Chromatin accessibility analysis reveals distinct functions for HDAC and EZH2 activities in early appendage...

Xenopus tropicalis tadpoles have the capacity for scarless regeneration of appendages including the limb and tail. Following injury, transcriptional programs must be activated and inactivated with high spatial and temporal resolution to result in a properly patterned appendage. Functional studies have established that histone-modifying enzymes that act to close chromatin are required for regeneration, but the genomic regions sensitive to these activities are not fully established. Here we show that early inhibition of HDAC or EZH2 activity results in incomplete tail regeneration. To identify how each of these perturbations impacts chromatin accessibility, we applied an assay for transposase-accessible chromatin (ATAC-seq) to HDAC or EZH2-inhibited regenerating tadpoles. We find that neither perturbation results in a global increase in chromatin accessibility, but that both inhibitors have targeted effects on chromatin accessibility and gene expression. Upon HDAC inhibition, regulatory regions neighbouring genes associated with neuronal regeneration are preferentially accessible, whereas regions associated with immune response and apoptosis are preferentially accessible following EZH2 inhibition. Together, these results suggest distinct roles for these two chromatin-closing activities in appendage regeneration.