Neuronal-epithelial interactions in mammalian gustatory epithelium

There are two neurally controlled morphogenetic programmes in the fungiform papillae of the rodent tongue. When gustatory axons are present they not only promote the expression of taste receptor cells but also simultaneously suppress the outgrowth of an ectopic filiform spine. Innervation during development is essential for the initial formation of taste buds. Consequently, denervation during development irreversibly prevents the establishment of a permanent line of stem cells for taste buds, in contrast to the reliable re-emergence of taste buds after the reinnervation of denervated adult gustatory epithelium. Monoclonal antibodies to keratins selectively recognize cells in particular differentiated states and may contribute to an understanding of the cell lineages and cell-cell interactions that lead to taste buds and filiform spines. Regeneration may recapitulate the late steps in taste development but not the early steps, which are slower and subject to irreversible alteration with denervation. Arguments are set forth that the nerve dependence of taste buds and some other cutaneous receptor cells provides an important selective advantage. Nerve dependence ensures that a more protective integumental covering will replace any superficial, secondary sensory cells rendered useless by denervation.