Location, location, and location: compartmentalization of Hedgehog signaling at primary cilia

Primary cilia are solitary, microtubule‐based organelles that serve as signaling hubs for the Hedgehog (Hh) pathway, which regulates embryonic development and adult tissue homeostasis. While protein localization studies have suggested that the dynamic trafficking of Hh components at cilia plays an important role, the molecular basis of Hh signal transduction at cilia is not well understood. In a recent study published in Nature Cell Biology (He et al , 2014), He and colleagues demonstrate that the kinesin KIF7, a conserved regulator of Hh signaling, limits ciliary length by acting at the plus‐ends of microtubules to both reduce growth rate and increase catastrophe frequency. They propose that this biochemical activity establishes a specialized compartment at the tip of the cilia where the activity the Gli family of Hh transcription factors is regulated. Graphical Abstract KIF7 is a conserved kinesin involved in Hh signaling that associates with microtubule plus‐ends in cilia to regulate axonemal stability and length, and to generate a cilia‐tip compartment where Gli proteins processing is regulated.