Molecular mechanism of cytokinesis in animal cells

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1. Cleavage signaling pathwayWe found a new rho gene from the fission yeast and named it rho5^+.Disruptant of rho1 gene could not grow indicating that rho1^+ is an essential gene. We localized Rho1 by both immunofluorescence microscopy and expression of GFP-Rhol fusion protein in the fission yeast cell to growing tips during interphase and to septum during cytokinesis. Overexperssion of Rhol induced aberrant morphology, delocalization of actin patches, and thickening of cell wall. Overexperssion of Rho2 was lethal, cell morphology was aberrant and cell wall was abnormally thick. Disruption of rho3 gene induced aberrant morphology of the cell and abnormal division. Disruption of rho4 gene induced loss of cell polarity and abnormal division.2. Structure and foumation of the contractile ringWe found novel F-actin-binding proteins from sea urchin eggs by F-actin affinity chromatography. Among them, 60K protein was indentified as coronin and 150K protein was identified as myosin 6. Immunofluorescence microscopy showed that these proteins and ARP3, which we indentified in the last year, are present in the cleavage furrow cortex. We gene-cloned ARP3 from fission yeast and disrupted it. The terminal phenotype showed that actin patches were delocalized. ABP40, a protein which is concentrated in the cleavage furrow of the sea urchin egg, was demonstrated to have an F-actin-severing activity.