pipsqueak, an early acting member of the posterior group of genes, affects vasa level and germ cell-somatic cell interaction in the developing egg chamber.

We have identified a new member of the posterior group of genes, which we call pipsqueak. We show that pipsqueak acts after the establishment of the oskar posterior anchor but before the localization of vasa protein during oogenesis. Characterization of multiple alleles at the pipsqueak locus shows that pipsqueak, like vasa, is required for early stages of oogenesis, including but not limited to formation of the egg chamber and progression through Stage 6 of oogenesis. Genetic interaction studies suggest that pipsqueak acts at least partially through vasa; molecular studies indicate that pipsqueak affects vasa level in the ovary. We compare vasa and pipsqueak mutant phenotypes in order to determine whether pipsqueak acts solely through vasa, and present a model for the role of pipsqueak in posterior pattern formation.