Researchers have created an RNA molecule that can replicate for the first time.

The research sheds light on RNA's molecular evolution.

For the first time, researchers from the University of Tokyo have been able to create an RNA molecule that replicates, diversifies, and develops complexity in accordance with Darwinian evolution. This is the first time that simple biological molecules have been shown to lead to the emergence of complex lifelike systems.

There are many big questions in life, one of which is where did we come from. Maybe you've seen the T-shirts with the ape to human transformation (to tired office worker). But what if you went from a simple molecule to a complex cell and then to an ape? For decades, one theory has been that RNA molecules (which are essential for cell function) coexisted with proteins and other biological molecules on primitive Earth. Then, around 4 billion years ago, they began to self-replicate and evolve from a single molecule into a complex array of molecules. This gradual evolution may have eventually resulted in the emergence of life as we know it — a diverse range of animals, plants, and everything in between.

Although there have been numerous discussions about this theory, physically creating such RNA replication systems has proven difficult. In a study published in Nature Communications, Project Assistant Professor Ryo Mizuuchi and Professor Norikazu Ichihashi of the University of Tokyo's Graduate School of Arts and Sciences, along with their team, describe how they conducted a long-term RNA replication experiment in which they witnessed the transition from a chemical system to biological complexity.

What the team saw piqued their interest. "We discovered that a single RNA species evolved into a complex replication system: a replicator network with five types of RNAs and diverse interactions, supporting the plausibility of a long-envisioned evolutionary transition scenario," Mizuuchi said.

The team used a unique RNA replication system that can undergo Darwinian evolution, i.e., a self-perpetuating process of continuous change based on mutations and natural selection, which allowed different characteristics to emerge and the ones that were adapted to the environment to survive.

"To be honest, we were sceptical at first that such diverse RNAs could evolve and coexist," Mizuuchi said. "The 'competitive exclusion principle' states that multiple species cannot coexist if they are competing for the same resources in evolutionary biology. This means that the molecules must devise a strategy for sequentially utilising various resources in order to achieve long-term diversification. We wondered if nonliving chemical species could spontaneously develop such innovation because they are just molecules."

So, what comes next? "Compared to biological organisms, the simplicity of our molecular replication system allows us to examine evolutionary phenomena with unprecedented resolution," Mizuuchi says. The complexity evolution we observed in our experiment is only the beginning. There should be many more events leading up to the emergence of living systems."

Of course, there are still many questions to be answered, but this research has provided more empirically based insight into an early RNA replicator's evolutionary path on primitive Earth. "The findings could be a clue to solving the ultimate question that humans have been asking for thousands of years — what are the origins of life," Mizuuchi said.

Ryo Mizuuchi, Taro Furubayashi, and Norikazu Ichihashi, "Evolutionary transition from a single RNA replicator to a multiple replicator network," Nature Communications, 18 March 2022.

DOI: 10.1038/s41467-022-29113-x http://dx.doi.org/10.1038/s41467-022-29113-x

Grant-in-Aid for Scientific Research (Assignment No.: JP19K23763, JP21H05867, JP15KT0080, JP18H04820, JP20H04859), JST PRESTO (Assignment No.: JPMJPR19KA), Astrobiology Center Project Research (Assignment No.: JPMJPR19KA), JST PRESTO (Assignment No.: JPMJ (Assignment No. AB021005).