FORMATION OF THE DROSOPHILA OVARIAN RING CANAL INNER RIM DEPENDS ON CHEERIO

In Drosophila oogenesis, the development of a mature oocyte depends on having properly developed ring canals that allow cytoplasm transport from the nurse cells to the oocyte. Ring canal assembly is a step-wise process that transforms an arrested cleavage furrow into a stable int er cellular bridge by the addition of several proteins. Here we descri be a new gene we named cheerio that provides a critical function for r ing canal assembly. Mutants in cheerio fail to localize ring canal inn er rim proteins including filamentous actin, the ring canal-associated products from the hu-li tai shao (hts) gene, and kelch. Since hts and kelch are present but unlocalized in cheerio mutant cells, cheerio is likely to function upstream from each of them. Examination of mutants in cheerio places it in the pathway of ring canal assembly between cl eavage furrow arrest and localization of hts and actin filaments. Furt hermore, this mutant reveals that the inner rim cytoskeleton is requir ed for expansion of the ring canal opening and for plasma membrane sta bilization.