Team:Danci-K8/Description

Genetic Analysis of the ability to taste food ingredients

followed by in-vitro editing of taste related SNPs by CRISPR

The ability of humans to sense food taste is driven in part by genetic polymorphisms in the taste receptor cells (TRCs) organized in taste buds located within gustatory papillae.

Single nucleotide polymorphism (SNP) in genes encoding to taste receptors (belonging to the G-proteins coupled receptors family) have been found to influence peoples abilities to taste bitter (PTC, Coffee, Grapefruit juice), sweet, umami (Monosodium gluten), salts, Cilantro preference and more.

The method we present will be able to perform two actions

  1. An attempt to develop a rapid test for taste-related SNPs, using Taq-man genotyping analysis preformed in the Fluidigm 96.96 Dynamic Array IFC high throughput system
  2. 2. Test the possibility to modify the desired alleles using CRISPR on synthetic DNA, as a feasibility test to change people's taste sensing and improve consumption of necessary oral medications.

The ability to perform the desired test and / or operation to modify the genotype which will allow opening new channels in the study of evolution, innovative assistance in the field of nutrition which prevents and even helps people who cannot swallow pills.

Theoretical Background

Sense of Taste

Mammals are able to distinguish between 5 types of basic tastes: sweet, sour, bitter, salt and umami, the taste of monosodium glutamate (this is the undefined taste of the glutamate substance. This substance enhances the other tastes and users add it to certain foods).

Spiciness is not considered a taste because it stimulates the pain receptors in the mouth and on the tongue and not the taste receptors.

Pic. 1 - The tongue structure

The tongue is composed with a top layer from many varied taste buds. There are two conflicting variants about the structure of the tongue. The old-fashioned and conventional variant claims that the surface of the tongue has different areas where there is excessive concentration of one type of taste bud and other areas where there are more buds of a different type. For this reason, the tongue is divided into areas; each area can identify different tastes. The front of the tongue has buds sensitive to sweet, salty on the sides of the tongue, the sour taste is in the center and the back of the tongue there are the bitter taste buds.

According the second variant, all tastes can be receptive all over the surface of the tongue.

In any event each one of the tastes has taste buds capable of sensing the same taste by identifying different chemical molecules. The bitter taste has the most types of taste buds due to evolutionary reasons.

In Addition People's ability to consume oral medications is driven in part by their sensitivity to drug bitterness.

More than Taste,HOW DOES THE BRAIN CONSTRUCT FLAVOR?

Pic. 2 - The sense of taste system

The taste receptors are found on the surface of the tongue and the gums. The tongue is covered by a layer of Papillae, each of which contains many taste bubbles which have cells - Gustatory Cell type that actually perform the tasting.

The ends of the nerves transfer the signal of the taste it receives from the gustatory to the brain through nerve impulses. The brain decodes the signals, and we feel the taste.

The tongue detects basic tastes, but the nose—with hundreds of receptors for chemicals that waft off food—contributes more to flavor. The brain draws on all the senses to assemble a complex “flavor image” that lingers in our memory.

Pic. 3 - The Taste Buds

The genetic basis of taste sensing

There are two main families of receptors for the sense of taste: T1R, T2R.

These receptors are common in the digestive system and not only in the mouth. Each one of these families includes a wide variety of receptors sorted with the ability to detect tastes. Genetic research will allow distinguishing a variety of alleles that determine the taste of food.

Thorough research will allow us to understand the reasons for preferring different flavors or inability to eat other foods. Today, the majority of sequences of receptors responsible for decoding flavors are known. One of the cases indicates a relationship between the number of visits to a dentist and the preference for sweet taste, another research shows many similarities in food preference or aversion to foods with identical twins, another study carried out on two African tribes, one vegetarian and one only eats meat showed the link dispersing some of the personal genetics. These data provide information about the genetic influence on dietary preference. We will demonstrate the rationale in detail by referring to the ability to sense the "bitter taste".

The Bitter Taste

The ability to sense the bitter taste is a significant anthropological evolution. There are those who align it with the initial period in which the first human being decided on his food 500 million years ago. Because of this ability to avoid eating toxins, the development of high sensitivity to bitterness that characterizes many toxins was based.

The connection between the ability to sense tastes and genetics was first proved in 1930 by Albert Blakeslee. This researcher proved that the ability to sense the bitter taste of a PTC solution is a recessive trait.

Bitter-tasting compounds are recognized by receptor proteins on the surface of taste cells.. There are approximately 30 genes for different bitter taste receptors in mammals. Those genes contain unusually high levels of allelic variation.

The gene for the PTC taste receptor, TAS2R38. It's sequencing identified three nucleotides. Using a Single-Nucleotide Polymorphism ( SNP) to Predict Bitter-Tasting Ability. Positions that vary within the human population—each variable position is termed a single nucleotide polymorphism (SNP).

One specific combination of the three SNPs, termed a haplotype, correlates most strongly with tasting ability.

The “FLAVOFF” in the future

Multiple receptors to certain flavors indicate the desire to eat more of the same taste. Thus, intentional genetic modification of a variety of receptors, of different tastes can affect many processes in the human body.

In the future “Flavoff” will be able to change the alleles of different tastes. The change will be done by spraying into the mouth.

The ability to change the taste could be helpful in many different areas:

  1. Smart Diet.Descendants of families prone to obesity can avoid certain products by changing the ability to distinguish the taste of the product. Equally you can get people to like certain food products. For example by eliminating the receptor that identifies the taste of broccoli, or other cruciferous vegetables, as a very bitter taste.
  2. Genetic modification for dental reasons.People suffering from tooth decay in most cases will have a connection to the sweet taste. We assume that the respective number of sweet taste receptors in their bodies is high. Changing the number of taste receptors could significantly reduce the need to visit the dentist.
  3. Improve the ability to swallow pills. People with bitter taste sensitivity are unable to swallow pills. Temporary neutralization of the bitter taste will help chronically ill patients to improve their ability to swallow pills.

“Flavoff” will change the face of future nutrition. This is an exceptional combination of genetics and diet and is actually a transition to a new world, a smarter world, a more nutritious and modern world.

TaqMan SNP genotyping

The TaqMan SNP genotyping technology utilizes the 5’ nuclease activity of Taq polymerase to generate a fluorescent signal during PCR. For each SNP, the assay uses two TaqMan probes that differ in sequence only at the SNP site, with one probe complementary to the wild-type allele and the other to the variant allele. The technique utilizes the FRET technology whereby a 5’ reporter dye and a 3’ quencher dye are covalently linked to the wild-type and variant allele probes. When the probes are intact, fluorescence is suppressed because the quencher dyes are in the proximity of the reporter dyes. In the PCR annealing step, the TaqMan probes hybridize to the targeted SNP site. During PCR extension, the reporter and quencher dyes are released due to the 5’ nuclease activity of the Taq polymerase, resulting in an increased characteristic fluorescence of the reporter dye. Exonuclease activity only happens on the perfectly hybridized probes, since a probe containing a mismatched base will not be recognized by the Taq polymerase.

At the end of the PCR reaction, the fluorescent signal for the two reporter dyes is measured. The ratio of the signals will be indicative for the genotype of the sample (see pic 4).

Pic. 4 - TaqMan SNP genotyping

Taken from http://www.dnavision.com/taqman-genotyping-assays.php

In most assays, the fluorescent signals of the two reporter dyes are normalized using the signal of a third dye, of which the intensity is proportional to the template DNA concentration and the extent of the PCR reaction. Typically, the reporter dye signals are visualized in a plot. A number of related genotyping systems utilize the reporter-quencher technology and can be analyzed and visualized in the same way as TaqMan probes using the SNP genotyping plugin.

References
  1. Blakeslee, A.F. (1932). Genetics of Sensory Thresholds: Taste for Phenyl Thio Carbamide.
  2. Proc. Natl. Acad. Sci. U.S.A. 18:120-130.
  3. Fox, A.L. (1932). The Relationship Between Chemical Constitution and Taste. Proc. Natl.
  4. Acad. Sci. U.S.A. 18:115-120.
  5. Kim, U., Jorgenson, E., Coon, H., Leppert, M., Risch, N., and Drayna, D. (2003). Positional
  6. Cloning of the Human Quantitative Trait Locus Underlying Taste Sensitivity to Phenylthiocarbamide. Science 299:1221-1225.
  7. Mueller, K.L., Hoon, M.A., Erlenbach, I., Chandrashekar, J., Zuker, C.S., and Ryba, N.J.P. (2005). The Receptors and Coding Logic for Bitter Taste. Nature 434:225-229.
  8. Scott, K. (2004). The Sweet and the Bitter of Mammalian Taste. Current Opin. Neurobiol. 14:423-427.

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