Disease relevance of MYO7A

• MYO7A mutations are responsible for Usher syndrome type Ib, the most common genetic subtype of Usher I [1].
• While most MYO7A mutations cause USH1, some cause nonsyndromic hearing impairment, and one USH3 phenotype has been described [2].
• Although a wide spectrum of MYO7A mutations have been identified in Usher Ib patients, four mutations have been reported to cause DFNB2, a recessive deafness without retinal degeneration, and one mutation has been implicated in a single case of dominant nonsyndromic hearing loss (DFNA11) [1].
• Here, we demonstrate by pharmacological and genetic approaches that both myosin VIIa and vezatin are crucial for Listeria internalization [3].

Psychiatry related information on MYO7A

• Characterization of the motor activity of mammalian myosin VIIA [4].

High impact information on MYO7A

• 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 [5].
• By linkage analysis of a single family whose members were affected with profound deafness, some of them presenting with vestibular dysfunction, DFNB2 has been mapped to chromosome 11q13 (ref. 3). The gene responsible for a form of Usher syndrome type I, USH1B, has been assigned to the same chromosomal region [6].
• It has been demonstrated that the murine shaker-1 and human USH1B phenotypes result from mutations in the gene encoding myosin-VIIA [6].
• We propose that the shaping of the hair bundle relies on a functional unit composed of myosin VIIa, harmonin b and cadherin 23 that is essential to ensure the cohesion of the stereocilia [7].
• In myosin VIIA-defective mutants, inactivity of the vezatin-myosin VIIA complex at both sites could account for splaying out of the hair cell stereocilia [8].

Biological context of MYO7A

• MYO7A is on chromosome region 11q13 and USH2A is on 1q41 [2].
• The phenotype resulting from MYO7A and USH2A mutations is variable [2].
• METHODS: We performed SSCP screening of MYO7A in 12 unrelated patients suffering from Usher syndrome type 1 (USH1) and USH2A in 28 unrelated patients affected by Usher syndrome type 2 (USH2) [9].
• Like MYO7A, PCDH15 is critical for the development of hair bundles in cochlear and vestibular hair cells, controlling hair bundle morphogenesis and polarity [10].
• Myosin VIIA has been implicated in membrane trafficking and/or endocytosis in the inner ear [11].

Anatomical context of MYO7A

• METHODS: History, examination, and audiometric testing in the proband, brother, and son; quantitative rotational testing in the proband and son; histopathology of the cochlea and vestibular labyrinth in the proband; sequencing candidate genes COCH and MYO7A in the brother and son [12].
• Functional effects of the p.R853C mutation were investigated in a physiological cellular environment by expressing MYO7A IQ5-containing peptides in smooth muscle cells of microarteries, in which overexpression of wildtype IQ5 (with intact calmodulin binding) would be expected to compete with myosin light chain kinase (MLCK) for CaM binding [13].
• In the retinal pigment epithelium cells, MyRIP, myosin VIIa and Rab27A are associated with melanosomes [14].
• In transfected PC12 cells, overexpression of MyRIP was shown to interfere with the myosin VIIa tail localization [14].
• Myosin-VIIa is also highly expressed in testis, where it is associated with specialized adhesion plaques termed ectoplasmic specializations (ES) that form between Sertoli cells and germ cells [15].

Associations of MYO7A with chemical compounds

• We propose that via its binding to myosin VIIa and/or harmonin, sans controls the hair bundle cohesion and proper development by regulating the traffic of USH1 proteins en route to the stereocilia [16].

Other interactions of MYO7A

• A previous screening of 18 unrelated USH1 patients, without a detected MYO7A mutation, for the three USH1C mutations described to date had demonstrated the presence of the 238-239insC mutation in the heterozygous state in four of them [17].
• In contrast to CDH23 and PCDH15, where most of the changes are truncating mutations, myosin VIIA has both nonsense and missense mutations [18].
• 5. Two loci for nonsyndromic forms of deafness, DFNA5 and DFNA11, have previously been mapped to these two chromosomal regions [19].
• Vezatin, a novel transmembrane protein, bridges myosin VIIA to the cadherin-catenins complex [8].
• Since it has been reported that another gene for dominant non-syndromic hearing loss (DFNA3) has been mapped to the same region as the first gene for recessive hearing loss (DFNB1), it is possible that different mutations in the DFNB2 gene may result in either dominant or recessive hearing loss [20].

Analytical, diagnostic and therapeutic context of MYO7A

• In the current study, a panel of 189 genetically independent Usher I cases were screened for the presence of mutations in the N-terminal coding portion of the motor domain of MYO7A by heteroduplex analysis of 14 exons [21].
• A cosmid, P1, PAC, and long PCR contig that contained the entire MYO7A gene was assembled [22].
• Myosin-VIIa and Keap1 copurify with ES and colocate with each other and with F-actin at the electron microscopy level [15].
• In an effort to understand the molecular mechanisms that determine hair cell fate in the inner ear, and with the goal of developing a valuable tool for gene therapy and for the generation of conditional knockouts, we initiated a search for cis-acting DNA sequences that regulate the expression of the murine Myo7a and human MYO7A genes [23].
• In situ hybridization analysis in human embryos demonstrates that the myosin VIIA gene is expressed in the pigment epithelium and the photoreceptor cells of the retina, thus indicating that both cell types may be involved in the USH1B retinal degenerative process [24].

References