Targeted mutation of the Lhx8 gene by homologous recombination. (A) Schematic representation of the wild-type Lhx8 gene, the targeting vector, and the mutated Lhx8. (B) Southern (Left) and PCR (Right) analyses of genomic DNA derived from offspring of a cross between heterozygous parents. After SacI digestion, the 5′ probe detected an 11-kb band of the wild-type allele and a 9-kb band of the mutant allele (arrowheads). The 3′ probe detected a 6.6-kb band of the wild-type allele and a 4.6-kb band of the mutant allele (arrowheads) after PstI digestion. PCR amplified an 150-bp band from the wild-type allele and a 550-bp band from the mutant allele (arrowheads). B, BamHI; P, PstI; Sa, SacI; Sm, SmaI; neo, the neomycin resistance gene; tk, the thymidine kinase gene.