Fig. 1. Generation of Dbx1-iCre PAC transgenic mice and expression of the transgene. (A) Map of PAC 631-M19 indicating the extent of upstream and downstream genomic regions in the PAC insert. (B) Schematic of the endogenous Dbx1 locus, including intron-exon structure and the relative locations of the BglII and HindIII restriction sites. (C) The targeting vector used in homologous recombination, indicating the positions of the iCre coding sequences, the chloramphenicol resistance cassette (Cm^r) and the loxP sites, and the location of the 0.5 kb 3' UTR probe used to hybridize to Southern blots of BglII-digested genomic DNA. The locations of PCR primers used for genotyping are also indicated. (D) Expression of the iCre transgene at E11.5, as revealed by in situ hybridization. Four independent founders had the same pattern of expression at this age. One founder was chosen for further study. (E) Diagram of neuroepithelial precursor domains in the spinal cord, and the reported patterns of Dbx1 and Dbx2 expression at E11.5 (Pierani et al., 2001). FP, floor plate; RP, roof plate.