Proteolytic processing of Blattella germanica vitellin during early embryo development

Abstract

In the eggs of the cockroach Blattella germanica, vitellin (Vt) utilization i s initiated 4 days postovulation by the proteolytic processing of its three subunits. These reactions yield a specific set of peptides that are consumed by the developing embryo. A yolk proteinase activity, believed central to this processing event, has been investigated. First expressed at day 3 postovulation, just prior to Vt's processing, its specific activity with synthetic substrates increased fourfold to 18-fold through day 6. In addition, a mixing experiment showed that these proteinases(s) can also process Vt's large subunits in vitro. A relationship between Vt processing and proteinase specific activity was also noted with two B. germanica translocation heterozygotes, which displayed differences in the extent of Vt processing. One group of eggs (group A) failed to process any Vt subunit. A second group (6) processed the M,102,000 subunit but not the M,95,000. A third group (C) processed their Vt normally. Proteinase specific activities in the yolk of translocant's eggs at day 6 mirrored the extent of processing, being highest in group C eggs and effectively absent from the yolk of group A eggs. Eggs defective in Vt processing also contained arrested embryos. It i s concluded that the yolk proteinase activity described here participates in Vt processing at day 4 postovulation. Microscopic exarnination of yolk obtained from eggs of wild type females showed that, as processing began in vivo (day 4), the yolk granules also underwent an abrupt decrease in size from diametersof15-30ym to3-10pm. Yolkgranulesof those translocant's eggs that were defective in Vt processing did not undergo this size decrease, suggesting that granule reorganization and Vt proteolysis may be linked functionally.

A Cysteine Protease That Processes Insect Vitellin

“…Similar processing events are characteristic of Vt utilization in other insect species also (see Ref. 9, and references therein).…”

“…Previous work demonstrated that Vt utilization in Blattella germanica eggs is initiated at days 3-4 postovulation by proteolytic processing to a distinct set of peptides, which are then accessed by the embryo during development (9,15,16). Similar processing events are characteristic of Vt utilization in other insect species also (see Ref.…”

“…Yolk granules contain proteases that degrade their constituent proteins (5)(6)(7)(8)(9)(10). Cysteine (6,7,11,12) aspartyl (10), and serine (13,14) proteases have been identified.…”

“…Assays of B. germanica yolk with synthetic substrates revealed that protease activity, first detectable at days 2-3 postovulation, increased in specific activity through day 5, suggesting it could be important in Vt processing (9). Greater than 90% of this proteolytic activity was inhibitable by cysteine protease inhibitors (9), suggesting that this class of proteases play a major role in the processing event.…”

Serosa membrane plays a key role in transferring vitellin polypeptides to the perivitelline fluid in insect embryos

“…Insect embryos develop by utilizing a store of maternally derived proteins or vitellins (Nordin et al 1990;Giorgi et al 1999). These proteins are deposited in the oocyte during ovarian development as high molecular weight precursors or vitellogenins (Vg) by a process of receptor-mediated endocytosis (Raikhel 1984;Sappington et al 1995;Mellman 1996;Snigirevskaya et al 1997).…”