THE RHO-GTPASE AND A PUTATIVE RHOGEF MEDIATE A SIGNALING PATHWAY FOR THE CELL-SHAPE CHANGES IN DROSOPHILA GASTRULATION

The Rho GTPases mediate actin rearrangements that are likely to be req uired for the numerous cell shape changes in a developing embryo. In a genetic screen for Rho signaling pathway components in Drosophila, we identified a gene, DRhoGEF2, that encodes a predicted Rho-specific gu anine nucleotide exchange factor. Embryos lacking DRhoGEF2 fail to gas trulate due to a defect in cell shape changes required for tissue inva gination, and expression of a dominant-negative Rho GTPase in early em bryos results in similar defects. Evidence is also presented that DRho GEF2 mediates these specific cell shape changes in response to the ext racellular ligand, Fog. Together, these results establish a Rho-mediat ed signaling pathway that is essential for the major morphogenetic eve nts in Drosophila gastrulation.