Original Academic Jingwei
In the human genome, not all our own genes. The results of genome sequencing tell us that about 8% of the sequences of are from viruses, which are more than the gene sequences encoding proteins. It is estimated that it is the "sewallowing" left by our primate ancestors who suffered from viral infection millions of years ago. Viruses such as
belong to retrovirus —the same as HIV we know today, that is, when they replicate themselves, they need to "reversely transcribe" their genetic material RNA into DNA, and then use the cell transcription mechanism to insert them into the genome of the host cell. Usually, retroviral-infected cells are not passed down from generation to generation, but by extreme chance, when animal germ cells are infected by retrovirals, the DNA derived from the virus has the opportunity to be included in the host's genome, becoming the so-called " endogenous retroviral " (ERV). Scientists have discovered the existence of endogenous retroviruses in mammals such as mice, pigs, and cats.
Image source: 123RF
Today, more than 30 ancient retroviruses have been found in the human genome of . These sequences usually contain elements such as genes encoding viral proteins and promoters that regulate gene expression. Scientists once thought they were nothing more than "trash" fragments accumulated in the human genome, but some new research has gradually revealed that endogenous retrovirus genes may be much more "active" than we thought.
Recently, a new study published in the journal Science proves that comes from some genes and regulatory elements of endogenous retroviruses, and has even been used by us to "anti-viral" - helping human cells resist other exogenous viruses .
In this new study, researchers at Cornell University (Cornell University) used computational genomics methods to search for endogenous retroviral sequences that may still be active in the human genome. To this end, they targeted the sequences related to the envelope protein . The envelope is equivalent to a coat of this type of virus. Its protein binds to the receptor indicated by the host cell, which is the key to the retrovirus being able to enter the cells. The spike protein of the new coronavirus that we are familiar with today is a envelope protein of the virus.
Researchers tested all potential envelope protein coding sequences that may retain receptor binding activity, , identifying which of these genes still express gene products in specific types of human cells. "We found through clear evidence that many of express in early embryos and germ cells, and some are expressed in immune cells after infection," said Professor Cedric Feschotte, who is responsible for the study.
Then, the researchers focused on an envelope protein called Suppressyn, which exhibited high levels of expression in placental and early stages of human embryo development. Moreover, inhibin is known to bind to the receptor ASCT2, which is the portal for a type of D retrovirus to enter cells.
researchers then conducted experiments in human placenta-like cells. When these cells are exposed to a D-type retrovirus RD114 that is usually capable of infecting cats, placental stem cells and embryonic stem cells are not infected, while other human cell types that do not express inactin are susceptible to infection. The researchers tried to remove inactin from placental stem cells, and the cells became susceptible to virus infection; and replenishing the inactin, their antiviral ability also recovered.
Inhibin can help human cells defend against exogenous viruses, and it was further verified in another set of experiments: the researchers introduced inhibin cells in embryonic kidney cell line cells that usually cannot resist RD114. As a result, these cells obtained additional antiviral ability
▲Science The word "domestication" is used in the commentary article to describe this relationship: some genetic elements of endogenous retroviruses are "domesticated" by the human genome (Image source: Reference [2])
Combined with these results, proteins from endogenous retroviruses occupy cell surface receptors, thus closing the channels for similar viruses to enter our cells and blocking many viruses that are spreading in other species from the embryos. In this way, retroviruses that infected humans in ancient times are now used by us to protect ourselves .
researchers believe that this discovery is not occasionally, and continuing to explore in depth will reveal a natural antiviral protein library. "Our results show that there is a protein library in the human genome of , which has the potential to block the wide range of viruses ," said Professor Feschotte.
