VITELLOGENESIS IN THE MUD CRAB SCYLLA SERRATA-AN IN VIVO ISOTOPE STUDY

Abstract

Vitellogenesis in the mud crab Scylla serrata was investigated in vivo using the radiolabeled amino acid ['4C]phenylalanine to trace the synthetic site(s) of the major yolk protein lipovitellin. The incorporation of [14C]phenylalanine into the synthesized proteins of different tissues, such as ovary (OV), hepatopancreas (HP), subepidermal adipose tissue (SAT), and hemolymph (HL) of vitellogenic phases I and II, provided the first in vivo demonstration of possible extraovarian synthesis of lipovitellin precursor, vitellogenin, in S. serrata. The results indicated that among different tissues of vitellogenic phase I, SAT and HP actively take part in synthesizing the yolk proteins which are immediately released into the HL. This is evidenced by a high level of ['4C]phenylalanine incorporation into the protein fraction of the HL. The incorporation of ['4C]phenylalanine into the synthesized proteins of the OV indicates the fact that OV is also capable of synthesizing the precursors to some extent. However, a dramatic increase of ['4C]phenylalanine incorporation into the synthesized ovarian proteins of vitellogenic phase II, concurrent with a decline in the level of ['4C]phenylalanine incorporation into the HL proteins, suggests the probable sequestration of the synthesized proteins from an extraovarian site. The data also suggest a dual role for the HP, in-asmuch as it synthesizes and stores the vitellogenin prior to its release into the OV for sequestration during intense vitellogenesis.