What is the role of genome viral DNA in our disease and development? Humans are made up of 8% of the virus genome. The genetic remnants of ancient viruses that remain in the human genome play a role in our diseases and development.
What is the role of genome viral DNA in our disease and development?
In this article we are going to examine the role of genome viral DNA in our disease and development . Remnants of ancient viral infections that entered our genomes in the form of viral DNA sequences are still active in healthy people, according to a recently published study.
Human endogenous retroviruses (HERVs) makeup about 8% of the human genome, left over from infections that infected our primate ancestors millions of years ago. They became part of the human genome due to the method of reproduction.
Like today’s HIV, ancient retroviruses had to insert their genetic material into the host’s genome to replicate. Usually, this type of viral genetic material is not transmitted from one generation to the next. But some ancient retroviruses gained the ability to infect germ cells, such as egg or sperm cells, which pass their DNA on to future generations. Targeting germ cells, these retroviruses integrated themselves into the genome of human ancestors over millions of years and may have implications for how diseases are screened and tested today.
Active viral genes in the human genome
Viruses insert their genome into their host’s genome in the form of a provirus. Today, there are about 30 different types of endogenous human retroviruses in humans, which include more than 60,000 proviruses. They show the long history of many worlds that humanity has been exposed to during its evolution.
Scientists think these viruses at some point in time infected the population widely because they have been shown not only in the genomes of humans but also in the genomes of gorillas, chimpanzees, and other primates. In vitro studies have shown that the genes of endogenous human retroviruses are active in diseased tissues such as tumors and are also active during human embryonic development. But it has not been clear how active HERV genes are in healthy tissues.
To find the answer to this question, the researchers decided to focus on a group of endogenous human retroviruses called HML-2. This group became active later than other groups and became extinct less than 5 million years ago. Even now, some of the proviruses of this group in the human genome have retained the ability to produce viral proteins.
The researchers analyzed the genetic material in a database containing more than 14,000 donated tissue samples from all over the body. They looked for sequences that matched each of the HML-2 proviruses in the genome and found 37 different HML-2 proviruses that were still active.
All 54 tissue samples analyzed by the researchers showed evidence of the activity of one or more of these proviruses. In addition, each tissue sample also contained genetic material from at least one provirus that could still produce viral proteins.
The role of endogenous human retroviruses in human health and disease
The fact that thousands of pieces of the ancient virus still exist in the human genome and can even make proteins has attracted the attention of many researchers; Especially since related viruses are still active today and can cause breast cancer and AIDS-like diseases in animals. Whether genetic remnants of endogenous human retroviruses can cause disease in humans is still being studied.
Read More: Why was the human genome never completed?
Researchers have identified HML-2 virus-like particles in cancer cells. In various studies, the presence of HERV genetic material has been observed in the tissues of patients with diseases such as Lou Gehrig’s disease or amyotrophic lateral sclerosis, as well as multiple sclerosis and even schizophrenia. The new study adds a new perspective to these data by showing that HERV genes are present even in healthy tissues. Therefore, the presence of HERV RNA may not be sufficient to link the virus to disease.
More importantly, HERV genes or proteins may no longer be good targets for drugs. Human endogenous retroviruses have been explored as targets for several potential drugs, including antiretroviral drugs, antibodies for breast cancer therapy, and T-cell-based therapies for melanoma. In addition, therapies that use HERV genes as cancer biomarkers should also consider their activity in healthy tissue.
On the other hand, new research shows that endogenous human retroviruses can even be beneficial to humans. The most well-known HERV found in human and animal genomes is called syncytin, a gene derived from an ancient retrovirus that plays an important role in placenta formation. Pregnancy in all mammals depends on a protein derived from the virus that the gene encodes. Similarly, mice, cats, and sheep have also found a way to use endogenous retroviruses to protect themselves against the original ancient virus that created them. While viral genes embedded in the host’s genome cannot use the host’s machinery to produce a complete virus, enough of their incomplete fragments circulate in the host’s body to disrupt the replication cycle of its ancestral virus if it encounters a complete virus.
Scientists theorize that one of the identified endogenous retroviruses may have played this protective role in humans millions of years ago. The new study emphasizes that several other recently introduced HERVs may play the same role.
Unknowns
New research reveals a level of HERV activity in the human body that was previously unknown and raises many questions.
There are still many unknowns about the ancient viruses that have settled in the human genome; Including whether their presence is useful and what mechanism causes their activity. It will also be important to see if each of these genes actually makes a protein.
Answering these questions could reveal the unknown functions of these ancient viral genes and help researchers better understand the human body’s response to evolve alongside these ancient viral artifacts.