Fig. 4. Generation of mice that lack the ASE of Pitx2. (A) Schematic representation of the mouse wild-type Pitx2 allele, a targeting vector designed to delete the 0.6 kb region of Pitx2 that contains the ASE (red oval), as well as the targeted allele before and after Cre-mediated recombination. Pitx2 contains six exons (black boxes) and two promoters, with transcription beginning at exon 1 or exon 1c. (B) Southern blot analysis of Nsi-digested DNA from ES cells of the indicated Pitx2 genotypes before Cre-mediated recombination. The probe used for hybridization is shown by the blue bar on the top. The wild-type and mutant alleles give rise to hybridizing fragments of >23 and 11 kb, respectively. Green triangles, loxP sequences; neo, neomycin resistance gene under the control of the phosphoglycerate kinase gene promoter; DT, diphtheria toxin gene.