Expression profiles and localization of vitellogenin mRNA and protein during ovarian development of the giant tiger shrimp Penaeus monodon

Ovarian maturation of the giant tiger shrimp (Penaeus monodon) results from rapid synthesis and accumulation of a major yolk protein, vitellin which is derived from its precursor, vitellogenin. The expression profiles and localization of P. monodon vitellogenin 1 (PmVtg1) were examined. PmVtg1 mRNA was expressed only in ovaries and hepatopancreas but not in other tissues of female and testes of male broodstock. In wild intact broodstock, PmVtg1 mRNA was expressed at a low level in stage I ovaries and up-regulated in stages II and III being significantly reduced in stage IV ovaries (P < 0.05). In eyestalk-ablated broodstock, the expression level of PmVtg1 mRNA was increased to nearly a peak level in vitellogenic (stage II) ovaries and peaked in cortical rod (stage III) ovaries (P < 0.05). The level of PmVtg1 mRNA in hepatopancreas of intact shrimp with stages II and III ovaries was significantly greater than those with stages IV and V (post-spawning) ovaries. Interestingly, PmVtg1 mRNA in hepatopancreas was 25-40 times higher than that in ovaries of intact shrimp with stages I-III of ovarian development. In situ hybridization revealed that PmVtg1 mRNA was clearly localized in the cytoplasm of follicular cells surrounding late previtellogenic, vitellogenic and cortical rod oocytes. Quantitative real-time PCR against different periods of spawned eggs suggested that PmVtg1 mRNA was also synthesized in oocytes. Western blot analysis revealed a similar profile of ovarian P. monodon vitellin and PmVtg1 mRNA during ovarian development and also suggested that the Vtg protein in hepatopancreas and Pm-vitellin in ovaries should have encoded from different Vtg genes. Immunohistochemistry confirmed that Pm-vitellin was localized in developing, vitellogenic and mature oocytes but not in the follicular cells.