This transgene consists of a 187 kb BAC clone, RP24-512K19, containing the endogenous Msx2 locus and flanking sequences (134 kb upstream and 47 kb downstream of Msx2; accession number AC154808) and a modified rtTA gene that replaced part of the first exon right after the start codon, followed by a FRT-flanked neomycin cassette and polyA sequences and was made using a two-step recombineering strategy. Two founding lines were established, 885 and 888. Western blot analysis failed to detect any truncated or fusion Msx2 protein. This BAC clone contains six additional predicted genes, which may be overexpressed.