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The ability to sense sweet, bitter, salty, sour, and savory (also called umami) is innate, says Hojoon Lee, a postdoctoral researcher in Zuker's lab who led the study, which is published August 9 in the journal Nature. "We are born to be averse to sour or bitter tastes and attracted to sweet things," he says.
Although it may seem like taste is merely a matter of pleasure (or mild disgust), those responses can be key to survival, especially for other animals. Sweet tastes can signal nutrient-dense fare, whereas bitter tastes can mark a deadly poison.
Job - Taste - System - Turnover - String
For such an important job, the taste system has remarkably high turnover. Like a string of fritzy Christmas lights, the cells on the tongue that detect tastes are constantly dying and being replaced. These cells, called taste receptor cells, are nestled on the taste buds and live for only about two weeks -- which means that stem cells need to churn out new taste receptor cells continually.
The short life span of taste cells created a conundrum, Zuker says: Amid such high turnover, how does the taste system do its job reliably? Connections between cells in the taste buds and neurons must be re-wired correctly each time for the taste system to work. "If you don't connect properly, you're going to be triggering the wrong behavioral responses," Zuker says. But just how the taste system pulled off this feat was a mystery.
Wiring - Taste - System - Lee - Genetics
"Essentially, very little was known about the wiring of the taste system," Lee says. Using sophisticated genetics and single-cell functional imaging, Zuker, Lee, and colleagues created genetically modified mice with mixed-up taste systems. Then, the researchres watched how the miswiring linked bitter taste receptor cells to sweet neurons or sweet receptor cells to bitter neurons.
Each taste receptor cell is tuned to detect one of the five flavors....
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