Morphogenesis of Drosophila ovarian ring canals.

We analyzed the structure of cytoplasmic bridges called ring canals in Drosophila egg chambers. Two mutations, hu-li tai shao (hts) and kelch, disrupt normal ring canal development. We raised antibodies against the carboxy-terminal tail of hts and found that they recognize a protein that localizes specifically to ring canals very early in ring canal assembly. Accumulation of filamentous actin on ring canals coincides with the appearance of the hts protein. kelch, which is localized to the ring canals hours after hts and actin, is necessary for maintaining a highly ordered ring canal rim since kelch mutant egg chambers have ring canals that are obstructed by disordered actin and hts. Anti-phosphotyrosine antibodies immunostain ring canals beginning early in the germarium before hts and actin and throughout egg chamber development. The use of antibody reagents to analyze the structure of wild-type and mutant ring canals has shown that ring canal development is a dynamic process of cytoskeletal protein assembly, possibly regulated by tyrosine phosphorylation of some ring canal components.