Abstract 14621: Disruption of the Myocardial Gata4 and Tbx5 Interaction Results in Defects in Cardiomyocyte Proliferation and Atrioventricular Septation
GATA4 and TBX5 encode for cardiac transcription factors that play central roles in heart development and mutations in these genes are associated with human congenital heart defects. We previously reported that Gata4+/-;Tbx5+/- compound heterozygote mice display embryonic lethality after E15.5 with decreased myocardial proliferation, thin myocardium and atrioventricular septal defects (AVSD). To elucidate the molecular basis for this genetic interaction, we examined Gata4+/-;Tbx5+/- mouse embryos and found decreased atrial and ventricular myocardial wall thickness as early as E11.5, prior to atrioventricular septation. We noted that while Gata4 and Tbx5 are co-expressed in the murine atria and ventricle until E13.5, Tbx5 ventricular expression is drastically reduced after E15.5. Colocalization and coimmunoprecipitation studies demonstrated interaction of Gata4 and Tbx5 in the atria throughout development but reduced ventricular interaction after E15.5. To determine the cell lineages in which the genetic interaction was functionally significant in vivo, we generated mice that were heterozygous for Gata4 in the myocardium or endocardium and haploinsufficient for Tbx5 (referred to as Gata4MyoDel/wt;Tbx5+/- and Gata4EndoDel/wt;Tbx5+/-, respectively). The Gata4MyoDel/wt;Tbx5+/- mice displayed embryonic lethality, thin myocardium with reduced cell proliferation, and AVSD similar to the Gata4+/-;Tbx5+/- embryos while the Gata4EndoDel/wt;Tbx5+/- mice had no overt phenotype. Reduced expression of Cdk4 and Cdk2, cyclin-dependent kinases important for cell proliferation, was noted in the Gata4+/-;Tbx5+/- hearts, and siRNA knockdown of Gata4 and Tbx5 in primary cardiomyocytes caused similar gene expression changes. Interestingly, Cdk2;Cdk4 double knockout mice display a similar cardiac phenotype as Gata4+/-;Tbx5+/- embryos. Cdk4 is a known direct target of Gata4. In transactivation assays using the murine Cdk4 promoter, Tbx5 showed no activation ability but when co-expressed with Gata4 demonstrated synergistic activation. Our findings suggest that myocardial Gata4 and Tbx5 regulate cardiomyocyte proliferation during embryogenesis and disruption of this interaction causes a thin walled myocardium and AVSD.
- © 2013 by American Heart Association, Inc.