Did Viruses Help Build Complex Life? A New Discovery Rekindles the Question
The line between viruses and cellular life may be thinner than previously thought. A new study describes a giant virus that infects amoebae and replicates in a way that closely resembles the behavior of a cell nucleus – the structure that contains DNA in the cells of plants, animals and humans.
Published in the Journal of VirologyThe research reports the discovery of a previously unknown DNA virus whose replication strategy reflects the key characteristics of a nucleus. This finding adds new evidence to the long-debated idea that viruses may have helped shape complex cells by contributing structures or functions that were then integrated into cellular life.
“Giant viruses can be considered a treasure trove of which the world has not yet been fully understood. One of the future possibilities of this research is to provide humanity with a new vision connecting the world of living organisms with the world of viruses,” said Masaharu Takemura, lead author of the study, in a press release.
Learn more: Why do viruses like COVID-19 and flu mutate quickly and what does this mean for vaccines?
When viruses start to look like cells
Unlike cells, viruses cannot reproduce on their own. They carry genetic material – DNA or RNA – but lack the machinery to make proteins or generate energy. For decades, this simplicity kept viruses away from the traditional tree of life.
This view began to change in the early 2000s with the discovery of giant DNA viruses – viruses so large and genetically complex that they rival bacteria. When these viruses infect cells, they often build specialized compartments called virus factories, where viral DNA is copied and new viral particles are assembled.
Some of these plants are surrounded by membranes and function in a way that is very much like a nucleus. That resemblance revived an idea first proposed more than two decades ago: that the core itself might come from an ancient viral infection that became a permanent part of its host instead of killing it.
Recently, scientists have discovered a growing variety of giant viruses that infect amoebae, each using slightly different strategies to take over their host cells. Together, these viruses provide a natural record of how viruses and cells may have evolved side by side.
A giant virus that disrupts the cell nucleus
The newly identified virus, named ushikuvirus after Lake Ushiku in Japan, belongs to this expanding group of giant viruses infecting amoebae. Amoebae are particularly useful for studying giant viruses because they resemble early single-celled life forms and can host multiple types of viruses at once.
Ushikuvirus shares many characteristics with related viruses, including a large spiky outer envelope and a DNA genome filled with genes rarely found in viruses. But it behaves differently once inside its host. Instead of replicating silently in the nucleus, ushikuvirus disrupts the nuclear membrane by producing new viral particles.
This behavior places ushikuvirus in an intriguing middle ground – between viruses that rely on an intact core to replicate and others that dismantle the core entirely. Rather than pointing to a single evolutionary pathway, the results suggest a spectrum of viral strategies that may have changed over time in response to different hosts.
What Ushikuvirus reveals about the origin of complex cells
By comparing how giant viruses interact with their hosts, researchers are beginning to understand how viruses and cells could have evolved together. The unusual behavior of ushikuvirus suggests that viral replication strategies have changed over time, potentially leaving lasting marks on modern cells.
If viruses had indeed played a role in the origin of the nucleus, they would not only be agents of disease: they would have participated in one of the major transitions of life.
The discovery could also have practical implications. Some amoebae cause serious human infections, and understanding how giant viruses destroy them could eventually inform new medical approaches, but further study is still needed.
This article does not offer medical advice and should be used for informational purposes only.
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