Molecular mechanism of cytokinesis

点击翻译按钮获取中文摘要

1)It has been considered that some signal is transfered from the mitotic apparatus to the cell cortex in order to form the contractile ring at a proper position. However, its mechanism has not been clarified yet. I investigated role of wheat germ agglutinin (WGA) receptors in this process, using fluorescein-labeled WGA. WGA receptors distributed on the surface of the egg during metaphase. They were aggregated into clusters during anaphase, which became fibrous in late anaphase. At telophase, they accumulated in the anticipated furrow region forming a ring. The distribution observed above was quite similar to that of actin filaments visualized by fluorescent phalloidin staining. It has been shown that the WGA receptors have intimate relationship to actin filament-anchoring sites on the plasma membrane. A possibility was denied that the receptors accumulate in the anticipated furrow region at first and then induce actin filament assembly. 2) When the unfertilized sea urchin eggs were incubated with calyculin A, a sponge toxin which inhibits activities of protein phopsphatases, cleavage was induced. Neither mitotic apparatus nor aster was formed in these eggs. Actin, myosin, and WGA receptors were accumulated in the furrow region. This process was inhibited by protein kinase inhibitors. It is suggested that protein phosphorylation is involved in the contractile ring formation. In addition, chromosomes were condensed and histone 1 kinase activity was increased in a cyclin Bindependent manner. 3) Last year, I reported isolation of cleavage furrows from Clypeaster japonicus eggs using a detergent-containing medium. I extended the isolation with Scaphechinus mirabilis eggs. I also isolated clevage furrows from eggs of Anthocidaris crassispina and Hemicentrotus pulcherrimus using modified medium. We found several proteins in 2-D gels common to these eggs and now determining partial peptide sequences.