Selective demethylation of two CpG sites causes postnatal activation of DAO gene and consequent removal of D-Serine within mouse cerebellum

Programmed epigenetic modifications occurring at early postnatal brain developmental stages may have long-lasting impact on brain function and complex behaviour throughout the life. In this work we provide a comprehensive DNA methylation and mRNA expression analysis, in murine hippocampus, cortex and cerebellum at four different postnatal stages, of genes (D-amino acid oxidase, serine racemase and D-aspartate oxidase) controlling the mammalian brain levels of D-Serine and D-Aspartate. We report for the first time consistent spatio-temporal modifications occurring at D-ammino acid oxidase gene during neonatal development in a specific brain region (cerebellum) and within specific cell-types (astrocytes). Dynamic demethylation at two specific CpG sites located just downstream the transcription start site was sufficient to strongly activate DAO gene, promoting ultimately the complete physiological degradation of cerebellar D-Serine levels few days after mouse birth. Notably, ultradeep methylation analysis allowed us to track the dynamic evolution of DAO epialleles (specific methyl-CpGs arrangements). The present investigation, that can be considered a proxy of single cell analysis, demonstrated that epialleles distribution in the cell populations differs among areas and stages. Grouped epiallelic patterns in the different brain areas and developmental stages at DAO locus likely reflect different cell types composition and functions.