What octopus and human brains have in common
If we go far enough back in evolutionary history, we encounter the last known common ancestor of humans and cephalopods: a primitive wormlike animal with minimal intelligence and simple eyespots. Later, the animal kingdom can be divided into two groups of organisms—those with backbones and those without. While vertebrates, particularly primates and other mammals, went on to develop large and complex brains with diverse cognitive abilities, invertebrates did not. With one exception: the cephalopods.
Scientists have long wondered why such a complex nervous system was only able to develop in these mollusks. Now, an international team led by researchers from the Max Delbrück Center and Dartmouth College in the United States has put forth a possible reason. In a paper published in Science Advances, they explain that octopuses possess a massively expanded repertoire of microRNAs (miRNAs) in their neural tissue—reflecting similar developments that occurred in vertebrates.
科学家们一直想知道为什么如此复杂的神经系统只能在这些软体动物身上发育。现在，由Max Delbrück中心和美国达特茅斯学院的研究人员领导的一个国际团队提出了一个可能的原因。在《科学进展》杂志上发表的一篇论文中，他们解释说，章鱼在神经组织中拥有大量扩展的microRNAs (miRNAs)，这反映了脊椎动物发生的类似发展。
“So this is what connects us to the octopus,” says Professor Nikolaus Rajewsky, scientific director of the Berlin Institute for Medical Systems Biology of the Max Delbrück Center (MDC-BIMSB), head of the Systems Biology of Gene Regulatory Elements Lab, and the paper’s last author. He explains that this finding probably means miRNAs play a fundamental role in the development of complex brains.
“所以这就是我们和章鱼之间的联系，”Nikolaus Rajewsky教授说，他是Max Delbrück中心(MDC-BIMSB)柏林医疗系统生物学研究所的科学主任，基因调控元件系统生物学实验室的负责人，也是这篇论文的最后一位作者。他解释说，这一发现可能意味着miRNA在复杂大脑的发育中起着重要作用。
In 2019, Rajewsky read a publication about genetic analyses conducted on octopuses. Scientists had discovered that a lot of RNA editing occurs in these cephalopods—meaning they make extensive use of certain enzymes that can recode their RNA.
“This got me thinking that octopuses may not only be good at editing, but could have other RNA tricks up their sleeve too,” says Rajewsky. And so he began a collaboration with the Stazione Zoologica Anton Dohrn marine research station in Naples, which sent him samples of 18 different tissue types from dead octopuses.
Rajewsky说:“这让我想到章鱼可能不仅擅长编辑，而且可能还有其他RNA的诀窍。”因此，他开始与那不勒斯的Stazione zoanton Dohrn海洋研究站合作，该研究站向他发送了18种不同类型的死亡章鱼组织样本。
The results of the analyses were surprising: “There was indeed a lot of RNA editing going on, but not in areas that we believe to be of interest,” says Rajewsky. The most interesting discovery was in fact the dramatic expansion of a well-known group of RNA genes, microRNAs.
A total of 42 novel miRNA families were found—specifically in neural tissue and mostly in the brain. Given that these genes were conserved during cephalopod evolution, the team concludes they were clearly beneficial to the animals and are therefore functionally important.
Rajewsky has been researching miRNAs for more than 20 years. Instead of being translated into messenger RNAs, which deliver the instructions for protein production in the cell, these genes encode small pieces of RNA that bind to messenger RNA and thus influence protein production. These binding sites were also conserved throughout cephalopod evolution—another indication that these novel miRNAs are of functional importance.
New microRNA families
“This is the third-largest expansion of microRNA families in the animal world, and the largest outside of vertebrates,” says lead author Grygoriy Zolotarov, MD, a Ukrainian scientist who interned in Rajewsky’s lab at MDC-BIMSB while finishing medical school in Prague, and later. “To give you an idea of the scale, oysters, which are also mollusks, have acquired just five new microRNA families since the last ancestors they shared with octopuses—while the octopuses have acquired 90.”
Oysters, adds Zolotarov, aren’t exactly known for their intelligence.
Rajewsky’s fascination with octopuses began years ago, during an evening visit to the Monterey Bay Aquarium in California. “I saw this creature sitting on the bottom of the tank and we spent several minutes—so I thought—looking at each other.” He says that looking at an octopus is very different to looking at a fish: “It’s not very scientific, but their eyes do exude a sense of intelligence.” Octopuses have similarly complex “camera” eyes to humans.
From an evolutionary perspective, octopuses are unique among invertebrates. They have both a central brain and a peripheral nervous system—one that is capable of acting independently. If an octopus loses a tentacle, the tentacle remains sensitive to touch and can still move. The reason why octopuses are alone in having developed such complex brain functions could lie in the fact that they use their arms very purposefully—as tools to open shells, for instance.
Octopuses also show other signs of intelligence: They are very curious and can remember things. They can also recognize people and actually like some more than others. Researchers now believe that they even dream, since they change their color and skin structures while sleeping.
“They say if you want to meet an alien, go diving and make friends with an octopus,” says Rajewsky. He’s now planning to join forces with other octopus researchers to form a European network that will allow greater exchange between the scientists. Although the community is currently small, Rajewsky says that interest in octopuses is growing worldwide, including among behavioral researchers.
Read more at Phys.org