Mutations in <i>Bcl9</i> and <i>Pygo</i> genes cause congenital heart defects by tissue-specific perturbation of Wnt/β-catenin signaling

Abstract

Bcl9 and Pygopus (Pygo) are obligate Wnt/β-catenin cofactors in <i>Drosophila</i>, yet their contribution to Wnt signaling during vertebrate development remains unresolved. Combining zebrafish and mouse genetics, we document a conserved, β-catenin-associated function for BCL9 and Pygo proteins during vertebrate heart development. Disrupting the β-catenin-BCL9-Pygo complex results in a broadly maintained canonical Wnt response yet perturbs heart development and proper expression of key cardiac regulators. Our work highlights BCL9 and Pygo as selective β-catenin cofactors in a subset of canonical Wnt responses during vertebrate development. Moreover, our results implicate alterations in <i>BCL9</i> and <i>BCL9L</i> in human congenital heart defects.