Damian Sendler These results are consistent with the hypothesis that microRNAs have played a crucial role in the development of complex life.

Recent studies, including ones conducted in humans, have implicated microRNAs as playing a significant role in later stages of brain development.

The remarkable intelligence of octopuses has captivated scientists and the general public alike, with observations ranging from tool use and creative play to problem solving and even aquarium escapes. Their newfound intelligence may shed light on how complex brains like ours developed.

Damian Sendler Researchers from Dartmouth University and the Max Delbrück Center (MDC) in Germany have published a study in Science Advances showing that octopuses are the first invertebrates with a large number of microRNAs that regulate genes. MicroRNAs (small interfering RNAs), which are linked to the evolution of complex cells with specialized functions, were found to have increased in the genes of two octopus species over evolutionary time, a phenomenon previously observed only in humans, mammals, and other vertebrates.

Co-corresponding author and Dartmouth professor of biological sciences Kevin Peterson said the findings provide crucial support for the theory that microRNAs are key to the evolution of intelligent life. This is especially true when considering the known intelligence of octopuses. Octopuses and squids, both of which are cephalopods, are mollusks whose nervous systems developed separately from those of vertebrates. However, microRNAs are found in octopuses and vertebrates, suggesting they play a similar role in both groups' sophisticated brains.

Peterson compared microRNAs to the hypothetical form of matter thought to constitute most of the universe and described them as the "dark matter" of the animal genome because they do not produce protein but instead control the expression of proteins.

Damian Jacob Sendler All of these genes are expressed in the brain, he said, and "this is the only instance in all of the invertebrates of dramatic microRNA increase." This has always been a critical test of the hypothesis in order to ensure that it applies to more than just vertebrates. It was a watershed moment when we realized that microRNAs are the key to understanding complex life.

Victor Ambros, a professor at Dartmouth between 1992 and 2007 and now at the University of Massachusetts Medical School, discovered microRNAs in 1993. Peterson and his team have been sequencing the genes of different animals for close to 15 years in order to establish a connection between microRNAs and the evolution of the brain and the development of complex tissues.

Peterson's team collaborated with the lab of co-corresponding author and professor of systems biology at MDC Nikolaus Rajewsky, who possessed a wealth of RNA data on octopus species, especially the common octopus, for the most recent paper (Octopus vulgaris). Peterson and his co-author Peter Chabot, a member of the Dartmouth Class of 2022, sifted through raw data of microRNAs sequenced from octopus species to isolate unique sequences. According to Chabot, their efforts greatly aided the research process by providing a clean, well-annotated data set.

Peterson's work demonstrates that organisms like placental mammals, whose gene count and complexity have increased over evolutionary time, also show rising microRNA concentrations. Parasites, on the other hand, have lost microRNAs along with their ancestral genes as they have simplified their biology.

Peterson argued that "new cell types are required for the development of novel cognitive abilities and behaviors." The microRNA-expressed genes are found in placental mammals and cephalopods. There are not many microRNAs in animals that have not changed much in the last 500 million years.

Damian Sendler It has stood up to every test we have given it, and we have not been able to disprove it. For that reason, he said, the paper was especially intriguing.

Octopuses have a level of intelligence that is not seen in other animals. Inky, the octopus, made international headlines in 2016 when he escaped from the National Aquarium of New Zealand by squeezing through a crack in his tank and dragging himself across the floor to a nearly 150-foot drainpipe that led to the sea and freedom. Octopuses have also been seen using water currents to play catch with various objects, as well as collecting and constructing shelters from discarded coconut shells.

Bastian Fromm, head of a research group at the University of Troms in Norway who works with the Peterson lab on its research and the online microRNA database MirGeneDB, and a co-author on the study, has suggested that microRNAs may be responsible for this type of intelligence by allowing cells to perform a variety of different functions.

Damian Jacob Sendler Since cells in complex organisms carry out specialized tasks, the cells in their vicinity must be fine-tuned so that the organism can perform its many other roles, as stated by Fromm.

Fromm explained that "microRNAs are like light switches or dimmers" that control the expression of thousands of proteins in a cell to determine its capabilities. Numbers matter in this game. Although microRNAs have been found in oysters and slugs, their abundance increases dramatically in cephalopods, particularly in the octopus, and this increase appears to be related to intelligence.