title: Sonic hedgehog-expressing basal cells are general post-mitotic precursors of functional taste receptor cells.
abstract: BACKGROUND
  Taste buds contain ∼60 elongate cells and several basal cells. Elongate cells comprise three functional taste cell types: I, glial cells; II, bitter/sweet/umami receptor cells; and III, sour detectors. Although taste cells are continuously renewed, lineage relationships among cell types are ill-defined. Basal cells have been proposed as taste bud stem cells, a subset of which express Sonic hedgehog (Shh). However, Shh+ basal cells turn over rapidly suggesting that Shh+ cells are post-mitotic precursors of some or all taste cell types.
  
  
  RESULTS
  To fate map Shh-expressing cells, mice carrying ShhCreER(T2) and a high (CAG-CAT-EGFP) or low (R26RLacZ) efficiency reporter allele were given tamoxifen to activate Cre in Shh+ cells. Using R26RLacZ, lineage-labeled cells occur singly within buds, supporting a post-mitotic state for Shh+ cells. Using either reporter, we show that Shh+ cells differentiate into all three taste cell types, in proportions reflecting cell type ratios in taste buds (I > II > III).
  
  
  CONCLUSIONS
  Shh+ cells are not stem cells, but are post-mitotic, immediate precursors of taste cells. Shh+ cells differentiate into each of the three taste cell types, and the choice of a specific taste cell fate is regulated to maintain the proper ratio within buds.
authors.affiliation: Department of Oral Physiology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Kagoshima, Japan.
authors.forename: Hirohito
authors.initials: H
authors.lastname: Miura
authors.forename: Jennifer K
authors.initials: JK
authors.lastname: Scott
authors.forename: Shuitsu
authors.initials: S
authors.lastname: Harada
authors.forename: Linda A
authors.initials: LA
authors.lastname: Barlow
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000235:genetics; D002478:Cells, Cultured; D053595:Embryonic Stem Cells / Q000378:metabolism / Q000502:physiology*; D004847:Epithelial Cells / Q000378:metabolism / Q000502:physiology*; D005260:Female; D018507:Gene Expression Regulation, Developmental; D053823:Hedgehog Proteins / Q000235:genetics* / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008938:Mitosis / Q000235:genetics; D011984:Sensory Receptor Cells / Q000502:physiology*; D013650:Taste Buds / Q000166:cytology / Q000196:embryology* / Q000378:metabolism
chemical_list: D053823:Hedgehog Proteins; C465570:Shh protein, mouse
keywords: Cre recombinase; Shh; cell lineage; lineage tracing; molecular genetics; mouse; regeneration; tamoxifen; taste bud