Figure 1. Model for the action of Drosophila dorsal group serine proteases in the PVS of the egg. Horizontal arrows denote the conversion of an inactive version of the respective protein to its activated form, indicated by the presence of an asterisk (*). Vertical black arrows have at their bases, the proteins that directly mediate those activation events. Activation/processing of Snk (white horizonal arrow) occurs uniformly around the egg/embryo DV circumference, while activation of Ea, Spz and Toll (gray horizonal arrows) is restricted to the ventral side of the egg/embryo. Black diagonal arrows denote positive regulatory inputs; the bar originating from Spn27A indicates inhibition. Note that GD directly processes and activates Snk, as well as facilitating Snk*-mediated processing of Ea via a mechanism that requires Pipe activity. Our experiments indicate that processing of Snk can be performed by the GD zymogen, a conclusion that is supported by observations of Steen et al.²⁶ It has not yet been determined whether GD's influence upon Ea processing by Snk requires that GD itself undergo processing. Thus, GD is not marked with an asterisk.