Localization of Rho GTPase in sea urchin eggs.

We isolated the urho1 (urchin rho in English or uni rho in Japanese) gene from the sea urchin cDNA library which encodes a Rho GTPase. Anti-URho1 antibodies specifically recognized a 22 kDa protein in the extracts of echinoderm eggs. URho1 was concentrated in the cortices from both unfertilized and fertilized eggs as judged by immunoblot analysis. URho1 may bind directly to the cell membrane but not be a component of the cortical layer. Immunofluorescence microscopy revealed that URho1 is localized to the cleavage furrow and the midbody during cytokinesis.