Zombies in our genes helped us evolve, and could help battle cancers

GS Paper III Science and Technology

Research suggests that around 8% of the human genome is composed of Endogenous Retroviruses (ERVs) often referred to as ‘zombie’ regions.

What are Endogenous Retroviruses (ERVs)?

Endogenous Retroviruses (ERVs) are sequences in the genome that originate from ancient viral infections. Unlike typical viruses that invade cells and replicate, ERVs are embedded in the DNA of the host organism and are inherited across generations.

A virus is an infectious microbe consisting of a segment of nucleic acid (either DNA or RNA) surrounded by a protein coat.

The genome is the complete set of DNA instructions present in a cell.
The human genome is made up of a tiny chromosome in the cell’s mitochondria and 23 pairs of chromosomes that are found in the nucleus of the cell.
A genome contains all of the information required for a person to develop and function.

Characteristics
- Integration into Host DNA: ERVs are the remnants of retroviruses that integrated their genetic material into the DNA of germ cells (sperm or egg cells), allowing them to be passed onto offspring.
- Transmission: Once integrated, ERVs become a permanent part of the host genome and are transmitted vertically from parent to offspring.
- Structure: They retain some structural elements of retroviruses, including long terminal repeats (LTRs) and viral genes (gag, pol, env), but are usually defective and incapable of producing infectious virus particles.

Scientists recently discovered a protein called MERVL-gag derived from an ERV.
Key Role: 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.

Examples and Research:

Syncytins:
- 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 become 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.
ERVs in Cancer: Research has shown that specific ERVs can influence tumor formation and progression, such as the LTR10 element associated with colorectal cancer.
Preeclampsia: Dysregulation of ERV-derived RNAs has been implicated in conditions like preeclampsia, indicating their ongoing influence on human health.

They refer to inactive viral sequences within the genome that no longer produce functional viruses but remain as embedded genetic fossils.
These regions are a result of retrovirus integration that has lost its ability to replicate and produce proteins, yet they persist in the host’s DNA.

Regenerative Medicine: Understanding ERVs can lead to breakthroughs in regenerative therapies.
Cancer Therapies: Insights into ERV roles in cancer could enhance treatment strategies.
Personalized Medicine: ERV research contributes to tailored medical treatments based on individual genetic makeup.

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