Hedgehog (Hh) proteins constitute one family of a small number of secreted signaling
proteins that together regulate multiple aspects of animal development, tissue homeostasis
and regeneration. Originally uncovered through genetic analyses in Drosophila, their
subsequent discovery in vertebrates has provided a paradigm for the role of morphogens in
positional specification. Most strikingly, the Sonic hedgehog protein was shown to mediate
the activity of two classic embryonic organizing centers in vertebrates and subsequent …