Characterization of Yolk Proteins in the Freshwater Crab Travancoriana schirnerae

Abstract

Vitellogenesis, the most important part of the reproductive process, involves the synthesis of yolk proteins and their deposition in oocytes. The objective of this study was to characterize yolk proteins of the freshwater crab Travancoriana schirnerae using sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The results revealed that the hemolymph yolk protein, vitellogenin is composed of two high molecular weight polypeptide subunits 153.53 and 166.73 kDa. The ovarian yolk protein, vitellin is composed of four polypeptide subunits with molecular weights 60.25, 69.25, 82.68 and 115 kDa. The high molecular weight vitellin polypeptides, 82.68 and 115 kDa appeared in early primary vitellogenic ovary. The vitellin fraction of late primary and secondary vitellogenic ovaries contained a low molecular weight subunit, 69.25 kDa besides the 82.68 and 115 kDa fractions. All the four polypeptide fractions were detected in the tertiary vitellogenic ovary and freshly oviposited eggs. Vitellin polypeptides were not demonstrated in previtellogenic or spent ovaries. Biochemical analyses revealed that vitellin is a lipoglycoprotein as it is stainable with Sudan Black B and periodic acid Schiff’s reagent. It was concluded that the two vitellogenin subunits may possibly undergo proteolytic cleavage to give rise to four vitellin subunits of the ovary.