C. elegans worms whose grandparents had the ability to fight viruses using a fleet of tiny RNA molecules retain these molecules even when they don’t have the genes for them. They can pass these molecules down for more than a hundred generations.
A research team engineered worms that didn’t have the genes to make the RNAs—which work by inhibiting the virus replication machinery—and then bred them with worms that did for several generations. They ended up with some worms whose ancestors had had the virus-fighting molecules, but did not themselves possess the necessary genes. The team then watched these worms under the microscope and saw that they still attacked viruses in exactly the same way as their grandparents.
Numerous control experiments confirmed that the effect was real, and only happened in worms who had ancestors with the genes. The researchers collected all the various RNA molecules in these worms and saw that indeed, they possessed the virus-fighting variety.After about three generations, the effect seemed to wear off; most worms without the genes stopped being able to attack viruses. But for some worms, it never stopped. The team bred those worms for more than one hundred generations, nearly a year, and the creatures never flagged in their ability to defend themselves.
How is this possible? The team keeps mum on any ideas of how this inheritance works. But they do uncover some tantalizing details that give us room for speculation. One possibility is that the RNA molecules made by the original worms in response to a virus attack were floating around in the cytoplasm of the eggs and sperm that became their offspring. If that’s the case, then the offspring are basically using their parents’ leftovers, with each generation having a bit less of the original stuff.
The researchers mention this possibility of the original RNA being “diluted” with each generation, but don’t, as far as we can tell, try to test that.But what about the worms that hang on to the RNA indefinitely? The researchers found that for that to happen, a particular enzyme that builds RNAs has to be present. Maybe, then, these worms manage to jerry-rig a way to make copies of the virus-fighting RNA with that enzyme (which isn’t part of the usual machinery), even though they lack the gear required to make it in the normal fashion. The gene for that enzyme would then be passed on as normal.
Via Sakis Koukouvis, Dr. Stefan Gruenwald