Is There Extraovarian Synthesis of Vitellogenin in Penaeid Shrimp?

Abstract

Extraovarian synthesis of vitellogenin (Vg), has been reported for several crustaceans, mainly in the subepidermal adipose tissue (SAT) or the hepatopancreas (HEP). The precise site(s) of Vg synthesis in penaeid shrimp is hitherto unknown and was investigated in a large local species Penaeus semisulcatus de Haan. Protein synthesis was determined in SAT and HEP tissue pieces incubated in vitro. Incubations were at 25{deg}C for eight hours in an oxygen enriched atmosphere, under sterile conditions in a physiological medium, containing 14C-leucine. At the end of the incubation period, tissue homogenates and medium samples were analyzed for de novo protein synthesis. Total protein synthesis was determined by trichloroacetic acid precipitation. Specific vitellin (Vt) synthesis was determined by radioimmunoprecipitation with a polyclonal Vt-specific antiserum. Characterization of other de novo synthesized proteins was carried out by fluorography from polyacrylamide gels. Subepidermal adipose tissues removed from females at all stages of ovarian development did not synthesize Vt-specific proteins, in spite of the fact that total protein synthesis levels were high. The major protein synthesized de novo in the SAT of males and females is a protein with an identical electrophoretic mobility as hemocyanin in polyacrylamide gels. In vitro protein synthesis in HEP tissues was low compared to SAT or ovary systems. Vt-specific de novo synthesized protein was identified in HEP's from early vitellogenic females, but constituted less than 15% of total protein synthesis. We have previously shown that ovarian tissues from vitellogenic females incubated in vitro exhibited high levels of protein synthesis, an average of 38% of which is Vt-specific (Browdy et al., 1990, J. Exp. Zool. 255:205-215). The calculated Vt synthesis rates in ovaries were up to 23 times higher than in HEP. We conclude that the extraovarian contribution to vitellogenesis in P. semisulcatus is low.