Differential binding of non-canonical histone variant H2A.Z & its de-acetylation is evident in enhanced cognitive function

Abstract

Although histone modifications and DNA methylation have been meticulously studied in the context of learning & memory formation, very few studies have demonstrated non-canonical histone variants as potential regulators of memory formation. Compared to canonical histones, these histone variants are expressed independently of DNA replication and are important for many physiological events as they confer altered chromatin structures, thereby regulating transcription. Recently, H2A.Z (variant of canonical histone, H2A) has been reported as a novel epigenetic regulator in memory formation (Zovkic et. al. 2014), which raised the question, whether differential binding of H2A.Z or its modification (e.g acetylation) across the whole genome could be a stable modulator for life-long memory acquisition and cognition. Here, we investigated genomic regions bound by H2A.Z and its acetylated variant (H2A.Zac) using chromatin immunoprecipitation followed by sequencing (ChIP-seq) in FACS-sorted neuronal and nonneuronal nuclei from hippocampal CA1 region. Initially, mRNA levels of H2afz (gene of H2A.Z) were assessed in CA1 region of aged (16 months old) and Alzheimer’s model mice (5XFAD) comparing them to young (3 months old) and wild type mice respectively. Furthermore, ChIP protocols for H2A.Z and H2A.Zac were optimized, as it has not been done before in this context. As a model of enhanced cognition, hippocampal CA1 regions from mice subjected to 4 months enriched environment (EE) were used for ChIP-seq against H2A.Z and H2A.Zac, comparing to home caged animals as controls. ChIP-seq analysis showed decreased binding of H2A.Z and its de-acetylation at specific promoter regions in CA1 neurons upon environmental enrichment. Promoters with decreased binding or decreased acetylation were found to be involved in genes functionally associated with neurogenesis, synaptic plasticity and several biosynthetic pathways. Further study is needed to prove their effect on transcription of those genes.