Primary and motile cilia are eukaryotic organelles that perform crucial roles in cellular signalling and motility. Intraflagellar transport (IFT) contributes to the formation of the highly specialized ciliary proteome by active and selective transport of soluble and membrane proteins into and out of cilia. IFT is performed by the IFT-A and IFT-B protein complexes, which together link cargoes to the microtubule motors kinesin and dynein. In this Review, we discuss recent structural and mechanistic insights on how the IFT complexes are first recruited to the base of the cilium, how they polymerize into an anterograde IFT train, and how this complex imports cargoes from the cytoplasm. We will describe insights into how kinesin-driven anterograde trains are carried to the ciliary tip, where they are remodelled into dynein-driven retrograde trains for cargo export. We will also present how the interplay between IFT-A and IFT-B complexes, motor proteins and cargo adaptors is regulated for bidirectional ciliary transport.

初级和运动纤毛是真核细胞器，在细胞信号传导和运动中起关键作用。鞭毛内转运 （IFT） 通过可溶性蛋白和膜蛋白主动和选择性转运进出纤毛，有助于高度专业化纤毛蛋白质组的形成。IFT 由 IFT-A 和 IFT-B 蛋白复合物执行，它们共同将货物连接到微管马达驱动蛋白和动力蛋白。在这篇综述中，我们讨论了关于 IFT 复合物如何首先被募集到纤毛基部、它们如何聚合成顺行 IFT 序列以及该复合物如何从细胞质中输入货物的最新结构和机制见解。我们将介绍驱动蛋白驱动的顺行列车如何被带到纤毛尖端，在那里它们被改造成动力蛋白驱动的逆行列车用于货物出口。我们还将介绍 IFT-A 和 IFT-B 复合物、运动蛋白和货物接头之间的相互作用如何被调节以实现双向纤毛运输。