Department of Otolaryngology, Head and Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
PLoS One. 2010 Sep 15;5(9):e12765. doi: 10.1371/journal.pone.0012765.
The mammalian otoconial membrane is a dense extracellular matrix containing bio-mineralized otoconia. This structure provides the mechanical stimulus necessary for hair cells of the vestibular maculae to respond to linear accelerations and gravity. In teleosts, Otolin is required for the proper anchoring of otolith crystals to the sensory maculae. Otoconia detachment and subsequent entrapment in the semicircular canals can result in benign paroxysmal positional vertigo (BPPV), a common form of vertigo for which the molecular basis is unknown. Several cDNAs encoding protein components of the mammalian otoconia and otoconial membrane have recently been identified, and mutations in these genes result in abnormal otoconia formation and balance deficits.
Here we describe the cloning and characterization of mammalian Otolin, a protein constituent of otoconia and the otoconial membrane. Otolin is a secreted glycoprotein of ∼70 kDa, with a C-terminal globular domain that is homologous to the immune complement C1q, and contains extensive posttranslational modifications including hydroxylated prolines and glycosylated lysines. Like all C1q/TNF family members, Otolin multimerizes into higher order oligomeric complexes. The expression of otolin mRNA is restricted to the inner ear, and immunohistochemical analysis identified Otolin protein in support cells of the vestibular maculae and semi-circular canal cristae. Additionally, Otolin forms protein complexes with Cerebellin-1 and Otoconin-90, two protein constituents of the otoconia, when expressed in vitro. Otolin was also found in subsets of support cells and non-sensory cells of the cochlea, suggesting that Otolin is also a component of the tectorial membrane.
Given the importance of Otolin in lower organisms, the molecular cloning and biochemical characterization of the mammalian Otolin protein may lead to a better understanding of otoconial development and vestibular dysfunction.
哺乳动物耳石膜是一种富含生物矿化耳石的致密细胞外基质。该结构为前庭斑毛细胞提供了对线性加速度和重力作出反应所需的机械刺激。在硬骨鱼中，Otolin 对于将耳石晶体正确锚定在感觉斑上是必需的。耳石的脱离和随后被困在半规管中可能导致良性阵发性位置性眩晕（BPPV），这是一种常见的眩晕形式，其分子基础尚不清楚。最近已经鉴定出编码哺乳动物耳石和耳石膜蛋白成分的几个 cDNA，这些基因的突变导致异常耳石形成和平衡缺陷。
本文描述了哺乳动物 Otolin 的克隆和特征，Otolin 是耳石和耳石膜的一种蛋白成分。Otolin 是一种分泌型糖蛋白，分子量约为 70 kDa，C 端球状结构域与免疫补体 C1q 同源，含有广泛的翻译后修饰，包括羟脯氨酸和糖基化赖氨酸。像所有 C1q/TNF 家族成员一样，Otolin 可以多聚化成更高阶的寡聚复合物。Otolin mRNA 的表达局限于内耳，免疫组织化学分析在前庭斑和半规管嵴的支持细胞中鉴定出 Otolin 蛋白。此外，Otolin 在体外与 Cerebellin-1 和 Otoconin-90 形成蛋白复合物，这两种蛋白均为耳石的成分。Otolin 也存在于耳蜗的支持细胞和非感觉细胞亚群中，这表明 Otolin 也是盖膜的一种成分。
鉴于 Otolin 在低等生物中的重要性，哺乳动物 Otolin 蛋白的分子克隆和生化特征分析可能有助于更好地理解耳石发育和前庭功能障碍。
