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

Our previous study failed to show vitellin synthesis in the ovary of the pr awn Macrobrachium rosenbergii (Sagi et al., 1995); thus the role of the hep atopancreas as a possible site of synthesis was evaluated. Extracts of hepa topancreas and hemolymph of a secondary-vitellogenic female exhibited highe r levels of yolk protein than those from a primary-vitellogenic female. Cle ar 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 polypepti des released into the culture medium of the hepatopancreas of a secondary-v itellogenic female were similar to those found in the hemolymph and ovary ( 92 and 105kDa). The most prominent immune-reactive polypeptide in the hepat opancreas extract was a relatively low-molecular-weight species (42 kDa). D e novo synthesis of cross-reactive-vitellin polypeptides (34, 38 and 42 kDa ) was detected in the hepatopancreas of a secondary-vitellogenic female. Sy nthesis of these polypeptides were not detected in the secondary-vitellogen ic ovary or in the male hepatopancreas. The appearance of similar polypepti des following incubation of a secondary-vitellogenic ovarian extract with a glycosidase suggests that these polypeptides could be subunits of a core p rotein of vitellogenin, which was synthesized in the hepatopancreas and the n 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.