The researchers created mice with the same sweet-tooth preferences as humans by inserting the gene that codes for a human sweet-taste receptor protein into the animals. They also inserted an entirely different receptor gene into the taste cells of mice, thereby producing animals that perceive a previously tasteless molecule as sweet.

Both of these experiments demonstrate that receptor molecules on the tongue for both the sweet and "savory" umami tastes are what triggers taste cells on the tongue and palate to transmit taste signals to the brain. Umami taste responds to amino acids such as monosodium glutamate.

The researchers said their findings open the way for tracing the circuitry for sweet and umami tastes all the way to the centers in the brain that perceive those tastes. The findings also suggest that individual variations in the "sweet tooth" response may lie in subtle genetic differences in receptor molecules that perceive sweet taste.

The findings were reported in the October 31, 2003, issue of the journal Cell by a research team led by Howard Hughes Medical Institute investigator Charles Zuker at the University of California, San Diego, and Nicholas Ryba of the National Institute of Dental and Craniofacial Research.

"In our previous work, we reported that we had found the best candidate sweet and umami receptor molecules," said Zuker. "But there remained two major outstanding questions. First, do these receptors function in vivo as taste detectors? And second, are they members of a larger group of such receptors, or are they the receptors for sweet and umami taste? The
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Contact: Jim Keeley
keeleyj@hhmi.org
301-215-8858
Howard Hughes Medical Institute
31-Oct-2003