Analysis of cell lineage relationships in taste buds

Abstract

Taste buds are a heterogeneous population of cells exhibiting diverse morphological and biochemical characteristics. Because taste buds arise from multiple progenitors, the different types of taste cells may represent distinct lineages. The present study was undertaken to determine the following: (1) how many progenitors contribute to a taste bud, and (2) whether the specific subpopulation of serotonin-immunoreactive (IR) taste cells are related by lineage to a restricted set of progenitor cells. These questions were addressed using cell lineage analysis of taste buds from H253 X-inactivation mosaic mice. After random X-inactivation of the lacZ transgene, the tongue of hemizygous female mice displays discrete patches of epithelial cells, which are either beta-galactosidase (beta-gal) positive or beta-gal negative. By analyzing the proportion of the two differently stained cell populations in taste buds located at the boundary between positive and negative epithelial patches, we can determine the minimum number of progenitors that may contribute to the formation of a taste bud. The presence of taste buds containing only 6-12% labeled cells indicates that at least eight progenitors contribute to an average taste bud of 55 cells, assuming progenitors contribute equally to the cell population. Cell lineage analysis of serotonin-IR taste cells in such mixed taste buds suggests that this subpopulation likely arises from only one to two progenitors and often is related by lineage. Thus, at least some of the cell types in a taste bud represent distinct lineages of cells and are not merely phenotypic stages as a cell progresses from a young to a mature state.

Fig. 1.

The expected results of two or three progenitors giving rise to cells in a taste bud if the progenitors contribute equally to the cell population. Dark shadingindicates β-gal+ cells, and white indicates β-gal− cells.

Fig. 2.

Light microscopic image of lingual tissue from an adult male H253 mouse treated with Simvistatin. Tissue was sectioned, stained with X-gal, and then counterstained with nuclear fast red. Blue, nuclear precipitate indicates β-gal activity. Basal cells in nontaste bud-bearing epithelium lack X-gal staining (arrow), as do perigemmal cells surrounding the taste bud (arrowhead). Scale bar, 20 μm.

Fig. 3.

Light microscopic images of 5 μm serial sections through circumvallate taste buds from an H253 mosaic mouse. The adult female mouse was treated with Simvistatin, and the tissue section was stained with X-gal solution as described in Materials and Methods, embedded in Historesin, resectioned, and stained with nuclear fast red. Asterisks indicate a taste bud with few β-gal+ cells (blue). Scale bar, 20 μm.

Fig. 4.

Confocal image of circumvallate taste buds from an H253 mosaic mouse, triple labeled for β-gal-IR (magenta), 5-HT-IR (green), and propidium iodide (blue). This figure was obtained by merging two confocal images using Photoshop software as described in Materials and Methods. The Photoshop filter “dust and scratches” was used to remove artifactual speckles from the merged image (pixel value was 3). Note that both 5-HT-IR only cells (green) and double-labeled cells (green and magenta) are present in individual taste buds (e.g., bud indicated by asterisk). This indicates that more than one progenitor gave rise to the 5-HT-IR cells in those buds. Scale bar, 20 μm.

Fig. 5.

Schematic diagram showing possible lineage relationships in taste buds. A, In this scheme, the embryonic progenitor cells give rise to lineage-restricted basal cells that generate the different types of taste cells.B, In this scheme, the embryonic progenitors give rise to multipotent epithelial stem cells that generate lineage-restricted basal cells.