Tissue-specific vitellogenesis and 17β-estradiol facilitate ovarian maturation of the swimming crab Portunus trituberculatus

The present study investigated the changes of expression and localization of PtVg mRNA, tissue Vg/ Vn concentrations, the contents of progesterone and 17ß-estradiol during the ovarian development of P. trituberculatus. The results showed that: 1) The most abundant mRNA levels of PtVg were found in stage IV, and hepatopancreatic PtVg mRNA was markedly greater than that in ovaries from stage II to stage V. The positive signal of PtVg mRNA was found in the follicular cells (FC), the cytoplasm of previtellogenic oocytes (PRO) and endogenous vitellogenic oocytes (EN), and hepatopancreatic fibrillar (F) cells and resorptive (R) cells. 2) The ovarian Vn contents reached the peak at stage V. In the hemolymph and hepatopancreas, the level of Vg/Vn markedly increased from stage II to stage IV. Immunohistochemistry findings confirmed that the PtVg protein was primarily distributed in the FC and the oocyte cytoplasm of late stages (II-V). 3) The highest levels of progesterone in the ovaries, hepatopancreas and hemolymph all appeared in stage II and then declined gradually from stage II to stage V. Ovarian 17β-estradiol concentration show an increasing trend from stage I to IV and remarkably decreased at stage V, while the peak levels of 17β-estradiol in hepatopancreas and hemolymph was found in stage III. 4) Positive correlations were found between ovarian and hepatopancreatic 17β-estradiol content and the corresponding Vg mRNA level, while significantly negative correlations were found between the tissue progesterone titers and the corresponding GSI or Vg/Vn contents during ovarian maturation. In conclusion, the vitellogenesis characteristics of P. trituberculatus are stage-specific, and most vitellogenin is produced by the hepatopancreas, which is also highly correlated to the changes of tissue 17β-estradiol content during the ovarian developmental cycle.