JAYASANKAR, V. * 1; TSUTSUI, N. 2; JASMANI, S. 1; SAIDO-SAKANAKA, H. 1; AIDA, K. 2; WILDER, M.N. 1: Yolk Processing and Vitellogenin Gene Expression during Ovarian Maturation in the Giant Freshwater Prawn, Macrobrachium rosenbergii

Recently, a cDNA encoding vitellogenin (Vg) was cloned in Macrobrachium rosenbergii, and its amino acid sequence deduced. Based on this sequence and analysis of Vg and vitellin (Vn) subunits found in the hemolymph and ovary during ovarian maturation, post-translational processing of Vg in M. rosenbergii was clearly demonstrated for the first time. The hepatopancreas is the main site of Vg mRNA expression. Vg, after being expressed in the hepatopancreas, is likely cleaved proteolytically into two subunits and released into the hemolymph, where it undergoes further processing before being sequestered by the ovary to give rise to the Vns. In order to determine the correlation between Vg mRNA expression and ovarian maturation, Vg mRNA was quantified in the hepatopancreas and ovary of intact and eyestalk ablated animals at differing stages of reproduction using real-time quantitative PCR. Intact animals showed an increase in gonadosomatic index (GSI) 12 days after molting, with GSI reaching a maximum prior to the next molt. Vg mRNA levels also showed a corresponding increase in these animals. Eyestalk ablation accelerated ovarian maturation and Vg synthesis. In these animals, both GSI and Vg mRNA expression started increasing as early as 4 days after molting. Vg mRNA expression was highest 8-12 days after molting and decreased thereafter, with minimum synthesis occurring around 20 days after the first molt. In both groups, the ovary showed negligible Vg mRNA expression, confirming that although eyestalk ablation accelerates ovarian maturation, it does not alter the dynamics of Vg gene expression.