Sex-specific differences in expression of histone demethylases Utx and Uty in mouse brain and neurons

Abstract

Although X inactivation is thought to balance gene expression between the sexes, some genes escape inactivation, potentially contributing to differences between males and females. Utx (ubiquitously transcribed tetratricopeptide repeat gene on X chromosome) is an escapee gene that encodes a demethylase specific for lysine 27 of histone H3, a mark of repressed chromatin. We found Utx to be expressed higher in females than in males in developing and adult brains and in adult liver. XX mice had a higher level of Utx than XY mice, regardless of whether they had testes or ovaries, indicating that the sexually dimorphic gene expression was a consequence of the sex chromosome complement. Females had significantly higher levels of Utx than males in most brain regions except in the amygdala. The regional expression of the Y-linked paralogue Uty (ubiquitously transcribed tetratricopeptide repeat gene on Y chromosome) was somewhat distinct from that of Utx, specifically in the paraventricular nucleus of the hypothalamus (high Uty) and the amygdala (high Utx), implying that the two paralogues may be differentially regulated. Higher expression of Utx compared with Uty was detected in P19 pluripotent embryonic carcinoma cells as well as in P19-derived neurons. This transcriptional divergence between the two paralogues was associated with high levels of histone H3 lysine 4 dimethylation at the Utx promoter and of histone H4 lysine 16 acetylation throughout the gene body, which suggests that epigenetic mechanisms control differential expression of paralogous genes.

Figure 1.

a, b, Expression of Utx (a) and Ddx3x (b) by in situ hybridization on sections of adult mouse brain. Specific brain regions, including the olfactory bulb (OB), piriform cortex (Pir), habenula (H), hypothalamus [SCN, ventromedial hypothalamic nucleus (VMH), arcuate nucleus (Arc), etc.], hippocampus (CA and DG), and cerebellum (Cb) had a relatively higher expression level. Utx was detected specifically in the amygdala (A). Ddx3x was detected in the fornix (F), whereas Utx was not. 7N, Facial nucleus; BST, bed nucleus of the stria terminalis; C, cortex; DM, dorsomedial hypothalamic nucleus; EPI, external plexiform layer of olfactory bulb; LS, lateral septal nucleus; M, mammillary nucleus; MPOA, medial preoptic area; PMV, premammillary nucleus; Pn, pontine nuclei; PVA, paraventricular thalamic nucleus; RtTg, reticulotegmental nucleus; SuMM, supramammillary nucleus; St, striatum.

Figure 2.

Utx expression quantified by in situ hybridization to sections of male and female adult mouse brains. Female mice had significantly higher Utx expression than males in the cortex, striatum, SCN, PVN, pyramidal layer of the hippocampus (CA1/CA3), DG, and habenula, but not in the amygdala. The in situ hybridization labeling intensity was measured as the mean pixel density minus background in six to eight pairs of females and males processed in parallel on the same slides. *p < 0.05.

Figure 3.

Utx expression in male and female neonatal mouse brains and in adult livers. Expression determined by Northern blot analysis was higher in females compared with males. Gapdh was used as a loading control.

Figure 4.

Utx expression in brains from XX females, XY⁻ females, XXSry males, and XY⁻Sry males. Each of the three samples per genotype was derived from two adult brains. Gapdh was used as a loading control. Error bars indicate SEM. *p < 0.05.

Figure 5.

Utx and Uty differential expression in male mouse brain. Top, Expression patterns of Uty and Utx by in situ hybridization on adjacent adult male brain sections. Uty was expressed more highly in the PVN, but less in the amygdala (A) relative to Utx. The graphs below show the quantification of expression levels of Uty and Utx in the amygdala and PVN, using the habenula (H) as a reference area, based on sections that contained all three regions (n = 6). *p < 0.05.