Life without viruses is impossible
Viruses play a crucial role in the evolution and survival of the species
Anna Yudina, "Scientific Russia"
The study claims that endogenous retroviruses contribute to genetic diversity and speciation, according to the Cincinnati Children's website (Satoshi Namekawa, Viruses Play a Critical Role in Evolution and Survival of the Species).
As the world struggles to control the growing COVID-19 coronavirus pandemic, a new study in Nature Structural & Molecular Biology shows that viruses also play a key evolutionary role in mammals' ability to reproduce and survive.
Scientists at the Cincinnati Children's Perinatal Institute and Azabu University in Japan obtained their data by studying laboratory mice and human germ cells.
In two separate articles published in the same issue of the journal (1, 2), they reveal two different fundamental processes underlying germline transcriptomes. They also show that species-specific transcriptomes are fine-tuned by endogenous retroviruses in the mammalian germ line.
Germ line transcriptomes include all the informational RNA in germ line cells that contain the male or female half of chromosomes transmitted as hereditary genetic material to offspring during mating of species. This means that germline transcriptomes determine the unique character of sperm and eggs to prepare for the next generation of life.
According to Satoshi Namekawa, the principal investigator of both articles and a scientist from the Department of Reproductive Science of the Cincinnati Children's Center, although the studies are conducted separately, they complement each other.
"In one article, Maezawa and Sakashita et al., investigate superenhancers, which are reliable and evolutionarily conservative gene regulatory elements in the genome. They fuel a strictly regulated surge of important germline genes as sperm begins to form," Namekawa said. – The second study by Sakashita and other authors includes endogenous retroviruses that act as another type of enhancer – gene regulatory elements in the genome – to control the expression of newly emerged genes. This helps fine tune species-specific transcriptomes in mammals such as humans, mice, and others.
According to scientists, together these studies have significant potential ramifications for clinical practice, which includes multidisciplinary biologists, bioinformatics and immunobiologists. A violation of the regulation of gene expression during the formation of male sperm is closely related to male infertility and birth defects.
The researchers report that viruses, especially endogenous retroviruses (ERV), which are an integral part of mammalian biology, can significantly affect gene expression. ERVs are molecular remnants of retroviruses that infect the body and eventually become incorporated into the genome.
"From our study, we learned that, in general, viruses play an important role in development," Namekawa explained. "In the long run, viruses have a positive effect on our genome and shape evolution."
In the study of Maezawa, Sakashita and others, biological testing of mouse models and human germ line cells is combined with computer biology, including genome-wide profiling of regulatory elements of genes in germ line cells.
These tests showed that the reorganization of superenhancers throughout the genome causes bursts of germ line gene expression after germ cells enter meiosis, a special form of cell division that produces the haploid genome of germ cells.
The study also demonstrates the molecular process by which super-enhancers switch in germ cells. Superenhancers are regulated by two molecules that act as gene explosion control switches – transcription factor A-MYB and SCML2 – a critical protein that suppresses sperm formation.
Endogenous retroviruses are a group of transported elements – mobile genetic elements that make up approximately 40-50 percent of the genome of a given mammal. Also called "jumping genes", the transported ones have long been considered genetic threats because transposition can be harmful if, for example, the process disrupts the genes encoding the protein.
Based on the findings of the 1950s that transported elements could function as genetic regulatory elements, Namekawa and his collaborators obtained data showing that ERV-controlled mechanisms help fine tune species-specific transcriptomes.
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