For the first time, researchers create an RNA molecule that replicates
The experiment sheds light on the molecular evolution of RNA.
Researchers from the University of Tokyo have for the first time been able to create a RNA molecule that replicates, diversifies and develops complexity, following Darwinian evolution. This provided the first empirical evidence that simple biological molecules can lead to the emergence of complex and realistic systems.
Life has many big questions, including where do we come from? Maybe you’ve seen the T-shirts with images ranging from monkey to human (to tired office worker). But what about the simple molecule to the complex cell via the monkey? For several decades, it has been hypothesized that RNA molecules (which are vital for cellular functions) existed on early Earth, possibly along with proteins and other biological molecules. Then, about 4 billion years ago, they began to self-replicate and grow from a simple single molecule into various complex molecules. This step-by-step change may have ultimately led to the emergence of life as we know it – a beautiful array of animals, plants, and everything in between.
Although there have been many discussions on this theory, it has been difficult to physically create such RNA replication systems. However, in a study published in Nature Communicationproject assistant professor Ryo Mizuuchi and professor Norikazu Ichihashi of the University of Tokyo Graduate School of Arts and Sciences, and their team, explain how they conducted a long-term RNA replication experiment in which they witnessed the transition from a chemical system to biological complexity.
The team was really excited by what they saw. “We found that the single RNA species evolved into a complex replication system: a network of replicators comprising five RNA types with diverse interactions, supporting the plausibility of a long-considered evolutionary transition scenario,” said Mizuuchi said.
Compared to previous empirical studies, this new result is novel because the team used a unique RNA replication system that can undergo Darwinian evolution, i.e. a self-sustaining process of continuous change based on mutations and natural selection, which allowed different characteristics to emerge, and those that were adapted to the environment to survive.
“Honestly, we initially doubted that such diverse RNAs could evolve and coexist,” Mizuuchi commented. “In evolutionary biology, the ‘competitive exclusion principle’ states that more than one species cannot co-exist if they compete for the same resources. This means that molecules must establish a way to use different resources one after another for sustained diversification. They are only molecules, so we wondered if it was possible for non-living chemical species to spontaneously develop such an innovation.
What next? According to Mizuuchi, “The simplicity of our molecular replication system, compared to biological organisms, allows us to examine evolutionary phenomena with unprecedented resolution. The evolution of complexity observed in our experiment is only the beginning. Many other events are expected to occur towards the emergence of living systems.
Of course, there are still many questions to be answered, but this research has provided additional empirical insight into a possible evolutionary path an ancient RNA replicator might have taken on early Earth. As Mizuuchi said, “The results could be a clue to solving the ultimate question that human beings have been asking for thousands of years: what are the origins of life?”
Reference: “Evolutionary Transition from a Single RNA Replicator to a Multiple Replicator Network” by Ryo Mizuuchi, Taro Furubayashi, and Norikazu Ichihashi, March 18, 2022, Nature Communication.
This research is primarily supported by Grant-in-Aid for Scientific Research (Assignment No.: JP19K23763, JP21H05867, JP15KT0080, JP18H04820, JP20H04859), JST PRESTO (Assignment No.: JPMJPR19KA), Astrobiology Center Project Research (Assignment No. AB021005) .