The p38/JNK signaling pathways affect ovarian ring canal growth. N.S. Sokol , L. Cooley. Dept. of Genetics, Yale Medical School, 333 Cedar Street SHM I-363, New Haven, CT 06520.

   Ovarian ring canals present a powerful system to dissect the mechanisms by which signal transduction pathways regulate cytoskeletal dynamics. Ring canals contain a robust inner rim of filamentous actin that attaches to the plasma membrane, also termed the ring canal outer rim. In addition to F-actin, ring canal inner rims contain cytoskeletal proteins encoded by the cheerio, hts and kelch genes and are regulated by the Src64 and Tec29 tyrosine kinases. Antibodies against phosphorylated, human JNK and p38 as well as Drosophila p38b strongly recognize ring canals beginning in region 2A of the germarium. Like Tec29, JNK and p38 appear to be components of the outer rim since they localize in hts and cheerio mutants that are unable to recruit an actin inner rim, and do not colocalize with the disorganized actin inner rims of kelch mutant ring canals. To genetically assess the importance of this antibody staining, hemipterous (hep) and licorne (lic) double germline clones were examined. hep encodes Drosophila JNKK and lic a Drosophila MKK3/JNKK homolog. hep lic egg chambers are weakly dumpless with a mild ring canal defect; ring canals occasionally appear kinked or broken. Antibodies to human phospho-JNK and phospho-p38 still stain hep lic ring canals, suggesting that Hep and Lic are redundant with another kinase and perhaps explaining the weakness of their germline phenotype. However, removing one copy of Drosophila MKK4, an activator of both JNK and p38, significantly enhances the hep lic phenotype, producing strongly dumpless egg chambers whose ring canals are disorganized. Intriguingly, in other systems MKK4 has been shown to bind to Filamin whose Drosophila homolog is the product of the cheerio locus. To assess the role of MKK4 in ring canal growth, we are currently screening for MKK4 mutants and are also generating flies that will express dominant-negative or constitutively -active forms of the kinase in their germline.