April 23, 2001. Copyright 2001. Graphic News. All rights reserved.

Scientists lick puzzle of the sweet tooth

LONDON, April 23, Graphic News: Two research teams trawling human and mouse genetic blueprints, or genomes, think they have found the gene that may be responsible for some people craving for sweets.

The difference between those of us who take three sugars and those who opt for none could all be due to the gene T1r3 -- a finding that could help in designing the next generation of artificial sweeteners.

Cells in our tongues sense four basic tastes -- sweet, salty, sour and bitter -- plus a fifth, called umami, which is found in the flavouring monosodium glutamate and many protein-rich foods like meat, fish and cheese. But until now the taste for sweet things has remained elusive. 

T1r3 is turned on in the cells of our taste buds, neurobiologist Dr Linda Buck and her team at Harvard Medical School have found.

ÒWe feel this is an excellent candidate for a sweet receptor,Ó said Buck. She and colleagues, including postdoctoral fellow Jean-Pierre Montmayeur, who found the gene, say T1r3 makes a receptor protein that may stick to sugars that come into contact with the tongue. This triggers a biochemical cascade, sending sweetness signals along nerve fibres to the brain. Something similar happens in mice, Marianna Max and a team at New York University also report in the latest journal Nature Neuroscience.

Buck was a member of the Harvard team which discovered the ÒbitterÓ gene last year.

Being able to identify sweet things probably played a crucial role in our evolution. It enabled our ancestors to distinguish between bitter food sources, such as deadly plants, and sugary food, which is rich in energy.

There is now considerable commercial interest in developing new sweeteners, and scientists have been searching for the mechanisms underlying sweet taste.

To find the gene, both teams followed up on a prior finding in mice. Some strains are less sensitive to sweet taste than others, and scientists had found the approximate location of the responsible gene on a mouse chromosome.

Scientists then used information from the powerful Human Genome Project database -- which has sequenced the entire DNA in our chromosomes -- to call up the corresponding location in human DNA. Searching though it, they found a whole cluster of genes coding for cell receptors. 

Now, to link T1r3 directly with sweet-tasting ability, researchers are testing whether mice that lack this gene respond less to sugar than do normal mice.

ÒHaving the gene is important to teasing out the effects of receptors and tongue anatomy,Ó says Linda Bartoshuk, who studies taste differences in humans at Yale University in New Haven, Connecticut. The number of taste buds also influences taste perception -- people who are sensitive to small amounts of sweet and bitter substances are known to have more taste buds, she points out. 

Finding the sweet gene is also important for understanding how our genes influence eating behaviour. How we taste affects what we like to eat, says nutrition researcher Valerie Duffy of the University of Connecticut. 

She has found that women who are genetically less sensitive to bitter substances also taste sweetness less intensely and enjoy sweets more than do bitter Òsupertasters.Ó

The T1r3 gene may also play some role in promoting obesity. Knowing an individualÕs genetic taste-preference profile could help dieticians to predict food preferences and tailor a healthy and enjoyable diet, says Duffy.
/ENDS
Source: Nature Neuroscience