Long before written history, our ancestors encountered viruses that left permanent marks in the human genome. These relics, called endogenous retroviruses (ERVs), now make up an estimated 8% of human DNA. Far from being inactive fossils, some of these viral sequences continue to affect biology—sometimes in surprising or even vital ways. Explore twelve ancient viruses that have withstood millions of years, and learn what their hidden legacies mean for humanity.

1. HERV-K (Human Endogenous Retrovirus K)

HERV-K is among the most recent and intact families of endogenous retroviruses in humans. Predominantly active during embryonic development, HERV-K elements are also expressed in certain cancers, including melanoma and breast cancer. Their proteins can be detected in tumor tissues, suggesting a role in tumorigenesis. Research continues to explore both the potential risks and evolutionary advantages of HERV-K, including its involvement in placental development. (en.wikipedia.org)

2. HERV-W

Best known for giving rise to syncytin-1, a gene crucial for placental development, HERV-W made the leap from infection to essential human biology. Syncytin-1 enables fusion of cells to form the placenta’s outer membrane, proving that ancient viruses can be vital to our survival. Abnormal expression of HERV-W is also associated with disorders such as multiple sclerosis. Read in-depth.

3. HERV-H

HERV-H sequences, while no longer able to produce infectious particles, play pivotal roles in early human embryogenesis and pluripotency—the ability of stem cells to become any cell type. Recent studies suggest HERV-H regulates key genes in embryonic stem cells. Disturbances in its activity are linked to certain cancers and neurological conditions. Explore more.

4. HERV-L

HERV-L is among the oldest classes of endogenous retroviruses, present in the primate lineage for over 60 million years. Although now defective and incapable of infection, its sequences can still influence nearby host genes. Some HERV-L fragments have even been co-opted into regulating genes involved in early development. View details.

5. HERV-Fc1

HERV-Fc1 has drawn attention for its possible association with autoimmune diseases, particularly multiple sclerosis (MS). Studies report that higher expression of HERV-Fc1 correlates with disease progression and relapses. While its precise role remains debated, researchers continue to assess how ancient viral remnants might impact immunity. (pubmed.ncbi.nlm.nih.gov)

6. HERV-E

HERV-E elements, integrated into the human genome millions of years ago, are expressed in kidney and placental tissues. Studies suggest that HERV-E may regulate host gene activity, potentially influencing immune system functioning. Additionally, aberrant activation of HERV-E has been observed in cases of lupus nephritis, an autoimmune kidney disorder. (pubmed.ncbi.nlm.nih.gov)

7. HERV-P

HERV-P fragments can be traced to both humans and other primates, indicating their presence since before the divergence of these lineages. While these remnants are largely inactive, their sequences add to the complexity of human genome regulation and variation. Full report.

8. HERV-R (ERV3)

ERV3, also known as HERV-R, integrated into the human genome approximately 30 million years ago. While now inactive, its envelope gene is expressed in the placenta, potentially modulating the maternal immune response during pregnancy. This immunosuppressive function may help prevent maternal rejection of the fetus. Additionally, ERV3 expression has been observed in various cancers, suggesting a possible role in tumor suppression. (pmc.ncbi.nlm.nih.gov)

9. HERV-I

HERV-I fragments are present throughout the human genome, indicating their integration millions of years ago. While less studied than other HERVs, some researchers suggest they may have played roles in primate evolution, including gene regulation in neurological tissues. The functional impact of HERV-I remains an important area for future investigation. See overview.

10. HERV-9

HERV-9 elements are primarily found in ape and human genomes, suggesting a relatively recent integration. Some of its proteins have immunosuppressive properties, and HERV-9 expression is noted in certain cancers, hinting at ongoing roles in tumor biology. Read more.

11. HERV-T

HERV-T is a family of endogenous retroviruses found in primates and was only recently recognized for its evolutionary impact. Some HERV-T remnants remain transcriptionally active, and their presence in both humans and Old World monkeys points to ancient cross-species infections. See study.

12. HERV-S

HERV-S is a rare and ancient viral family present in both humans and apes. These elements are scattered throughout the genome, and ongoing studies probe their influence on the regulation of neighboring genes, especially during early development. Reference.

Conclusion

Ancient viral sequences, known as endogenous retroviruses (ERVs), have not only shaped our evolutionary history but continue to play active roles in our biology. (en.wikipedia.org) These remnants, comprising about 8% of the human genome, influence various physiological processes, including gene regulation, immune responses, and development. (pubmed.ncbi.nlm.nih.gov) Ongoing research aims to elucidate whether these elements act as beneficial contributors or potential contributors to diseases such as cancer and autoimmune disorders. (pubmed.ncbi.nlm.nih.gov) As genomic studies advance, a clearer understanding will emerge of how these ancient invaders, now integral to our DNA, might even contribute to future medical advancements. (pubmed.ncbi.nlm.nih.gov)

Disclaimer

This article is for informational purposes only and should not be considered medical advice. Consult a healthcare provider for any health concerns.

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