The hepatopancreas as a site of yolk protein synthesis in the prawn Macrobrachium rosenbergii

Abstract

Our previous study failed to show vitellin synthesis in the ovary of the prawn Macrobrachium rosenbergii (Sagi et al., 1995); thus the role of the hepatopancreas as a possible site of synthesis was evaluated. Extracts of hepatopancreas and hemolymph of a secondary-vitellogenic female exhibited higher levels of yolk protein than those from a primary-vitellogenic female. Clear vitellin immuno-cross-reactivity was observed in hepatopancreas sections from a secondary-vitellogenic female while no such reaction was found in a male hepatopancreas. Furthermore, vitellin-immuno-cross-reactive polypeptides released into the culture medium of the hepatopancreas of a secondary-vitellogenic female were similar to those found in the hemolymph and ovary (92 and 105kDa). The most prominent immuno-reactive polypeptide in the hepatopancreas extract was a relatively low-molecular-weight species (42kDa). De novo synthesis of cross-reactive-vitellin polypeptides (34, 38 and 42kDa) was detected in the hepatopancreas of a secondary-vitellogenic female. Synthesis of these polypeptides were not detected in the secondary-vitellogenic ovary or in the male hepatopancreas. The appearance of similar polypeptides following incubation of a secondary-vitellogenic ovarian extract with a glycosidase suggests that these polypeptides could be subunits of a core protein of vitellogenin, which was synthesized in the hepatopancreas and then released to the hemolymph following post-translational modifications. Our findings thus suggest the hepatopancreas to be a likely site of synthesis of a yolk protein precursor in M. rosenbergii.