In the adult tongue, taste buds are located on taste papillae and are constantly renewed throughout life to maintain gustatory sensing. The sonic hedgehog (SHH) pathway has been shown to regulate taste bud formation in development, whereby SHH activity inhibits taste placode formation. Linda Barlow and colleagues now find (p. ) that SHH has an apparently opposite activity in the adult mouse tongue, promoting the differentiation of taste cells. Remarkably, they find that the ectopic expression of SHH can induce taste bud formation in regions of the tongue outside taste papillae – where taste buds would never normally form. Moreover, these ectopic taste buds develop and are maintained in the absence of nerve innervation, as opposed to endogenous taste buds whose maintenance is strictly nerve dependent. The authors thus propose that SHH signalling can trigger the whole programme of taste bud development in the adult tongue, and suggest that one important role of taste bud innervation might be to induce SHH expression, which then supports taste cell differentiation and bud maintenance.
