The locus was disrupted by the insertion of Dkk1 cDNA and the PGK-neo cassette flanked by two loxP sites. The neomycin cassette was removed by crossing with mice expressing cre recombinase in the germ line. Dkk1 expression was detected in epiblast at E6.5 and in the entire rostral brain region at E7.8, in addition to endogenous expression domains. RT-PCR confirmed the absence of Otx2 transcript in mutant embryos.