INSERTIONAL MUTATION ON MOUSE CHROMOSOME-18 WITH VESTIBULAR AND CRANIOFACIAL ABNORMALITIES

A dominant mutation was generated in transgenic mice as a consequence of insertional mutation. Heterozygous mice from transgenic line 9257 ( Tg9257) are hyperactive with bidirectional circling behavior and have a distinctive facial appearance due to hypoplasia of the nasal bone. M orphological analysis of the inner ear revealed asymmetric abnormaliti es of the horizontal canal and flattening or invagination of the crist a ampullaris, which can account for the circling behavior. The sensory epithelium appeared to be normal. The transgene insertion site was lo calized by in situ hybridization to the B1 band of mouse chromosome 18 . Genetic mapping in an interspecific backcross demonstrated the gene order centromere-Tg9257-8.8 +/- 3.4-Grl-1, Egr-1, Fgf-1, Apc-14.7 +/- 4.3-Pdgfr. The phenotype and the mapping data suggest that the transge ne may be inserted at the Twirler locus. Homozygosity for the transgen e results in prenatal lethality, but compound heterozygotes carrying t he Tw allele and the transgene are viable. The function of the closely linked ataxia locus is not disrupted by the transgene insertion. This insertional mutant will provide molecular access to genes located in the Twirler region of mouse chromosome 18.