The segment polarity gene hedgehog plays a central role in cell patter
ning during embryonic and post-embryonic development of the dipteran,
Drosophila melanogaster. Recent studies have identified a family of he
dgehog related genes in vertebrates; one of these, Sonic hedgehog is i
mplicated in positional signalling processes that show interesting sim
ilarities with those controlled by its Drosophila homologue.