A Cardiac Transcriptional Enhancer is Repurposed During Regeneration to Activate an Anti-proliferative Program

Zebrafish have a high capacity to regenerate their hearts. Several studies have surveyed transcriptional enhancers to understand how gene expression is controlled during heart regeneration. We have identified REN or the r unx1 en hancer that during regeneration regulates the expression of the nearby runx1 gene. We show that runx1 mRNA is reduced with deletion of REN (Δ REN) and cardiomyocyte proliferation is enhanced in both Δ REN and Δ runx1 mutants only during regeneration. Interestingly, in uninjured hearts, Δ REN mutants have reduced expression of adamts1 , a nearby gene that encodes a Collagen protease. This results in excess Collagen within cardiac valves of uninjured hearts. The Δ REN Collagen phenotype is rescued even by Δ runx1 mutations, suggesting that in uninjured hearts REN regulates adamts1 independently of runx1 . Taken together, this suggests that REN is rewired from adamts1 in uninjured hearts to stimulate runx1 transcription during regeneration. Our data point to a previously unappreciated mechanism for gene regulation during zebrafish heart regeneration. We report that an enhancer is rewired from expression in a distal cardiac domain to activate a different gene in regenerating tissue.