Mice with dominant white spotting occurred spontaneously in the C3.NSY-(D11Mit74-D11Mit229) strain. Linkage analysis indicated that the locus for white spotting was located in the vicinity of the Pax3 gene on chromosome 1. Crosses of white-spotted mice showed that homozygosity for the mutation caused tail and limb abnormalities and embryonic lethality as a result of exencephaly; these phenotypes were analogous to those found in other Pax3 mutants. Sequence analysis identified a missense point mutation (c.101G>A) in exon 2 of Pax3 that resulted in a methionine to isoleucine conversion at amino acid 62 of the PAX3 protein. This mutation site was located in the N-terminal HTH (helix-turn-helix) motif of the paired domain of Pax3, which is necessary for binding to DNA and is highly conserved in vertebrate species. Alteration of DNA binding affinity was responsible for embryonic lethality in homozygotes and white spotting in heterozygotes. We named the mutant allele as Pax3Sp-Nag. The C3H/HeN-Pax3Sp-Nag strain may be useful for analyzing the function of Pax3 as a new model of the human disease, Waardenburg Syndrome.
Keywords: Pax3 gene; embryonic lethal; missense mutation; mouse; white spotting.