Tanah Ghosh says the discovery of myelin may be just another step in an emerging field.
Washington:
Ancient viruses that infected vertebrates hundreds of millions of years ago played a key role in the evolution of our advanced brains and large bodies, a study said Thursday.
The study, published in the journal Cell, examined the origins of myelin, an insulating layer of fatty tissue that forms around nerves and allows electrical impulses to travel faster.
According to the authors, genetic sequences obtained from retroviruses (viruses that invade host DNA) are critical for the production of myelin, and the code is now found in modern mammals, amphibians and fish.
“What I find most striking is that the diversity of all modern vertebrates we know of and the sizes they have reached: elephants, giraffes, anacondas, bullfrogs, vultures, doesn’t happen,” said senior author and Neurosurgeon Scientist Robin Franklin of the Altos Laboratory at the Cambridge Institute of Science told AFP.
In the new study, led by Tanay Ghosh, a computational biologist and geneticist in the Franklin Lab, analysts searched through genome databases in an attempt to discover genetics that might be relevant to the cells that produce myelin.
Specifically, he is interested in exploring mysterious “non-coding regions” of the genome that have no obvious function and were once dismissed as junk but are now considered to be of evolutionary importance.
Ghosh’s research identified a specific sequence derived from endogenous retroviruses that has long been dormant in our genes, which the team calls “retromyelin.”
To test their findings, the researchers conducted experiments in which they knocked down the RetroMyelin sequence in rat cells and found that they no longer produced the basic protein needed for myelin formation.
Faster reactions, bigger body
Next, they looked for RetroMyelin-like sequences in the genomes of other species and found similar codes in jawed vertebrates (mammals, birds, fish, reptiles and amphibians), but not in jawless vertebrates or No similar code has been found in invertebrates.
This led them to believe that the sequence appeared in the tree of life around the same time as jaws, which first evolved about 360 million years ago during the Devonian period, known as the Age of Fishes.
“There has always been evolutionary pressure to make nerve fibers conduct electrical impulses faster,” Franklin said. “If they do it faster, then you can take action faster,” he adds, which is important for people trying to capture things. Useful to both predators and prey trying to escape.
Myelin conducts impulses quickly without enlarging the diameter of nerve cells, allowing them to be packed closer together.
It also provides structural support, which means the nerves can grow longer, resulting in longer limbs.
In the absence of myelin, invertebrates found other ways to transmit signals faster—giant squid, for example, evolved wider nerve cells.
Finally, the team wanted to understand whether retroviral infection occurred once in a single ancestral species, or if it occurred more than once.
More discoveries await?
To answer this question, they used computational methods to analyze reverse myelin sequences from 22 jawed vertebrate species and found that the sequences were more similar within species than between species.
The team says the discovery suggests multiple waves of infection led to the diversity of vertebrate species we see today.
“People tend to think of viruses as pathogens or disease-causing agents,” Franklin said.
But the reality is more complicated, he said: At various points in history, retroviruses have entered the genome and integrated themselves into the germ cells of species, allowing them to be passed on to future generations.
One of the most famous examples is the placenta – one of the defining characteristics of most mammals – which we acquired from pathogens that embedded themselves in our genomes in ancient times.
The discovery of myelin may be just another step in an emerging field, Ghosh said. “From a biological perspective, there’s still a lot to understand about how these sequences drive different evolutionary processes,” he said.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
