FAT TRANSPORT IN THE PENAEID SHRIMP PENAEUS-SEMISULCATUS (DEHAAN)

Vitellogenesis is associated with the accumulation in the ovary of lar ge amounts of protein (mainly vitellin; Vt) and lipids, mainly triacyl glycerol (TG), phosphatidylcholine (PC), and cholesterol. This accumul ation depends partly on de novo synthesis of proteins and lipids by th e ovary and in the case of lipids, on the continuous supply of precurs ors from the diet. Ovarian tissue sections that were incubated in vitr o with C-14-acetate yielded C-14-labelled long chain saturated (74%) a nd mono-unsaturated (26%) fatty acids. These were incorporated into ti ssue TG and PC. Between 10-30% of the newly synthesized lipid was boun d to Vt and was precipitated from tissue homogenates with the Vt antis erum. Lipoproteins (LP's) were isolated from the hemolymph by density gradient centrifugation at 1.22 g ml-1. In the male, a single LP - LPI - was isolated. In the females, an additional LP - vitellogenin (Vg), which reacted with the Vt antiserum, was found. These LP's carried ma inly PC and cholesterol. The hepatopancreas (HEP) has been suggested t o function as a storage organ of absorbed lipids for subsequent use in vitellogenesis. Twenty-four hours after feeding C-14-palmitate to mal e and female shrimp, the hemolymph LP contained PC of high specific ra dioactivity. Approximately 1 0% of the radioactivity was recovered in the HEP TG (70%) and PC (30%), while ovaries contained less radioactiv ity. Incubations in vitro of HEP fragments with C-14-leucine yielded r adiolabelled proteins, of which LPI was identified by radioimmunopreci pitation with specific antibodies. In the female, an additional protei n (LPII; Vg) was obtained after precipitation with the Vt antiserum. W e suggest that these proteins function as lipid carries from the HEP t o the ovary. Recently, we have immunoisolated Vt from a cell-free tran slation system programmed with mRNA, extracted from vitellogenic ovari es by the use of specific polyclonal Vt rabbit antiserum.