Tissue Regeneration Enhancer Element Discovery by Chromatin Accessibility Profiling of Regenerating Zebrafish Fins

Mammalian genomes likely encode all gene products required to regenerate an amputated limb, yet they lack the correct instructions for strategically modulating those gene products to accomplish limb regeneration. Zebrafish and many other non-mammalian vertebrates possess these instructions, which exist as gene cis-regulatory elements. Here, to identify candidate tissue regeneration enhancer elements (TREEs) important for zebrafish fin regeneration, we performed ATAC-seq from bulk tissue or purified fibroblasts of uninjured and regenerating caudal fins. We identified thousands of DNA regions from each tissue type with dynamic accessibility during regeneration, and assigned these regions to proximal genes with corresponding changes in RNA levels. To determine whether these profiles revealed bona fide TREEs, we tested the sufficiency of several sequences in stable transgenic and mutant lines. These experiments identified new regulatory sequences near several induced and/or required genes, including fgf20a, cx43, and mdka, with unique expression domains for each confirmed TREE. Deletion of TREE sequences from the zebrafish genome revealed requirements and redundancies surrounding cis-regulatory regions. Our study generates a novel resource for dissecting the regulatory mechanisms of appendage regeneration.