Myo15 function is distinct from Myo6, Myo7a and pirouette genes in development of cochlear stereocilia.

The unconventional myosin genes Myo15, Myo6 and Myo7a are essential for hearing in both humans and mice. Despite the expression of each gene in multiple organs, mutations result in identifiable phenotypes only in auditory or ocular sensory organs. The pirouette (pi) mouse also exhibits deafness and an inner ear pathology resembling that of Myo15 mutant mice and thus may be functionally related to Myo15. In order to investigate possible interactions between Myo15 and Myo6, Myo7a, and the gene affected in pirouette, we crossed Myo15(sh2/sh2) mice to the three other mutant mouse strains. Hearing in doubly heterozygous mice was similar to age-matched singly heterozygous animals, indicating that partial deficiency for both Myo15 and one of these other deafness genes does not reduce hearing. Viable double mutants were obtained from each cross, indicating that potential overlapping functions between these genes in other organs are not essential for viability. All critical cell types of the cochlear sensory epithelium were present in double mutant mice and cochlear stereocilia exhibited a superimposition of single mutant phenotypes. These data suggest that the function of Myo15 is distinct from that of Myo6, Myo7a or pi in development and/or maintenance of stereocilia.