In vivo fate tracing studies of mammalian taste cell progenitors

Abstract

In mammals, the homogeneous lingual epithelium in the process of development forms specialized placodal cells that undergo a series of morphogenetic changes to form a papilla. Taste buds appear in the papillary epithelium around birth and thus papillae serve to house the taste buds in the adult. However, evidence for a precise lineage relationship between a putative embryonic taste progenitor population and functional adult taste buds has so far been elusive and is primarily indirect. Also, mammalian taste papillae are reminiscent of epithelial appendages suggesting that the mesenchymal tissue of the papillae could be involved in the formation of these lingual structures. These major questions in the field of mammalian taste development have remained unanswered due to lack of fate mapping studies that would label embryonic cell populations and remain indelibly marked in the adult. Taking advantage of a genetic fate mapping approach to label cell populations both in the lingual epithelium and mesenchyme and following their fate during development would be an ideal way to assess each of these tissues contribution in taste bud formation. Fate mapping studies using tissue specific cre strains crossed with reporter alleles would uncover unique features in the formation of these specialized sensory cells and also provide us with an in vivo model system for taste organ specific experimental manipulations during development.

Figure 1

Schematic representation showing fungiform placode and taste bud development at embryonic day 12 and Post natal day 4 in mice. Placodes undergo morphogenesis with a mesenchymal core (stars) to form papillae that house taste buds at their apices at the time of birth.

Fig 2

Diagram of ShhCreERT2 fate mapping strategy and timeline of tamoxifen induced cre recombination. Top panel: ShhCreERT2 males are crossed with a R26R-stop-LacZ reporter female and transient activation of the CreERT2 by tamoxifen adminstration, excises the R26R stop cassette flanked by lox P sites resulting in permanent ß-galactosidase expression. Bottom panel: Tamoxifen adminstration at specific time points of fungiform placode development enables us to follow the fate of Shh descendent cells from the time point of tamoxifen adminstration through to the postnatal stages.