CHAN, S.-M.; The University of Hong Kong: Vitellogenin and vitellogenesis in decapod crustaceans: knowledge from proteomic and molecular studies
Vitellogenin (Vg) is the precursor for one of the major yolk proteins that supplies the embryos and larvae with nutrients for development and growth. During ovarian maturation of decapod crustaceans, vitellogenins are synthesized and transported to the ovary for oocyte uptake by receptor-mediated endocytosis. Although the biochemical characterization of vitellin and vitellogenin has been the major research focus in the past decades, there are still controversial issues regarding the synthesis sites, number of vitellogenin gene, sizes of transcripts and the processing mechanisms for the vitellogenin subunits. By proteomic approaches, amino acid sequencing of hepatopancreas and ovary proteins extracted from reproductive females have confirmed the presence of vitellogenin subunits in both tissues. However, the results from proteomic study suggested that the hepatopancreas may contribute to the production of small vitellogenin subunits. By molecular approach, the gene for several decapods vitellogenin had been cloned. Results from genomic Southern blot, genomic PCR and RT-PCR analyses confirmed the presence of multiple Vg genes in a single species. The Vg gene organization of different decapods is highly similar which suggests that the Vg gene organization is highly conserved during evolution. When we compared the Vg sequence among different decapods (i.e. lobster vs shrimp), they shared much lower sequence identities. Both the hepatopancreas and the ovary of females express Vg during gonad maturation. Although the 7.8 kb RNA Vg transcript was reported, smaller transcript specific to the Vg had also been detected in Northern blot. These smaller transcripts may contribute to the production of smaller Vg subunits by the hepatopancreas and ovary. Both post-transcriptional and post-translational modifications may be involved in the final production of vitellin in the ovary. (Supported by HKSAR Government RGC Grant # HKU7214/02M)
