Most of us think of viral invaders as malevolent pieces of code on the internet which do nasty things to our computers or the original DNA/RNA form which do nasty things to our biological health. But these bits of code (whether biological or binary) are more interesting and subtle than that. Few non-biologists are aware that mitochondria, the cellular organelles mainly concerned with energy production, contain DNA of very, very ancient viral origin which have been recruited by evolution into an entirely different biological role.
In the 1970s, scientists discovered that viruses, specifically retroviruses, could be found in the human genome right in the nucleus. It has very recently become evident that this phenomenon is much more prevalent than previously believed and involves a much wider variety of viruses and species than suspected. The RSS Feed from Discover Magazine contains two excellent blogs from The Loom and Not Exactly Rocket Science which refer to a new paper in PLOS Genetics which significantly extends these findings and suggests new functions and evolutionary pathways for this phenomenon:
“The presence of retrovirus sequences in animal genomes has been recognized since the 1970s, but is readily explained by the fact that these viruses integrate into chromosomal DNA as part of their normal replication cycle. Unexpectedly, however, we identified a large and diverse population of sequences in animal genomes that are derived from non-retroviral viruses. Analysis of these sequences—which represent all known virus genome types and replication strategies—reveals new information about the evolutionary history of viruses, in many cases providing the first and only direct evidence for their ancient origins. Additionally, we provide evidence that the functionality of one of these sequences has been maintained in the host genome over many millions of years, raising the possibility that captured viral sequences may have played a larger than expected role in host evolution.” Author summary by Aris Katzourakis and Robert J Gifford.
The paper itself may be technical for non-scientists but the two blogs are worth a visit. In fact there is some strongly suggestive evidence to suggest that schizophrenia (and possibly other forms of mental illness) may have a viral origin in many cases. Wait for an explosion of interest and significant discoveries in this field.