Cardiac gene expression was evaluated by ISH. The expression of Tbx2 is apparently decreased in the AVC myocardium overexpressing Tbx20 (arrows in B) compared to its normal expression in the littermate control heart (arrows in A). The expression of Tbx5 (arrows in D) is also decreased throughout the DTG myocardium, compared to littermate control (arrows in C). In contrast, Bmp10 expression in trabecular cardiomyocytes in the DTG heart is comparable to the littermate control (arrows in E and F). Nppa and Smpx are expressed in the DTG myocardium overexpressing Tbx20 (arrows in H and J), as well as in control littermates (arrow in G and I). Likewise the expression of Mlc2v, which marks the developing ventricle, is apparent in DTG hearts (arrow in L) and littermate STG controls (arrow in K). (M) Expression of genes analyzed by ISH was quantified in DTG relative to STG hearts by qRT-PCR of RNA isolated at E9.5 (n = 5). Statistical significance is determined by Student’s t test, where * denotes p < 0.05.