Bidirectional Post-Mitotic Reprogramming of H3K27me3 Underlies Neuronal Maturation and Plasticity in the Cerebellum

Terminally differentiated cells including neurons dynamically regulate their genome despite leaving the cell-cycle early in life in order to assimilate new information throughout adulthood. The molecular basis of this dynamic gene regulation remains poorly understood yet when disrupted contributes to defects in synaptic plasticity and cognition. Work from our lab has shown the dynamic, post-mitotic redistribution of the repressive histone modification H3K27me3 in a locus-specific fashion across the genome of the maturing cerebellar granule neuron (CGN). We are interested in asking how a fully fate committed neuron marks particular loci for differential histone methylation, how is this controlled in maturing neurons and what is the biological consequence of this process.

We are using the maturation of CGNs in the murine cerebellum as a model system to study post-mitotic chromatin regulation. CGN-precursors terminally differentiate postnatally and undergo several timed gene expression events in order to migrate, populate the innermost layer of the cerebellar cortex, and undergo dendrite outgrowth and synaptogenesis. We are utilizing Chromatin Immunoprecipitation to ask how CGNs in culture and in vivo redistribute H3K27me3 in response to genetic, pharmacological, and physiological perturbations. Additionally, we use CRISPR-based epigenome editing methods to ask whether this modification causally acts to regulate gene expression.

We find that the activity of H3K27me3 regulators EZH2 and KDM6B temporally regulates genes essential for cerebellar maturation. EZH2-mediated H3K27me3 is required for expression of genes that signify commitment to the neuronal fate, whereas KDM6B-mediated H3K27 demethylation promotes the expression of a set of late expressed CGN genes that are associated with maturation of synaptic function. Taken together these data show that dynamic regulation of the repressive chromatin state afforded by H3K27me3 is important for timing programs for gene expression in maturing postmitotic neurons long after closure of the period of fate commitment.