Phenotypic and Expression Analysis of a Novel Spontaneous Myosin VI Null Mutant Mouse

Abstract

Abstract:In humans, hearing is a major factor in quality of life. Mouse models are important tools for the discovery of genes responsible for genetic hearing loss, often enabling analysis of the processes that regulate the onset of deafness in humans. Thus far, at least 400 deafness mutants have been discovered in laboratory mouse populations and used in the study of deafness. Here we report the discovery of a new spontaneous recessive Rinshoken shaker/waltzer (rsv) mutant derived from our in-house C57BL/6J stock, which exhibits circling and/or head-tossing behaviour and complete lack of auditory brain response to any sound pressure. The hearing and balance phenotypes are associated with structural defects, in particular, disorganisation and fusion of stereocilia in the inner ear hair cells. Two sets of intersubspecific N 2 mice were generated for the positional cloning of the rsv mutation. The mutant locus was mapped to a 4.8-Mb region of chromosome 9, which contains myosin VI (Myo6), a gene responsible for deafness in humans and Snell's waltzer mutation in mice. The rsv mutant showed reduced expressions of Myo6 mRNA and MYO6 protein in the inner ear. Moreover, no immunoreactivity was observed in the cochlear and vestibular hair cells in the rsv mutant mice. We sequenced the genomic region (30,154 bp) of Myo6, including all coding exons, a non-coding exon, UTRs and the Myo6 promoter; however, no mutation was discovered in these regions. We therefore speculate that loss of MYO6 expression might cause shaker/waltzer behaviour and deafness in the rsv mutant; also, loss of MYO6 expression might be the result of mutations in an unidentified regulatory region(s) of the gene.

Characterization of a novel ENU-generated myosin VI mutant mouse strain with congenital deafness and vestibular dysfunction

“…jaxmice.jax.org), twist (Schwander et al, 2007) and Tailchaser (Hertzano et al, 2008). An additional published strain, Rinshoken shaker/waltzer (Mochizuki et al, 2010), is suspected to harbour a Myo6 mutation although the causative mutation has not been reported. The Snell's waltzer mouse (Myo6 sv ) is a spontaneous mutant that arose in the Jackson Laboratory in the 1950s, although it was not until 1995 that the causative mutation in the Myo6 gene was identified (Avraham et al, 1995).…”

Myosin 6 Is Required for Iris Development and Normal Function of the Outer Retina

“…Our results add to the literature noting critical roles for myosin 6 at the inner and outer ear stereocilia in mice and in human deafness. 4,15,[28][29][30][31][32][33] Moreover, our analysis of the functional and structural effects of the tvrm89 mutation provides a detailed report of the retinal phenotype in Myo6 mutants.…”

“…14 In the mouse photoreceptor, myosin 6 is localized exclusively to the inner segment. Myo6 sv and two allelic mutants (Myo6 sv-2J and Myo6 sv-4J ), which are all effective Myo6-null mutants, display reductions in a-wave and b-wave amplitudes as early as age 6 weeks, 15 with no evidence of photoreceptor degeneration or disruption in disc morphogenesis. 12 In the RPE, myosin 6 is localized to the periphery of the cell and colocalizes with LysoTracker 12 corroborating its role in vesicle trafficking [16][17][18][19] and providing a potential explanation for the functional abnormalities found despite the absence of anatomical changes to the retina.…”

Advantages of a Mouse Model for Human Hearing Impairment

“…CDH23 and PCDH15 are expressed in developing bundles, where they localize to transient lateral and kinocilial links [51,56,75,101,104]. Developing hair bundles also express a harmonin splice variant, harmonin-b (HARMb), in the stereocilia upper tip-link density (UTLD), and HARMb [69], Myo15 sh2/sh2 (B) [93], [107], Ush1g js/js (D) [54] and Myo6 rsv/rsv (E) mice [77]. binds CDH23, PCDH15, and F-actin, suggesting that HARMb establishes a connection between cadherins and F-actin [2,11,101,103].…”

“…Myo6 is mutated in Snell's waltzer (Myo6 sv ) mice and in two forms of human nonsyndromic deafness, DFNA22 and DFNB37 [3,8,73]. Myo6 sv and allelic series mice exhibit deafness and circling behaviors and have fused cochlear and vestibular hair cell stereocilia [8,77,100]. In the inner ear, MYO6 is normally located in the cytoplasm of the organ of Corti, in vestibular hair cells within the cuticular plate and the pericuticular necklace ( Fig.…”