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Abstract
Sexual dimorphism of the behaviors or physiological functions in mammals is mainly due to the sex difference of the brain. A number of studies have suggested that the brain is masculinized or defeminized by estradiol converted from testicular androgens in perinatal period in rodents. However, the mechanisms of estrogen action resulting in masculinization/defeminization of the brain have not been clarified yet. The large-scale analysis with microarray in the present study is an attempt to obtain the candidate gene(s) mediating the perinatal estrogen effect causing the brain sexual differentiation. Female mice were injected with estradiol benzoate (EB) or vehicle on the day of birth, and the hypothalamus was collected at either 1, 3, 6, 12, or 24 h after the EB injection. More than one hundred genes down-regulated by the EB treatment in a biphasic manner peaked at 3 h and 12-24 h after the EB treatment, while forty to seventy genes were constantly up-regulated after it. Twelve genes, including Ptgds, Hcrt, Tmed2, Klc1, and Nedd4, whose mRNA expressions were down-regulated by the neonatal EB treatment, were chosen for further examination by semiquantitative RT-PCR in the hypothalamus of perinatal intact male and female mice. We selected the genes based on the known profiles of their potential roles in brain development. mRNA expression levels of Ptgds, Hcrt, Tmed2, and Nedd4 were significantly lower in male mice than females at the day of birth, suggesting that the genes are down-regulated by estrogen converted from testicular androgen in perinatal male mice. Some genes, such as Ptgds encoding prostaglandin D2 production enzyme and Hcrt encording orexin, have been reported to have a role in neuroprotection. Thus, Ptgds and Hcrt could be possible candidate genes, which may mediate the effect of perinatal estrogen responsible for brain sexual differentiation.
Highlights
Sexual dimorphism of the behaviors or physiological functions in mammals is mainly due to the sex difference of the brain
Male and female perinatal Crlj:CD1 (ICR) mice were used for semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis to determine the sex differences in expressions of the candidate genes obtained by the microarray analysis
To acquire a general overview of gene expression by neonatal estradiol benzoate (EB) treatment, transcripts of each time points were plotted in the form of a heatmap (Figures S2 - S6)
Summary
Sexual dimorphism of the behaviors or physiological functions in mammals is mainly due to the sex difference of the brain. Sex-specific patterns of endocrine function, sexual behavior and morphology have been reported in the rats. Female rats show cyclic release of luteinizing hormone (LH), that is a surge-mode secretion (LH surge), while males do not show the surge [1]. Male rodents show mounting behavior, while females show lordosis behavior [1]. It has been well known that the size of some nuclei in the brain show sex difference, and these nuclei are called sexual dimorphic nuclei [2]. The mechanisms of brain sexual differentiation responsible for these sex differences have not been fully clarified yet
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