Taste organs: formation and regulation

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Project Summary/Abstract Taste bud cells, the sensory end organs that transduce chemical stimuli into neural signals conveyed to the central nervous system, reside in taste papillae in the mammalian tongue. Therefore, taste papillae host the epithelium that will differentiate to include taste bud cells. However, the field of taste biology lacks a complete understanding of: (1) what constitutes possible taste cell precursors in developing papillae; (2) how and when the precursors differentiate in lingual epithelium to acquire taste papilla and taste bud cell phenotypes; and (3) how and via what factors the underlying mesenchyme signals to tongue epithelium in papilla and taste bud development. Our preliminary data on neural crest derived cell (NCDC) distributions in lingual epithelium, and of phenotypic alterations of tongue and taste papillae induced by genetic modifications in mesenchymal NCDCs, suggest neural crest contributions to both epithelium and mesenchyme in the formation of taste organs. Cre-mediated, tissue-specific, genetic labeling and modifications provide powerful tools for these cell lineage assays and functional analyses. Two well-characterized transgenic mouse lines for neural crest assays, Wnt1- and P0-Cre, are used. We have found that: (1) In tongue epithelium, P0-Cre labeled NCDCs are first distributed in single, scattered elements at E11.5-12.5 to a clustered pattern later in taste papillae and taste buds. The localization of P0-Cre labeled cells in taste buds indicate a neural crest derivation of taste cells. We propose that the single, scattered P0-Cre labeled epithelial cells are neural crest precursors and these will undergo cell differentiation to specific cell types in taste papillae and taste buds. (2) In tongue mesenchyme, both Wnt1- and P0-Cre labeled NCDCs are closely associated with taste papillae and taste buds. Wnt1- and P0-Cre driven, conditional genetic modifications of type I receptor Alk2 for bone morphogenetic proteins (BMPs) and significantly alter the development of tongue and taste papillae, suggesting that tongue mesenchyme, via BMP signaling, interacts with the overlying epithelium in papilla differentiation. The proposed studies will address fundamental issues about formation of the taste papilla organ, using modern techniques (Cre-mediated genetic modifications) and combination of in vivo and in vitro studies. Our goals are to: (Aim 1) demonstrate where and when neural crest cells migrate to the epithelium of tongue or primordium; how and when these cells differentiate in lingual epithelium to acquire specific cell phenotypes; what types and proportions of taste bud cells are derived from neural crest; (Aim 2) characterize how the tongue mesenchyme, via BMP signaling through specific receptors in mesenchymal NCDCs, interacts with the overlying epithelium in the development of tongue and taste papillae. Overall, the proposed studies for demonstration of cell origin, differentiation and mesenchymal interactions in taste papillae and taste buds will contribute to understanding development of the taste organ and will bring new information and novel perspectives to the field for neural crest contributions to taste papillae and taste bud cells. Key words: tongue; taste papillae; neural crest derived cells