CYK-1 - A C-ELEGANS FH GENE REQUIRED FOR A LATE STEP IN EMBRYONIC CYTOKINESIS

A maternally expressed Caenorhabditis elegans gene called cyk-1 is req uired for polar body extrusion during meiosis and for a late step in c ytokinesis during embryonic mitosis. Other microfilament- and microtub ule-dependent processes appear normal in cyk-1 mutant embryos, indicat ing that cyk-1 regulates a specific subset of cytoskeletal functions. Because cytokinesis initiates normally and cleavage furrows ingress ex tensively in cyk-1 mutant embryos, we propose that the wild-type cyk-1 gene is required for a late step in cytokinesis, Cleavage furrows reg ress after completion of mitosis in cyk-1 mutants, leaving multiple nu clei in a single cell. Positional cloning and sequence analysis of the cyk-1 gene reveal that it encodes an FH protein, a newly defined fami ly of proteins that appear to interact with the cytoskeleton during cy tokinesis and in the regulation of cell polarity. Consistent with cyk- 1 function being required for a late step in embryonic cytokinesis, we show that the CYK-1 protein colocalizes with actin microfilaments as a ring at the leading edge of the cleavage furrow, but only after exte nsive furrow ingression, We discuss our findings in the context of oth er studies suggesting that FH genes in yeast and insects function earl y in cytokinesis to assemble a cleavage furrow.