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Horrible food poisoning is not an experience to be forgotten. The commonly studied microscopic nematode Caenorhabditis elegans Not only does he make sure he remembers, but he genetically incorporates the threat of skanky meals into his children to force them to stay away as well.
What if one of these worms got bogged down anyway? The warning encoded in the RNA can escape their decaying body, potentially picked up by any member of the passing species.
This remarkable means of memory transfer was spotted by researchers at the Murphy Lab at Princeton University in the United States as part of a series of studies on the nematode’s hereditary behaviors.
Due to the existence of a fairly strict barrier between the germ cells that give birth to a new generation and the parent’s own body cells, it was once believed that events affecting the physiology of a parent could not be imprinted. on their offspring.
This view disappeared with the findings of environmental stresses in animals such as C. elegans changing the way genes are turned on not just in their offspring, but in their offspring’s own children … and so on, for generations to come.
It’s not just a worm story either. The genes of the offspring of fruit flies and even mice can be altered by signals in their parents’ environment, effectively altering the biological functions of future generations.
Last year, researchers in molecular biologist Coleen Murphy’s lab published their findings on C. elegans reactions to consuming the bacteria Pseudomonas aeruginosa – an attractive food source that quickly becomes unpleasant in their digestive system.
The team found that the worms were taking strands of RNA from their toxic meal through their intestines, which included a stretch of non-coding RNA called P11.
This nucleic acid band was found to bind to a corresponding code in the genome of the worm – a gene called maco-1 – which was already known to play a role in sensory perception. As a result, the worm “learns” to avoid P. aeruginosa in the future.
Surprisingly, this change in behavior also affects the offspring of a mother worm, teaching at least the next four generations to avoid this particular microbial meal as well.
This latest experiment demonstrates that genetic memory is not strictly a family affair, with evidence that it can be transmitted laterally from worm to worm.
Tragically, the teacher has to be pulped first.
“We have found that a worm can learn to avoid this pathogenic bacteria and if we grind this worm, or even just use the medium that the worms swim in, and give that medium or the ground worm lysate to naive worms, these by now “learn” how to avoid the pathogen as well, “says Murphy.
Research on nematodes unable to learn this avoidance trick has suggested that despite the established role of maco-1 in avoidance P. aeruginosa, the presence of the gene alone could not explain why the behavior was inherited. Something else was going on.
The team therefore set out to search for other factors at the origin of eccentric neurological adaptation.
(Murphy Laboratory)
The prime suspect was a traveling “jumper” gene called Cer1, already known to have the right characteristics to jump from one part of a genome to another like a virus.
“What we found is that a retrotransposon called Cer1 which forms viral-like particles appears to carry memory not only between tissues (from the germ line of the worm to its neurons) but also between individuals,” Murphy explains. The worms that naturally lacked Cer1, or had suppressed it, just couldn’t resist taking a bite of Cer1. P. aeruginosa.
This whole learning experience is not without its risks. The retrotransposon’s skipping behavior can also cause damage as it fits into parts of the animal’s genome, suggesting that there must be some cost benefit.
As fascinating as they are today, hints that behavior-altering experiences can be inherited would have been surprisingly controversial half a century ago, when American animal psychologist James V. McConnell rose to fame – and infamous. – because of suggestions that tapeworms might inherit memories by consuming other, more educated tapeworms.
McConnell’s chapter in the History of Biology has since influenced the debate on the permeability of this barrier between parent and child, and whether the experiences of one generation of the world can directly affect how the next the addresses.
The extent to which this could occur in humans is still under investigation, but there are some tantalizing signs that we are not immune to either.
This research was published in Cell.
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