Animals have evolved to occupy almost all corners of the Earth. To survive, no matter the weather outside, the chemical reactions that run their bodies must adjust to the temperature. This is easy for warm-blooded animals like humans, because we have the ability to maintain our body temperature.

But cold-blooded animals can’t do that. When the weather changes and the mercury swings, their cells get exposed to that change in temperature. Yet cold blooded animals survive just fine. Michael Welte, associate professor of biology at the University of Rochester, may have just discovered one way such animals compensate. His team’s findings have been published in the Journal of Cell Biology.

One key to an organism’s survival at any temperature is to ensure that proteins are being made at the right time and in the right amount. But making proteins requires chemical reactions, and those reactions are sensitive to temperature.

Every cell in the body has something like an assembly line for making proteins. This is partly driven by motor proteins, which pick up messenger RNAs from where they’re made by copying DNA in the cell’s nucleus. They deliver these RNAs to special organelles, called ribosomes, which decode the message and make the protein.

“We have found a molecule that keeps protein production balanced when temperatures change,” said Welte. “It happens to do so by controlling cellular transport.”

Theirs was a serendipitous discovery. Welte and his team were studying fruit flies, which happen to be cold blooded, when they found that making some proteins is difficult for the flies when temperatures change.

As temperatures fall, the ribosome slows down more than the motor proteins that deliver its RNA. This creates an imbalance where the motor proteins keep delivering cargo, but the ribosomes can’t use it quickly enough. Some messenger RNA molecules could end up being discarded, and the cell will waste energy making more than it needs.

But Welte found a special protein, called Klar, that keeps the balance intact. Klar behaves like the emergency brakes of a cargo train. As soon as the temperature drops, Klar slows down the motor proteins that carry messenger RNA molecules. Now the pace of delivery matches the rate of protein production, so the assembly line stays balanced.

In fruit flies, Welte found that the protein assembly line balance is especially important for making a protein called Oskar. In egg cells, motor proteins move Oskar messenger RNA to where the posterior end will be. The posterior end of the cell will later give rise to the tail after hatching. If Oskar is not made in the right location, fly eggs are not able to hatch.

When Welte removed the Klar gene from fruit fly eggs, he found that losing Klar had no effect on flies that hatched at normal temperature. But as soon as the temperature was lowered, the eggs would not hatch. Development of the fruit fly at colder temperatures only works when Klar is present in the egg cell.

Klar is found in all insects in the animal kingdom, and Welte thinks that it might be playing a similar role in other species. But we don’t yet know whether any similar protein operates in other cold-blooded animals.

Body temperature in humans does not fluctuate as much as it does in flies. But, with fevers and other conditions, our cells could be exposed to fluctuations in temperature as well. Welte speculates that a similar mechanism could be taking place in our cells, keeping our protein production stable. “While we don’t have the Klar protein in our cells, the mechanism for producing proteins is very similar,” Welte said.

Journal of Cell Biology, 2014. DOI: 10.1083/jcb.201310010 (About DOIs).



This article was originally published at The Conversation.