The WD Repeat-containing Protein IFTA-1 Is Required for Retrograde Intraflagellar Transport

Abstract

The assembly and maintenance of cilia require intraflagellar transport (IFT), a microtubule-dependent bidirectional motility of multisubunit protein complexes along ciliary axonemes. Defects in IFT and the functions of motile or sensory cilia are associated with numerous human ailments, including polycystic kidney disease and Bardet-Biedl syndrome. Here, we identify a novel Caenorhabditis elegans IFT gene, IFT-associated gene 1 (ifta-1), which encodes a WD repeat-containing protein with strong homology to a mammalian protein of unknown function. Both the C. elegans and human IFTA-1 proteins localize to the base of cilia, and in C. elegans, IFTA-1 can be observed to undergo IFT. IFTA-1 is required for the function and assembly of cilia, because a C. elegans ifta-1 mutant displays chemosensory abnormalities and shortened cilia with prominent ciliary accumulations of core IFT machinery components that are indicative of retrograde transport defects. Analyses of C. elegans IFTA-1 localization/motility along bbs mutant cilia, where anterograde IFT assemblies are destabilized, and in a che-11 IFT gene mutant, demonstrate that IFTA-1 is closely associated with the IFT particle A subcomplex, which is implicated in retrograde IFT. Together, our data indicate that IFTA-1 is a novel IFT protein that is required for retrograde transport along ciliary axonemes. INTRODUCTIONCilia and flagella are highly conserved cellular appendages found on many, if not most, mammalian cell types as well as on cells of countless multi-and unicellular lower eukaryotes, including Caenorhabditis elegans and Chlamydomonas reinhardtii. Cilia are grossly characterized as motile (e.g., Chlamydomonas flagella) or nonmotile (e.g., primary cilia of mammals and C. elegans). Motile cilia enable fluid/cell movement, whereas nonmotile cilia are implicated in sensory processes such as olfaction, chemosensation, mechanosensation, and photoreception (Davenport and Yoder, 2005). The physiological importance of cilia function is highlighted by the existence of numerous human ciliopathies, including polycystic kidney disease, nephronophthisis, retinal dystrophy, organ laterality defects, and phenotypically complex disorders such as Bardet-Biedl syndrome (BBS), Alström syndrome, and Meckel syndrome (Ansley et al., 2003;Otto et al., 2003;Afzelius, 2004;Pazour, 2004;Hearn et al., 2005;Kyttala et al., 2006;Smith et al., 2006).The assembly and maintenance of the microtubule-dependent cilia and flagella structures depends on intraflagellar transport (IFT). Initially described in Chlamydomonas flagella, IFT is a bidirectional motility of multisubunit protein complexes, which deliver various cargo proteins that serve to build and maintain the structure and function of cilia and flagella (Kozminski et al., 1993;Rosenbaum and Witman, 2002;Scholey 2003). Anterograde IFT from the basal body, at the base of cilia, to the distal ciliary tip is driven by microtubule plus-ended kinesin-2 motors (Cole et al., 1993;Signor et al., 1999a;Snow et al., 2004), and an IFT-dynein motor ...

Biallelic Mutations in CFAP43 and CFAP44 Cause Male Infertility with Multiple Morphological Abnormalities of the Sperm Flagella

“…41 Both CFAP43 and CFAP44 contain WD repeat domains, which are highly enriched in the intraflagellar transport proteins of sperm flagella. 42,43 This evidence also supports the involvement of CFAP43 and CFAP44 in vertebrate spermatogenesis.…”

Tetrahymena IFT122Ais not essential for cilia assembly but plays a role in returning IFT proteins from the ciliary tip to the cell body

“…Accumulations of IFT proteins in cilia were also reported in C. elegans IFT-A mutants che-11/IFT140 and daf-10/IFT122A (Perkins et al, 1986). Another gene, ifta-1, which phenocopied retrograde IFT defects when it was mutated, is a strong candidate for an uncharacterized IFT-A gene, IFT122B (Blacque et al, 2006). These results from Tetrahymena and C. elegans collectively argue strongly that the IFT-A complex plays an important role in retrograde IFT.…”

A novel function for the atypical small G protein Rab-like 5 in the assembly of the trypanosome flagellum

“…This inhibition leads to formation of short flagella filled with IFT proteins but these proteins cannot be recycled to the cell body (Blacque et al, 2006;Pazour et al, 1999;Porter et al, 1999;Signor et al, 1999 RNAi mutant (Fig. 6C).…”