A 5 kb genomic fragment of Hoxa5 (containing the temporal (T) control region, the brachial spinal cord (BSC) enhancer, proximal Hoxa5 promoter, both exons and the intron of Hoxa5) drives cre epxression in this transgene. An IRES-EGFPcre cassette was inserted into exon 1 of Hoxa5 downstream of the translation initiation codon. A 2.1 kb fragment containing the mesodermal (MES) enhancer was added at the 3' end of the construct to produce the 7.1 Hoxa5/Cre transgene. Nine founder lines were obtained andLine 444C was established. This line has 2 copies of the transgene.