Around 8% of human DNA is made up of genetic sequences acquired from ancient viruses. These sequences, often known as human endogenous retroviruses (or Hervs), date back lots of of 1000’s to hundreds of thousands of years – with some even predating the emergence of .
Our latest research suggests that some ancient viral DNA sequences within the human genome play a job in susceptibility to psychiatric disorders reminiscent of schizophrenia, bipolar disorder and major depressive disorder.
Hervs represent the remnants of those infections with ancient retroviruses. Retroviruses are viruses that insert a replica 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 generationsbecoming a everlasting a 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 develop into evident that this so-called junk DNA is chargeable for more functions than originally hypothesised.
First, researchers found that Hervs can regulate the expression of other human genes. A genetic feature is alleged to be “expressed” if its DNA segment is used to supply RNA (ribonucleic acid) molecules. These RNA molecules can then function intermediaries resulting in the production of specific proteinsor help to regulate other parts of the genome.
Initial research suggested that Hervs regulate the expression of neighbouring genes with necessary biological functions. One example of this can be a Herv that regulates the expression of a gene involved in modifying connections between brain cells.
Hervs have also been found to supply RNAs and even proteins in blood and brain samples. These molecules have the potential to exert a big selection of functions, as they’ll travel across cellular compartments to execute different roles.
Scientists have also found evidence suggesting certain human genes are derived from Hervs. This indicates there have been instances during evolution where Hervs were co-opted for specialised biological functions. For example, the human genes syncytins 1 and a pair of, that are derived from Hervs, play pivotal roles in placental development.
HERVs in psychiatric disorders
Considering the abundance of Hervs within the genome and their potentially quite a few functions, we wanted to higher understand whether genetic susceptibility to certain psychiatric disorders was related to differences in Herv expression.
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In our studywe profiled Herv expression in nearly 800 autopsy brain samples. This helped us discover DNA variations that influenced Herv expression within the brain.
We then cross-referenced this information with findings from large genetic studies which had compared genetic differences between tens of 1000’s of individuals – each with and without mental health conditions. These studies identified variations in DNA related to different psychiatric conditions.
We found that that the expression of 4 Hervs was linked with genetic susceptibility to major psychiatric disorders. The expression of two of those Hervs was related to schizophrenia, one Herv with each schizophrenia and bipolar disorder, and one with depression. These results suggest that Hervs could also be playing a more necessary role within the brain than initially thought.
There are many genes involved in psychiatric disorders – and Hervs are only an element of this puzzle. Although the precise impact of those Hervs on brain cells and on an individual’s susceptibility to certain psychiatric disorders requires further research, our study is the primary to indicate that genetic susceptibility for a psychiatric disorder also acts through these ancient viral DNA sequences.
It’s still too early to find out the sensible applications of our findings – and whether or not they could be used to develop latest treatments. But we’re optimistic about this line of research. By linking Herv expression within the brain with psychiatric disorders, our research recognises the importance of those mysterious sequences within the human genome, which have been ignored for years.
