Studies on zebrafish midline mutants, which have a characteristic curved body shape and defects in cell-fate specification in the ventral neural tube and somites, are unravelling the role of the Hedgehog (Hh) family of intercellular signalling molecules in vertebrate development. By studying the midline mutant iguana (igu), Sekimizu et al. identify a new regulator of Hh signalling: the zinc-finger protein Dzip1 (see ). They show that while mutations in igu reduce expression of Hh target genes in the ventral neural tube, there is expanded expression of Hh target genes in somites. The researchers explain this by suggesting that the ventral neural tube and somites have different threshold responses to Hh signals. Additional experiments lead Sekimizu and co-workers to conclude that Dzip1 is a necessary permissive factor that is required for the proper regulation of Hh signalling.
