Fig. 1. Targeted mutagenesis of Alx3. (A) Structure of the Alx3 locus: exon 2, 3 and 4 are depicted by open rectangles. The homeobox and the aristaless box (encoding the aristaless/OAR domain) are coloured. (B) Targeting vector: a 6 kb lacZ-loxP-pGK-TKNEOpA-loxP cassette was inserted in sequences of exon 2 upstream of the homeobox. 5' 1.9 and 3' 5.5 homologous sequences are indicated. Arrows in cassette indicate direction of transcription. (C) Targeted allele. The NcoI-XhoI probe corresponds to a region not present in the targeting construct, whereas the SstI-StuI probe detects the short homology arm. Relevant restriction sites and probes are indicated. Restriction fragments for Southern analysis are indicated with broken arrows above wild-type Alx3 allele and under targeted Alx3 allele. Coloured boxes: black, probes; red, loxP sites; blue, lacZ cassette; yellow, pGK-TKNEOpA cassette; green, homeobox; pink, aristaless-box. Restriction sites: B, BamHI; N, NcoI; P, PstI; RI, EcoRI; S, StuI; Sa, SalI.