Figure 1.

(A,B) Illustrations of Pitx2 expression in the developing fetal embryo (E14.5) in longitudinal histological sections. (A) Illustrate the expression of Pitx2 at the level of the left ventricle (lv) and left atria (la), showing the robust expression of Pitx2 in the developing left atrial chamber, whereas (B) illustrates the expression of Pitx2 at the level of the right ventricle (rv) and right atrium (ra). Observe the marked contrast of expression between the right atrium (low) and the left atrium (high) as revealed by the arrows. Note also the dorso-ventral difference of Pitx2 expression at the ventricular level [arrowheads, (A,B)]. (C) Schematic representation of the current state-of-the-art role of Pitx2 in the developing and adult atrial chambers linked to atrial arrhythmogenesis. Pitx2 controls miR-1 expression in the left atrial chamber, providing thus a regulatory mechanism for I_K1 and Gja1 function. In addition Pitx2 regulates I_Na while inhibits the expression right atrial (Bmp10) and sinoatrial (Shox2) markers in the left atrium, which in turn play key regulatory roles on cardiomyocyte cell cycle and pacemaker activity, providing additional links to atrial arrhythmias.