A novel type of myosin encoded by the mouse deafness gene shaker-2

遗传性听力障碍在出生时影响约2，000名儿童中的一名。大多数遗传性耳聋是非综合征性的，其中听力损失与任何其他异常无关。常染色体隐性遗传型非综合征性耳聋（DFNB）是最严重的耳聋，几乎完全是由于内耳感觉神经上皮细胞的异常。已经绘制了10个耳聋的基因座，并确定了编码非常规肌球蛋白VIIA和连接蛋白26的两个基因的突变。一个基因座DFNB 3被分配到17p11.2- 17 q12，其与小鼠11号染色体上的shaker-2（sh-2）基因座同源。纯合子sh-2小鼠表现出内耳缺陷小鼠的转圈、摇头、耳聋和多动等症状，其中一些症状与DFNB 3相似，这意味着DFNB 3和sh-2具有相同的未知基因。有了这个遗传和物理图谱，我们进行了定位克隆的方法来确定sh-2突变。在这里，我们报告使用的定位克隆的方法，显示在sh-2小鼠突变的基因编码一种新型的非常规肌球蛋白。在sh-2中检测到保守的肌动蛋白结合结构域中的半胱氨酸到酪氨酸的G到A转变，但在属于不同小鼠亚种和种的实验室品系和野生小鼠中不存在。基于保守的同线性和突变，新的肌球蛋白基因是DFNB 3的强有力的候选者。

Genetic hearing impairment affects about one in 2,000 children at birth. The majority of genetic deafness is non-syndromic, in which hearing loss is not associated with any other abnormalities. Autosomal recessive forms of non-syndromic deafness (DFNB) account for most profound deafness and are almost exclusively due to abnormalities of the sensory neuroepithelia of the inner ear. Ten loci for such deafness have been mapped and mutations in two genes encoding unconventional myosin VIIA and connexin 26 have been identified. One locus, DFNB3, is assigned to 17p11.2-17q12 which is homologous to the shaker-2 (sh-2) locus on mouse chromosome 11. Homozygous sh-2 mice exhibit the circling, headtossing, deafness, and hyperactivity seen in mice with inner ear defects and some of these symptoms resemble those of DFNB3, implying that the same unidentified gene underlies DFNB3 and sh-2.We constructed a contig consisting of 21 BAC clones across an approximately 700-kb region which covers the entire nonrecombinant region of sh-2. With this genetic and physical maps, we carried out a positional cloning approach to identify the sh-2 mutation. Here we report the use of a positional cloning approach to show that the gene mutated in sh-2 mice encodes a novel type of unconventional myosin. A G-to-A transition changing cysteine to tyrosine in the conserved actin binding domain is detected in sh-2 but absent in laboratory strains and wild mice belonging to different mouse subspecies and species. Based on conserved synteny and the mutation, the novel myosin gene is a strong candidate for DFNB3.