A targeting vector was constructed that contains a Sox10 open reading that changes amino acids 71-73 from CIR to AAA, followed by a loxP flanked neo cassette. The region mutated is necessary for DNA-dependent dimerization of this transcription factor. The vector replaced the entire open reading frame of Sox10 by deleting exons 3 through 5. The neo cassette was removed via in vivo Cre mediated recombination. Quantitative RT-PCR and immunoprecipitation on mid-stage embryos indicated that mRNA and protein levels of the mutated gene were similar to the wild-type gene. (J:124679)