An in frame lacZ-loxP-PGK-TKNEOpA-loxP cassette 28bp upstream of the homeobox in exon 2 replaced sequences encoding the conserved protein domains. Analysis of beta-galactosidase expression in heterozygous embryos of E9.5 to E12.5 showed essentially no differences with endogenous Alx3 expression. (J:71880)