Zebrafish chemical screening reveals an inhibitor of Dusp6 that expands cardiac cell lineages

The dual-specificity Phosphatase 6 (Dusp6) functions as a feedback regulator of Fibroblast Growth Factor (FGF) signaling to limit the activity of extracellular signal-regulated kinases (ERKs) 1 and 2. We have identified a small-molecule inhibitor of Dusp6-(E)-2-benzylidene-3-(cyclohexylamino)-2,3-dihydro-1H-inden-1-one (BCI)-using a transgenic zebrafish chemical screen. BCI treatment blocked Dusp6 activity and enhanced FGF target gene expression in zebrafish embryos. Docking simulations predicted an allosteric binding site for BCI within the Phosphatase domain. In vitro studies supported a model in which BCI inhibits Dusp6 catalytic activation by ERK2 substrate binding. We used BCI treatment at varying developmental stages to uncover a temporal role for Dusp6 in restricting cardiac progenitors and controlling heart organ size. This study highlights the power of in vivo zebrafish chemical screens to identify new compounds targeting Dusp6, a component of the FGF signaling pathway that has eluded traditional high-throughput in vitro screens.