Cells in D.C.: The American Society for Cell Biology

IFT172 turns traffic around lagella and cilia are constantly turning over proteins at their tips. Assembly at the tip and removal of turnover products require the intraflagellar transport (IFT) system, which uses axonemal microtubules as tracks to drop off flagellar tip proteins and return turnover products to the cell body. The change in IFT direction at the tip was discussed by Lotte Pedersen (Yale University, New Haven, CT), whose work implicates IFT172 as an orchestrator of IFT traffic at flagellar tips. Along with different cargo, the two IFT directions come with different motors—kinesin-2 brings the IFT complex and its cargo out to the tip, and cyto-plasmic dynein 1b/2 drives retrograde transport back to the cell body. Axonemal microtubules point their plus ends toward flagellar tips, so Pedersen thought perhaps plus-end tracking proteins might be involved in IFT turnaround at the tip. Sure enough, she and coworkers found the algae version of the microtubule F EB1 (red) is found at the tips of flagella. plus-end tracking protein EB1 out on flagellar tips. This localization was disturbed in a temperature-sensitive IFT mutant called fla11 ts. These mutant flagella accumulated IFT particles at the tips, as though the transport machinery was unable to head back into the cell body. Pedersen and colleagues have now found that FLA11 encodes an IFT complex protein called IFT172. They see that IFT172 and EB1 interact, but only when IFT172 is not bound to some of the other IFT proteins. Pedersen hypothesizes that IFT172 helps to link the IFT machinery to cytoplasmic dynein 1b/2. " At the tip, " she says, " when IFT172 encounters EB1, we think it binds to EB1, and somehow that promotes the reorganization of the IFT particle. " This reorganization may switch the particle from kinesin-to dynein-mediated transport. Since Pedersen still needs proof that EB1 is involved, she plans to use RNAi to get at its flagellar function. NL lthough it is known that actin function and turnover are essential for endocytosis in budding yeast, the order of events remains elusive. presented a sharper picture of actin's role using two-color, real-A Fluorescent phalloidin reveals yeast actin cortical patches and cables. DRUBIN time fluorescence microscopy. The beauty of the system is that one can light up endocytic proteins and actin and watch an endocytic patch being born, invaginating, and moving off into the cytoplasm. Additionally, yeast endocytic mutants can be screened using this system …