The mis-expression of posterior Hox-4 genes in talpid (ta³) mutant wings correlates with the absence of anteroposterior polarity

Developing chicken wings homozygous for the talpid (ta³/ta³) mutation are polydactylous and have defects in the establishment of their anteroposterior polarity. We analysed the expression domains of the posteriorly restricted homeobox Hox-4 genes in such mutant wings. The Hox-4 genes are now expressed right across the anteroposterior axis instead of being expressed just posteriorly. This correlates well with the absence of clear morphological differences between the talpid³ digits and reinforces the idea that vertebrate Hox-4 genes are involved in setting up the limb anteroposterior asymmetry.