Cooperative recruitment of Yan to paired high affinity ETS sites organizes repression to confer specificity and robustness to cardiac cell fate specification

Cis regulatory elements (CREs) are defined by unique combinations of transcription factor binding sites. Emerging evidence suggests that the number, affinity and organization of sites play important roles in regulating enhancer output and ultimately gene expression. Here, we investigate how the cis-regulatory logic of a tissue-specific CRE responsible for even-skipped (eve) induction during cardiogenesis organizes the competing inputs of two ETS members, the activator Pointed (Pnt) and the repressor Yan. Using a combination of reporter gene assays and CRISPR-Cas9 gene editing, we show that Yan and Pnt have distinct preferences for affinity of sites. Not only does Yan prefer high affinity sites, but a tandem pair of such sites is necessary and sufficient for Yan to tune Eve expression levels in newly specified cardioblasts and to block ectopic Eve induction and cell fate specification in surrounding progenitors. Mechanistically, the cooperative Yan recruitment promoted by this conserved high affinity ETS pair not only biases Yan-Pnt competition at the specific CRE, but also organizes Yan repressive complexes in 3D across the eve locus. Taken together our results uncover a novel mechanism by which differential interpretation of CRE syntax by a competing repressor-activator pair can confer both specificity and robustness to developmental transitions.