Fossils in Our Genes: Giant Viruses Leave Mark on Animal Relative

Recent research published in Science Advances uncovers an unexpected twist in the evolutionary history of complex life.

Researchers at Queen Mary University of London revealed that a single-celled creature, a close relative of animals, contains the vestiges of ancient giant viruses woven into its genetic code.

This discovery sheds light on how sophisticated creatures may have inherited some of their genes and emphasizes the dynamic interaction between viruses and hosts.

The research focused on Amoebidium, a unicellular parasite common in freshwater habitats. By analyzing Amoebidium’s genome, researchers headed by Dr Alex de Mendoza Soler, Senior Lecturer at Queen Mary’s School of Biological and Behavioural Sciences, discovered a startling quantity of genetic material derived from enormous viruses, some of the giant viruses known to science.

These viral sequences were extensively methylated, which is a chemical marker that commonly silences genes.

It is like finding Trojan horses hiding inside the Amoebidium's DNA. These viral insertions are potentially harmful, but Amoebidium seems to be keeping them in check by chemically silencing them.”

Dr Alex de Mendoza Soler, Senior Lecturer, School of Biological and Behavioural Sciences, Queen Mary University of London

The researchers next researched how common this phenomenon might be. They analyzed the genomes of various Amoebidium isolates and discovered considerable differences in viral content. This implies that the viral integration and silencing process is continuous and dynamic.

Soler added, “These findings challenge our understanding of the relationship between viruses and their hosts. Traditionally, viruses are seen as invaders, but this study suggests a more complex story. Viral insertions may have played a role in the evolution of complex organisms by providing them with new genes. And this is allowed by the chemical taming of these intruders DNA.”

Furthermore, the discoveries from Amoebidium provide fascinating parallels to how the human genomes interact with viruses. Humans and other mammals, like Amoebidium, have Endogenous Retroviruses, which are remains of ancient viruses incorporated into their DNA. While these fragments were once assumed to be inert “junk DNA,” some could be useful.

Endogenous Retroviruses are much smaller than the huge viruses found in Amoebidium, and the human genome is substantially bigger. Future studies might examine these parallels and contrasts to better comprehend the complex interactions between viruses and complex life forms.