The Pitx2 protein in mouse development.

The Rieger syndrome, an autosomal dominant disorder involving ocular, dental, and umbilical defects is caused by mutations in PITX2, a Bicoid-type homeobox protein. Mouse Pitx2 mRNA is expressed in eye, tooth and umbilicus consistent with the human Riegers phenotype. Moreover, Pitx2 is involved in the Nodal/Sonic hedgehog pathway that determines left/right polarity. In this report we demonstrate a 32-kDa polypeptide on Western blots of nuclear extracts from a rat pituitary cell line, using a Pitx2 specific antibody (designated P2R10). We describe also for the first time expression of the Pitx2 protein in mouse. Pitx2 protein immunostaining was detectable during the development of the eye, tooth, umbilicus, and also in the pituitary, heart, gut, and limb. We demonstrate for the first time directly that Pitx2 is asymmetrically expressed in early heart, gut, and lung development.