Autoproteolysis and feedback in a protease cascade directing Drosophila dorsal-ventral cell fate

Three serine protease zymogens, Gastrulation defective (GD), Snake (Snk) an d Easter (Ea), and a nerve growth factor-like growth factor ligand precurso r, Spaetzle, are required for specification of dorsal-ventral cell fate dur ing Drosophila embryogenesis. The proteases have been proposed to function in a sequential activation cascade within the extracellular compartment cal led the perivitelline space. We examined biochemical interactions between t hese four proteins using a heterologous co-expression system. The results i ndicate that the three proteases do function in a sequential activation cas cade, that GD becomes active and initiates the cascade and that interaction between GD and Snk is sufficient for GD to cleave itself autoproteolytical ly. The proteolytically active form of Ea cleaves GD at a different positio n, revealing biochemical feedback in the pathway. Both GD and Snk bind to h eparin-Sepharose, providing a link between the pipe-defined ventral prepatt ern and the protease cascade. Our results suggest a model of the cascade in which initiation is by relief from inhibition, and spatial regulation of a ctivity is due to interaction with sulfated proteoglycans.