The following essay is reprinted with permission from The Conversation, an online publication covering the latest research.
Around 8% of human DNA is made up of genetic sequences acquired from ancient viruses. These sequences, known as human endogenous retroviruses (or Hervs), date back hundreds of thousands to millions of years – with some even predating the emergence of Homo sapiens.
Our latest research suggests that some ancient viral DNA sequences in the human genome play a role in susceptibility to psychiatric disorders such as schizophrenia, bipolar disorder and major depressive disorder.
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Hervs represent the remnants of these infections with ancient retroviruses. Retroviruses are viruses that insert a copy of their genetic material into the DNA of the cells they infect. Retroviruses probably infected us on multiple occasions during our evolutionary past. When these infections occurred in sperm or egg cells that generated offspring, the genetic material from these retroviruses was passed on to subsequent generations, becoming a permanent part of our lineage.
Initially, scientists considered Hervs to be “junk DNA” – parts of our genome with no discernible function. But as our understanding of the human genome has advanced, it’s become evident that this so-called junk DNA is responsible for more functions than originally hypothesised.
First, researchers found that Hervs can regulate the expression of other human genes. A genetic feature is said to be “expressed” if its DNA segment is used to produce RNA (ribonucleic acid) molecules. These RNA molecules can then serve as intermediaries leading to the production of specific proteins, or help to regulate other parts of the genome.
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