X chromosome encoded histone demethylase UTX regulates mammalian axon regeneration via microRNA-124
Neurons in the mammalian central nervous system (CNS) gradually lose their intrinsic regeneration capacity during maturation mainly because of altered transcription profile. Recent studies have made great progress by identifying genes that can be manipulated to enhance CNS regeneration. However, as a complex process involving many genes and signaling networks, it is of great importance to deciphering the underlying neuronal chromatin and transcriptomic landscape coordinating CNSregeneration. Here we identify UTX, an X-chromosome associated gene encoding a histone demethylase, as a novel regulator of mammalian neural regeneration. We demonstrate that UTX acts as a repressor of spontaneous axon regeneration in the peripheral nerve system (PNS). In the CNS, either knocking out or pharmacological inhibiting UTX in retinal ganglion cells (RGCs) leads to significantly enhanced neuronal survival and optic nerve regeneration. RNA-seq profiling revealed that deleting UTX switches the RGC transcriptomics into a developmental-like state. Moreover, microRNA-124, one of the most abundant microRNAs in mature neurons, is identified as a downstream target of UTX and blocking endogenous microRNA124-5p results in robust optic nerve regeneration. These findings revealed a novel histone modification-microRNA epigenetic signaling network orchestrating transcriptomic landscape supporting CNS. Overall design: To gain mechanistic insights into promoting effect of UTX on axon regeneration, we performed RNA sequencing (RNA-seq) of the enriched RGCs across different developmental stages (postnatal day 1, 14 and 21) and at 3 days after injury of adult (P42) wild type (AAV2-GFP) or UTX knockout mice (AAV2-Cre). Dissociated RGCs were labeled with Thy1.2 antibody, subjected to  fluorescence-activated cell sorting (FACS) for RGC enrichment, and identified by labelling for Tuj1. Totally, 13 bulk RNA-seq libraries were generated from FACS-purified RGCs.