Comprehensive mapping of 5-hmC epigenetic dynamics in axon regeneration

In contrast to CNS neurons, dorsal root ganglia (DRG) neurons can switch to a regenerative state after peripheral axotomy. In a screen for chromatin regulators of the regenerative responses in this conditioning lesion paradigm, we identified Tet methylcytosine dioxygenase 3 (Tet3) as upregulated, along with increased 5-hydroxymethylcytosine (5-hmC) in DRG neurons. We generated genome-wide 5-hmC maps in adult DRG, which demonstrated that peripheral and central axotomy (no regenerative effect) triggered differential 5-hmC changes that are associated with distinct signaling pathways. 5-hmC was altered in half of regeneration-associated genes (RAGs), supporting its role for RAG regulation. Our analyses predicted transcription factors HIF-1, STAT and IRF that may collaborate with Tet3 for 5-hmC modifications. Intriguingly, central axotomy lead to widespread 5-hmC modifications with little overlap with peripheral axotomy, thus potentially constituting a roadblock for regeneration. Our study revealed 5-hmC as a previously unrecognized epigenetic mechanism underlying the divergent responses after axonal injury. Overall design: 5-hmC profiles generated from DRGs at 3 conditions (PL, DCL, Ctrl) plus Input, performed in triplicate