Gata4 potentiates second heart field proliferation and Hedgehog signaling for cardiac septation.

Abstract

<i>GATA4</i>, an essential cardiogenic transcription factor, provides a model for dominant transcription factor mutations in human disease. Dominant GATA4 mutations cause congenital heart disease (CHD), specifically atrial and atrioventricular septal defects (ASDs and AVSDs). We found that second heart field (SHF)-specific <i>Gata4</i> heterozygote embryos recapitulated the AVSDs observed in germline <i>Gata4</i> heterozygote embryos. A proliferation defect of SHF atrial septum progenitors and hypoplasia of the dorsal mesenchymal protrusion, rather than anlage of the atrioventricular septum, were observed in this model. Knockdown of the cell-cycle repressor phosphatase and tensin homolog (<i>Pten</i>) restored cell-cycle progression and rescued the AVSDs. <i>Gata4</i> mutants also demonstrated Hedgehog (Hh) signaling defects. Gata4 acts directly upstream of <i>Hh</i> components: Gata4 activated a <i>cis</i>-regulatory element at <i>Gli1</i> in vitro and occupied the element in vivo. Remarkably, SHF-specific constitutive Hh signaling activation rescued AVSDs in Gata4 SHF-specific heterozygous knockout embryos. Pten expression was unchanged in <i>Smoothened</i> mutants, and Hh pathway genes were unchanged in <i>Pten</i> mutants, suggesting pathway independence. Thus, both the cell-cycle and Hh-signaling defects caused by dominant <i>Gata4</i> mutations were required for CHD pathogenesis, suggesting a combinatorial model of disease causation by transcription factor haploinsufficiency.