CHAN, S.-M.; The University of Hong Kong: VITELLOGENESIS IN THE SHRIMP Metapenaeus ensis : MOLECULAR AND BIOCHEMICAL CHARACTERIZATION OF VITELLOGENINS

The vitellin from M. ensis was purified and used to raise vitellin antibody. Several ovary polypeptides with large molecular weight (157, 78, 76 kDa) were identified as major vitellogenin subunits. Vitellogenin immunopositve signals could be detected in the ovary and hemolymph and only weak signals were detected in the hepatopancreas. In the hepatopancreas and hemolymph, polypeptides with sizes identical to ovary vitellogenins (i.e. 78, 76 and 157 kDa) were reacted to the vitellin antibody. Using molecular approach, the cDNA and the gene encoding the shrimp vitellogenins (MeVg1 and MeVg2) have been cloned. With a 5� end MeVg1 cDNA probe, mRNAs of 8.0 and 2.5 kb were detected in different hepatopancreas and ovary RNA samples. In the hepatopancreas, the major transcripts are the small RNAs (i.e. 2.3 and 1.5 kb) and the large (i.e. 8.0 kb) transcript only constitute <10% of the total RNA. The smaller RNAs transcripts may represent alternatively expressed products of the MeVg genes. Furthermore, the small transcripts constituted >90% overall MeVg mRNAs. Some of these small transcripts were cloned by PCR and confirmed to carry transcripts with deleted exons of the MeVg gene. The presence of a large quantity of the smaller vitellogenin transcripts in the hepatopancreas suggest that post-transcriptional modification constitute an important process in the contribution of vitellogenin synthesis in shrimp. This research was supported in part by a HKU institutional block grant (CRCG grant) and the Research Grant Council of the Hong Kong Government Special Administrative Region (HKU 7214/02M) awarded to SMC.