The Living Dead Gene
By Kelly Wood, P1, 41772805
Researchers at Washington University have discovered a gene that appears to have been dead for at least 25 million year in primate evolution but has been resurrected in modern humans and Great Apes. This miraculous recovery could mean big things for the non-coding sections of our genome that are currently considered “Junk.”
How it Happened
IRGs (Immune Related GTPases) are a family of genes present in most mammals and vital to their immune system. In the human form, IRGM, it is known to protect us from maladies such as TB and Chron’s Disease. However, while it is present and active in humans, the Great Apes and the prosimian family (lemurs, loris’, tarsiers, etc.), there is no functional copy in apes and monkeys. This suggests that the death of this gene must have occurred at the split between the prosimians and anthropoids some 50 million years ago. By mapping the evolution of the IRG family in primates, they found that it converged into a single pseudogene (non-coding) at this point due to a muddling of its sequence by a gene called Alu. Its ability to code proteins (Open Reference Frame) was revived 25 million years later by the introduction of an endogenous retrovirus called ERV9. ERV9 still exists in the human genome and is now thought to be the “functional promoter driving human gene expression” (2). It critically rewired the transcription and expression mechanisms of the IRGM gene, bringing it, zombie-like, back from the grave.
What this means for junk
This sort of rejuvenation has never been seen before and suggests that genes have a real ability to respond and adapt to various environmental pressures. And the ramifications are massive: opening many new avenues of research in gene locus evolution especially within inactive genes or “junk DNA” sections of the genome. The possibility now exists that much of this junk had definite functions in our past and could well shape future human evolution. Each dead gene is just waiting for that vital spark…
Sources
1. (2009), New Scientist Magazine, “’Dead’ gene comes back to life,” Volume 201, No2699, pp 15
2. Bekpen C, Marques-Bonet T, Alkan C, Antonacci F, Leogrande MB, et al. (2009) Death and Resurrection of the Human IRGM Gene, PloS Genetics Open Access Journal, PLoS Genet 5(3): e1000403. http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1000403
3. AnneH (2009) “Don’t Call it a Comeback: The Life, Death and Rebirth of the IRGM Gene,” The Spittoon, http://spittoon.23andme.com/2009/03/06/dont-call-it-a-comeback-the-life-death-and-rebirth-of-the-human-irgm-gene/
