Abstract
Intraflagellar transport (IFT) trains, multimegadalton assemblies of IFT proteins and motors, traffic proteins in cilia. To study how trains assemble, we employed fluorescence protein-tagged IFT proteins in Chlamydomonas reinhardtii. IFT-A and motor proteins are recruited from the cell body to the basal body pool, assembled into trains, move through the cilium, and disperse back into the cell body. In contrast to this 'open' system, IFT-B proteins from retrograde trains reenter the pool and a portion is reused directly in anterograde trains indicating a 'semi-open' system. Similar IFT systems were also observed in Tetrahymena thermophila and IMCD3 cells. FRAP analysis indicated that IFT proteins and motors of a given train are sequentially recruited to the basal bodies. IFT dynein and tubulin cargoes are loaded briefly before the trains depart. We conclude that the pool contains IFT trains in multiple stages of assembly queuing for successive release into the cilium upon completion.
Highlights
IntroductionThe assembly of most cilia and flagella (terms used interchangeably) depends on bidirectional intraflagellar transport (IFT) (Rosenbaum and Witman, 2002)
The assembly of most cilia and flagella depends on bidirectional intraflagellar transport (IFT) (Rosenbaum and Witman, 2002)
To analyze the dynamics of IFT proteins in the pool surrounding each of the two flagella-bearing basal bodies of Chlamydomonas reinhardtii, we employed strains expressing fluorescent protein (FP)-tagged IFT particle and motor proteins (Figure 1A)
Summary
The assembly of most cilia and flagella (terms used interchangeably) depends on bidirectional intraflagellar transport (IFT) (Rosenbaum and Witman, 2002). The IFT trains transport proteins in and out of cilia to support ciliary assembly, maintenance, and signaling (for review: [Lechtreck, 2015]). They are composed of IFT motors and IFT particles, the latter consisting of 22 conserved IFT proteins organized into biochemically stable IFT-A, IFT-B1 and IFT-B2 subcomplexes each consisting of equimolar amounts of 6, 10 and 6 proteins, respectively (Cole et al, 1998; Katoh et al, 2016; Taschner et al, 2012, 2016). Numerous protein-protein interactions within the IFT particle have been identified and a 15-subunit IFT-B
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