Pitx1 expression in developing and regenerating axolotl limbs

The expression of the homeobox transcription factor Pitx1 was investigated in the Mexican axolotl (Ambystoma mexicanum) during limb development and regeneration by whole-mount mRNA in situ hybridizations. This clone shares high amino acid identity with Pitx1 from other vertebrates (92% Xenopus; 87% chick; 75% human and mouse) within the region isolated. In the developing limbs, Pitx1 was expressed in hindlimb mesenchyme, as has been reported in other species. The expression pattern in the hindlimb might have been conserved during evolution. In the regenerating limbs, Pitx1 was expressed in both fore- and hindlimb blastemas. Our observations suggest two roles of Pitx1 in the axolotl: one is to determine the hindlimb pattern during development, and the other that relates to proliferation of regenerating tissues without regard to fore- or hindlimb.