Research seminars An intraflagellar transport protein is required for transport of motility-related proteins into cilia/flagella

Cilia and flagella are hair-like organelles that protrude from the surface of cells and are important for making driving forces and sensing extracellular signals. Cilia/flagella are assembled and maintained by the process of intraflagellar transport (IFT), a highly conserved mechanism involving more than 20 IFT proteins as well as motor proteins. However, the functions of individual IFT proteins are mostly unclear. To help address this issue, we focused on a putative IFT protein TTC26/DYF13, which is conserved in ciliated organisms. TTC26/DYF13 localizes to cilia/flagella in mammalian cultured cells and Chlamydomonas reinhardtii. GFP-labeled mouse TTC26 moved bi-directionally along the length of cilia in mammalian cells. TTC26/DYF13 was also biochemically confirmed as an IFT complex B protein in mammalian cells and C. reinhardtii. The dyf13 mutant in C. reinhardtii exhibits shorter flagella and motility defects. Surprisingly, IFT particle assembly and speed were normal in dyf13 mutant flagella, unlike in other IFT complex B mutants. Comparative proteomic analysis, as well as biochemical examination of dynein arm components, indicated that a particular set of proteins involved in motility was specifically depleted in the dyf13 mutant. Thus, although TTC26/DYF13 is a bona fide IFT complex B protein, it is not required for IFT complex assembly or motility, but instead plays a specialized role in transporting a discrete subset of cilia/flagella proteins into flagella in order to allow assembly of full-length cilia with normal motility.