The transgene consists of a mouse Prrx1 promoter fused to a mutant Hand2 cDNA deleted for residues 1-90 and 155-217. The mouse Prrx1 promoter was used to drive transgene expression in the forelimb bud and anterior mesoderm of the hindlimb in E10.5 embryos. The Hand2 construct also contains an N-terminal Myc epitope tag and a 3' human growth hormone polyadenylation signal.