Functional analysis of an individual IFT protein: IFT46 is required for transport of outer dynein arms into flagella

Abstract

Intraflagellar transport (IFT), which is the bidirectional movement of particles within flagella, is required for flagellar assembly. IFT particles are composed of ∼16 proteins, which are organized into complexes A and B. We have cloned Chlamydomonas reinhardtii and mouse IFT46, and show that IFT46 is a highly conserved complex B protein in both organisms. A C. reinhardtii insertional mutant null for IFT46 has short, paralyzed flagella lacking dynein arms and with central pair defects. The mutant has greatly reduced levels of most complex B proteins, indicating that IFT46 is necessary for complex B stability. A partial suppressor mutation restores flagellar length to the ift46 mutant. IFT46 is still absent, but levels of the other IFT particle proteins are largely restored, indicating that complex B is stabilized in the suppressed strain. Axonemal ultrastructure is restored, except that the outer arms are still missing, although outer arm subunits are present in the cytoplasm. Thus, IFT46 is specifically required for transporting outer arms into the flagellum.

Keeping an eye on I1: I1 dynein as a model for flagellar dynein assembly and regulation

“…Anchoring of the outer dynein arm is mediated in part through additional complexes called outer dynein arm-docking complexes (ODA-DC and the Oda5 complex) [Takada and Kamiya, 1994;Wakabayashi et al, 2001;Casey et al, 2003;Wirschell et al, 2004]. Moreover, additional mutations have revealed the outer dynein arm is transported into the axoneme specifically through an interaction with the intraflagellar transport component IFT46 and Oda16p-a novel non-dynein transport factor required for outer dynein arm assembly [Ahmed and Mitchell, 2005;Hou et al, 2007]. Evidence suggests that single-headed inner arms are also transported into the flagellum by IFT [Piperno et al, 1996].…”

Intraflagellar transport proteins 172, 80, 57, 54, 38, and 20 form a stable tubulin‐binding IFT‐B2 complex

“…Other axonemal components known to travel by IFT in Chlamydomonas are the nexin–dynein regulatory complex proteins DRC2 and DRC4 and the central pair protein PF16 (Wren et al , 2013). Outer dynein arms (ODAs) are also likely cargoes for IFT via interaction with IFT46 through the adaptor protein ODA16 (Hou et al , 2007; Ahmed et al , 2008). Several subunits of the BBSome, a cargo adapter for membrane proteins, have also been demonstrated to move by IFT (Blacque et al , 2004; Lechtreck et al , 2009a) as have several integral and associated membrane proteins (Qin et al , 2005; Huang et al , 2007).…”

Structural and Functional Recovery of Sensory Cilia in C. elegans IFT Mutants upon Aging

“…Similar mechanisms may operate in other organisms to maintain cilia function in IFT mutants. In Tetrahymena and Chlamydomonas, flagellar defects due to partial loss of IFT proteins can be bypassed in some suppressor strains under conditions of oxygen deprivation [80,[91][92][93], and it has been suggested that a stress-induced chaperone mechanism stabilizes the IFT-B complex to permit cilia function under these conditions [92]. Moreover, Hsp90 is localized to cilia, and regulates cilia stability in response to stress in mammalian cells [94][95][96].…”