Fig. 3. TBX5 and TBX20 morphants fail to undergo looping and chamber formation and display reduced cardiac cell numbers. Cryosections of TBX5 and TBX20 morphant hearts taken at the anterior (outflow), middle (ventricular) and posterior (atrial) regions. (A-D) ControlMO, (E-H) TBX5MO and (I-L) TBX20MO. Sections stained for tropomyosin (red), DAPI (blue) and cardiac actin (green). (D,H,L) Same sections as B, F and J stained with cardiac actin. In the looped control heart, the middle ventricular section also contains the atrium. (M) Mean number of cells per heart obtained by cell counts of heart tissue in serial sections derived from a minimum of three embryos.