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12 April 2017

Scientists look to Fruit Flies in Effort to Understand the Evolution of Cold Tolerance

As larger species began to migrate ever closer to the poles, they were subjected to the reduced temperatures that come along with higher latitudes, and their bodies had to adjust accordingly. Scientists have hypothesized that this may have been achieved by alterations to metabolism, burning through reserves faster in order to create the necessary additional heat; however the exact driving mechanism behind this have up until now remained largely a mystery.

In humans, one of the key differences between those living in Arctic latitudes as opposed to tropical regions is a gene known as THADA, which we now know is responsible for controlling how our bodies burn energy from fat. New research published to the journal Cell Development has now shown that fruit flies also make use of this gene to regulate their metabolisms. When the gene is knocked out, the flies become obese and burn less energy.

“When you remove THADA, then the cells store more fat and produce less heat. When you restore THADA function, the cells store less fat and burn more energy,” explains study co-author Aurelio Teleman of the German Cancer Research Center (DKFZ) in Heidelberg, Germany. “It's a metabolic regulator that affects the balance between how much energy your body turns into fat versus how much of it gets burned.

“We suspected that fatter animals would have better insulation and be more resistant to the cold, but in this case, they were more sensitive to cold.”

And therein lies the somewhat bizarre and wholly unexpected revelation – obese flies are more vulnerable to cold; but why? It would make logical sense that flies with a higher fat reserve would actually be more hardy in terms of cold, insulated as they are by said fat reserve, but this study showed that the opposite is in fact true. They tested this by putting the flies into a walk-in refrigerator; not only were the obese flies more vulnerable, but they also took longer to wake up after passing out as a result of the extreme cold.

The research team do however state that the surprising fact does make sense in light of the observed correlation between tropical latitudes and obesity, as in warmer regions, the heat generating by burning fat is less relied upon than in colder climates. The slowed metabolism of these obese flies means that they burn less fat, making them unable to rapidly adapt to colder environments.

When it comes to applying this to humans, the waters get a little muddy; we are of course very different to flies anatomically-speaking, and this makes it difficult to compare human obesity to the fat storage of fruit flies, as Teleman explains: “Unlike humans, flies have an exoskeleton, which means they have a solid carapace on the outside and that constrains how much they can expand,

“So if you just look at a fat fly from the outside, it's hard to notice any difference, but then if you open it up and look inside, then you can see that there's a bunch more fat in the abdomen.”

However, previous fly studies have identified metabolic genes that turned out to be standout predictors of obesity predisposition in humans, indicating there may be similarities between human and fly metabolism at a cellular level. When taken into consideration alongside the results of another study which compared the genomes of Siberian people to genomes of people from the lower latitudes of Southeast Asia and found that THADA was one of the genes in which the two populations most differed, there is hope for the prospect of this research being applied to human metabolisms in the future. This was further demonstrated during this most recent study, as the researchers found that the THADA knockout flies responded the same way when THADA was reintroduced regardless of whether the gene came from flies or humans.

“All the hints are there that THADA will probably be an important metabolic regulator in mammals as well,” says Teleman.

The team are now looking to expand upon their research by studying the effects of the THADA gene in mice.

Sam Bonson

Sam is an aspiring novelist with a passion for fantasy and crime thrillers. He is currently working as a content writer, journalist & editor in an attempt to expand his horizons.