Father’s Light Exposure Changes Kids’ Memory Through Tiny Sperm Messengers

A new study shows that a dad’s exposure to constant light can hurt his children’s memory. The researchers used male mice and kept them in a 24‑hour light environment. When the offspring were born, only the male pups showed trouble learning and remembered things less well than normal. Female pups seemed fine. The scientists looked inside the dads’ sperm and found that the light stress changed many small RNA molecules, especially microRNAs. These tiny RNAs can travel to the egg after fertilisation and influence how genes are read in early embryos. The changes were linked to parts of the sperm DNA that are normally open for gene activity, suggesting the problem starts in the earliest stem cells of the sperm.In human samples the team confirmed that one microRNA, miR‑92a‑3p, was higher in men who had been exposed to continuous light. To test whether these RNAs could cause the memory problems, they injected either all small RNAs from light‑exposed sperm or just the two microRNAs (miR‑92a‑3p and miR‑25‑3p) into fertilised eggs. The resulting mice behaved like the light‑exposed group, showing poor memory. When the researchers blocked these microRNAs in the eggs, the memory problems were partly fixed. These findings suggest that what a father does before he fathers can be passed on to his children through sperm RNAs. It also shows that the timing of light exposure matters for brain development in the next generation.