Maternal Influence on Exonic CpG Island Methylation in the Developing Hippocampus [HELP]

Maternal 5-HT1A-receptor (R) is required for the timely development of the hippocampus and the establishment of emotional behaviors in Swiss-Webster (SW) mice. A partial and/or complete loss of maternal 5-HT1AR results in delayed ventral dentate granule cell (v-DGC) development and subsequent anxiety-like phenotype in the wild-type offspring by a non-genetic, presumably epigenetic mechanism. Here we tested v-DGCs for genome-wide DNA methylation changes elicited by the receptor deficient maternal environment. We identified a set of hypomethylated regions in the offspring of receptor deficient mothers. A significant fraction of these maternal-differentially methylated regions (m-DMRs) mapped to strong CpG islands, sequences that are typically not methylated or if methylated, resistant to environmental-induced changes. Many m-DMRs mapped to exons and some were associated with expression changes. Their hypomethylation was due to an arrest in de novo methylation and, to a lesser extent, to demethylation during postnatal life indicating that the perturbation in methylation coincides with the developmental delay in DGC maturation in the offspring of receptor deficient mothers. Inhibiting methylation in differentiating neurons impaired their maturation further suggesting a link between de novo methylation and neuronal differentiation. These data suggest that methylation at specific exonic CpG-islands may contribute to the mechanism through which maternal 5-HT1AR modulates hippocampal development and consecutively the level of anxiety in the SW offspring. Reduced 5-HT1AR-binding has been reported in individuals, particularly in association with anxiety/depression, including peri/postpartum depression. Therefore, maternal receptor deficit may contribute, via a non-genetic mechanism, to the high prevalence and heritability of anxiety disorders in human. Comparison of methylation patterns in ventral Dentate Gyrus cells of wild type mice versus 5HT1A receptor knockouts, as well as the effect of the maternal 5HT1A genotype