Cilia and Hedgehog: When and how was their marriage solemnized?

Primary cilia are essential for Hedgehog (Hh) signaling in mammals, and this requirement appears to be conserved in other vertebrates as well. Here, I review recent work that has scrutinized the evolution of the link between the Hh pathway and cilia, discuss what we have learnt from these studies and speculate on how this fascinating problem can be further explored. (C) 2011 International Society of Differentiation. Published by Elsevier B.V. All rights reserved.