Intraflagellar transport (IFT) cargo

TLDR

Intraflagellar transport moves multisubunit protein complexes along axonemal microtubules and is essential for flagella and cilia assembly and maintenance, including delivering precursors to the flagellar tip. The study investigates whether radial spokes, axonemal subunits of 22 polypeptides, serve as cargo for IFT. Coimmunoprecipitation of soluble flagellar fractions confirmed interactions among IFT particles, motors, radial spokes, and other axonemal proteins. Radial spokes are partially assembled in the cell body and transported to the flagellar tip by anterograde IFT, while fully assembled spokes are removed by retrograde IFT, showing that IFT shuttles axonemal proteins in and out of the flagellum.

Abstract

Intraflagellar transport (IFT) is the bidirectional movement of multisubunit protein particles along axonemal microtubules and is required for assembly and maintenance of eukaryotic flagella and cilia. One posited role of IFT is to transport flagellar precursors to the flagellar tip for assembly. Here, we examine radial spokes, axonemal subunits consisting of 22 polypeptides, as potential cargo for IFT. Radial spokes were found to be partially assembled in the cell body, before being transported to the flagellar tip by anterograde IFT. Fully assembled radial spokes, detached from axonemal microtubules during flagellar breakdown or turnover, are removed from flagella by retrograde IFT. Interactions between IFT particles, motors, radial spokes, and other axonemal proteins were verified by coimmunoprecipitation of these proteins from the soluble fraction of Chlamydomonas flagella. These studies indicate that one of the main roles of IFT in flagellar assembly and maintenance is to transport axonemal proteins in and out of the flagellum.