MOLECULAR CHARACTERIZATION OF HEPATOPANCREAS VITELLOGENIN AND ITS EXPRESSION DURING THE OVARIAN DEVELOPMENT BY IN SITU HYBRIDIZATION IN THE BANANA SHRIMP FENNEROPENAEUS MERGUIENSIS

A complete cDNA sequence of vitellogenin (Vg-H) was cloned from the hepatopancreas of Fenneropenaeus merguiensis (De Man, 1888). The full-length Vg-H gene consists of 7958 bp and contains an ORF of 7761 bp. It encodes a polypeptide of 2587 amino acids, comprising a predicted molecular mass of 283 kD and the theoretical pI is 6.5. The amino acid sequences of the mature vitellogenin (Vg) composed of a signal peptide, three possible O-glycosylation sites, three phosphorylation sites and putative possessing sites (R-X-K/R-R) recognized by subtilisin-like endoproteases. Cleavage at residues 725 to 728 will produce two Vg subunits (78 and 200 kD), which the N-terminal amino acid sequence of 7810 subunit is identical to that of vitellin purified from the ovary. These properties suggest that Vg protein encoding by Vg-H undergoes processing at its synthetic sites prior to being transported to developing oocytes. The deduced primary structure of Vg-H showed the highest identity (98.8%) to the Vg-O previously cloned from the ovary of the same species. It is more related to the penaeid Vg sequences than that of nonpenaeids. In situ hybridization revealed that mRNA encoding Vg was expressed both in follicle cells in the ovary and parenchyma cells in the hepatopancreas. In the developing ovary, highest levels were detected during the early vitellogenic stage 2, declining thereafter. In the hepatopancreas, Vg mRNA levels reached a maximum at stage 3 of ovarian development. Profiles of Vg mRNA expression in the ovary and hepatopancreas suggest that the contribution of these tissues to vitellogenesis is inversely related during gonad maturation. Thus, Vg gene sequences expressed in the ovary and hepatopancreas are most likely identical and both tissues are responded for yolk protein synthesis in F. merguiensis.