Distribution and bulk flow analyses of the intraflagellar transport (IFT) motor kinesin-2 support an “on-demand” model for Chlamydomonas ciliary length control

IF 2.4 4区 生物学 Q4 CELL BIOLOGY Cytoskeleton Pub Date : 2024-03-08 DOI:10.1002/cm.21851
Mansi B. Patel, Paul J. Griffin, Spencer F. Olson, Jin Dai, Yuqing Hou, Tara Malik, Poulomi Das, Gui Zhang, Winston Zhao, George B. Witman, Karl F. Lechtreck
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Abstract

Most cells tightly control the length of their cilia. The regulation likely involves intraflagellar transport (IFT), a bidirectional motility of multi-subunit particles organized into trains that deliver building blocks into the organelle. In Chlamydomonas, the anterograde IFT motor kinesin-2 consists of the motor subunits FLA8 and FLA10 and the nonmotor subunit KAP. KAP dissociates from IFT at the ciliary tip and diffuses back to the cell body. This observation led to the diffusion-as-a-ruler model of ciliary length control, which postulates that KAP is progressively sequestered into elongating cilia because its return to the cell body will require increasingly more time, limiting motor availability at the ciliary base, train assembly, building block supply, and ciliary growth. Here, we show that Chlamydomonas FLA8 also returns to the cell body by diffusion. However, more than 95% of KAP and FLA8 are present in the cell body and, at a given time, just ~1% of the motor participates in IFT. After repeated photobleaching of both cilia, IFT of fluorescent kinesin subunits continued indicating that kinesin-2 cycles from the large cell-body pool through the cilia and back. Furthermore, growing and full-length cilia contained similar amounts of kinesin-2 subunits and the size of the motor pool at the base changed only slightly with ciliary length. These observations are incompatible with the diffusion-as-a-ruler model, but rather support an “on-demand model,” in which the cargo load of the trains is regulated to assemble cilia of the desired length.

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对鞭毛内运输(IFT)马达驱动蛋白-2的分布和散流分析支持衣藻纤毛长度控制的 "按需 "模型。
大多数细胞都严格控制纤毛的长度。这种调控可能涉及纤毛内运输(IFT),这是一种多亚基微粒的双向运动,它们组成列车将构件送入细胞器。在衣藻中,前向 IFT 运动驱动蛋白-2 由运动亚基 FLA8 和 FLA10 以及非运动亚基 KAP 组成。KAP 在纤毛顶端与 IFT 分离,并扩散回细胞体。这一观察结果导致了纤毛长度控制的 "扩散即尺规 "模型,该模型推测,KAP会逐渐固着在伸长的纤毛中,因为其返回细胞体需要越来越多的时间,从而限制了纤毛基部的马达可用性、列车组装、构件供应和纤毛生长。在这里,我们发现衣藻的 FLA8 也能通过扩散返回细胞体。然而,超过 95% 的 KAP 和 FLA8 存在于细胞体内,在给定时间内,只有 ~1% 的马达参与 IFT。在反复对两个纤毛进行光漂白处理后,荧光驱动蛋白亚基的 IFT 仍在继续,这表明驱动蛋白-2 从大细胞体池中循环穿过纤毛并返回。此外,生长中的纤毛和全长纤毛含有相似数量的驱动蛋白-2 亚基,纤毛基部马达池的大小仅随纤毛长度略有变化。这些观察结果与 "扩散即标尺 "模型不符,而是支持 "按需模型",即通过调节列车的载货量来组装所需长度的纤毛。
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来源期刊
Cytoskeleton
Cytoskeleton CELL BIOLOGY-
CiteScore
5.50
自引率
3.40%
发文量
24
审稿时长
6-12 weeks
期刊介绍: Cytoskeleton focuses on all aspects of cytoskeletal research in healthy and diseased states, spanning genetic and cell biological observations, biochemical, biophysical and structural studies, mathematical modeling and theory. This includes, but is certainly not limited to, classic polymer systems of eukaryotic cells and their structural sites of attachment on membranes and organelles, as well as the bacterial cytoskeleton, the nucleoskeleton, and uncoventional polymer systems with structural/organizational roles. Cytoskeleton is published in 12 issues annually, and special issues will be dedicated to especially-active or newly-emerging areas of cytoskeletal research.
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