DRHOGEF2 ENCODES A MEMBER OF THE DB1 FAMILY OF ONCOGENES AND CONTROLSCELL-SHAPE CHANGES DURING GASTRULATION IN DROSOPHILA

We have identified a gene, DRhoGEF2, which encodes a putative guanine nucleotide exchange factor belonging to the Dbl family of oncogenes. D RhoGEF2 function is essential for the coordination of cell shape chang es during gastrulation. In the absence of maternal DRhoGEF2 gene activ ity, mesodermal and endodermal primordia fail to invaginate. The pheno type seen in DRhoGEF2 mutants is more severe than the defects associat ed with mutations in two previously identified gastrulation genes, fol ded gastrulation and concertina, suggesting that DRhoGEF2 acts in a si gnaling pathway independent of these. dominant-negative DRhoA during g astrulation results in phenocopies of the DRhoGEF2 mutant, suggesting that a signaling cascade involving DRhoGEF2 and the small GTPase DRhoA is responsible for the regulation of cell shape changes during early Drosophila morphogenesis.