons of ATP synthesis resulted in exit of the La NLS-gfp fusion from the nucleus. Interestingly, this fusion protein accumulated at several discrete sites in the cytoplasm, rather than equilibrating between the nucleus and the cytoplasm. When ATP levels returned to normal, the protein reentered the nucleus, demonstrating that the process was energy dependent. Finally, using fusion proteins that localize to the nucleoplasm or the nucleolus, we identified a subpopulation of mitotic cells in which the chromosomes have segregated but the daughter nuclei remain connected by a thin thread-like structure. We propose that cells containing this structure represent a late stage in nuclear division that can be placed after chromosome segregation, but before completion of karyokinesis.

Amino Acid Sequence↗
PubMed2004

Expression of basic fibroblast growth factor isoforms in postmitotic sympathetic neurons: synthesis, intracellular localization and involvement in karyokinesis.

Low and high molecular weight isoforms of the mitogen and multifunctional cytokine basic fibroblast growth factor (FGF-2) are up-regulated in neurons and glial cells in response to peripheral nerve lesion. While synthesis, regulation and functions of FGF-2 in non-neuronal cells are well established, the significance of neuronal FGF-2 remains to be investigated in the peripheral nervous system. Therefore, the expression, intracellular localization and possible effects of FGF-2 isoforms were analyzed in primary sympathetic neurons derived from the rat superior cervical ganglion. FGF-2 is detected in the nucleus and in perinuclear Golgi fields of early postnatal neurons which also express mRNA and protein for the FGF receptor type 1. Biolistic transfection of plasmids encoding FGF-2 isoforms fused to fluorescent proteins demonstrates nuclear targeting of 18 kDa FGF-2 and 23 kDa FGF-2 with prominent accumulation in the nucleolus of neurons. Neither overexpression nor treatment with FGF-2 isoforms promotes survival of sympathetic neurons deprived of nerve growth factor; however, neuronal transfection of the high molecular weight FGF-2 isoform in dissociated and slice cultures results in a bi- or multinuclear phenotype. The present study provides evidence for neuronal synthesis and targeting of FGF-2 to the nucleus and Golgi apparatus supporting a dual role of FGF-2 in the nucleus and secretory pathway of sympathetic neurons.

Animals↗
PubMed1975

Disturbances of karyokinesis and its relation to the nuclear pattern.

The main causes of mitotic disturbances of spindle formation and inadaequate development of the mitotic apparatus. Quantitatively of the greatest importance in both groups are collapse of the prophase and failure of cytokinesis, respectively. The division of polyploid nuclei is, in addition, complicated by alterations of multicentric spindles. Results of mitotic disturbances are changes in the degree of ploidy of cells or nuclei. In irreversible post-mitotic tissues these occur already in the growth phase, as is shown in the example of the heart. In reversible post-mitotic tissues these changes in the degree of ploidy modify the nuclelar pattern predominantly during the processes of ageing, reparation and regeneration, as is well documented in the liver.

Aging↗