Vitellin processing and degradation during embryogenesis in Rhodnius prolixus

Abstract

The fate of vitellin (VT), the major yolk protein in Rhodnius prolixus, was studied during embryogenesis by electrophoretic and immunological techniques. Analysis of the protein content of the eggs by polyacrylamide gel electrophoresis (PAGE) under non-denaturing conditions shows a continuous alteration in the VT molecule following oviposition. Two distinct phases of VT processing can be observed: (1) when limited proteolysis is dominant; and (2) when an extensive degradation of VT occurs inside the digestive system of the embryo. In the first phase (days 0–10 after oviposition), as embryogenesis proceeds, the two principal bands of VT give rise to several bands that migrate progressively further into the gel. Analysis of the same samples by SDS-PAGE reveals a continuous proteolysis of the subunits of the VT molecule. When the VT is analysed by rocket immunoelectrophoresis very little alteration in the total VT content per egg is observed from day 0 to day 10, suggesting that the antibodies used also recognize polypeptides produced by partial proteolysis. Western blot analysis demonstrated that some of the new polypeptides (112, 103, 64 and 56 kDa) generated during embryonic development are in fact derived from VT by limited proteolysis. After cleavage, the polypeptides remain in the same lipoprotein macromolecular complex. In the second phase of VT degradation, an extensive degradation of VT takes place, such that by day 14 after oviposition (hatching), VT content has declined to about half of the initial value. The VT remaining in the first instar is located entirely in the crop and disappears within 5 days after hatching.