[The primary cilium: methodological advances leading to major conceptual breakthroughs]

The primary cilium, first identified in the mid-19th century, is present on the surface of most vertebrate cells. It acts as a cellular antenna that is essential for detecting extracellular signals in many organisms. Dysfunction of the primary cilium underlies various human genetic diseases known as "ciliopathies". Significant methodological advances over the past decade have led to a better understanding of mechanisms governing cilium assembly and the identification of new functions. For instance, it has been discovered that the primary cilium releases extracellular vesicles and participates in new types of intercellular contacts. At the same time, new coordinating functions of primary cilia have been discovered in various tissues and organs, highlighting the complexity and diversity of their roles in numerous physiological and developmental processes.