Most of our cells contain an immobile primary cilium, an antenna used to transfer information from the surrounding environment. Some cells also have many mobile cilia that are used to generate movement. The ‘skeleton’ of the cilium consists of microtubule doublets, which are ‘pairs’ of proteins essential for their formation and function. Defects in the assembly or functioning of the cilia can cause various pathologies called ciliopathies. Scientists from the University of Geneva (UNIGE), Switzerland, have developed an in vitro system capable of forming microtubule doublets, and have uncovered the mechanism and dynamics of their assembly. Their study, published in the journal Science, reveals the crucial role of tubulin, a real building block, in preventing the uncontrolled formation of ciliary structures. This method will make it possible to discover and exploit possible differences between the cilia of human cells and those of pathogens, allowing for the development of new treatments.