Sex Differences in Expression of Estrogen Receptor Alpha but not Androgen Receptor mRNAs in the Fetal Lamb Brain

摘要

Gonadal steroid hormones play important roles during critical periods of development to organize brain structures that control sexually dimorphic neuroendocrine responses and behaviors. Specific receptors for androgens and estrogens must be expressed at appropriate times during development in order to mediate these processes. The present study was performed to test for sex differences in the relative expression of estrogen receptor-α (ERα) and androgen receptor (AR) mRNA during the window of time in gestation that is critical for behavioral masculinization and differentiation of the ovine sexually dimorphic nucleus (oSDN) in the sheep. In addition, we examined whether ERα and AR mRNA expression is localized within the nascent oSDN and could be involved in its development. Using quantitative RT-PCR, we found that females expressed more ERα mRNA than males in medial preoptic area and medial basal hypothalamus during the mid-gestational critical period for brain sexual differentiation. No sex differences were found for AR mRNA in any tissue examined or for ERα in amygdala and frontal cortex. Using radioactive in situ hybridization, we found that the distributions of ERα and AR mRNA overlapped with aromatase mRNA, which delineates the boundaries of the developing oSDN and identifies this nucleus as a target for both androgens and estrogens These data demonstrate that the transcriptional machinery for synthesizing gonadal steroid receptors is functional in the fetal lamb brain during the critical period for sexual differentiation and suggest possible mechanisms for establishing dimorphisms controlled by gonadal steroids may exist at the level of steroid hormone receptor expression.