The breakthrough, by researchers at the Monell Chemical Sciences Center, USA, will help to develop new techniques to grow and manipulate fully functional taste cells for use in research and clinical treatments, say the scientists behind the finding.
Writing in the journal Stem Cells, the Monell team explains that for decades taste scientists have attempted to identify the stem - or progenitor - cells that spawn the different taste receptor cells. This elusive challenge also sought to establish whether one, or several, progenitors were involved, and where they were located, they said.
Led by senior author Dr Peihua Jiang, the research team said that the identification of the location and certain genetic characteristics of taste stem cells on the tongue will kick-start research that better understands the make-up of human taste, and could someday help treat clinical taste dysfunctions.
"This is just the tip of the iceberg," said Jiang. "Identification of these cells opens up a whole new area for studying taste cell renewal, and contributes to stem cell biology in general."
"Cancer patients who have taste loss following radiation to the head and neck and elderly individuals with diminished taste function are just two populations who could benefit from the ability to activate adult taste stem cells," explained Dr Robert Margolskee, who also worked on the study.
The team explained that taste cells are located in clusters called taste buds, which in turn are found in papillae, the raised bumps visible on the tongue's surface. In these structures, there are two types of taste cells that contain the chemical receptors that initiate perception of sweet, bitter, umami, salty, and sour taste qualities – while a third type appears to serve as a supporting cell.
“A remarkable characteristic of these sensory cells is that they regularly regenerate,” said the researchers. “All three taste cell types undergo frequent turnover, with an average lifespan of 10-16 days. As such, new taste cells must constantly be regenerated to replace cells that have died.”
Using knowledge from other areas of research, the Monell team used a marker for intestinal stem cells to analyse for the presence of stem cells on the tongue.
Stains for this stem cell marker – known as Lgr5 (leucine-rich repeat-containing G-protein-coupled receptor 5) – showed two patterns of expression in taste tissue.
The first was a strong signal underlying taste papillae at the back of the tongue while the second was a weaker signal immediately underneath taste buds in those papillae.
Jiang and his team not believe that these two levels of expression could indicate two different populations of stem cells.
The cells that more strongly express Lgr5 could be true taste stem cells, whereas those with weaker expression could represent those stem cells that have begun the transformation into functional taste cells, they suggest.
Further research by the team has found that stem cells expressing Lgr5 are able to develop in to any one of the three major taste cell types.
The team said that they will now focus on identifying the signalling factors that program the Lgr5-expressing stem cells to differentiate into the different taste cell types, and explore how to grow these cells in the lab – so providing a renewable source of taste receptor cells for research and perhaps even clinical use.
Source: Stem Cells
Published online ahead of print, doi: 10.1002/stem.1338
“Lgr5-EGFP Marks Taste Bud Stem/Progenitor Cells in Posterior Tongue”
Authors: Karen K. Yee, Yan Li, Kevin M. Redding, Ken Iwatsuki, Robert F. Margolskee, Peihua Jiang