Early sex differences in histone methyl transferase EZH2 expression in developing hypothalamus of the mouse brain

Abstract

In mammals, the primary agents causing phenotypic sex differences are encoded by sex chromosomes. Many of X-and Y-linked genes are epigenetic modifiers and pivotal evidence in past 7 years implicates epigenetic mechanisms as mediators in brain sexual differentiation. We have recently demonstrated that X‑linked histone H3K27 demethylase Kdm6a regulates sexually dimorphic differentiation of hypothalamic neurons through a direct regulation of Neurogenin 3. Kdm6a interacts with numerous epigenetic modifiers, such as histone methyltransferases (HMT), implying that both epigenetic marks could act together, influencing each other in a context-dependent manner, writing a histone crosstalk language. Since H3K27 methylation regulates Ngn3 we first evaluated the mRNA expression of the HMT enzymes EZH1/2 in the hypothalamus of male and female mice at embryonic day 15 by qPCR. We found sex specific expression of Ezh2, higher in males than in females (p = 0.01). We next used the Four Core Genotype Mouse Model to evaluate a direct regulation of sex chromosomes (XX vs XY) independently of gonadal type. No differences were observed between genotypes (p > 0.05). Our results suggest that early sex differences in Ezh2 enzyme could determine a sexually dimorphic crosstalk between posttranslational histone modifications acting on H3K27 residues during development. Current experiments are evaluating the effect of Ezh2 inhibition on Ngn3 expression in neuronal hypothalamic cultures.