Fig. 4. (A) The ß-MHC promoter drives expression of mouse Tbx5 in the entire ventricle. By contrast, the MLC-2 promoter targets expression of the chick Tbx5-EGFP fusion gene to the right side of heart. (B) In the normal heart, the prospective right ventricle develops as a bulge (black arrowhead). (C) When Tbx5 was misexpressed in the entire heart, this bulge was disrupted. The prospective left ventricle was connected to the conus cordis with a small junction indicated by a red arrowhead. (D-G) When the Tbx5-EGFP fusion gene was expressed by the MLC-2 promoter, GFP signals were observed on the right side of the heart (D,F) and a swelling was formed (E,G) at E1.5 on the prospective right ventricle (red arrowheads). (H) When chick Tbx5 was used to detect its expression in the heart, this transgene was found to be expressed along a gradient in the prospective right ventricle. (I) In some cases, a small protrusion was formed on the surface of the right ventricle (blue arrowhead).

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