Cilia are beating hair-like projections protruding from the surface of some cells, and can function in propelling single-cell organisms or moving fluid over fields of cells with many cilia. The structure of cilia is precise and remarkable due to the arrangement of microtubules, the microtubule motor dynein, and associated proteins. Mutations in a protein called CEP290 cause cilia-related diseases in humans, and a recent paper uses the flagella, structures similar to cilia, of the single cell algae Chlamydomonas reinhardtii to understand the role of CEP290 in ciliary function. Image above shows a cross-section of the transition zone at the base of the flagella in normal or cep290 mutant cells. While the normal cells had Y-shaped connectors joining the microtubules to the flagellar membrane (arrowheads), the mutant cells did not.
Reference: Branch Craige, Che-Chia Tsao, Dennis R. Diener, Yuqing Hou, Karl-Ferdinand Lechtreck, Joel L. Rosenbaum, and George B. Witman, 2010. Originally published in Journal of Cell Bioloy. doi: 10.1083/jcb.201006105. Paper can be found here.