Developing and regenerating a sense of taste

Abstract

Taste is one of the fundamental senses, and it is essential for our ability to ingest nutritious substances and to detect and avoid potentially toxic ones. Taste buds, which are clusters of neuroepithelial receptor cells, are housed in highly organized structures called taste papillae in the oral cavity. Whereas the overall structure of the taste periphery is conserved in almost all vertebrates examined to date, the anatomical, histological, and cell biological, as well as potentially the molecular details of taste buds in the oral cavity are diverse across species and even among individuals. In mammals, several types of gustatory papillae reside on the tongue in highly ordered arrangements, and the patterning and distribution of the mature papillae depend on coordinated molecular events in embryogenesis. In this review, we highlight new findings in the field of taste development, including how taste buds are patterned and how taste cell fate is regulated. We discuss whether a specialized taste bud stem cell population exists and how extrinsic signals can define which cell lineages are generated. We also address the question of whether molecular regulation of taste cell renewal is analogous to that of taste bud development. Finally, we conclude with suggestions for future directions, including the potential influence of the maternal diet and maternal health on the sense of taste in utero.

Keywords: Cell lineage; Differentiation; Epithelial; FGF; Gustation; Lingual; Patterning; Placode; Shh; Stem cell; Tongue; Wnt/β-catenin.

Figure 1

Taste buds comprise 3 morphological cell types, I, II and III, which are recognized by their expression of specific marker proteins. A. Type I cells express NTPdase2, which localizes to cell membranes that tightly wrap other cells within the bud, such that individual NTPDase2+ cells are not discernable (see Miura et al., 2014 for detailed explanation). B. Type II cells express PLCβ2 in the cytosol, and the protein is excluded from nuclei of PLCβ2+ taste cells (*). C. NCAM marks the surface of Type III taste cells (*), as well as some nerve fibers extending into buds (arrows). All panels are images of taste buds from the circumvallate papilla of mice. Apical taste pores are indicated with arrowheads. Scale bar is 20µm.

Figure 2

Schematic diagram of taste bud cell types and lineage relationships. Type I (yellow), II (blue) and III (red) taste cells are elongate, postmitotic (open nuclei) cells, which arise from proliferating, K5+/K14+ keratinocytes (green, mitotic nuclei) outside of taste buds. These progenitors also give rise to non-taste epithelial cells (orange). Following their final division, cells destined to become taste cells enter taste buds and become taste bud precursors, which are Shh+ ovoid cells (lavender) located in the basal compartment of the taste bud. Shh+ cells are postmitotic, and differentiate into each of the 3 taste cell types. Black arrows indicate observed lineage relationships among cell types (see text for details), but are not absolute, nor exhaustive.