Immunolocalization and changes of 17beta-estradiol during ovarian development of Chinese mitten crab Eriocheir Sinensis

17beta-estradiol (E-2) is important for crustacean ovarian development. This study aims to investigate the distribution and change pattern of E-2 in the ovary, hepatopancreas, thoracic ganglion and brain ganglion as well as Vg-mRNA expression level during ovarian development of Chinese mitten crab Eriocheir sinensis. Results showed that strongly positive signals of E-2 were mainly distributed in follicle cells of ovaries for all developmental stages as well as oocyte cytoplasm of stages III to V ovaries. In hepatopancreas, the E-2-positive signal was mainly detected in the cytoplasm and nucleus of fibrillar cells and the nucleus of resorptive cells, while the maximum fluorescence intensity was observed in stage III hepatopancreas. On the contrary, the E-2 immunoreactivities in nervous tissues were relatively stable during ovarian development. Moreover, the changing pattern of E-2 concentration was similar within hemolymph, ovary and hepatopancreas during the ovarian development. From stages I to III, the E-2 content in three tissues increased significantly, then decreased gradually until stage V. As for the Vg-mRNA expression level in hepatopancreas and ovaries, an increasing trend was found in ovaries but no significant difference was detected during the period of ovarian stages III to V. Hepatopancreatic Vg-mRNA expression level increased significantly during stages I to IV and dramatically decreased at stage V. In conclusion, our study suggests that ovary, hepatopancreas, hemolymph and nervous tissues are the target organs of E-2 in E. sinensis and E-2 concentrations in different tissues are closely related to vitellogenesis in ovary and hepatopancreas during ovarian development.