Abstract 1238: CHF1/Hey2 Plays a Pivotal Role in Left Ventricular Maturation through Suppression of Ectopic Atrial Gene Expression
CHF1/Hey2 knockout mice show a thin walled left ventricle, however, the molecular basis for this phenotype is unknown. To assess for potential alteration in regional myocardial specification and differentiation, we performed in situ hybridization using ventricular, trabecular and atrial markers. No marked differences were observed between KO and wildtype mice in expression patterns of ventricular markers (mlc1v, mlc2v, n-myc and beta-MHC) and a trabecular marker (bmp10). These results suggested that the left ventricular compact myocardium of CHF1/Hey2 KO mice has ventricular cell identity, but not trabecular cell identity. Interestingly, the T-box transcriptional factor tbx5, which is normally expressed in the atrium and trabeculae, was expressed ectopically in the compact myocardium of the left ventricle of CHF1/Hey2 KO mice, the domain where CHF1/Hey2 is normally expressed. We also examined the expression pattern of the tbx5-dependent genes Atrial Natriuretic Factor (ANF) and connexin 40 (cx40). As expected, ANF and cx40 were also expressed ectopically in the left ventricular compact myocardium of CHF1/Hey2 KO mice. These results suggested that tbx5 is a downstream target gene of CHF1/Hey2. Furthermore, we examined the other atrial and trabecular markers (mlc1a and mlc2a), which were also expressed ectopically in the compact myocardium of the left ventricle of CHF1 KO mice. These results suggest that left ventricle has not only ventricular but also atrial cell character. To provide further evidence that these alterations in gene expression are dependent upon CHF1/Hey2, we crossed myocardial specific CHF1/Hey2 transgenic mice with the knockouts. The CHF1/Hey2 transgene suppressed ectopic expression of tbx5, ANF, cx40, mlc1a and mlc2a in the ventricular compact myocardium, but did not suppress normal expression in the atrium and trabeculae. These results suggested that CHF1/Hey2 is not sufficient to specify ventricular identities but may facilitate ventricular differentiation. Overall, our results indicate that CHF1/Hey2 regulates left ventricular maturation by suppressing atrial identity during heart development.