G protein signaling. For G proteins, we focused in particular on the role of the single D. melanogaster G 12/13A homologue, encoded by concertina, because this subfamily of G proteins has been shown to regulate cell migration and metastatic invasion and to directly interact with E-cadherin and Rho1. Cta protein is present in the germ cells and maternal loss of cta causes a gastrulation defect similar to G 13f and G 1. Again, we were able to rescue the gastrulation phenotype by early, somatic Cta expression, as described for G 1 and G 13f. In contrast to our findings with G and G mutants, however, cta mutant germ cells migrated normally to the gonad. To confirm this result, we transplanted mutant cta germ cells derived from cta mutant mothers into wild-type embryos. We found that cta germ cells migrated to the gonad with similar efficiency as transplanted wild-type control germ cells. Thus, G 12/13 does not act as the sole mediator of Tre1 GPCR activation. Our analysis of the available mutants in other G proteins did not reveal a single G protein that mediates the Tre1 signal, which perhaps indicates that redundant or overlapping functions of G proteins act downstream PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19835934 of Tre1. G 13f and G 1 signaling is required for germ cell polarization, dispersal, and transepithelial migration type germ cells at the blastoderm stage. At 
stage 9, as wild-type germ cells polarize, G 13f and Rho1 proteins were down-regulated along the germ cell membranes facing the midgut, and became highly enriched in the tail region. In early germ cells, G 13f and Rho1 proteins were uniformly distributed in tre1 mutants similar to the wild type; in contrast to the wild type, however, this uniform distribution persisted during stage 9. These results suggest that Tre1 receptor activation leads to germ cell polarization in part by causing the redistribution of downstream signaling molecules away from the leading edge and accumulation in the tail. Tre1 GPCR signaling controls localization of DE-cadherin Our observation that both G 13f and G 1 are required for germ cell dispersal and transepithelial migration suggests that Tre1 function in germ cells is mediated by a G proteindependent pathway, akin to the requirement for GPCR signaling seen during the directed migration of Dictyostelium discoideum amoeba and in neutrophils toward a chemokine gradient. To determine how Tre1 signaling may affect downstream components, we analyzed the localization of G 13f protein as well as the localization of Rho1, which we had previously shown to affect germ cell transepithelial migration in wild-type and tre1 mutant germ cells. We found that G 13f and Rho1 proteins were localized uniformly along the cell membrane of wild- As shown in Fig. 1, tre1 mutant germ cells failed to disperse at the onset of the migration, which suggests that tre1 regulates adhesion molecules in germ cells. DE-cadherin is a good candidate, as it is LY-411575 deposited maternally in the early embryo. We first tested the role of DE-cadherin in the adhesion of wild-type germ cells. For this analysis, we used a newly identified partial loss-of-function allele of D. melanogaster E-cadherin encoded by the shotgun gene, which allows normal oogenesis. In embryos derived from shgA9-49 mutant ovaries, germ cells did not organize into a radial cluster. Instead, germ cells separated from one another prematurely, at early stage 8 compared with stage 10 in the wild type. This dispersal phenotype was observed in embryos from homozygous ge
