Phosvitins in Fundulus oocytes and eggs. Preliminary chromatographic and electrophoretic analyses together with biological considerations.

Vitellogenin serves as the plasma precursor for the yolk proteins, lipovitellin and phosvitin, in nonmammalian vertebrates. 32P-Vitellogenin was isolated from the plasma of the teleost, Fundulus heteroclitus, and was used both to label phosvitin in the ovary and to indicate the phosvitin region in preparative chromatographs of ovarian extracts on DEAE-cellulose. Crude [32P]phosvitin could be resolved further into two labeled components with shallow gradients on DEAE-cellulose and into eight labeled components by electrophoresis on 12% polyacrylamide gels. Only the two largest electrophoretically resolved components could be correlated with Coomassie Blue staining bands, but several of the smaller components could be indicated with the cationic carbocyanine dye, Stains-all. Stains-all-dyed components were also generally indicated as multiple bands. The ovary of a reproductively active female contains vitellogenic oocytes, postvitellogenic oocytes undergoing maturation prior to ovulation, and ovulated eggs. Examination of various types of follicles and eggs on polyacrylamide gels revealed that during maturation, the largest phosvitin components formed during vitellogenesis either disappear or diminish, while smaller phosvitin components appear. The transformation of phosvitin components can also be achieved in vitro by incubating prematurational follicles in a saline medium containing deoxycorticosterone. These preliminary results demonstrate that a complex array of phosvitin-like components are present within a single ovary of F. heteroclitus. We also postulate that one reason for the anomalous yolk proteins generally found thus far in teleost eggs is that some of the proteins derived from vitellogenin during vitellogenesis undergo further proteolysis during oocyte maturation.