Splashed E-box and AP-1 motifs cooperatively drive regeneration-response and shape regeneration abilities

Abstract

Injury triggers genetic program to induce gene expression for regeneration. Several studies have recently reported the identification of regeneration-response enhancers (RREs) in zebrafish; however, it remains unclear whether a common mechanism operates in RREs. Here, we show that E-box and activator protein 1 (AP-1) motifs cooperatively function as RREs. We identified three RREs from the fn1b promoter by a search of conserved sequences and an in vivo transgenic assay for regeneration-response in zebrafish. Two of them derived from transposons displayed RRE activity only when combined with the -0.7 kb fn1b promoter, while another non-transposable element functioned as a standalone enhancer. A search for transcription factor-binding motifs and validation by transgenic assay revealed that both of E-box and AP-1 motifs are necessary and sufficient for RREs. Such RREs responded to variety of tissue injuries including zebrafish heart and Xenopus limb bud regenerations. Our findings highlight that regeneration is regulated by merging two activating signals evoked by tissue injuries. It is speculated that a large pool of potential enhancers in the genome shaped regenerative capacities during evolution. SUMMARY STATEMENTThe study revealed that regeneration-response enhancer is composed of two transcription factor-binding motifs. The fidelity of regeneration-dependent gene expression is ensured by merging two activating signals evoked by injuries.