Sex differences in active DNA demethylation machinery during the critical period of brain masculinization

Abstract

In mammals, perinatal peaks in gonadal testosterone organize a sex-typical neural circuitry during sensitive periods of development and a growing body of evidence suggest that epigenetic mechanisms are implicated. Some of the hormonal effects determine stable, sex-specific patterns of gene expression in neurons leading to the differentiation of neurochemical phenotypes relevant for the display of complex social behaviors in adulthood. We recently found that a neonatal inhibition of DNA methylation or demethylation reduces or eliminates sex differences in neurochemical phenotypes found in hypothalamic regions of the mouse brain. Here, we evaluated gene expression of TET 1-2-3, GAD45a-b and TDG (involved in the removal and replacement of 5-methylcytosine and 5-hydroxymethylcytosine) and the mRNA expression of the oxytocin receptor (OTR). mRNA expression was evaluated by qPCR in brain punches of prefrontal cortex (PFC) and preoptic area (POA) at postnatal day (P) 7 and P20. In PFC, we found sex differences (males > females) in TET3, TDG and Gad45b expression (p<0.05) and a trend for higher OTR-expression in males (p=0.06) at P7 suggesting higher DNA demethylation during the critical period of sexual differentiation. No sex differences were found at P20. Other brain regions and oxytocin expression are being evaluated. Overall, these results suggest that a sex-specific pattern of active DNA demethylation machinery could underline the organizational effects of hormones.