Expression in cochlea and retina of myosin VIIa, the gene product defective in Usher syndrome type 1B.

Myosin VIIa is a newly identified member of the myosin superfamily of actin-based motors. Recently, the myosin VIIa gene was identified as the gene defective in shaker-1, a recessive deafness in mice [Gibson, F., Walsh, J., Mburu, P., Varela, A., Brown, K.A., Antonio, M., Beisel, K.W., Steel, K.P. & Brown, S.D.M. (1995) Nature (London) 374, 62-64], and in human Usher syndrome type 1B, an inherited disease characterized by congenital deafness, vestibular dysfunction, and retinitis pigmentosa [Weil, D., Blanchard, S., Kaplan, J., Guilford, P., Gibson, F., Walsh, J., Mburu, P., Varela, A., Levilliers, J., Weston, M.D., Kelley, P.M., Kimberling, W.J., Wagenaar, M., Levi-Acobas, F., Larget-Piet, D., Munnich, A., Steel, K.P., Brown, S.D.M. & Petit, C. (1995) Nature (London) 374, 60-61]. To understand the normal function of myosin VIIa and how it could cause these disease phenotypes when defective, we generated antibodies specific to the tail portion of this unconventional myosin. We found that myosin VIIa was expressed in cochlea, retina, testis, lung, and kidney. In cochlea, myosin VIIa expression was restricted to the inner and outer hair cells, where it was found in the apical stereocilia as well as the cytoplasm. In the eye, myosin VIIa was expressed by the retinal pigmented epithelial cells, where it was enriched within the apical actin-rich domain of this cell type. The cell-specific localization of myosin VIIa suggests that the blindness and deafness associated with Usher syndrome is due to lack of proper myosin VIIa function within the cochlear hair cells and the retinal pigmented epithelial cells.