Biologists from the Altos Institute, Cambridge Institute of Science, and the University of Cambridge have discovered that genetic elements derived from retroviruses (retrotransposons) are essential for the production of myelin (the insulating sheath that surrounds nerve axons) in mammals, amphibians, and animals. I discovered that fish. This gene sequence, called retromyelin, is likely the result of an ancient retroviral infection, and comparisons of retromyelin in mammals, amphibians, and fish indicate that retroviral infection and genome invasion events occurred separately in each of these groups. suggests that it has occurred.
gauche other. suggest that retrovirus internalization played an important role in the emergence of vertebrate myelin. Image credit: Ghosh other., doi: 10.1016/j.cell.2024.01.011.
Myelin, the complex fatty tissue that lines vertebrate nerve axons, allows rapid impulse conduction without the need to increase axon diameter. This means that the nerves can be packed more closely together.
It also provides metabolic support for the nerves, allowing them to lengthen.
Myelin first appeared on the tree of life around the same time as the jaw, and its importance in vertebrate evolution has been recognized for a long time, but until now it is unclear what molecular mechanism caused its appearance. was.
Tanay Ghosh and colleagues at Altos Labs-Cambridge Institute of Science noticed the role of retromyelin in myelin production while studying the gene networks used by oligodendrocytes, the cells that produce myelin in the central nervous system. .
Specifically, they were studying the role of non-coding regions, including retrotransposons, in these gene networks. This has not been previously studied in the context of myelin biology.
“Retrotransposons make up about 40% of our genome, but we know nothing about how they helped animals acquire specific traits during evolution.” said Dr. Ghosh.
“Our motivation was to learn how these molecules serve evolutionary processes, especially in the context of myelination.”
Researchers discovered that in rodents, retromyelin RNA transcripts regulate the expression of myelin basic protein, one of the key components of myelin.
When we experimentally inhibited retromyelin in oligodendrocytes and oligodendrocyte progenitor cells (the stem cells from which oligodendrocytes are derived), the cells were no longer able to produce myelin basic protein.
To find out whether retromyelin is present in other vertebrate species, scientists looked for similar sequences within the genomes of jawed vertebrates, jawless vertebrates, and some invertebrate species. Searched for.
They identified similar sequences in all other classes of jawed vertebrates (birds, fish, reptiles, amphibians) but found no similar sequences in jawless vertebrates or invertebrates. did not.
Robin Franklin, a neuroscientist at the Altos Institute at the Cambridge Institute of Science, said: “There was an evolutionary drive to speed up the conduction of impulses in axons, because the faster the impulse conduction, the faster we can grab objects and move away from them.'' Because they can run away.”
Next, the authors wanted to know whether retromyelin was integrated once in the ancestor of all jawed vertebrates, or whether there were separate retroviral invasions in different branches.
To answer these questions, they constructed a phylogenetic tree from 22 jawed vertebrate species and compared their retromyelin sequences.
This analysis revealed that retromyelin sequences are more similar within species than between species, suggesting that retromyelin has been acquired multiple times through a process of convergent evolution.
The researchers also showed that retromyelin plays a functional role in myelination in fish and amphibians.
When they experimentally disrupted the retromyelin gene sequence in fertilized zebrafish and frog eggs, they found that the developing fish and tadpoles produced significantly less myelin than normal.
“Our findings open new avenues of research exploring how retroviruses are involved in directing evolution more generally,” said Dr. Ghosh.
of study It was published in the magazine cell.
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Tanai Ghosh other. 2024. Retroviral involvement in vertebrate myelination through retrotransposon RNA-mediated control of myelin gene expression. cell 187 (4): 814-830; doi: 10.1016/j.cell.2024.01.011
Source: www.sci.news
