Life, death and Sonic hedgehog

The secreted glycoprotein Sonic hedgehog (SHH), a vertebrate homologue of the Drosophila segment polarity gene Hedgehog, is essential for the development of diverse tissues during embryogenesis. Studies of SHH function during neural tube and somite development have focused on its role in specifying the dorsoventral polarity of these structures, but a recent report by Ahlgren and Bronner-Fraser(1) supports the possibility that SHH has additional functions in cell survival and cell proliferation. Perturbation of SHH signaling after the early dorsoventral specification of the cranial neural tube leads to increased cell death in both the neural tube and the neural crest. This implies that SHH is continually required as a trophic and/or mitogenic factor during brain development, and expands the variety of cellular responses to SHH signaling. BioEssays 22:499-502, 2000.