Hedgehog signaling requires motile cilia in the sea urchin

Mol Biol Evol. 2014 Jan;31(1):18-22. doi: 10.1093/molbev/mst176. Epub 2013 Oct 11.


A relatively small number of signaling pathways govern the early patterning processes of metazoan development. The architectural changes over time to these signaling pathways offer unique insights into their evolution. In the case of Hedgehog (Hh) signaling, two very divergent mechanisms of pathway transduction have evolved. In vertebrates, signaling relies on trafficking of Hh pathway components to nonmotile specialized primary cilia. In contrast, protostomes do not use cilia of any kind for Hh signal transduction. How these divergent lineages adapted such dramatically different ways of activating the signaling pathway is an unanswered question. Here, we present evidence that in the sea urchin, a basal deuterostome, motile cilia are required for embryonic Hh signal transduction, and the Hh receptor Smoothened (Smo) localizes to cilia during active Hh signaling. This is the first evidence that Hh signaling requires motile cilia and the first case of an organism requiring cilia outside of the vertebrate lineage.

Keywords: cell biology; cell signaling; evolution and development.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Cilia / metabolism*
  • Evolution, Molecular
  • Hedgehog Proteins / genetics
  • Hedgehog Proteins / metabolism*
  • Microscopy, Electron, Scanning
  • Receptors, G-Protein-Coupled / genetics
  • Receptors, G-Protein-Coupled / metabolism
  • Sea Urchins / genetics*
  • Signal Transduction*


  • Hedgehog Proteins
  • Receptors, G-Protein-Coupled