November 12, 2013
Bitter Taste Gene May Have Been Beneficial To Human Evolution
Brett Smith for redOrbit.com - Your Universe Online
It can be puzzling sometimes when someone else finds the taste of your favorite food to be disgusting, but research has shown we all perceive the taste of various compounds differently.
A new study from researchers at the University of Pennsylvania has found a genetic mutation making certain people more sensitive to the taste of a bitter compound could have been beneficial for certain human populations in Africa, resulting in the mutation being passed on from generation to generation.
Study researchers said their work, which was published in the journal Molecular Biology and Evolution, represents the first time that this bitter-sensitivity gene known as TAS2R16 was studied in a large set of ethnically and culturally diverse African populations.
“Because Africa is the site of origin of all modern humans,” said study author Sarah Tishkoff, a professor in the University of Pennsylvania’s Department of Genetics, “Africans are going to have a large amount of diversity and non-Africans are going to have a subset of that diversity. In Africa, you get an opportunity to observe how these genetic variants are influencing phenotypes that you wouldn’t have if you were only studying non-Africans.”
The new study built on previous research from the same research team that looked at the evolutionary history of a gene called TAS2R38, which conveys the ability to sense the bitter tasting compound PTC. In that research, the scientists realized a factor other than taste perception must have pushed for the selection of that gene.
The new study examined the related TAS2R16 gene that codes for a receptor that attaches to salicin, a bitter chemical found naturally in willow bark and the source of aspirin. Salicin acts as a beneficial anti-inflammatory but can be toxic in large doses. It can also be found in many nuts, fruits and vegetables.
In the study, the researchers sampled DNA from almost 600 people in 74 populations across Africa with a wide range of lifestyles, such as hunting-gathering and agriculture. The team sequenced the TAS2R16 gene in all of these individuals as well as samples from 94 non-Africans. The researchers were able to identify 15 variants of the gene in total, most of which were only found in Africa.
In addition to providing DNA samples, nearly 300 African participants performed taste tests of various concentrations of salicin, reporting when they could detect a bitter taste. The researchers also performed a cellular analysis to see the molecular effects of different TAS2R16 variants.
"The taste testing shows that the mutations in TAS2R16 had functional significance for the bitter taste perception system," said study author Paul Breslin, an experimental psychologist from Rutgers University. "In this case, the mutation caused a gain of taste function."
When the study team matched individuals’ genetic profiles to their taste test performances, they discovered a strong connection between one of the variants and an increased sensitivity to salicin. The cellular analysis showed those participants with this particular genetic variant had almost twice as many receptors for salicin than those with other forms of the TAS2R16 gene.
The researchers also noted the “high-sensitivity” variant was more common in individuals from East Africa than in those from West Central or Central Africa. Non-Africans were found to only have the “high-sensitivity” version of the gene. East Africans with this high-sensitivity variant, which popped up roughly 1.1 million years ago, showed genetic signs the TAS2R16 mutation was selected for, indicating it conferred an evolutionary advantage.
“The types of populations we're studying are diverse and they have diverse diets,” Tishkoff said, “suggesting that there is likely something else going on here. By getting a handle on how much variation is in these populations, where it is located and what are the particular signatures of selection, it might start giving us clues as to what we should be looking at in terms of the biomedical or physiological significance of these genes.”