The Hedgehog (Hh) signalling pathway regulates growth and patterning in invertebrates and vertebrates. Although this pathway is well delineated in Drosophila, the more complex vertebrate pathway is not fully understood. Liu and colleagues now reveal that during mouse limb development,intraflagellar transport (IFT) - the transport of cargos along microtubules -regulates the activator and repressor functions of Gli transcription factors,the principal targets of Hh signalling (see ). They report that mice carrying hypomorphic mutations in Ift88 or Ift52,which encode proteins needed for cilia formation, have defects in ventral neural cell specification and develop polydactyly owing to defects in Gli3 processing and to the loss of Hh signalling. They conclude that IFT is an essential component of the vertebrate Hh ligand-induced signalling cascade that acts downstream of Hh to regulate both Gli activator function and the proteolytic processing of Gli3 into a transcriptional repressor.
