The Biosynthesis and Processing of Vitellogenin in the Fat Bodies of Females and Males of the Cockroach Leucophaea maderae

Abstract

The juvenile hormone analog (JHA) methoprene was used to induce the synthesis of the yolk protein precursor vitellogenin (Vg) in adult females and males of the cockroach Leucophaea maderae. The female- and male-produced vitellogenin (VgF and VgM, respectively) contained polypeptides of 112, 95, 92, and 54kDa. Also present in the secreted vitellogenins was a small quantity of a short-lived transitional 155kDa Vg polypeptide, and a variable amount of an 85kDa species. Quantitatively, the VgF and VgM were significantly different in the Vg112 and Vg95 units (VgF>VgM), and in the Vg85 polypeptide (VgF<VgM). In the present study, the biosynthesis of Vg precursors in the fat bodies of females and males was examined using a short radiopulse with 35S-methionine/cysteine and 32P-orthophosphate. The glycosylation of the Vg precursors was examined by digestion with endoglycosidase H and by the inhibition of N-linked glycosylation with tunicamycin. The data showed that in both females and males, the synthesis of the vitellogenin precursor occurred in a stepwise fashion: (1) the co-translational glycosylation of Vg203; (2) the post-translational phosphorylation of Vg203 to form Vg220; (3) the proteolytic processing of Vg220 to form the constituent Vg polypeptides. The 203 and 220kDa Vg precursors of females and males appeared to be similarly glycosylated and phosphorylated. The additional processing of Vg112 to Vg85 was more pronounced in the fat bodies of males than in females, and appears to account for the quantitative difference in the distribution of these polypeptides in VgF and VgM. Finally, the major oligosaccharides of VgF and VgM appear to be those of N-linked mannose residues. The treatment of females and males with tunicamycin indicated that the co-translational glycosylation of Vg precursors was required for the phosphorylation of the Vg precursor, as well as the secretion of Vg from the fat body.