Attempted rescue of circling mice by hair cell-specific expression (Myo7a promoter) of tmie transgene

The spontaneous mutant circling mouse (cir/cir) is deaf and displays abnormal behavior, particularly circling and head tossing. To rescue the circling mouse phenotype, we produced transgenic mice with hair cell-specific expression of the transmembrane inner ear (tmie) gene, using the Myo7a promoter, and generated cir/cir homozygous mice carrying the transgene (cir/cir-tgMyo7a) by breeding with circling mice. The cir/cir-tgMyo7a mice still exhibited circling behavior and were unable to swim in water unlike cir/cir-tgCMV mice and wild-type mice. An auditory brainstem response (ABR) test demonstrated that the cir/cir-tgMyo7a mice could not respond to sound. Immunohistochemical analysis showed enhanced green fluorescent protein, a marker of tmie expression, in the inner and outer hair cells of the cir/cir-tgMyo7a mice. Hair cells and spiral ganglion neurons in the cir/cir-tgMyo7a mice were recovered, but not completely. This study demonstrates that tmie transgene expression in hair cells alone could not restore wild-type hearing and behavior in circling mice.