As you read this story, you will learn the following:
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All life on Earth can be traced back to the Last Universal Common Ancestor (LUCA) that evolved approximately 4.2 billion years ago.
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While the true nature of this organism—and the environment in which it emerged on early Earth—is a very active area of research, a new study considers how to look beyond LUCA to understand the biological processes that created it.
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The study investigated “universal paralogs,” a family of genes present in all organisms that are involved in protein production and the movement of molecules across cell membranes, and showed that these characteristics predate LUCA.
If you go back far enough in the genetic lineage on the tree of life (roughly 4.2 billion years or so), all living things on Earth – humans, ferns or fungi – share a last universal common ancestor, LUCA. Scientists have no direct evidence of this creature, but they have a good guess that it may be an anaerobic, ultramicrobial prokaryote that lives near hydrothermal vents in the ocean. Yet even with this overview, experts continue to find information that challenges our best guesses about the causes of this most important form of life.
First, an important area of investigation is an obvious one: Luca clearly didn’t appear out of thin air. Previous research has established that things like cell membranes and DNA genomes must have existed before LUCA arrived, but how do we study them when LUCA represents some kind of evolutionary dead end? In a new study published in the journal Cell GenomicsScientists from MIT, Oberlin College, and the University of Wisconsin-Madison explain how they devised a method to study “universal paralogs” that can provide evidence of evolutionary events forward The arrival of Luca.
“Although the last universal common ancestor is the oldest organism we can study using evolutionary methods, some genes in its genome are much older,” Aaron Goldman, lead author of the Oberlin College study, said in a press statement.
First, a quick biology lesson. Paralogs are gene families with multiple members that may have arisen through DNA copying errors over millions of years. One example is a genetic paralog of hemoglobin, the iron-containing protein in red blood cells. The human body contains eight versions of this gene, but they all originate from the same ancient globin gene that existed 800 million years ago. As the name suggests, universal paralogs are a specialized family of genes that are present in at least two copies in every organism today. Since they are ubiquitous in all life on Earth, it is likely that these paralogues existed before LUCA.
“While we know very few universal paralogs,” Goldman said in a press statement, “they can tell us a lot about what life was like before the last universal common ancestor.”
By surveying all known universal paralogues, Goldman and his team found that they are all involved in the production of proteins and the movement of molecules across cell membranes. This means that these behaviors must have existed in some way before life first evolved on Earth. The emergence of artificial intelligence research tools that can sift through large data sets may make these paralogs an even more active area of research.
“The history of these universal paralogs is the only information we have about these earliest cell lineages, so we need to carefully extract as much knowledge as possible from them,” Greg Fournier, a co-author of the MIT study, said in a press statement.
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