TAS2R38
Supertasters?
They Might Be Giants - John Lee Supertaster. By RWappin. Prod. They Might Be Giants. YouTube. N.p., 20 Mar. 2014. Web. 20 May 2014. <https://www.youtube.com/watch?v=Roc_XZ86WRc>.
How do we taste?
Taste receptors are a kind of receptor that control one’s perception of taste, and are split into two main categories: bitter and sweet. After foods and other materials enter the mouth, molecules mix with saliva and become attached to taste receptors in the oral cavity. On a structural level, 50 to 150 taste receptor cells are bundled together to form taste buds. The taste receptor cells in a bud bunch together so their tips to form a tiny taste pore, out of which microvilli with taste receptors extend from. In turn, taste buds bind together to form structures called papillae.
Three different variety of papillae are connected to taste: fungiform papillae, foliate papillae, and circumvallate papillae. The fourth kind, filiform papillae, do not contain taste buds. Taste receptors are found outside of papillae structures, and exist within sections of the digestive system like the larynx and esophagus. Scientists also recently found bitter taste receptors in human lung tissue, which allows the airways to loosen whenever a bitter material is encountered. Evolutionary, this response is beneficial to an organism since the relaxed airways can assist the removal of lung infections.
Taste receptors are a kind of receptor that control one’s perception of taste, and are split into two main categories: bitter and sweet. After foods and other materials enter the mouth, molecules mix with saliva and become attached to taste receptors in the oral cavity. On a structural level, 50 to 150 taste receptor cells are bundled together to form taste buds. The taste receptor cells in a bud bunch together so their tips to form a tiny taste pore, out of which microvilli with taste receptors extend from. In turn, taste buds bind together to form structures called papillae.
Three different variety of papillae are connected to taste: fungiform papillae, foliate papillae, and circumvallate papillae. The fourth kind, filiform papillae, do not contain taste buds. Taste receptors are found outside of papillae structures, and exist within sections of the digestive system like the larynx and esophagus. Scientists also recently found bitter taste receptors in human lung tissue, which allows the airways to loosen whenever a bitter material is encountered. Evolutionary, this response is beneficial to an organism since the relaxed airways can assist the removal of lung infections.
http://en.wikipedia.org/wiki/File:1402_The_Tongue.jpg
The sense of taste is useful in aiding an organism that is about to consume toxic substances while also upholding a steady nutrition level. Certain molecules in food posses unique shapes that lock into proteins that exist on the surface of the tongue. Once the molecule is locked into the protein, a taste nerve (wound between the taste buds) fires and sends a signal to the brain indicating that one has tasted one of the five basic tastes: sweet, sour, salt, bitter, salty, and umami. However, if you do not have the version of a gene that codes for a specific taste receptor, you will not be able to sense the molecule that would normally fit into this receptor
Sources:
Bowen, R. "Taste Receptor Cells, Taste Buds and Taste Nerves." Physiology of Taste. Colorado State, 10 Dec. 2006. Web. 20 May 2014. <http://www.vivo.colostate.edu/hbooks/pathphys/digestion/pregastric/taste.html>.
Perman, Anna. "The 'brussels sprouts' gene: TAS2R38: As the annual sprout-eating ritual approaches, Anna Perman explains why you either love them or hate them." The Guardian. N.p., 1 Nov. 2011. Web. 20 May 2014. <http://www.theguardian.com/science/blog/2011/nov/01/brussel-sprout-gene>.
Sources:
Bowen, R. "Taste Receptor Cells, Taste Buds and Taste Nerves." Physiology of Taste. Colorado State, 10 Dec. 2006. Web. 20 May 2014. <http://www.vivo.colostate.edu/hbooks/pathphys/digestion/pregastric/taste.html>.
Perman, Anna. "The 'brussels sprouts' gene: TAS2R38: As the annual sprout-eating ritual approaches, Anna Perman explains why you either love them or hate them." The Guardian. N.p., 1 Nov. 2011. Web. 20 May 2014. <http://www.theguardian.com/science/blog/2011/nov/01/brussel-sprout-gene>.
What is TAS2R38?
TAS2R38 encodes for a seven-transmembrane G protein-coupled receptor (GPCRs), which belongs to a family of proteins that first sense molecules or specific stimuli outside of the cell and then trigger a certain cellular response within the cell. Essentially all GPCRs serve as a type of molecular switch, and they are referred to as seven-transmembrane receptors since the proteins pass through the cell membrane seven times.
In particular, TAS2R38 produces a distinct GPCRs that regulates an individual's capability to taste glucosinolates, a compound that supplies certain foods with a bitter or hot taste. Examples of foods that contain glucosinolates include horseradish, black mustard, radish, pak-choi, turnips, and stinkweed. Chemicals that resemble glucosinolates, phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP), both contain the N-C=S group in their chemical structures and are used frequently in experiments involving TAS2R38:
TAS2R38 encodes for a seven-transmembrane G protein-coupled receptor (GPCRs), which belongs to a family of proteins that first sense molecules or specific stimuli outside of the cell and then trigger a certain cellular response within the cell. Essentially all GPCRs serve as a type of molecular switch, and they are referred to as seven-transmembrane receptors since the proteins pass through the cell membrane seven times.
In particular, TAS2R38 produces a distinct GPCRs that regulates an individual's capability to taste glucosinolates, a compound that supplies certain foods with a bitter or hot taste. Examples of foods that contain glucosinolates include horseradish, black mustard, radish, pak-choi, turnips, and stinkweed. Chemicals that resemble glucosinolates, phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP), both contain the N-C=S group in their chemical structures and are used frequently in experiments involving TAS2R38:
http://patentimages.storage.googleapis.com/US20120058965A1/US20120058965A1-20120308-C00001.png
TAS2R38 is located on the long arm of Chromosome 7 and is 1,143 base pairs long. More specifically, its cytogenetic location is 7q34, and runs from base pair 141,972,630 to base pair 141,973,772.
http://ghr.nlm.nih.gov/gene/TAS2R38
Sources:
"TAS2R38." Genetics Home Reference: Your Guide to Understanding Genetic Conditions. N.p., 12 May 2014. Web. 20 May 2014. <http://ghr.nlm.nih.gov/gene/TAS2R38>.
"TAS2R38." Tastes are Different - Genes too! N.p., n.d. Web. 20 May 2014. <http://www.gbt-ursprung.at/gbt/projekte/steviaron/en/index.php?seite=TAS2R38>.
"TAS2R38." Genetics Home Reference: Your Guide to Understanding Genetic Conditions. N.p., 12 May 2014. Web. 20 May 2014. <http://ghr.nlm.nih.gov/gene/TAS2R38>.
"TAS2R38." Tastes are Different - Genes too! N.p., n.d. Web. 20 May 2014. <http://www.gbt-ursprung.at/gbt/projekte/steviaron/en/index.php?seite=TAS2R38>.
TAS2R38 Mutations
The TAS2R38 gene can have three SNPs (single-nucleotide polymorphisms); in other words, there are three positions where the order of DNA base pairs may vary due to mutations. Depending on the mutation, the corresponding amino acids could change. Though there are eight possible forms, the most common two create the PAV and AVI alleles, “tasting” and “nontasting” variations. The PAV/PAV homogenous variant of the gene corresponds to an exceptional perception of bitterness, whereas the AVI/AVI homogenous variant of the gene corresponds to minimal perception of bitterness. There is also the PAV/AVI heterogenous variant which corresponds to moderate perception of bitterness.
Sources:
"TAS2R38." Tastes are Different - Genes too! N.p., n.d. Web. 20 May 2014. <http://www.gbt-ursprung.at/gbt/projekte/steviaron/en/index.php?seite=TAS2R38>.
The TAS2R38 gene can have three SNPs (single-nucleotide polymorphisms); in other words, there are three positions where the order of DNA base pairs may vary due to mutations. Depending on the mutation, the corresponding amino acids could change. Though there are eight possible forms, the most common two create the PAV and AVI alleles, “tasting” and “nontasting” variations. The PAV/PAV homogenous variant of the gene corresponds to an exceptional perception of bitterness, whereas the AVI/AVI homogenous variant of the gene corresponds to minimal perception of bitterness. There is also the PAV/AVI heterogenous variant which corresponds to moderate perception of bitterness.
Sources:
"TAS2R38." Tastes are Different - Genes too! N.p., n.d. Web. 20 May 2014. <http://www.gbt-ursprung.at/gbt/projekte/steviaron/en/index.php?seite=TAS2R38>.
Discovery of TAS2R38
In 1931, the chemist Arthur Fox was placing powdered PTC into a beaker, generating a cloud of PTC in the process. While Fox could not smell anything, a chemist working closeby started to complain about a horrible smelling odor. Fox was hooked, and set out to discover why some people could smell and taste PTC while others could not. He solicited family and friends, and had them state whether or not they could taste PTC. Fox was able to successfully predict whether or not most people would be able to taste the PTC by examining how their close relatives had reacted to the chemical. This association allowed Fox to include that the ability to sense PTC was linked to people’s genetic material. Subsequent studies run by Albert Blakeslee, at the Carnegie Department of Genetics also showed that the inability to taste PTC is a recessive trait that varies in the human population. For many years, PTC was used in paternity testing, since genetic fingerprinting did not exist throughout the 1930s and 1940s. In the test, the father’s and child’s ability to taste PTC was used as evidence of whether or not the two were related. However this method was not very sound, as taste can be influenced by many factors including age, smoking, and habitual food/drink patterns for example. Although there are approximately 30 genes for different bitter taste receptors in mammals, the gene for the PTC taste receptor, TAS2R38, was identified in 2003.
Sources:
Perman, Anna. "The 'brussels sprouts' gene: TAS2R38: As the annual sprout-eating ritual approaches, Anna Perman explains why you either love them or hate them." The Guardian. N.p., 1 Nov. 2011. Web. 20 May 2014. <http://www.theguardian.com/science/blog/2011/nov/01/brussel-sprout-gene>.
"Using a Single-Nucleotide Polymorphism to Predict Bitter-Tasting Ability." DNA Kits Learning Center. Dolan DNA Learning Center, Cold Spring Harbor Laboratory, 2006. Web. 20 May 2014. <https://wiki.brown.edu/confluence/download/attachments/71140633/Predict+Bitter+Tasting+Ability+manual.pdf>.
In 1931, the chemist Arthur Fox was placing powdered PTC into a beaker, generating a cloud of PTC in the process. While Fox could not smell anything, a chemist working closeby started to complain about a horrible smelling odor. Fox was hooked, and set out to discover why some people could smell and taste PTC while others could not. He solicited family and friends, and had them state whether or not they could taste PTC. Fox was able to successfully predict whether or not most people would be able to taste the PTC by examining how their close relatives had reacted to the chemical. This association allowed Fox to include that the ability to sense PTC was linked to people’s genetic material. Subsequent studies run by Albert Blakeslee, at the Carnegie Department of Genetics also showed that the inability to taste PTC is a recessive trait that varies in the human population. For many years, PTC was used in paternity testing, since genetic fingerprinting did not exist throughout the 1930s and 1940s. In the test, the father’s and child’s ability to taste PTC was used as evidence of whether or not the two were related. However this method was not very sound, as taste can be influenced by many factors including age, smoking, and habitual food/drink patterns for example. Although there are approximately 30 genes for different bitter taste receptors in mammals, the gene for the PTC taste receptor, TAS2R38, was identified in 2003.
Sources:
Perman, Anna. "The 'brussels sprouts' gene: TAS2R38: As the annual sprout-eating ritual approaches, Anna Perman explains why you either love them or hate them." The Guardian. N.p., 1 Nov. 2011. Web. 20 May 2014. <http://www.theguardian.com/science/blog/2011/nov/01/brussel-sprout-gene>.
"Using a Single-Nucleotide Polymorphism to Predict Bitter-Tasting Ability." DNA Kits Learning Center. Dolan DNA Learning Center, Cold Spring Harbor Laboratory, 2006. Web. 20 May 2014. <https://wiki.brown.edu/confluence/download/attachments/71140633/Predict+Bitter+Tasting+Ability+manual.pdf>.
Evolutionary Significance
Evolutionarily, plants initially developed toxic compounds in order to prevent themselves from being eaten. As a response to that, humans as well as other animals evolved the ability to taste these toxins through bitter taste. Being able to taste bitterness can allow organisms to either completely avoid the consumption of these plants, or at least learn how to regulate intake. By being able to taste bitterness, it is possible to eat some of these toxins while being able to measure how much you’ve consumed. This may seem like supertasters thus have the evolutionary advantage over non-tasters, and that non-tasters should have been eliminated through process of natural selection, but scientists hypothesize that these non-tasters may have the ability to taste a different bitter compound.
Sources:
"PTC: Genes and Bitter Taste." Learn Genetics: Genetic Science Learning Center. University of Utah, n.d. Web. 20 May 2014. <http://learn.genetics.utah.edu/content/inheritance/ptc/>.
Evolutionarily, plants initially developed toxic compounds in order to prevent themselves from being eaten. As a response to that, humans as well as other animals evolved the ability to taste these toxins through bitter taste. Being able to taste bitterness can allow organisms to either completely avoid the consumption of these plants, or at least learn how to regulate intake. By being able to taste bitterness, it is possible to eat some of these toxins while being able to measure how much you’ve consumed. This may seem like supertasters thus have the evolutionary advantage over non-tasters, and that non-tasters should have been eliminated through process of natural selection, but scientists hypothesize that these non-tasters may have the ability to taste a different bitter compound.
Sources:
"PTC: Genes and Bitter Taste." Learn Genetics: Genetic Science Learning Center. University of Utah, n.d. Web. 20 May 2014. <http://learn.genetics.utah.edu/content/inheritance/ptc/>.
Iodine/Thyroid Function
Glucosinolates block both the creation of organic iodine and the movement of iodine into the thyroid. Normal functioning of the thyroid gland requires certain levels of iodine, and in areas where iodine is scare, cases of enlarged thyroids (endemic goiter) are more common in order to keep adequate levels of thyroid hormone. In these instances, glucosinolates and other various thyroid toxins contribute to issues with normal thyroid functioning, and the results can be drastic (mental issues and delayed sexual development are common in areas with low-iodine levels).
Studies have already shown that the family of TAS2R taste receptors evolved in order to developed specific avoidance of toxic compounds found in plants. These works used synthetic compounds like PTC/PROP as the bitter components to demonstrate that individual’s possessing different versions of TAS2R receptors experienced taste in different manners. New research proved that distinct genetic editions of the specific TAS2R38 receptor particularly determine a person’s comprehension of plants that produce glucosinolates.
Despite iodine supplements helping to relieve thyroid issues in low-iodine areas, there are still 1 billion people in the world who are still at risk for faulty thyroid activity. This points to the evolutionary need to sense anti-thyroid compounds through various selective mechanisms. In particular, experiments with TAS2R38 demonstrate the significance of individual taste receptor genes influencing how we experience food. In particular, the effect of a mutation within one single gene can have a huge influence over how an individual interprets a whole type of vegetables.
Sources:
"Don't Care For Broccoli? A Bitter Taste Receptor Gene's Variation Suggests An Evolutionary Excuse." Science Daily. N.p., 19 Sept. 2006. Web. 20 May 2014. <http://www.sciencedaily.com/releases/2006/09/060918165721.htm>.
Glucosinolates block both the creation of organic iodine and the movement of iodine into the thyroid. Normal functioning of the thyroid gland requires certain levels of iodine, and in areas where iodine is scare, cases of enlarged thyroids (endemic goiter) are more common in order to keep adequate levels of thyroid hormone. In these instances, glucosinolates and other various thyroid toxins contribute to issues with normal thyroid functioning, and the results can be drastic (mental issues and delayed sexual development are common in areas with low-iodine levels).
Studies have already shown that the family of TAS2R taste receptors evolved in order to developed specific avoidance of toxic compounds found in plants. These works used synthetic compounds like PTC/PROP as the bitter components to demonstrate that individual’s possessing different versions of TAS2R receptors experienced taste in different manners. New research proved that distinct genetic editions of the specific TAS2R38 receptor particularly determine a person’s comprehension of plants that produce glucosinolates.
Despite iodine supplements helping to relieve thyroid issues in low-iodine areas, there are still 1 billion people in the world who are still at risk for faulty thyroid activity. This points to the evolutionary need to sense anti-thyroid compounds through various selective mechanisms. In particular, experiments with TAS2R38 demonstrate the significance of individual taste receptor genes influencing how we experience food. In particular, the effect of a mutation within one single gene can have a huge influence over how an individual interprets a whole type of vegetables.
Sources:
"Don't Care For Broccoli? A Bitter Taste Receptor Gene's Variation Suggests An Evolutionary Excuse." Science Daily. N.p., 19 Sept. 2006. Web. 20 May 2014. <http://www.sciencedaily.com/releases/2006/09/060918165721.htm>.
http://pixabay.com/p-2458/?no_redirect
Alcoholism
Studies have found that the TAS2R38 gene may also provide more information about the genetic causes for alcoholism. It has been shown that nontasters, with the AVI/AVI variant of the gene, find alcohol to be more sweet and pleasing than others, and can drink twice as much alcohol as supertasters. Supertasters, PAV/PAV variants, on the other hand, are much more sensitive and find the taste of alcohol to be less pleasurable. Researchers at the University of Connecticut screened a total of 84 people--all light-to-moderate drinkers of various TAS2R38 genotypes--and found that PAV/PAV people had an average of 133 drinks a year, while PAV/AVI people had 180, and AVI/AVI people had 285.
Sources:
Gosline, Anna. "Genetic variation gives a taste for alcohol." New Scientist. Reed Business Information Ltd., 15 Nov. 2004. Web. 20 May 2014. <http://www.newscientist.com/article/dn6668-genetic-variation-gives-a-taste-for-alcohol.html#.U3u9WNxN3wJ>.
Studies have found that the TAS2R38 gene may also provide more information about the genetic causes for alcoholism. It has been shown that nontasters, with the AVI/AVI variant of the gene, find alcohol to be more sweet and pleasing than others, and can drink twice as much alcohol as supertasters. Supertasters, PAV/PAV variants, on the other hand, are much more sensitive and find the taste of alcohol to be less pleasurable. Researchers at the University of Connecticut screened a total of 84 people--all light-to-moderate drinkers of various TAS2R38 genotypes--and found that PAV/PAV people had an average of 133 drinks a year, while PAV/AVI people had 180, and AVI/AVI people had 285.
Sources:
Gosline, Anna. "Genetic variation gives a taste for alcohol." New Scientist. Reed Business Information Ltd., 15 Nov. 2004. Web. 20 May 2014. <http://www.newscientist.com/article/dn6668-genetic-variation-gives-a-taste-for-alcohol.html#.U3u9WNxN3wJ>.
Mapping the Gene
Using PCR, we were able to map our TAS2R38 gene in our own DNA. In order to do so, we selected two primers, a left primer and a right primer:
Using these two primers, we expected our PCR product size to be 494 base pairs long. Along a 100 bp ladder, the result should look like this:
And finally, these were our results when we performed the gel electrophoresis. Our samples were in slots 2 and 3, while slots 1 and 12 were the ladder DNA in order to check length.
Not much seems to be visible from slot 3, but in slot 2, a faint line can be seen parallel to the most distinct line in slot 1. Upon checking against the 100 bp ladder, that seems to be very close to the 500 bp line, meaning that we were likely able to accomplish cutting a 494 bp as expected!
https://www.flickr.com/photos/galaxyfm/199841303/