Pitx2 is asymmetrically expressed in the left lateral plate mesoderm and derived organs such as heart and gut during chick, mouse and Xenopus development. Pitx2 appears to be downstream effector of Shh and Nodal. Misexpression of Pitx2 is sufficient to produce reversed organs of body rotation. Defect of Pitx2 in human may cause Rieger syndrome. Pitx2 seems to be a key conserved signalling molecules that mediates left-right asymmetry in vertebrate.