The vitellin-processing protease of Blattella germanica is derived from a pro-protease of maternal origin

Abstract

Proteolytic processing of vitellin in Blattella germanica embryos is accomplished by activation of a yolk-borne cysteine protease (Mr 29 000) derived from a pro-protease precursor of Mr 40 000 ( Liu et al., 1997). In the present study, fat body, ovaries and embryos of different developmental stages were examined immuno-cytochemically with purified murine anti-proprotease antibodies ( Liu, 1995) to determine the intracellular location of the pro-protease. Proenzyme was detected in discrete secretory granules of the fat body and in large lysosome-like vesicles of both the follicle cell cytoplasm and the cortical ooplasm of previtellogenic ovarian follicles. In vitellogenic oocytes, coated pits and vesicles are scantily labelled for proprotease and no clear gold pattern could be discerned over the yolk granules. During embryonic development, pro-protease is associated with some, but not all, yolk granules. In newlyovulated eggs (day 0), pro-protease is either distributed over the entire granule or confined to some internal vesicles. As development proceeds, it becomes associated with almost every yolk granule and restricted to the superficial layer. By day 6, pro-protease is evident over all yolk granules but the intensity of reaction has greatly diminished, due probably to conversion of the pro-protease to the mature enzyme. Yolk granules are flanked along their margin by vesicles that are stained after zinc-osmium fixation. This observation suggests that the pro-protease may be transferred between yolk granules via vesicular shuttling. B. germanica embryos of different developmental stages were also exposed to [ 3H]-DAMP. Data show that autoradiographic grains are not evenly distributed among closely adjacent yolk granules within vitellophagic cells, a result consistent with the known slight temporal asynchrony of the acidification event.