Study On Vitellogenin MRNA Expression In Ovary And Hepatopancreas Of Shrimp Fenneropenaeus Chinensis

The primary role of the yolk proteins is to provide nutrition to the developing embryos and early larval in penaied shrimp. Vitellin is the major constituents of the yolk protein. It was extracted and purified from the ovaries of many female oviparous animals. Vitellin is a lipo-glyco-carotenoprotein complex accumulating in the developing oocyte. Vitellogenin circulating in the hemolymph is suggested as a precursor of vitellin. The site of yolk biosynthesis vary according to the species examined. Some crustaceans rely solely on the ovary to complete vitellogenesis. Others may use the fat body as a primary source of yolk as is the case with most insects. The hepatopancreas and ovary are common sites for yolk biosynthesis in several penaeid shrimp. The results of the study in the shrimp Fenneropenaeus chinensis show that ovary and hepatopancreas are the site of vitellogenin synthsis. So far, there is a few studys on vitellogenin mRNA gene expression in ovary and hepatopancreas of Fenneropenaeus chinensis. By real-time fluorescence quantitative PCR,the study is to determine the expression of vitellogenin mRNA in ovary and hepatopancreas at the different stages with ovarial development. The experimental result will clarify the source and synthesis process of vitellogenin in Fenneropenaeus chinensis. It is important to artificial propagation .The histological structure and development of the ovary of Fenneropenaeus chinensis are studied. The ovary is consists of five parts, called anterior lobe, central lobe, sidearm lobe, the front of abdominal lobe and the back of abdominal lobe. The tissues were made into paraffin section after fixed with stationary liquid and dye them with hematoxylin and sosin.The cycle of the ovarian development can be divided into five stages according to the color of ovary, the index of ovary and the diameter of oocyte and nucleus. The five stages are the multiplication oogoniium, previtellogenesis, primary vitellogenesis, second vitellogenesis and declining stages. This study shows that: the 5 parts of the ovary are at the same stage, expect a few ovary show that the back of abdominal lobe is develop slower than the others.Designing the specificity primes of vitellogenin mRNA gene and 18S ribosomal RNA gene and optimizeing the system of PCR amplify and reaction condition. The total RNA was extracted from the ovary and hepatopancreas amplified by real-time fluorescence quantitative PCR. Then, the expression of vitellogenin mRNA in the two tissues of Fenneropenaeus chinensis at different ovarian development stages, ingcluding multiplication oogoniium, previtellogenesis, primary vitellogenesis, second vitellogenesis and declining stages was determined by real-time fluorescence quantitative PCR. The results show that the vitellogenin mRNA is expressed in both ovary and hepatopancreas of shrimp Fenneropenaeus chinensis. That the ovary and hepatopancreas are both the site of vitellogenesis is confirmed again. The expression of vitellogenin mRNA in ovary increased from multiplication oogoniium to primary vitellogenesis stage, The relative expression levels were 0.04,0.23,1.03 respectively, but decreased at secondary vitellogenesis stage to 0.16. However in declining stage it incresed to 1.00. The expression of vitellogenin mRNA is high at primary vitellogenin stage and declining stage. The expression of vitellogenin mRNA is low at previtellogenesis and primary vitellogenesis stage. In hepatopancreas, the expression of mRNA increased from multiplication oogoniium to secondary vitellogenesis stage. The relative expression levels were 0.01,0.07,0.19,1.29 respectively,and it decreased to 0.74 at decling stage. The peak of expression is at the secondary vitellogenesis stage. The expression of vitellogenin mRNA is low at multiplication oogoniium stage and primary vitellogenesis stage.Compare the expression of vitellogenin mRNA in ovary with heaptopancreas. Except the secondary vitellogenesis, the expression of vitellogenin mRNA in ovary was higher than heaptopancreas at the other four stages. At multiplication oogoniium stage, previtellogenesis, primary vitellogenesis stage, declining stages, The expression of vitellogenin mRNA in ovary was 4.0,3.2,5.4,1.3 times by heaptopancreas. On the contrary, the expression in heaptopancreas was 8.2 times by ovary at second vitellogenesis stage. With the ovary and heaptopancreas supplement each other, the expression of vitellogenin mRNA was keep in a high level from primary vitellogenesis stage to declining stage.