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Taste block. Extra sugar molecules (red) on an altered sweet receptor may quell a mouse's sweet tooth.

Sweet Genes Are Made of This

Can't resist sweets? Scientists have discovered a new gene that may be responsible for your hankerings. Variations in the gene seem to explain why some mice prefer sweet flavors more than others do, and the same may be true for humans.

Taste cells on the tongue recognize five distinct tastes: sweet, sour, bitter, salty, and umami (or monosodium glutamate). Scientists believe that sweet, bitter, and umami tastes are recognized by cellular receptors that bind to particular chemicals in food and then send messages to the brain. Genes that possibly encode umami (ScienceNOW, 26 January 2000) and bitter (ScienceNOW, 21 March 2000) receptors were discovered just last year. Sweet receptor genes, however, have remained elusive.

Four groups of researchers went on a search, combing the human genome sequence. They found a candidate gene that seems to have the right characteristics: The gene is located in a region that, in mice, genetically determines whether an animal prefers sweets (a so-called taster) or does not (a nontaster). The sequence of the protein encoded by the gene suggests that it is a member of a family of proteins that span the cell membrane and transmit signals into the cell--which a taste receptor is expected to do. In addition, the mouse gene is expressed exclusively in taste cells, and variations in the gene sequence distinguish taster mice from nontaster mice.

Preliminary results from scientists at the Monell Chemical Senses Institute in Philadelphia indicate that humans also carry sequence variations in the gene, although whether those variations are responsible for differences in human sweet preferences awaits further study.

Proof that the gene truly encodes a sweet receptor will require further studies in mice and cultured cells. But taste physiologist Sue Kinnamon of Colorado State University in Boulder says that the discovery already is "very exciting. It allows you to really start asking what is the whole pathway that mediates this response."

The work is published in the May issue of Nature Neuroscience by Robert Margolskee and co-workers at the Mount Sinai School of Medicine; the May Nature Genetics by Linda Buck's group at Harvard Medical School; and the May Journal of Neurochemistry by a team led by Susan Sullivan at the National Institute on Deafness and Other Communication Disorders. A fourth group, led by Gary Beauchamp at Monell, will announce their results on 27 April in Sarasota, Florida, at the annual meeting of the Association for Chemoreception Sciences.

Related sites

Monell Chemical Senses Institute
Linda Buck's Faculty Page
Susan Sullivan's Page