Fig. 4. Generation of the Hesx1-Cre targeted allele. (A) Top to bottom: structure of the murine Hesx1 wild-type locus, Hesx1-Cre targeting vector and Hesx1-Cre allele prior to and after flipase excision of the neo cassette. The map of the targeting vector shows the replacement of the Hesx1 coding region by a cassette containing the Cre recombinase gene and the neomycin resistance gene under the PGK promoter (PGK-Neo) flanked by Frt sites (red triangles). (B) Southern blot hybridisation of DNA samples from wild type (+/+) and two heterozygous (Cre/+) ES cell clones cut with EcoRI and hybridised with an external probe (brown line in A). (C) Representative example of PCR genotyping of DNA samples from wild-type, Hesx1^Cre/+ and Hesx1^Cre/Cre embryos. (D) Wild-type embryo (left) and Hesx1^Cre/Cre mutant showing lack of AFB tissue (telencephalon and eye).