| Summary: | Methyl CpG binding protein-2 (MeCP2) isoforms (E1 and E2) are important epigenetic regulators in brain cells. Accordingly, MeCP2 loss- or gain-of-function mutation causes neurodevelopmental disorders, including Rett syndrome (RTT), <i>MECP2</i> duplication syndrome (MDS), and autism spectrum disorders (ASD). Within different types of brain cells, highest MeCP2 levels are detected in neurons and the lowest in astrocytes. However, our current knowledge of <i>Mecp2</i>/MeCP2 regulatory mechanisms remains largely elusive. It appears that there is a sex-dependent effect in X-linked MeCP2-associated disorders, as RTT primarily affects females, whereas MDS is found almost exclusively in males. This suggests that <i>Mecp2</i> expression levels in brain cells might be sex-dependent. Here, we investigated the sex- and cell type-specific expression of <i>Mecp2</i> isoforms in male and female primary neurons and astrocytes isolated from the murine forebrain. Previously, we reported that DNA methylation of six <i>Mecp2</i> regulatory elements correlated with <i>Mecp2</i> levels in the brain. We now show that in male brain cells, DNA methylation is significantly correlated with the transcript expression of these two isoforms. We show that both <i>Mecp2</i> isoforms are highly expressed in male neurons compared to male astrocytes, with <i>Mecp2e1</i> expressed at higher levels than <i>Mecp2e2</i>. Our data indicate that higher DNA methylation at the <i>Mecp2</i> regulatory element(s) is associated with lower levels of <i>Mecp2</i> isoforms in male astrocytes compared to male neurons.
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