Vitellin cleavage products are proteolytically degraded by ubiquitination in stick insect embryos

Knockdown of E1- and E2-ubiquitin enzymes triggers defective chorion biogenesis and modulation of autophagy-related genes in the follicle cells of the vector Rhodnius prolixus

In insects, the last stage of oogenesis is the process where the chorion layers (eggshell) are synthesized and deposited on the surface of the oocytes by the follicle cells. Protein homeostasis is determined by the fine-tuning of translation and degradation pathways, and the ubiquitin-proteasome system is one of the major degradative routes in eukaryotic cells. The conjugation of ubiquitin to targeted substrates is mediated by the ordered action of E1-activating, E2-conjugating, and E3-ligase enzymes, which covalently link ubiquitin to degradation-targeted proteins delivering them to the proteolytic complex proteasome. Here, we found that the mRNAs encoding polyubiquitin (pUbq), E1, and E2 enzymes are highly expressed in the ovaries of the insect vector of Chagas Disease Rhodnius prolixus. RNAi silencing of pUbq was lethal whereas the silencing of E1 and E2 enzymes resulted in drastic decreases in oviposition and embryo viability. Eggs produced by the E1- and E2-silenced insects presented particular phenotypes of altered chorion ultrastructure observed by high-resolution scanning electron microscopy as well as readings for dityrosine cross-linking and X-ray elemental microanalysis, suggesting a disruption in the secretory routes responsible for the chorion biogenesis. In addition, the ovaries from silenced insects presented altered levels of autophagy-related genes as well as a tendency of upregulation in ER chaperones, indicating a disturbance in the general biosynthetic-secretory pathway. Altogether, we found that E1 and E2 enzymes are essential for chorion biogenesis and that their silencing triggers the modulation of autophagy genes suggesting a coordinated function of both pathways for the progression of choriogenesis.

Vitellin of Pteromalus puparum (Hymenoptera: Pteromalidae), a pupal endoparasitoid of Pieris rapae (Lepidoptera: Pieridae): Biochemical characterization, temporal patterns of production and degradation

Vitellin (Vt) and vitellogenin (Vg) profiles were analyzed in Pteromalus puparum, a pupal endoparasitoid of Pieris rapae. Non-denaturing and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analyses indicated that both native Vt and Vg were likely 370 kDa in size, consisting of two subunits of approximate 206 and 165 kDa. An indirect double antibody enzyme-linked immunosorbent assay (ELISA) for monitoring hemolymph Vg and ovarian Vt levels was developed using a monoclonal antibody and a polyclonal antibody made specially against P. puparum Vt. The synthesis and uptake of Vg in this wasp was initiated immediately after adult eclosion. The hemolymph Vg and ovarian Vt reached their highest level of 0.58 and 4.51 microg per female 24 and 48 h after adult eclosion, respectively. Both Vg synthesis and uptake were in parallel with ovarian development. The Vt levels in the developing embryos decreased progressively except 12h after parasitism. Meanwhile, nine new polypeptides with sizes ranging from 59.2 to 151 kDa, possibly resulting from the limited proteolysis of Vt originally accumulated in newly laid eggs, were detected de-novo during embryonic development using Western blotting with the monoclonal antibody against Vt. These studies provide the basis for future investigation into endocrinal regulations of vitellogenesis and understanding the reproductive strategy in this wasp.

The utilization of lipovitellin during blue crab (Callinectes sapidus) embryogenesis

Embryos of the blue crab Callinectes sapidus develop in egg sacs carried on the abdomen of the female. They develop over a period of 10-13 days at 28 degrees C and are nutritionally dependent on yolk until they emerge from the egg sacs as free-swimming zoeae. The principal component of blue crab yolk is lipovitellin (LpII), a water-soluble lipoprotein composed of approximately equal amounts of lipid and protein. We followed changes in the concentration of apoproteins of LpII during embryogenesis by ELISA and Western blots, using monoclonal antibodies against two LpII apoprotein associated peptides identified as Protein A (107 kDa) and Protein B (75 kDa). During embryogenesis there was a decrease in Protein B but an increase in two smaller peptides (52 and 35 kDa) that reacted with the Protein B antibody. Utilization of LpII during embryogenesis was also followed morphologically by immunohistochemistry. Utilization of LpII was slow in early embryonic stages, followed by rapid utilization in late embryonic stages, such that only traces of LpII were present at the end of embryogenesis. The cells of the developing hepatopancreas appear to play an important role in the utilization of LpII.