Lins U, Farina M, Kurc M, Riordan G, Thalmann R, Thalmann I, Kachar B
Section on Structural Cell Biology, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, Maryland 20892-4163, USA.
J Struct Biol. 2000 Jul;131(1):67-78. doi: 10.1006/jsbi.2000.4260.
A unique feature of the vertebrate gravity receptor organs, the saccule and utricle, is the mass of biomineral structures, the otoconia, overlying a gelatinous matrix also called "otoconial membrane" on the surface of the sensory epithelium. In mammals, otoconia are deposits of calcium carbonate in the form of composite calcite crystals. We used quick-freezing, deep etching to examine the otoconial mass of the guinea pig utricle. The deep-etching step exposed large expanses of intact and fractured otoconia, showing the fine structure and relationship between their internal crystal structure, their surface components, and the filament matrix in which they are embedded. Each otoconium has a compact central core meshwork of filaments and a composite outer shell of ordered crystallites and macromolecular aggregates. A distinct network of 20-nm beaded filaments covers the surface of the otoconia. The otoconia are interconnected and secured to the gelatinous matrix by surface adhesion and by confinement within a loose interotoconial filament matrix. The gelatinous matrix is a dense network made of yet another type of filament, 22 nm in diameter, which are cross-linked by shorter filaments, characteristically 11 nm in diameter. Our freeze-etching data provide a structural framework for considering the molecular nature of the components of the otoconial complex, their mechanical properties, and the degree of biological versus chemical control of otoconia biosynthesis.
脊椎动物重力感受器器官球囊和椭圆囊的一个独特特征是生物矿化结构耳石的质量，耳石覆盖在感觉上皮表面的凝胶状基质（也称为“耳石膜”）之上。在哺乳动物中，耳石是以方解石复合晶体形式存在的碳酸钙沉积物。我们使用快速冷冻、深度蚀刻技术来检查豚鼠椭圆囊的耳石团块。深度蚀刻步骤揭示了大片完整和破裂的耳石，展示了它们内部晶体结构、表面成分以及它们所嵌入的丝状基质之间的精细结构和关系。每个耳石都有一个由细丝组成的紧密中央核心网络以及一个由有序微晶和大分子聚集体构成的复合外壳。一个由20纳米串珠状细丝组成的独特网络覆盖着耳石表面。耳石通过表面粘附以及限制在松散的耳石间丝状基质中而相互连接并固定在凝胶状基质上。凝胶状基质是一个由另一种类型的细丝构成的密集网络，其直径为22纳米，由更短的细丝（典型直径为11纳米）交联而成。我们的冷冻蚀刻数据为考虑耳石复合体各成分的分子性质、它们的机械性能以及耳石生物合成的生物学与化学控制程度提供了一个结构框架。
