Cloning and expression pattern of chicken Pitx2: a new component in the SHH signaling pathway controlling embryonic heart looping.

Asymmetry along the left-right axis of the embryo is a vital feature of vertebrate embryogenesis. In this study, we report the isolation and characterization of a bicoid-related homeobox gene, cPitx2, which displays left-right asymmetric expression during early chick embryogenesis. Asymmetric expression of cPitx2 is first detected at stage 7 and is restricted to mesodermal tissues on the left side of the embryo including the left sided lateral mesoderm, the left sided precardiac mesoderm, and the left half epimyocardium of the primitive heart. cPitx2 is also detected in the presumptive blood islands and endothelia of the embryonic blood vessels. Implantation of Sonic hedgehog (SHH) protein soaked beads on the right side of embryos induced ectopic cPitx2 expression on that side. Based on these observations, we suggest that cPitx2 is a component in SHH signaling pathway and plays a role in determining left-right asymmetry and in vasculogenesis during avian embryogenesis.