You’re More Virus Than Your Genes ????

Our genomes entomb?"molecular fossils" called ERVs (Endogenous Retroviruses). These are remnants of ancient viral encounters enshrined within our DNA, holding secrets about our evolutionary journey.??

In fact, most estimates suggest that ERVs make up a whopping 8% of our total genome. That's four times more than the exomes - the sequences that actually code for proteins!??

So, how did these viral leftovers end up in our genomes???

(By the way, this is a pretty rare phenomenon. Because everything has to go JUST RIGHT for it to happen??)

1?? Retroviral Infection: Initially, a retrovirus infects a germ cell (sperm or egg) of an organism.?Retroviruses are RNA. Upon infection, the retrovirus converts its RNA into DNA using an enzyme called reverse transcriptase.

2?? Integration: The newly converted viral DNA integrates into the DNA of the germ cell. This integration is facilitated by integrase.

Now, they MUST integrate at just the right spots to not kill those cells AND those cells HAVE to be the lucky few that end up being fertilized.

3?? Vertical Transmission: During fertilization, the integrated viral DNA is inherited by the offspring, and passed down from one generation to the next. These viral hitchhikers have successfully found their way into the DNA of various organisms, spanning millions of years of evolution.

In 2001, biologists discovered part of an ancient virus trapped in our DNA - ERV-Fc (ERV-Feline Clone) which has left its mark on the genomes of almost every order of mammals alive today!

This was believed to have caused a pandemic that lasted for more than 15 million years.??

How much do we know about this virus???

Unfortunately, viruses do not leave fossils behind, meaning we know very little about how they originate and evolve.

-Prof. Welkin Johnson, from ?Boston College’s Biology Department.

But one of the reasons the virus was so successful in jumping from species to species may have been its ability to swap genes with other strains and other viruses.

This is called viral recombination. A number of studies show this is what allowed SARS-CoV2 to spread so successfully.

What disease did it cause?

Scientists looked at its closest living relatives to figure out what kind of infections it might have caused.??

Based on its genetic structure, ERV-Fc is a member of the ‘gammaretroviruses’. Example species are the?murine leukemia virus?and the?feline leukemia virus. They cause various sarcomas, leukemias, and immune deficiencies in mammals, reptiles, and birds.??

But, we can’t be sure what sort of cancer it caused in its hosts, if at all.

Do they do anything in our systems right now?

Well, no.

But viral fossils like these help us understand and predict how new viruses behave and spread today.