‘Zombies’ in our genes helped us evolve, and could help fight cancers

Sub : Science

Sec: Health

Context:

Most viruses can’t really affect the genome but retroviruses buck this trend as they can integrate and reshape the genomes of the hosts they infect.

What are retrovirus?

Retroviruses are viruses with RNA as genetic material and belong to the family Retroviridae of Retroviruses.
They can reverse-transcribe it to DNA and thus insert it into the host’s genome.
They perform reverse transcriptase where they convert the virus’s RNA into a corresponding DNA sequence.

How does retrovirus affect the genome?

In the life cycle of a retrovirus, the reverse-transcribed DNA is integrated into the host’s DNA along with another enzyme called integrase, which acts like glue to bind the two DNA genomes.
Once bound, the viral DNA is called a provirus, and is complete with all the ingredients it needs to be functional.
At the end of this process, the virus practically hijacks human cells and turns them into virus-making factories.
Retroviral genome invasions can sometimes mess up the integration process, causing ‘zombie’ regions in the host’s genome called as endogenous retroviruses (ERVs).
ERVs usually can’t replicate and produce functional proteins since they lack their regulatory regions.
If the abortive integrations involve the germ cells that produce the gametes, sperm cells and ova then the host will be able to transmit its ERVs to its offspring.
Thus retroviruses have left a number of genomic elements in the genome, sort of the genetic fossils of early infections.
These elements have long lost the potential to produce viruses but researchers believe they have played a big hand in the evolution of their hosts.

What is Syncytin?

Syncytins are a class of genes thought to be descended from an ERV.
These genes originally came from viruses and were acquired by chance as the mammalian host evolved.
With time they have became essential for the host because they helped create the placenta, an organ that became crucial to support a growing baby.
This change is thought to have been important for the evolution of mammals with placentas from their egg-laying ancestors.

What is MERVL-gag?

Scientists recently discovered a protein called MERVL-gag derived from an ERV.
They found that MERVL-gag plays a key role in controlling some other proteins during the transition.
They also found MERVL-gag works closely with another protein called URI, which helps the embryo transition from totipotency to pluripotency.