The vertebrate skeleton provides structural support and protection for vital organs but how its component bones acquire their unique shapes is unknown. Here (p. 2371), Charles Kimmel and colleagues investigate the genetic regulation of morphogenesis in dermal bones, which are formed by direct differentiation of mesenchymal cells into osteoblasts, by analyzing the development of the zebrafish opercle. The researchers report that the Hedgehog (Hh) family ligand Indian hedgehog a (Ihha) is specifically expressed in a population of osteoblasts localized along the growing edge of this craniofacial bone. Loss of ihha function reduces pre-osteoblast proliferation and bone growth, whereas hyperactive Hh signalling in mutants for the Hh receptor ptch1 has opposite effects. Time-lapse and live-imaging experiments show that ihha-dependent bone growth is region specific and begins at the start of a second phase of morphogenesis, during which the opercle acquires a more-complex form. These results suggest that dermal bone development is modular, with different genes functioning at specific times and locations to pattern growth.

© 2012.