Are all viruses harmful and have no benefits?

When it comes to viruses, what do you think of? Smallpox? Black Death? Ebola? Dengue fever and SARS? These are all viruses that have caused huge losses to mankind. There are countless viruses like colds and fevers. It seems that as long as it is a virus, it is harmful to people and has no benefits. Then a friend asked: In the long river of history, is there a virus that is beneficial to people after infection and makes people develop in a good direction?

I think there should be a large wave of viruses. Of course, if you ask me which one it is, wouldn’t it be like I’ve chosen one?

In the long history of human evolution, we have been fighting against viruses, bacteria and other microorganisms, and the final result is that we have merged some viruses and they are lying in our genome. Let's talk about this today.

01. Viruses that changed human evolution

In 2010, a paper was published in Nature Genetics, in which they discovered that viruses that invaded the human genome millions of years ago changed the way genes are turned on and off in human embryonic stem (ES) cells.

The changes they found were mainly achieved through the impact on transposons. Transposons, in layman's terms, are human gene movers that can move a gene from one place in our genes to another.

This is a sample image

ps: This article is very difficult to understand, and I was also confused when reading it.

02. Liberated Ancestral Virus

About 5% of the human genome is retroviral genes, and preliminary estimates show that there are nearly 100,000 retroviruses. Their origin is that human ancestors were infected with these viruses, and then these viruses eventually entered the human genome and were passed down from generation to generation.

I mentioned in a previous article that a 2015 study by Lund University in Sweden found that retroviruses in the genome can control the way cells function, making brain cells more active and energetic, thus making us smarter. (Friends who are interested can send me a private message to forward the article to everyone)

Retrovirus is one of the common viruses and belongs to RNA virus. Its typical feature is that genetic information is retained in RNA rather than DNA. For example, the famous HIV, the virus that causes AIDS, is a retrovirus.

Of course, in the past we believed that these viral genes were inactive, lying quietly in the genome, becoming traces of evolution.

But in this article, they found that these viral genes are not dead, but can be activated and have effects on the brain!!!

Their research ideas are as follows:

They are working on neural progenitor cells (NPCs)

Advance explanation: gag (core protein), pol (reverse transcriptase) and env (membrane protein) are standard for retroviruses, KO is knock out, wt is wild type, and asterisks indicate significance.

After research, it was found

1. Knockout of TRIM28 in NPCs leads to transcriptional activation of endogenous retroviruses (ERVs)

2. Endogenous retroviruses marked with H3K9me3 disappear upon TRIM28 deletion

3. Activation of endogenous retroviruses in neural progenitor cells can affect the expression levels of related genes

4. Activation of endogenous retroviruses in neural progenitor cells can produce long noncoding RNA (lncRNA)

In general, retroviruses do not just lie like corpses in the genome, but can be activated.

In particular, nerve cells in the brain are very active and even play the role of managers. Neural stem cells specifically control the activation of retroviral genes in this process.

03. Viruses that depend on how you open them

I believe everyone must know that one of the more popular methods at present is called gene therapy, the core of which is to intervene in human cells at the genetic level.

Of course, there are many types. For example, the introduction of exogenous normal genes is a mainstream idea, which refers to the introduction of exogenous normal genes into target cells to correct or compensate for diseases caused by gene defects and abnormalities to achieve the purpose of treatment. It also includes the application of transgenic technology. Others also include stem cell replacement, etc.

However, how can we accurately target and even integrate the introduced content into cells to exert its effects for a long time? One important method is virus-mediated delivery.

For example, the lentiviral system is a very commonly used amplification system, which itself comes from HIV-1 (human immunodeficiency virus type 1), commonly known as AIDS virus.

A very commonly used mammalian virus expression system; when the lentivirus infects the host cells, the exogenous genes it carries can be randomly and stably integrated into the host cell genome, achieving stable and long-term expression of the target gene. It is very suitable for the establishment of stable gene overexpression cell lines and RNAi research.

04. Obtain active immunity through viruses

Another type is to obtain active immunity through viruses, which are commonly referred to as inactivated vaccines or attenuated vaccines. Some vaccines are made by processing the virus to weaken or even inactivate it. This type of vaccine is essentially still a virus. It can retain the virus's replication ability and immunogenicity, but it has lost its pathogenicity.

The process of injecting this vaccine is itself a process of infection. However, since the vaccine loses its toxicity after processing, the human body eventually gains immunity but is not infected.

ref.

1. Virus invasion millions of years ago

Kunarso G, Chia NY, Jeyakani J, et al. Transposable elements have rewired the core regulatory network of human embryonic stem cells[J]. Nature genetics, 2010, 42(7): 631-634.

2. Activation of original viruses in the human genome

Fasching L, Kapopoulou A, Sachdeva R, et al. TRIM28 represses transcription of endogenous retroviruses in neural progenitor cells[J]. Cell reports, 2015, 10(1): 20-28

3. Viruses in the human genome

This virus is relatively recent, it seems to be only a few thousand years old, and it still retains a complete genome, but not all humans have it.

Wildschutte JH, Williams ZH, Montesion M, et al. Discovery of unfixed endogenous retrovirus insertions in diverse human populations[J]. Proceedings of the National Academy of Sciences, 2016: 201602336.