A Myo7a mutation cosegregates with stereocilia defects and low-frequency hearing impairment.
A phenotype-driven approach was adopted in the mouse to identify molecules involved in ear development and function. Mutant mice were obtained using N-ethyl- N-nitrosourea (ENU) mutagenesis and were screened for dominant mutations that affect hearing and/or balance. Heterozygote headbanger ( Hdb/+) mutants display classic behavior indicative of vestibular dysfunction including hyperactivity and head bobbing, and they show a Preyer reflex in response to sound but have raised cochlear thresholds especially at low frequencies. Scanning electron microscopy of the surface of the organ of Corti revealed abnormal stereocilia bundle development from an early age that was more severe in the apex than the base. Utricular stereocilia were long, thin, and wispy. Homozygotes showed a similar but more severe phenotype. The headbanger mutation has been mapped to a 1.5-cM region on mouse Chromosome 7 in the region of the unconventional myosin gene Myo7a, and mutation screening revealed an A>T transversion that is predicted to cause an isoleucine-to-phenylalanine amino acid substitution (I178F) in a conserved region in the motor-encoding domain of the gene. Protein analysis revealed reduced levels of myosin VIIa expression in inner ears of headbanger mice. Headbanger represents a novel inner ear phenotype and provides a potential model for low-frequency-type human hearing loss.
Rhodes
Charlotte R
CR
MRC Institute of Hearing Research, University Park, NG7 2RD, Nottingham, UK.
Hertzano
Ronna
R
Fuchs
Helmut
H
Bell
Rachel E
RE
de Angelis
Martin Hrabé
MH
Steel
Karen P
KP
Avraham
Karen B
KB
D000818:Animals; D001309:Auditory Threshold / Q000502:physiology; D001483:Base Sequence; D002874:Chromosome Mapping; D020090:Chromosome Segregation / Q000235:genetics; D002923:Cilia / Q000648:ultrastructure; D003433:Crosses, Genetic; D004247:DNA / Q000737:chemistry / Q000235:genetics; D004398:Dyneins; D005260:Female; D018069:Hair Cells, Vestibular / Q000002:abnormalities* / Q000648:ultrastructure; D034381:Hearing Loss / Q000235:genetics*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008809:Mice, Inbred C3H; D008808:Mice, Inbred CBA; D008855:Microscopy, Electron, Scanning; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D000081412:Myosin VIIa; D009218:Myosins / Q000235:genetics*; D009925:Organ of Corti / Q000002:abnormalities / Q000648:ultrastructure; D016133:Polymerase Chain Reaction; D019956:Stereotypic Movement Disorder / Q000235:genetics*
C000631455:MYO7A protein, human; C000631456:Myo7a protein, mouse; D000081412:Myosin VIIa; D004247:DNA; D009218:Myosins; D004398:Dyneins