Ancient Viruses Reveal Surprising Role in Evolution of Vertebrate Nervous Systems
Researchers have unveiled the unexpected contribution of an ancient retrovirus embedded in the DNA of jawed vertebrates to the evolution of their nervous systems. The findings, reported in the journal Cell on February 15, highlight the role of this retrovirus in triggering the production of a crucial protein essential for insulating nerve fibers, known as myelin.
The study, led by a team including stem cell biologist Robin Franklin from Altos Labs-Cambridge Institute of Science in England, sheds light on how myelin, a coating of fat and protein around nerve fibers, has played a pivotal role in the development of complex brains and rapid thought processes in vertebrates.
Retroviruses, specifically RNA viruses, are known for making DNA copies of themselves that become part of a host’s DNA. This particular retrovirus, described as a “handy trick,” has been identified as a recurring element in the evolution of vertebrates with jaws.
Contrary to the previous belief that remnants of ancient viruses were genetic garbage, scientists are increasingly recognizing their significant influence on the evolution of life. The identified retrovirus, named RetroMyelin, has now been linked not only to the evolution of the placenta and the immune system but also to the production of myelin.
Myelin, functioning as insulation around nerve fibers, allows for faster electrical signal transmission, enabling the growth of longer and thinner nerve fibers. This efficiency has contributed to the evolution of more complex brains and diverse vertebrate species. The study emphasizes that without myelination, the extensive vertebrate diversity observed today might not have occurred.
The researchers discovered high levels of RNA from RetroMyelin in the cells responsible for wrapping nerves in myelin. This RNA, when paired with the SOX10 protein, triggers the production of myelin basic protein, a crucial component in forming the tight sleeve around nerve cells.
Experiments involving a genetic manipulation to reduce RetroMyelin in rat brains, zebra fish, and frogs resulted in a decrease in the production of myelin basic protein. This underscores the crucial role played by RetroMyelin RNA in the myelination process.
Eirene Markenscoff-Papadimitriou, a developmental neuroscientist at Cornell University, noted the significance of this discovery, highlighting that while other retrotransposons have shaped evolution by creating genetic switches or new versions of proteins, producing RNA to influence gene activity is a novel finding.
Surprisingly, each species examined in the study possessed its own version of RetroMyelin, suggesting that the retrovirus infected multiple species at different times, leading to convergent evolution and a shared outcome.
