Search

The possible mechanisms underlying mitosis-induced focal adhesion disassembly and inactivation of integrin-mediated signaling were examined. Findings showed that focal adhesion kinase (FAK), paxillin and p130(supra CAS) become phosphorylated on serine and/or threonine residues in a mitosis-specific fashion. It was also found that the FAK/CAS/c-Src signaling complex is dissociated during mitosis.

A study was undertaken showing that the Drosophila embryonic spindles at metaphase and anaphase possessed abundant bundles of microtubules (MTs) running between the spindle poles. The mitotic bipolar kinesin, KLP61F, was immunolocalized within the spindles of the Drosophila embryos utilizing peptide antibodies monospecific for a phospho-epitope in the tail of the motor. Results showed that KLP61F contributed to the formation and function of bipolar mitotic spindles by cross-linking and sliding MTs in relation to one another. KLP61F was colocalized in the interpolar MT bundles.

Research was conducted to examine the hypothesis that fission yeast bub1 is a mitotic centromere protein essential for the spindle checkpoint and the preservation of correct ploidy through mitosis. In Schizosaccharomyces pombe bub1+ was shown to be a necessary requirement to detect changes in spindle structure or defects in kinetochore function. Results based on cytological and genetic observations lead to the conclusion that the loss of the bub1 gene causes defects in chromosome segregation which subsequently shows that bub1 function is also necessary in a normal mitosis.

A potential connection between the exceptional stability of centriole microtubules and the compartmentalization of glutamylated isoforms was examined by loading HeLa cells with the monoclonal antibody GT335, which specifically reacts with polyglutamylated tubulin. Findings showed that a posttranslational change in tubulin is essential for long-term stability of centriolar microtubules. Also, centrioles are important in animal cells for organizing centrosomal components into a structurally stable organelle.

The dependence of mitosis on the completion of the period of DNA replication in the cell cycle [synthesis (S) phase] ensures that chromosome segregation occurs only after the genome has been fully duplicated. A key negative regulator of mitosis, the protein kinase Wee1, was degraded in a Cdc34-dependent fashion in Xenopus egg extracts. This proteolysis event was required for a timely entrance into mitosis and was inhibited when DNA replication was blocked. Therefore, the DNA replication checkpoint can prevent mitosis by suppressing the proteolysis of Wee1 during S phase., Dividing cells depend on ubiquitin-mediated protein destruction for proper cell cycle progression. At least three distinct cell cycle transitions are regulated by proteolysis: passage from the prereplicative phase of growth [...]

Proteolysis of mitotic cyclins depends on a multisubunit ubiquitin-protein ligase, the anaphase promoting complex (APC). Proteolysis commences during anaphase, persisting throughout [G.sub.1] until it is terminated by cyclin-dependent kinases (CDKs) as cells enter S phase. Proteolysis of mitotic cyclins in yeast was shown to require association of the APC with the substrate-specific activator Hct1 (also called Cdh1). Phosphorylation of Hct1 by CDKs blocked the Hct1-APC interaction. The mutual inhibition between APC and CDKs explains how cells suppress mitotic CDK activity during [G.sub.1] and then establish a period with elevated kinase activity from S phase until anaphase., Entry into anaphase and exit from mitosis are promoted by APC-dependent proteolysis of regulatory proteins (1). Sister chromatid separation requires Pds1 degradation shortly before anaphase onset, whereas Cdk1 inactivation during [...]

The Xenopus polo-like kinase 1 (Plx1) is essential during mitosis for the activation of Cdc25C, for spindle assembly, and for cyclin B degradation. Polo-like kinases from various organisms are activated by phosphorylation by an unidentified protein kinase. A protein kinase, polo-like kinase kinase 1 or xPlkk1, that phosphorylates and activates Plx1 in vitro was purified to near homogeneity and cloned. Phosphopeptide mapping of Plx1 phosphorylated in vitro by recombinant xPlkk1 or in progesterone-treated oocytes indicates that xPlkk1 may activate Plx1 in vivo. The xPlkk1 protein itself was also activated by phosphorylation on serine and threonine residues, and the kinetics of activation of xPlkk1 in vivo closely paralleled the activation of Plx1. Moreover, microinjection of xPlkk1 into Xenopus oocytes accelerated the timing of activation of Plx1 and the transition from [G.sub.2] to M phase of the cell cycle. These results define a protein kinase cascade that regulates several events of mitosis., Progression through the eukaryotic cell cycle relies on the periodic activation or inactivation of various cyclin-dependent protein kinases (Cdks) (1). Cell cycle checkpoints monitor the fidelity of events in a [...]

Chromosome condensation is a fundamental cellular process that ensures the faithful segregation of genetic information during mitosis and meiosis. Activation of the protein kinase Cdc2 triggers a series of downstream […]