Tiny hair-like structures (cilia) are found on the surface of most cells. Cilia are responsible for the locomotion of cells (e.g. sperm cells), they process external signals and coordinate the correct arrangement of the inner organs during the development of an organism. For proper assembly and function of cilia, they need to be supplied with the appropriate building blocks. Scientists at the Max Planck Institute of Biochemistry (MPIB) in Martinsried near Munich, Germany, now identified the mechanism of how Tubulin, the main building block of cilia, is transported within the cilium. The result have now been published in the journal Science.