Figure 9.

Viewpoint for describing direction of rotation is always the outflow tract (OFT). Left- and right- originating regions of the embryonic myocardium are reported in green and magenta, respectively. Transversal sections are shown next to the corresponding cartoon. In wild-type hearts, at the end of cardiac jogging, twisting of the heart tube results in disposition of left-originating cardiomyocytes toward the outer curvatures of both the ventricle and atrium. The resulting twisting of the heart tube is driven by the clockwise rotation of the ventricle and counterclockwise rotation of the atrium, around a fixed hinge, the AV canal. In oug hearts, cardiac jogging is completed properly, but progression of cardiac looping is defective. Reduced twisting of the heart tube and chamber expansion are observed. Defective looping is accompanied by an expansion of the expression domain of tbx2b (spotted pattern), especially noticeable at the AV canal (see also Figure 1H). Legends: R: Right; L: Left.