VENTRALIZING SIGNAL DETERMINED BY PROTEASE ACTIVATION IN DROSOPHILA EMBRYOGENESIS

SPECIFICATION of dorsal-ventral cell fate during Drosophila embryogene sis is mediated by a signal transduction pathway1-4. Asymmetry of cell fates arises through the spatially restricted production of a ligand in an extracellular compartment called the perivitelline space5. The s nake and easter genes are required for the production of the ligand17 and they encode the proenzyme form of secreted extracellular serine pr oteases6,7. We have examined the effect of producing a preactivated fo rm of the snake protease on the generation of dorsal-ventral polarity. SP6 RNA microinjection experiments reveal that different cell fates a cquired at cellular blastoderm can be specified by the amount and spat ial distribution of activated snake protein. Our results support a pro tease cascade model in which localized activation of uniformly distrib uted protease proenzymes leads to the spatially restricted production of ligand in the perivitelline space on the ventral side of the embryo .