The Expression Pattern of Insulin-Like Growth Factor Subtype 3 (igf3) in the Orange-Spotted Grouper and Its Function on Ovary Maturation.

A new insulin-like growth factor (Igf) subtype 3 () has recently been found in the bony fish orange-spotted grouper (). However, the role of in the maturation of the ovary and sex differentiation in is currently unknown. We examined the ovarian localization and receptor binding of the novel ortholog Igf3 using qRT-PCR, and Western blotting, combined with in situ hybridization and immunohistochemistry methods. Results demonstrated the presence of mRNA and protein in mature oocytes. Furthermore, Igf3 protein expression was not detected in testis, brain, kidney and liver homogenates. The calculated molecular weight of Igf3 was 22 kDa, which was consistent with the deduced amino acid sequence from the full-length open reading frame. The immunoreactivity showed that Igf3 was strongly present in the follicle staining fully-grown stage. The mRNA expression level was significantly positively correlated with ovarian follicular maturation. Meanwhile, Igf3 increased germinal-vesicle breakdown in a time- and dose-dependent manner. In vitro, treatment of primary ovarian cells with Igf3 up-regulated significantly the mRNA expression level of genes related to sex determination and reproduction such as forkhead boxl2 (), dosage-sensitive sex reversal adrenal hypoplasia critical region on chromosome x gene 1 (), cytochrome P450 family 19 subfamily member 1 a (), cytochrome P450 family 11 subfamily a member 1 a () and luteinizing hormone receptor 1 (). Overall, our results demonstrated that promotes the maturation of the ovary and plays an important role in sex differentiation in .