Fluorescently labeled inhibitors detect localized serine protease activities in Drosophila melanogaster pole cells, embryos, and ovarian egg chambers.

Serine proteases are typically synthesized as proteolytically inactive zymogens that often become activated in a limited and highly localized manner. Consequently, determination of the spatial and temporal activation pattern of these molecules is of great importance to understanding the biological processes that they mediate. Until only recently, the tools to conveniently address the question of where and when serine proteases are active within complex tissues have been lacking. In order to detect spatially restricted serine protease activities in Drosophila embryos and ovaries we introduce a technique using fluorescent synthetic and protein-based inhibitors. With this approach we have detected a novel serine protease activity with a relative mobility of 37 kDa, localized to the surface of pole cells, the germ-line precursors, in embryos between nuclear cycles 11 and 14 in development. A second novel cell-specific protease activity was localized to the tissues of early gastrulating embryos. Microinjection of inhibitors into the perivitelline space of stage 2 embryos perturbed normal embryonic development. Fluorescein-conjugated chymotrypsin inhibitor and Bowman-Birk inhibitor labeled protease activity localized to the oocyte-somatic follicle cell interface of the developing egg chamber. Our results suggest that this technique holds promise to identify new spatially restricted activities in adult Drosophila tissues and developing embryos.