Nile tilapia exhibits strong sexual growth dimorphism. The potential role of sex steroid hormones in sexual growth dimorphism is not fully understood. We investigated the effects of estradiol (E 2 ) and testosterone (T) on growth rate, plasma sex hormones, and expression of growth hormone (GH)-insulin-like growth factor (IGF) axis genes and muscle regulatory factor (MRF) genes in female and male Nile tilapia. The results revealed that serum concentrations of E 2 and T were significantly higher after correlative injection (P < 0.05). Compared to male fish, female fish had lower growth rates. E 2 increased growth performance in females with no significant effects on males, whereas T significantly increased growth performance in males, with no significant effects on females. In females, E 2 significantly increased expression of ghr1, ghr2, igf1, and igf2, while T decreased igf2 and increased ghr1 and ghr2 expression. In males, T increased expression of igf1, igf2, ghr1, and ghr2, and E 2 decreased expression of igf1, ghr1, and ghr2. Additionally, E 2 (myod1, myod2, myog, and myf5) in female and male fish, respectively. The results suggest that sex steroid hormones play a role in sexual growth dimorphism by regulating the expression of GH-IGF axis and MRF genes.
and T enhanced the expression of MRF genes
Recent studies strongly indicate a bidirectional relationship between sexual distinction and sex steroid hormones. In this study, Western blotting and immunohistochemistry were used to estimate the level of estrogen receptor (ER) and androgen receptor (AR) in the liver, gonads, kidney, and intestine of female and male Nile Tilapia, Oreochromis niloticus. The effects of a single injection of 17β-estradiol (E 2 ), testosterone on the gene expression of ER-β and AR-α1 were determined. The expression of ER-β in females was higher than in the male liver and gonad (P<0.05). AR-α1 expression in in males was higher than females in the liver, gonad, and intestine (P<0.05). E 2 increased the expression of ER-β in the livers of female fish (P<0.05). Testosterone (T) increased the expression of AR-α in the liver and intestine of male fish (P<0.05). Contrary to the result of AR, a Western blot analysis indicated that the level of ER protein in the female liver and gonad was significantly higher than that of males (P<0.05). Immunopositive results were the highest in the gonad followed by the intestine and kidney. Moreover, the immunolabeling signal was intensified in females but not in males, as shown via Western blot.
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