Vitellogenesis and Vitellogenin Receptor in Shrimp: From the Sites of Synthesis to the Final Storage in the Ovary

This dissertation, "Vitellogenesis and Vitellogenin Receptor in Shrimp: From the Sites of Synthesis to the Final Storage in the Ovary" by Hiu-kwan, Tiu, 刁曉君, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled VITELLOGENESIS AND VITELLOGENIN RECEPTOR IN SHRIMP: FROM THE SITES OF SYNTHESIS TO THE FINAL STORAGE IN THE OVARY Submitted by Tiu Hiu Kwan for the degree of Doctor of Philosophy at The University of Hong Kong in October 2007 Shrimp produced from aquaculture have become an important source of quality protein for human consumption. One of the main obstacles for a further increase in production was the lack of information to manipulate female shrimp maturation in captivity. To obtain a better knowledge on the synthesis, transport and uptake of the extra-ovarian vitellogenin (Vg) during gonad maturation, the endocrine control of shrimp vitellogenesis was examined. Two vitellogenin genes (i.e. MeVg1 and MeVg2) of the shrimp Metapenaeus ensis were cloned. MeVg1 transcript can be detected in hepatopancreas and ovary whereas MeVg2 transcript can only be detected in the hepatopancreas. In comparison, the vitellogenin gene from the tiger shrimp Penaeus monodon (PmVg1) was also characterized. The presence of multiple vitellogenin genes in shrimps was confirmed and these Vg genes exhibited different expression profiles in the reproductive cycle. In early reproductive stages, hepatopancreas was the major site of vitellogenin synthesis; whereas in the later stages, when vitellogenin production in hepatopancreas decreases, the ovary becomes the major site of vitellogenin synthesis. Vitellogenesis in crustacean is a well-coordinated process controlled by endocrine factors such as farnesoic acid (FA), 20-hydroxyecdysone (20-HE) and eyestalk CHH/MIH/GIH family of neuropeptides. Here, the effects of these hormones on Vg expression were studied in vitro in explant cultures and in vivo by injection experiments. The results showed that FA could stimulate Vg gene expression in hepatopancreas and ovary whereas 20-HE could stimulate Vg gene expression in ovary only, but not in hepatopancreas. Injection of recombinant MeMIH-B could stimulate Vg expression in hepatopancreas and ovary. In contrast, vitellogenin gene expression was decreased in the hepatopancreas and ovary of shrimp when MeMIH-B expression was prohibited. The results demonstrated unequivocally that MeMIH-B has a function in vitellogenin stimulation. To study the uptake and processing of vitellogenin by developing oocytes, the cDNA encoding the tiger shrimp vitellogenin receptor (PmVgR) was characterized. The open reading frame of PmVgR cDNA is 5826 bp in length. It encodes for a protein of 1941 amino acid residues with a predicted molecular mass of 211 kDa. PmVgR consists of characteristics of the low density lipoprotein receptor (LDLR) superfamily. The expression of PmVgR is ovary-specific, and is related to female gonad maturation. By a ligand-blotting assay, a high molecular weight protein was detected in the ovary membrane protein under non-reducing condition. This protein was also immunoreactive to the VgR antibody. The expression of PmVgR was knocked down in shrimp treated with dsRNA. Consequently, vitellogenin produced by the hepatopancreas accumulated in the hemolymph and caused a significant reduction of. vitellin content in the ovary. The results provided evidence that PmVgR may be involved in the vitellogenin uptake by oocytes in shrimp. DOI: 10.5353/th_b3936062 Subjects: Gly