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Gene Review

Myo7a  -  myosin VIIA

Mus musculus

Synonyms: Hdb, Myo7, USH1B, Unconventional myosin-VIIa, nmf371, ...
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Disease relevance of Myo7a


High impact information on Myo7a

  • Mutant myosin VIIa causes defective melanosome distribution in the RPE of shaker-1 mice [3].
  • Recently, it has been shown that a gene encoding an unconventional myosin, myosin VIIA, underlies the mouse recessive deafness mutation, shaker-1 (ref. 5) as well as Usher syndrome type 1b [4].
  • The sh1 gene encodes an unconventional myosin molecule of the type VII family [5].
  • Reduced climbing and increased slipping adaptation in cochlear hair cells of mice with Myo7a mutations [6].
  • In stereocilia, constructed of cross-linked F-actin filaments, myosin-Ibeta is found mostly near stereociliary tips, myosin-VI is largely absent, and myosin-VIIa colocalizes with crosslinks that connect adjacent stereocilia [7].

Biological context of Myo7a


Anatomical context of Myo7a

  • In RPE cells from Myo7a-null mice, both the slow and rapid movements still occurred, except that more melanosomes underwent rapid movements, and each movement extended approximately five times longer (and further) [12].
  • In mice with mutant Myo7a, melanosomes in the retinal pigmented epithelium (RPE) are distributed abnormally [12].
  • Myo7a was expressed normally in the hair cells of P0 Cdh23(v2J) mutants demonstrating that cadherin 23 is not required for Myo7a expression at this stage [13].
  • We conclude that Myo7a is required for the normal processing of ingested disk membranes in the RPE, primarily in the basal transport of phagosomes into the cell body where they then fuse with lysosomes [8].
  • In sh-1 homozygotes this deafness is associated with neurophysiological abnormalities that may be accompanied by structural abnormalities of the inner ear [14].

Associations of Myo7a with chemical compounds

  • Transgenic analyses have revealed the presence of hair-cell-specific promoters in the genes encoding Math1, myosin VIIa, Pou4f3, and the alpha9 subunit of the acetylcholine receptor (alpha9 AChR) [15].
  • Myosin VIIa Mg-ATPase activity was detected; in the absence of Ca(2+) (i.e. with bound calmodulin), it was stimulated by f-actin with a K(cat) of 4.3 s(-1) and with 7 microM actin required for half-maximal activity [16].
  • Our studies demonstrate that harmonin and myosin VIIa are not localized in the same compartments in the mouse and human retinas, indicating that they do not interact in this organ, contrary to what has been shown in the inner ear [17].
  • Hair cells from homozygous mutant Myo7ash1 mice, with a mutation in a nonconserved region of the myosin VIIA head, respond rapidly to aminoglycoside treatment and accumulate high levels of gentamicin [18].

Physical interactions of Myo7a


Regulatory relationships of Myo7a

  • Under differentiating culture conditions, transfected E-cadherin inhibited expression of the cytoskeletal protein myosin VIIa and functional expression of both acetylcholine receptors and potassium channels, which are normally expressed by neonatal hair cells [21].

Other interactions of Myo7a

  • These data suggest that the function of Myo15 is distinct from that of Myo6, Myo7a or pi in development and/or maintenance of stereocilia [22].
  • Role of myosin VIIa and Rab27a in the motility and localization of RPE melanosomes [12].
  • One thousand fifty-two mice were analyzed for a protein polymorphism segregating for the distal flanking marker, beta-globin (Hbb), and 13 recombinants between Hbb and sh-1 were identified [11].
  • In the cuticular plate, a meshwork of actin filaments, myosin-Ibeta is excluded, myosin-VI is concentrated, and modest amounts of myosin-VIIa are present [7].
  • Complementation analysis provided evidence for a true repeat mutation at the sh-1 (shaker-1) locus (for the neurological mutations) and another at the here defined fit-1 (fitness-1) locus [23].

Analytical, diagnostic and therapeutic context of Myo7a


  1. Cdh23 mutations in the mouse are associated with retinal dysfunction but not retinal degeneration. Libby, R.T., Kitamoto, J., Holme, R.H., Williams, D.S., Steel, K.P. Exp. Eye Res. (2003) [Pubmed]
  2. Progressive hearing loss and increased susceptibility to noise-induced hearing loss in mice carrying a Cdh23 but not a Myo7a mutation. Holme, R.H., Steel, K.P. J. Assoc. Res. Otolaryngol. (2004) [Pubmed]
  3. Mutant myosin VIIa causes defective melanosome distribution in the RPE of shaker-1 mice. Liu, X., Ondek, B., Williams, D.S. Nat. Genet. (1998) [Pubmed]
  4. Mutations in the myosin VIIA gene cause non-syndromic recessive deafness. Liu, X.Z., Walsh, J., Mburu, P., Kendrick-Jones, J., Cope, M.J., Steel, K.P., Brown, S.D. Nat. Genet. (1997) [Pubmed]
  5. A type VII myosin encoded by the mouse deafness gene shaker-1. Gibson, F., Walsh, J., Mburu, P., Varela, A., Brown, K.A., Antonio, M., Beisel, K.W., Steel, K.P., Brown, S.D. Nature (1995) [Pubmed]
  6. Reduced climbing and increased slipping adaptation in cochlear hair cells of mice with Myo7a mutations. Kros, C.J., Marcotti, W., van Netten, S.M., Self, T.J., Libby, R.T., Brown, S.D., Richardson, G.P., Steel, K.P. Nat. Neurosci. (2002) [Pubmed]
  7. Unconventional myosins in inner-ear sensory epithelia. Hasson, T., Gillespie, P.G., Garcia, J.A., MacDonald, R.B., Zhao, Y., Yee, A.G., Mooseker, M.S., Corey, D.P. J. Cell Biol. (1997) [Pubmed]
  8. Abnormal phagocytosis by retinal pigmented epithelium that lacks myosin VIIa, the Usher syndrome 1B protein. Gibbs, D., Kitamoto, J., Williams, D.S. Proc. Natl. Acad. Sci. U.S.A. (2003) [Pubmed]
  9. A specific promoter of the sensory cells of the inner ear defined by transgenesis. Boëda, B., Weil, D., Petit, C. Hum. Mol. Genet. (2001) [Pubmed]
  10. A Myo7a mutation cosegregates with stereocilia defects and low-frequency hearing impairment. Rhodes, C.R., Hertzano, R., Fuchs, H., Bell, R.E., de Angelis, M.H., Steel, K.P., Avraham, K.B. Mamm. Genome (2004) [Pubmed]
  11. Close linkage of the olfactory marker protein gene to the mouse deafness mutation shaker-1. Brown, K.A., Sutcliffe, M.J., Steel, K.P., Brown, S.D. Genomics (1992) [Pubmed]
  12. Role of myosin VIIa and Rab27a in the motility and localization of RPE melanosomes. Gibbs, D., Azarian, S.M., Lillo, C., Kitamoto, J., Klomp, A.E., Steel, K.P., Libby, R.T., Williams, D.S. J. Cell. Sci. (2004) [Pubmed]
  13. Stereocilia defects in waltzer (Cdh23), shaker1 (Myo7a) and double waltzer/shaker1 mutant mice. Holme, R.H., Steel, K.P. Hear. Res. (2002) [Pubmed]
  14. Reverse genetics in the mouse and its application to the study of deafness. Rinchik, E.M., Johnson, D.K., Margolis, F.L., Jackson, I.J., Russell, L.B., Carpenter, D.A. Ann. N. Y. Acad. Sci. (1991) [Pubmed]
  15. Transgenic and gene targeting studies of hair cell function in mouse inner ear. Zuo, J. J. Neurobiol. (2002) [Pubmed]
  16. Actin-based motor properties of native myosin VIIa. Udovichenko, I.P., Gibbs, D., Williams, D.S. J. Cell. Sci. (2002) [Pubmed]
  17. Roles and interactions of usher 1 proteins in the outer retina. Lillo, C., Kitamoto, J., Williams, D.S. Adv. Exp. Med. Biol. (2006) [Pubmed]
  18. Myosin VIIA is required for aminoglycoside accumulation in cochlear hair cells. Richardson, G.P., Forge, A., Kros, C.J., Fleming, J., Brown, S.D., Steel, K.P. J. Neurosci. (1997) [Pubmed]
  19. Myosin XVa and whirlin, two deafness gene products required for hair bundle growth, are located at the stereocilia tips and interact directly. Delprat, B., Michel, V., Goodyear, R., Yamasaki, Y., Michalski, N., El-Amraoui, A., Perfettini, I., Legrain, P., Richardson, G., Hardelin, J.P., Petit, C. Hum. Mol. Genet. (2005) [Pubmed]
  20. Myosin VIIa participates in opsin transport through the photoreceptor cilium. Liu, X., Udovichenko, I.P., Brown, S.D., Steel, K.P., Williams, D.S. J. Neurosci. (1999) [Pubmed]
  21. E-cadherin and the differentiation of mammalian vestibular hair cells. Hackett, L., Davies, D., Helyer, R., Kennedy, H., Kros, C., Lawlor, P., Rivolta, M.N., Holley, M. Exp. Cell Res. (2002) [Pubmed]
  22. Myo15 function is distinct from Myo6, Myo7a and pirouette genes in development of cochlear stereocilia. Karolyi, I.J., Probst, F.J., Beyer, L., Odeh, H., Dootz, G., Cha, K.B., Martin, D.M., Avraham, K.B., Kohrman, D., Dolan, D.F., Raphael, Y., Camper, S.A. Hum. Mol. Genet. (2003) [Pubmed]
  23. A strategy for fine-structure functional analysis of a 6- to 11-centimorgan region of mouse chromosome 7 by high-efficiency mutagenesis. Rinchik, E.M., Carpenter, D.A., Selby, P.B. Proc. Natl. Acad. Sci. U.S.A. (1990) [Pubmed]
  24. The pattern of sensorineural degeneration in the cochlea of the deaf shaker-1 mouse: ultrastructural observations. Shnerson, A., Lenoir, M., van de Water, T.R., Pujol, R. Brain Res. (1983) [Pubmed]
  25. Effects of shaker-1 mutations on myosin-VIIa protein and mRNA expression. Hasson, T., Walsh, J., Cable, J., Mooseker, M.S., Brown, S.D., Steel, K.P. Cell Motil. Cytoskeleton (1997) [Pubmed]
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