Williams N E, Honts J E
Department of Biology, University of Iowa, Iowa City 52242.
Development. 1987 May;100(1):23-30. doi: 10.1242/dev.100.1.23.
The oral skeleton of Tetrahymena is a precisely arranged assemblage of basal bodies, microtubule bundles and connecting filaments found associated with the feeding structure in this cell type. Tubulin and filament proteins have been isolated but no actin has been recovered. The conditional mutant NP1 of Tetrahymena thermophila forms a normal oral skeleton at the permissive temperature (28 degrees C), but forms an abnormal one at the restrictive temperature (37 degrees C). Antibodies against tubulin and oral filament protein OF1 were used to visualize the abnormal oral skeleton and stages in its development, and ultrastructural comparisons of abnormal and wild-type oral skeletons were made. It was found that the overall pattern of organization was altered in the mutant, whereas the substructure appeared everywhere to be normal. Studies of cells in which the mutant phenotype was coming to expression revealed that normal basal bodies in the oral skeleton failed to move from the disordered state characteristic of early stages of development into the correct pattern of four organized clusters characteristic of later stages. Together, these results suggest that the lesion in NP1 does not affect cytoskeleton assembly per se, but instead affects a discrete mechanism responsible for the positioning of cytoskeletal elements with respect to each other after they have been formed (meta-assembly). Reasons for suspecting the involvement of the membrane skeleton are presented.
嗜热四膜虫的口部骨架是一种排列精确的基体、微管束和连接丝的组合，与这种细胞类型的摄食结构相关。微管蛋白和丝状蛋白已被分离出来，但未发现肌动蛋白。嗜热四膜虫的条件突变体NP1在允许温度（28摄氏度）下形成正常的口部骨架，但在限制温度（37摄氏度）下形成异常的口部骨架。利用针对微管蛋白和口部丝状蛋白OF1的抗体来观察异常口部骨架及其发育阶段，并对异常和野生型口部骨架进行超微结构比较。结果发现，突变体中整体的组织结构发生了改变，而亚结构在各处看起来都是正常的。对呈现出突变体表型的细胞的研究表明，口部骨架中的正常基体未能从发育早期特征性的无序状态转变为后期特征性的四个有组织的簇的正确模式。这些结果共同表明，NP1中的损伤本身并不影响细胞骨架的组装，而是影响一种离散机制，该机制负责在细胞骨架元件形成后它们彼此之间的定位（元组装）。文中还提出了怀疑膜骨架参与其中的原因。
