Taste - it's all in your head

When we taste a food, whether it be sweet, salty, bitter, sour, or umami (savory), we think that our tongue is responsible for telling the brain what it is. Instead, researchers found that the brain is responsible for interpreting what the taste is based on which group of neurons the chemical signal is sent to. To put it more simply, if you eat a sweet food and the sweet neurons are suppressed, the sweet taste receptors in the tongue will still be activated, but the food will not taste "sweet" anymore. On the other hand, if the sweet receptors are activated and the others are suppressed, all foods will "taste" sweet.

To test this, researchers gave mice a drug to suppress either the sweet or bitter neurons. Then they gave the mice sweet and bitter foods. The mice that had the bitter neurons suppressed could only taste the sweet foods and vice versa. They also tested these neuron groups by activating the sweet or bitter neurons while the mice were drinking water. When the sweet neurons were activated during drinking, they "observed behavioral responses in the mice associated with sweet, such as impressively increased licking". When the mice were drinking water with the bitter neurons were activated, the mice started gagging and performing "taste-rejection" behaviors. On the bright side, once the drugs were flushed out of the mice's system, all of their "tastes" returned back to normal.

Imagine if we could make all the healthy foods "taste good" and unhealthy foods taste bitter, especially to those who want to change their eating habits. More often than not, I don't eat healthy foods because some of them activate my gag reflex for some reason (other times it's the cost factor that keeps me away, but that's a different story). If I could take a pill before I eat to make that problem go away, I might be more inclined to eat those foods. Also, if I know I have a problem with over-eating sweets, I could take a pill to activate my bitter neurons to deter me from eating too much sugar. This was an interesting study to learn about and I'm curious to see where they take it from here.

References:

Scientists turn tastes on and off by activating and silencing clusters of brain cells

Yueqing Peng, Sarah Gillis-Smith, Hao Jin, Dimitri Tränkner, Nicholas J. P. Ryba, Charles S. Zuker. Sweet and bitter taste in the brain of awake behaving animals. Nature, 2015; DOI: 10.1038/nature15763

Telomeres - the giver of life and death

Telomeres are extra chunks of DNA at the ends of chromosomes that protect important segments of DNA from being lost during cell replication and division. As a cell keeps replicating, the telomeres become shorter. Once the telomere is gone, the cell stops dividing and becomes senescent before it eventually dies. Telomeres can be extended by the enzyme telomerase, which results in cell immortality as long as the telomerase is still functioning. This enzyme is present in immortal cells such as germ cells and stem cells. Additionally, telomerase is over-expressed in cancer cells, which is one of the many reasons why they are able to replicate uncontrollably. 

Telomerase was only discovered within the past 50 years, so details about its structure, function, and expression, among others, is still being researched or recently found. For example, ATM kinase has been known to be involved in DNA repair, but now researchers found that it is also involved in the elongation of telomeres. Getting to know how each enzyme and other proteins are involved in this process could allow them to be manipulated, such as shutting down elongation in cancerous cells or stimulating telomere elongation in aging cells. However, there is a delicate balance between elongating telomeres for longer-life spans/anti-aging and keeping them at a controlled length so that the cells don't become cancerous and have the opposite effect (i.e., death).

Reference:
Another Telomere-Regulating Enzyme Found

Tetragametic Chimeras - a.k.a. "Twin Eaters"

As a follow up from last week's post, I thought I'd go into more detail about the phenomenon of chimeras, specifically tetragametic chimeras. Chimeras are organisms that contain cells that are genetically different from each other. As the name suggests, tetragametic chimeras form from the fusion of two separate eggs that have been fertilized by two different sperm. More simply put, it is the fusion of two non-identical twin embryos during early development. Chimerism can be easily seen in several non-human animal species, such as the well-known example of Venus the Cat (right). However, in humans it can be less obvious (an exception would be true hermaphrodites).





In chimeric humans, different cell lines have one of the sets of DNA. For example, liver cells may have the same DNA found in saliva, but not the same DNA in brain cells or gametes. A famous case study of this phenomenon was regarding Lydia Fairchild (click on name to see video of her story), who found out she was not genetically the biological mother of her three children when she filed for welfare, which requires the parents to prove that the kids are theirs. Since she failed the maternity test, she was charged with welfare fraud and almost lost the case until doctors decided to test her DNA from multiple cell lines, such as her blood, hair, saliva, and cervical cells. Only the cervical cells provided a match to her children. As in vitro fertilization becomes more common, tetragametic chimeras have become more abundant, due to the practice of implanting several embryos into the mother to increase the chance of pregnancy, which increases the probability that two fertilized eggs might fuse (Strain 1998). To prevent future failed paternity and maternity tests, children who are the product of in vitro fertilization should have multiple cell lines screened to see if they are chimeric.

References:
Lisa Strain, Ph.D., John C.S. Dean, F.R.C.P.(Edin.), Mark P.R. Hamilton, F.R.C.O.G., and David T. Bonthron, M.R.C.P. A True Hermaphrodite Chimera Resulting from Embryo Amalgamation after in Vitro Fertilization. N Engl J Med 1998; 338:166-169. January 15, 1998 DOI: 10.1056/NEJM199801153380305

WEIRD OR WHAT? -- TETRAGAMETIC CHIMERA