February 20, 2015

Even the simplest and most elegant song or painting still has a complicated story behind it. That’s what I’m thinking about as I read about cilia today. Cilia are simple and beautiful, but the axonemal structure of cilia is far more complex than one might first appreciate. Today’s image is from a paper describing a protein required for one of the ciliary radial spokes. 

Motile cilia are structures on the surface of some microscopic organisms and certain types of cells, and function in locomotion or the movement of fluid over the cell. Inside each of these cilia is a microtubule-based axoneme structure—9 outer doublets of microtubules form a circle around a central microtubule pair, with radial spokes connecting the center pair with the outer microtubules. These radial spokes are important for regulating ciliary motility. The cilia of most species have three radial spokes, but these spokes are not identical to one another, suggesting that each spoke has a unique functional role. In a recent collaboration between the Nicastro and Gaertig labs, Vasudevan and colleagues found that the ciliary protein FAP206 likely serves as a microtubule docking protein for one of the radial spoke proteins (RS2) and dynein c. In the top images above, FAP206-GFP can be seen exclusively in the cilia of interphase (left) and dividing (right) Tetrahymena cells. In the absence of FAP26, the axoneme lacked proper assembly of the radial spoke RS2. Cryo-electron tomography images (bottom) show a wild-type axoneme (left), with RS2 connecting to the A-tubule of an outer microtubule doublet, compared to an axoneme lacking FAP206, which lacks RS2 (right, arrowhead).

Vasudevan, K., Song, K., Alford, L., Sale, W., Dymek, E., Smith, E., Hennessey, T., Joachimiak, E., Urbanska, P., Wloga, D., Dentler, W., Nicastro, D., & Gaertig, J. (2014). FAP206 is a microtubule-docking adapter for ciliary radial spoke 2 and dynein c Molecular Biology of the Cell, 26 (4), 696-710 DOI: 10.1091/mbc.E14-11-1506