Functional exploration of the IFT-A complex in intraflagellar transport and ciliogenesis.

Intraflagellar transport (IFT) particles or trains are composed of IFT-A and IFT-B complexes. To assess the working mechanism of the IFT-A complex in IFT and ciliogenesis, we have analyzed ift43 mutants of Chlamydomnonas in conjunction with mutants of the other IFT-A subunits. An ift43 null mutant or a mutant with a partial deletion of the IFT43 conserved domain has no or short flagella. The mutants accumulate not only IFT-B but also IFT-Ain the short flagella, which is in contrast to an ift140 null mutant. The IFT43 conserved domain is necessary and sufficient for the function of IFT43. IFT43 directly interacts with IFT121 and loss of IFT43 results in instability of IFT-A. A construct with a partial deletion of the IFT43 conserved domain is sufficient to rescue the instability phenotype of IFT-A, but results in diminishing of IFT-A at the peri-basal body region. We have further provided evidence for the direct interactions within the IFT-A complex and shown that the integrity of IFT-A is important for its stability and cellular localization. Finally, we show that both IFT43 and IFT140 are involved in mobilizing ciliary precursors from the cytoplasmic pool during flagellar regeneration, suggesting a novel role of IFT-A in transporting ciliary components in the cytoplasm to the peri-basal body region.