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Epigenetics in single-celled organisms opens new understanding of evolution

This blog post by Pam Baker originally appeared on the Alberta Epigenetics Network website on 30 December, 2018.

Our understanding of evolution is itself evolving. Once widely thought to be exclusively a function of DNA mutations, researchers have since found that epigenetics plays a significant role in inheritable changes too. Even so, epigenetics was assumed to be a relatively new development in evolution and present only in complex organisms like mammals and people. But now researchers know epigenetics have been here for a very long time.

"The surprise is that it's in these relatively primitive organisms, which we know to be ancient," said Paul Blum, Charles Bessey Professor of biological sciences at University of Nebraska, in a statement to the press. "We've been thinking about this as something (evolutionarily) new. But epigenetics is not a newcomer to the planet."

The Nebraska researchers found through a series of experiments that epigenetics can pass along specific, environmentally-responsive attributes– such as extreme acid resistance-- in microscopic, single-cell organisms too.

The team studied Sulfolobus solfataricus, a sulfur-eating species of archaea that share some features with both large organisms and tiny bacteria.  However, these microscopic, one-cell organisms are also very different. For one thing, this species thrives in “the boiling, vinegar-acidic springs of Yellowstone National Park.”

Researchers exposed this species to increasingly higher acid levels -- far above the levels these lifeforms already thrived in daily – over a period of several years. From that hostile, poisonous exposure “evolved three strains that exhibited a resistance 178 times greater than that of their Yellowstone ancestors.”

Ah, that’s how evolution works, you might say. Yes, this is true. But it is the specifics in how these three strains evolved that proved to be enlightening.

"We predicted that they'd be mutated, and we'd follow the mutations, and that would teach us what caused the extreme acid resistance," Blum said. "But that's not what we found."

What they actually found was that one strain evolved to this higher level of acid resistance with no changes to its DNA whatsoever. The other two strains did have mutations but in mutually exclusive genes that have nothing to do with acid resistance. And then there was one more surprise: “when the team disrupted the proteins thought to control the expression of resistance-relevant genes - leaving the DNA itself untouched - that resistance abruptly disappeared in subsequent generations.”

These findings are more than just interesting to the intellectually curious. Studying epigenetics in simple organisms like these archaea is a cheaper and faster way to learn how epigenetics works in humans and that can lead to important discoveries in new medicines and medical treatments.

"We don't know what flips the switch in humans that changes epigenetic traits," Blum said. "And we sure don't know how to reverse it very often. That's the first thing we'll go after: how to turn it on, how to turn it off, how to get it to switch. And that has benefits when you think about (managing) traits in us or traits in plants."

But like all new research, more questions than answers quickly come to light. In this case, researchers wonder why both large and small organisms adopted epigenetics as a method of inheritance.

"Maybe both of them had it because they diverged from a common ancestor that had it," said Payne, a doctoral student in biological sciences. "Or maybe it evolved twice. It's a really interesting concept from an evolutionary perspective."

The researchers also suspect that epigenetics may be the reason that archaea do not cause disease like bacteria do. After all, sickening or killing a host is not a good plan, evolutionary-speaking. Yet pathogens (bacteria, viruses, etc) do harm their hosts, sometimes fatally, but scientists believe that’s by accident. Which makes researchers wonder what made the archea evolve seemingly more intelligently? The researchers hope to answer that question more definitively soon. Meanwhile, here's a video explaining more on what we know about archaea now.

Epigenetics in single-celled organisms opens new understanding of evolution

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