Troutt L L, Wang E, Pagh-Roehl K, Burnside B
Department of Molecular and Cell Biology, University of California, Berkeley 94720.
J Neurocytol. 1990 Apr;19(2):213-23. doi: 10.1007/BF01217299.
Retinal photoreceptors have two separate populations of microtubules: axonemal microtubules of the modified cilium of the outer segment and cytoplasmic microtubules of the cell body. The axonemal microtubules originate from a basal body located at the distal tip of the photoreceptor inner segment and extend in a 9 + 0 configuration into the outer segment of rods and accessory outer segment of cones. The cytoplasmic microtubules of the cell body are axially aligned from the distal tip of the inner segment to proximal synapse, and are oriented with uniform polarity, their minus ends distal toward the outer segment and plus ends proximal toward the synapse (Troutt & Burnside, 1988). To investigate how this regular cytoplasmic microtubule array is generated, we have attempted to identify microtubule nucleation sites in the cones of the tropical teleost fish, Tilapia (Sarotherodon mossambicus) by examining the regrowth of cytoplasmic microtubules after cold disruption in whole retinas or in isolated cone fragments consisting of inner and outer segments (CIS-COS). Incremental stages of microtubule reassembly were examined both by electron microscopy of thin sections and by immunofluorescent localization of microtubules with an antitubulin antibody. Cold treatment completely abolished all cytoplasmic microtubules but did not disrupt axonemal microtubules. Within 2 min after rewarming, cytoplasmic microtubules reappeared in the most distal portion of the inner segment in a small aster-like array associated with the basal body, and subsequently appeared in more proximal parts of the cone. These observations suggest that a favoured microtubule nucleation site is associated with the basal body region of the cone outer segment, and thus that the basal body region could function as a microtubule organizing centre for the photoreceptor. These results are consistent with the findings of our previous investigation of cone microtubule polarity, which showed that the minus ends of the cytoplasmic microtubules of the cone are associated with the basal body region.
外段修饰纤毛的轴丝微管和细胞体的细胞质微管。轴丝微管起源于位于光感受器内段远端的基体，并以9 + 0的结构延伸到视杆细胞的外段和视锥细胞的附属外段。细胞体的细胞质微管从内段的远端轴向排列到近端突触，并且具有统一的极性，其负端朝向远端的外段，正端朝向近端的突触（特劳特和伯恩赛德，1988年）。为了研究这种规则的细胞质微管阵列是如何形成的，我们试图通过检查整个视网膜或由内段和外段组成的分离视锥片段（CIS-COS）在冷破坏后细胞质微管的重新生长情况，来确定热带硬骨鱼罗非鱼（莫桑比克罗非鱼）视锥细胞中的微管成核位点。通过薄切片的电子显微镜检查和用抗微管蛋白抗体对微管进行免疫荧光定位，研究了微管重新组装的各个阶段。冷处理完全消除了所有细胞质微管，但没有破坏轴丝微管。复温后2分钟内，细胞质微管在与基体相关的小星状阵列中重新出现在内段的最远端部分，随后出现在视锥细胞的更近端部分。这些观察结果表明，一个有利的微管成核位点与视锥细胞外段的基体区域相关，因此基体区域可能作为光感受器的微管组织中心发挥作用。这些结果与我们之前对视锥细胞微管极性的研究结果一致，该研究表明视锥细胞细胞质微管的负端与基体区域相关。
