A threshold level of JNK activates damage-responsive enhancers via JAK/STAT to promote tissue regeneration

Tissue regeneration requires the directed activity of numerous genes, which are often reused from development. Although the identities of many key factors have been established, how their expression is activated and subsequently coordinated over regenerative time remains unclear. One highly conserved signal central to diverse examples of regeneration is the stress activated MAP kinase JNK. In Drosophila , damage-induced JNK signaling promotes expression of multiple genes that direct proliferation, growth and changes in cellular identity. However, how these JNK targets are selectively upregulated in the context of injury, and subsequently expressed in specific patterns responsible for repair is unknown. Our work previously characterized Damage-Responsive, Maturity-Silenced (DRMS) enhancers; regulatory elements that are activated directly by JNK to promote regenerative gene expression. Here we have investigated how the damage-responsive (DR) module of these enhancers are engaged, finding that cell death is entirely dispensable for their activation. We identify JAK/STAT signaling as an additional direct input into DR enhancers downstream of JNK, which acts to broaden DR enhancer activity into the wound periphery where JNK levels are insufficient to promote regenerative gene expression alone. Finally, we demonstrate that a distinct threshold level of JNK activity exists that must be achieved to activate regenerative signaling via DR enhancers, which, alongside input from JAK/STAT, results in their temporally and spatially appropriate expression necessary for regeneration.