A ghastly bout of food poisoning is not an experience to forget. The commonly-studied microscopic nematode Caenorhabditis elegans not only ensures it remembers, it genetically embeds the threat of skanky meals into its babies to force them to remain clear also.
And if by some misfortune one among those worms goes belly-up anyway? The warning that encoded in RNA can leak of their disintegrating body, potentially to be picked-up by any passing member of the species.
This remarkable memory transfer was spotted by researchers from the Princeton University’s Murphy Lab in the US as a neighborhood of a series of studies on inherited behaviors in the nematode.
Due to the existence of a fairly strict barrier between germ cells which give rise to new generation and parent’s own body cells, it had been once believed events affecting a parent’s physiology could not be imprinted on their offspring.
That view has gone-out the window with discoveries of environmental stresses in animals like C. elegans changing the way genes switched on not only in their offspring, but in their offspring’s own children & so on, for generations down the line.
It is not just a worm thing, either. Genes in the offspring of fruit flies & even mice can be tweaked by cues in their parent’s environment, effectively changing the biological functions of future generations.
Last year, the researchers at molecular biologist Coleen Murphy’s lab published their findings on C. elegans reactions to consuming the bacterium Pseudomonas aeruginosa, an appealing food source that quickly turns nasty in their digestive system.
This slither of nucleic acid found to bind to a corresponding code in the worm’s genome, a gene called maco-1, which was already known to play a role in sensory perception. As a result, worm ‘learns’ to steer clear of P. aeruginosa in the future.
Amazingly, this behavioral shift as well as affects a mother worm’s descendants, teaching at least of subsequent 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, teacher has got to be pulped first.
“We found that one worm can learn to avoid this pathogenic bacterium and if we grind up that worm, or even just use the media the worms are swimming in and provides that media or the crushed worm lysate to naïve worms, those worms now ‘learn’ to avoid the pathogen also,” says Murphy.
Investigations of nematodes incapable of learning this avoidance-trick suggested that in spite of maco-1’s established role in avoiding P. aeruginosa, gene’s presence alone could not explain why the behavior was inherited. Something else was happening.
So, the team went on the search for other factors behind the quirky neurological adaptation.
Chief suspect was an itinerant ‘jumping’ gene, called Cer1, already known to possess the right characteristics to move from one a part of a genome to another just like a virus.
“What we discovered is that a retrotransposon, called Cer1 that forms viral-like particles seems to carry a memory not only between tissues (from the worm’s germline to its neurons) but also between individuals,” says Murphy.
Worms that naturally lacked Cer1 or had it edited-out, simply could not resist taking a nibble of P. aeruginosa.
This whole learning experience is not without its risks. The retrotransposon’s jumping behavior also can cause harm because it inserts itself into parts of the animal’s genome, suggesting there has got to be a benefit to its costs.
Fascinating as they’re now, hints that behavior altering experiences can be inherited would have been surprisingly controversial half a century ago, when American animal psychologist James V. McConnell shot to fame & infamy over suggestions that flatworms could inherit memories by consuming other, more educated flatworms.
McConnell’s chapter in the history of biology has since influenced debate over the permeability of that barrier between parent & child and whether one generation’s experiences of the planet can directly affect the way next approaches it.
The extent to which this might happen in humans still being explored, yet there are tantalizing signs we are not exempt, either.
This research was published in Cell.