Tripartite signaling of pattern: interactions between Hedgehogs, BMPs and Wnts in the control of vertebrate development.

A central issue in embryonic development is the resolution of how groups of equivalent cells are transformed into orderly and patterned arrays of distinct cell types. Recent studies suggest the involvement of the Hedgehog, Wnt and bone morphogenetic protein families in the patterning of different tissue types in vertebrate embryos. The integrated actions of members of these three families of signaling proteins appear to have been recruited in the patterning of neural tissue in addition to several different tissues. Over the past year, a clearer picture of the diverse roles of these signaling proteins in embryonic development has begun to emerge.