The Two SAS-6 Homologs in Tetrahymena thermophila Have Distinct Functions in Basal Body Assembly
The Two SAS-6 Homologs in Tetrahymena thermophila Have Distinct Functions in Basal Body Assembly
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DOI：
10.1091/mbc.e08-08-0838
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发表时间：
2009-03-15
影响因子：
3.3
通讯作者：
Winey, Mark
中科院分区：
文献类型：
--
作者：
Culver, Brady P.;Meehl, Janet B.;Winey, Mark
纤毛和鞭毛是在结构和功能上保守的细胞器，存在于基础和高等真核生物中。纤毛的组装需要以微管为基础的支架，称为基底体。基本体的九重对称性和结构上相似的中心粒围绕着一个轮辐结构被组织起来，称为侧翻。到目前为止，SAS-6是侧翻的两个明显保守的部件之一。在一些生物体中，SAS-6的过度表达会导致额外中心粒的形成。我们质疑SAS-6的中心粒组装启动能力是否独立于其在侧翻的结构作用，或与其直接相关。为了解决这个问题，我们使用了嗜热四膜虫，它表达两个SAS-6同源物，TtSAS6a和TtSAS6b。缺乏TtSAS6a或TtSAS6b的细胞在新的基底体组装中存在缺陷。TtSas6a均匀地定位于所有的基底层，而TtSas6b则在未纤毛的和组装的基体处富含。有趣的是，TtSAS6b的过度表达而不是TtSAS6a的过度表达导致了新的基底体簇在异常位置的组装。我们的数据表明了一种模型，其中TtSAS6a和TtSAS6b已经分化，使得TtSAS6a作为基本体的结构组件，而TtSAS6b影响新的基本体组装的位置。
Cilia and flagella are structurally and functionally conserved organelles present in basal as well as higher eukaryotes. The assembly of cilia requires a microtubule based scaffold called a basal body. The ninefold symmetry characteristic of basal bodies and the structurally similar centriole is organized around a hub and spoke structure termed the cartwheel. To date, SAS-6 is one of the two clearly conserved components of the cartwheel. In some organisms, overexpression of SAS-6 causes the formation of supernumerary centrioles. We questioned whether the centriole assembly initiation capacity of SAS-6 is separate from or directly related to its structural role at the cartwheel. To address this question we used Tetrahymena thermophila, which expresses two SAS-6 homologues, TtSAS6a and TtSAS6b. Cells lacking either TtSAS6a or TtSAS6b are defective in new basal body assembly. TtSas6a localizes to all basal bodies equally, whereas TtSas6b is enriched at unciliated and assembling basal bodies. Interestingly, overexpression of TtSAS6b but not TtSAS6a, led to the assembly of clusters of new basal bodies in abnormal locations. Our data suggest a model where TtSAS6a and TtSAS6b have diverged such that TtSAS6a acts as a structural component of basal bodies, whereas TtSAS6b influences the location of new basal body assembly.