Scientists accidentally discovered fragments of viral genetic material lurking in human DNA
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A false-color electron micrograph showing cells infected with human herpesvirus 6 (HHV6; red circle). Researchers at the Institute of Physics and Chemistry have discovered a new heritable structural variant derived from HHV6 in the human genome.
About 8% of the human genome can be traced back to retroviruses, that is, viruses that reverse the normal sequence of gene transcription. The RNA genome is reverse transcribed into DNA and then inserted into the genome of the host cell. The most notorious retrovirus is the human immunodeficiency virus (HIV).
Although retroviruses may have a devastating effect on human health, the genetic material of the virus inserted into our genome can provide useful functions. For example, the retroviral protein expressed in the placenta allows humans and other mammals to give birth to living offspring instead of an egg.
“In the process of human evolution, our ancestors acquired many virus-derived sequences, some of which confer useful functions,” said Masahira Kojima of the Institute of Integrative Medicine Science (IMS) of the Institute of Physics and Chemistry . “I used to think that viruses are a threat, but some of their genetic sequences are essential for human development.”
In the past two decades, researchers have discovered a lot of retroviral gene sequences in the human genome, as well as viral source sequences from non-retroviruses. But it is not yet clear how much these sequences differ from person to person, and whether the variants will produce different human characteristics.
Kojima Shohei and Two Institute of Physics and Chemistry Collaborators found that the degree of human-to-human variation of human endogenous viruses is surprising.
Now, Kojima, Anselmo Kamada, and Nicholas Parrish of IMS of the Institute of Physics and Chemistry in Japan use bioinformatics tools specifically designed for this task to investigate the virus mutations of 3,332 people from different populations. They found that the virus is related to unexpected structural mutations in the human genome, and they also found rare mutations in the germ line that can be traced back to human herpesvirus 6 (Figure 1).
However, not all viral genetic material they discovered has ancient origins. The trio found that some commonly used cell lines had been infected by the virus. “We think these sequences are probably caused by the infection of subjects who donated blood for human genetics research. The strange thing is that viruses usually do not infect B cells, and B cells are used to make the cell lines we use. , So we don’t fully understand how these viruses infect cells.”
The team intends to explore the possible functions of the sequences they have determined. Some studies have shown that there is an association between the genetic sequence of the virus and the high risk of certain diseases. If this is true, how and why are they maintained in the human community? Do they provide some benefits beyond cost?