Enhancer trapping method. The synthetic transposase mRNA, the transposon donor plasmid containing transposable elements with a minimal promoter, and the gene encoding green fluorescent protein (GFP) are co-injected into fertilized zebrafish eggs. The construct is excised from the donor plasmid and integrated into the endogenous genome. The activity of the “trapped” enhancer can be visualized in the injected embryo when the inserted transgene is expressed under control of nearby enhancers.

Zebrafish gene regulatory programs of heart regeneration. (A,B) Zebrafish mature heart: uninjured, injured heart after ablation, and regenerative heart by cardiomyocyte proliferation. (C) Enhancers that have no detectable activity in uninjured heart direct gene expression during heart regeneration.

Model of enhancer RNA mechanism. (A) Enhancer and gene sequences in chromatin prior to gene activity. (B) Partially or fully assembled sets of TFs can associate with the enhancer and the gene promoter. In the active state, the enhancer and its transcript may physically associate with the gene, triggering formation of a mediator complex [20,21,22,23,24].