Pedersen Lotte B, Geimer Stefan, Sloboda Roger D, Rosenbaum Joel L
Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520, USA.
Curr Biol. 2003 Nov 11;13(22):1969-74. doi: 10.1016/j.cub.2003.10.058.
Flagellar axonemes assemble and continuously turn over at the flagellar tip. The supply and removal of axonemal subunits at the tip are mediated by intraflagellar transport (IFT), a motility process essential for the assembly and maintenance of all eukaryotic flagella and cilia. IFT is characterized by the movement of large protein complexes (IFT particles) from the basal bodies to the flagellar tip by kinesin-II and from the tip back to the basal bodies by cytoplasmic dynein 1b. The IFT particles consist of approximately 16 polypeptides partitioned into two complexes, A and B, and associate with axonemal precursors/turn over products. The mechanisms by which IFT motor regulation and cargo loading/unloading occur at the flagellar tip are unknown. We identified a Chlamydomonas reinhardtii ortholog of the microtubule (MT) plus end-tracking protein EB1 [4] (CrEB1) and show here that CrEB1 localizes to the tip of flagella and to the proximal part of the basal bodies. Furthermore, we found that CrEB1 is depleted from flagella of the temperature-sensitive (ts) flagellar assembly-defective (fla) mutant fla11(ts) at the restrictive temperature. This depletion of CrEB1 is accompanied by a dramatic accumulation of IFT particle polypeptides near the flagellar tip.
鞭毛轴丝在鞭毛顶端组装并持续更新。轴丝亚基在顶端的供应和移除由鞭毛内运输（IFT）介导，这是一个对所有真核生物鞭毛和纤毛的组装及维持至关重要的运动过程。IFT的特征是大型蛋白质复合物（IFT颗粒）通过驱动蛋白-II从基体向鞭毛顶端移动，并通过胞质动力蛋白1b从顶端回到基体。IFT颗粒由大约16种多肽组成，分为A和B两个复合物，并与轴丝前体/更新产物相关联。IFT马达调节以及货物在鞭毛顶端装载/卸载的机制尚不清楚。我们鉴定出了衣藻中微管（MT）正端追踪蛋白EB1 [4]（CrEB1）的直系同源物，并在此表明CrEB1定位于鞭毛顶端和基体的近端部分。此外，我们发现，在限制温度下，温度敏感型（ts）鞭毛组装缺陷型（fla）突变体fla11(ts)的鞭毛中CrEB1缺失。CrEB1的这种缺失伴随着IFT颗粒多肽在鞭毛顶端附近的大量积累。
