SONIC HEDGEHOG IS EXPRESSED IN EPITHELIAL-CELLS DURING DEVELOPMENT OFWHISKER, HAIR, AND TOOTH

Sonic hedgehog (Shh) is a vertebrate gene homologous to a Drosophila s egment polarity gene. hedgehog, and functions as a secreted signaling molecule in limb pattern formation. differentiation of motor neurons. and sclerotome induction. We found that Shh is also expressed in epith elia of the developing whisker, hair, tooth, rugae, and thyroid primor dium of mouse embryos. In whisker and hair development. Shh is express ed in epithelial cells before condensation of the underlying mesenchym al cells and then in the placode. The expression of Shh continues in t he hair bulb surrounding the dermal papilla. Shh is also expressed in epithelial cells of the tooth bud. then localized to the enamel knot. The Shh expression continues in developing ameloblasts. These results suggest that SHH is an essential epithelial signaling molecule in epit helio-mesenchymal interactions for the terminal differentiation. (C) 1 996 Academic Press, Inc.