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In Crustacea, reproductive function and mechanisms regulating vitellogenesis have not been fully elucidated. This is due in great part to a lack of information concerning the biochemical nature of the vitellogenin molecule, the hemolymph precursor of yolk protein, vitellin, as well as the functional expression of the vitellogenin-encoding gene. We have therefore cloned a cDNA encoding vitellogenin in the kuruma prawn, Penaeus japonicus based on the N-terminal amino acid sequence of the 91 kDa subunit of vitellin. The open reading frame of this cDNA encoded 2,587 amino acid residues. This is the first investigation reporting a full-length cDNA and its corresponding amino acid sequence for vitellogenin in any crustacean species.Northern blot analysis and in situ hybridization have revealed that mRNA encoding vitellogenin was expressed in both the follicle cells in the ovary and the parenchymal cells in the hepatopancreas. In nonvitellogenic females, vitellogenin mRNA levels were negligible in both the ovary and hepatopancreas, but in vitellogenic females, levels were dramatically increased in both tissues. In the ovary, highest levels were observed during the early exogenous vitellogenic stage, and thereafter rapidly decreased, whereas in the hepatopancreas, high levels were maintained until the onset of the late vitellogenic stage. Differing profiles of vitellogenin mRNA levels in the ovary and hepatopancreas suggest that the contribution of these tissues to vitellogenin synthesis harbor separate and complementary roles during vitellogenesis.

A cDNA encoding vitellogenin (Vg) in the giant freshwater prawn, Macrobrachium rosenbergii, was cloned based on the cDNA sequence of vitellin (Vn) fragments A-N and B-42 determined previously, and its amino acid sequence deduced. The open reading frame (ORF) encoded 2,537 amino acid residues and its deduced amino acid sequence possessed three consensus cleavage sites, R-X-R-R, similar to those reported in Vgs of insects. The deduced primary structure of Vg in M. rosenbergii was seen to be similar to that of Penaeus japonicus, especially in the N-terminal region. It is therefore likely that Vgs in crustacean species including prawns and other related decapods exhibit a similar structural pattern. Based on the deduced primary structure of Vg and analysis of the various Vg and Vn subunits found in the hemolymph and ovary during ovarian maturation, we demonstrated the post-translational processing of Vg in M. rosenbergii. This is the first time that Vg processing has been clearly demonstrated in a crustacean species. Vg, after being synthesized in the hepatopancreas, is considered to be cleaved by a subtilisin-like endoprotease to form two subunits, A and proB, which are then released into the hemolymph. In the hemolymph, proB is possibly cleaved by a processing enzyme of unknown identity to give rise to subunits B and C/D. The three processed subunits A, B, and C/D are sequestered by the ovary to give rise to three yolk proteins, Macr-VnA, VnB, and VnC/D.

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