Searching for molecular markers to detect abnormalities of brain sexual differentiation in birds

<p>There is a growing concern about the reduction of reproductive functions in wild birds by the adverse effects of environmental chemicals such as pesticides. In birds, ovarian estrogens during the embryonic period play important roles in the sexual differentiation of the brain. Therefore, estrogenic chemicals, which are exposed to adult female bird and transferred to eggs may have a risk of reduced reproductive functions following abnormal brain sex differentiation. However, because of the mystery of the mechanism of avian brain sexual differentiation, there is no reliable molecular markers to detect abnormalities of avian brain sex differentiation. In this study, we identified the genes, the expression of which differ between sexes and changed with estrogens in the hypothalamus of Japanese quail embryos. Whole transcriptomes from the hypothalamus of male and female embryos at 12 days of incubation was examined by RNA sequencing to find the genes showing a sex difference in the expression. Additionally, transcriptomes from the hypothalamus of male embryos treated with estradiol benzoate (EB) from 6 to 12 days of incubation were analyzed to find estrogen-sensitive genes by comparing vehicle-treated group. As a result, we found 152 genes with sex differences, 92 EB-sensitive genes, and 6 genes showing both sex differences and EB-sensitivity. These 6 genes that are expressed in the hypothalamic brain of Japanese quail embryos during the critical period of brain sexual differentiation may be potential molecular markers to detect abnormalities of avian brain sex differentiation.</p>