Effects of estradiol-17beta treatment on in vitro and in vivo synthesis of two distinct vitellogenins in tilapia.

Two distinct vitellogenins (VTG) were purified from the blood of estradiol-17beta (E(2))-injected tilapia, Oreochromis mossambicus. Enzyme-linked immunosorbent assays (ELISA) of each VTG were developed to examine effects of E(2) treatment on induction of VTG synthesis in the primarily cultured tilapia hepatocytes. Two VTG molecules (VTG210 and VTG140) had apparent molecular masses of 370 and 220 kDa by gel filtration and 210 and 140 kDa by SDS-PAGE, respectively. Western blot analyses showed that antibodies raised against the purified VTG210 and VTG140 reacted only with each protein band. Furthermore, ELISA for each VTG was specific for target VTG. When E(2) was added into the media of primarily cultured tilapia hepatocytes, VTG210 and VTG140 were both detected from E(2) concentrations of 1x10(-7) M and 5x10(-7) M, respectively. Time course experiments showed that there was a difference in the detection time of VTG210 and VTG140 after the hormone treatment. Although the injection of different E(2) doses induced both VTGs in the plasma of male tilapia, the concentration of VTG210 was nearly five to eight times higher than that of VTG140. These results suggest that E(2) is a direct inducer of both VTGs in the tilapia hepatocytes in vitro and in vivo, and that there is difference in the hormone response in inducing the VTGs in the tilapia hepatocytes.