PRC2-mediated repression is essential to maintain identity and function of differentiated dopaminergic and serotonergic neurons [ChIP-Seq]

Neurons of the CNS must maintain their distinct identity over an entire lifespan. Apart from instructive information provided by transcription factors driving neuron specific genes, other gene programs need to be permanently silenced. The mechanisms governing enduring gene-silencing in neurons are largely unknown, as are the consequences if they fail. Here we show that loss of the Polycomb repressive complex 2 (PRC2) obligate unit Eed in differentiated murine midbrain dopamine (mDA) neurons resulted in progressive loss of the H3K27me3 histone modification followed by upregulation of PRC2 targets, also highly enriched for the constitutive heterochromatin H3K9me3 modification. This was followed by reduced expression of mDA neuron-identity genes, particularly evident in the Substantia nigra pars compacta. Consequently, mDA-neuronal function was severely disrupted, causing parkinsonian-like motor skill deficits. Deletion of Eed in differentiated serotonergic (5HT) neurons resulted in a similar upregulation of PRC2-targets and reduced expression of genes defining 5HT neurons, which promoted loss of serotonergic identity followed by loss of function and altered behaviour. Overall, our results reveal that PRC2 inactivation leads to a selective and progressive loss of mDA or 5HT neuronal identity and function, but not to any loss of cells. Thus, our study shows that PRC2-dependent maintenance of neuronal identity is essential and safeguards against expression of other non-relevant gene programs and loss of neuronal function. Evaluation of three different histone marks in dopaminergic neurons with and without functional Polycomb repressive complex 2 (PRC2)