Troutt L L, Burnside B
Department of Physiology-Anatomy, University of California, Berkeley 94720.
J Neurosci. 1988 Jul;8(7):2371-80. doi: 10.1523/JNEUROSCI.08-07-02371.1988.
We have characterized the polarity orientation of microtubules in teleost retinal photoreceptors. The highly polarized rods and cones contain large numbers of paraxially aligned microtubules and exhibit dramatic cell shape changes. The myoid portion of the inner segments of both rods and cones undergoes contraction and elongation in response to light or circadian signals. Previous studies in our laboratory have demonstrated that in cones but not rods myoid elongation is microtubule-dependent. To determine polarity orientation, we decorated microtubules in photoreceptors of the green sunfish Lepomis cyanellus, with hooks formed from either exogenous or endogenous tubulin subunits. The direction of curvature of the attached hooks in cross section indicates microtubule polarity orientation by allowing one to determine the relative positions within the cell of the plus (fast-growing) and minus (slow-growing) ends of the microtubules. We found that virtually all cytoplasmic microtubules in photoreceptors are oriented with plus ends directed toward the synapse and minus ends toward the basal body at the base of the outer segment. Axonemal microtubules in photoreceptor outer segments are oriented with minus ends toward the basal body as in cilia and flagella. We have suggested previously that cone myoid elongation is mediated by mechanochemical sliding between microtubules. The polarity observations reported here indicate that if microtubules do slide in cones, sliding would necessarily occur between microtubules of parallel orientation as is observed in cilia and flagella.
我们已经对硬骨鱼视网膜光感受器中微管的极性取向进行了表征。高度极化的视杆细胞和视锥细胞含有大量近轴排列的微管，并表现出显著的细胞形状变化。视杆细胞和视锥细胞内段的肌样部分会响应光信号或昼夜节律信号而发生收缩和伸长。我们实验室之前的研究表明，在视锥细胞而非视杆细胞中，肌样伸长依赖于微管。为了确定极性取向，我们用由外源性或内源性微管蛋白亚基形成的钩状结构来标记蓝鳃太阳鱼（Lepomis cyanellus）光感受器中的微管。横截面上附着钩状结构的弯曲方向通过确定微管正端（快速生长端）和负端（缓慢生长端）在细胞内的相对位置来指示微管的极性取向。我们发现，光感受器中几乎所有的细胞质微管都是正端朝向突触，负端朝向外侧段基部的基体。光感受器外侧段的轴丝微管与纤毛和鞭毛一样，负端朝向基体。我们之前曾提出，视锥细胞肌样伸长是由微管之间的机械化学滑动介导的。此处报道的极性观察结果表明，如果微管在视锥细胞中确实发生滑动，那么滑动必然会在平行取向的微管之间发生，就像在纤毛和鞭毛中观察到的那样。
