Letter: Mutant mitochondria

From Jonathan White

Reading the account of fast-ageing mice (29 May, p 14) left me somewhat puzzled. You reported that accumulated mutations in mitochondria are a potential cause of ageing, and this seems to suggest that mitochondria must somehow be rejuvenated at the point of conception.

I had understood that mitochondria reproduce asexually and independently of the surrounding cell. So my questions would be: “How old is my mitochondrial heritage?” and “Why didn’t I pick up the accumulated mutations of the entire female line back through evolution to the first eukaryote?”

Philip Cohen writes:

• If there were no way to screen out mitochondria with harmful mutations from the germ line we would not be having this correspondence. Cells in ageing organisms have a mixture of functional and dysfunctional mitochondria. During egg formation the number of mitochondria appears to be reduced, creating a strong selection pressure for eggs with a pure population of efficient mitochondria. The process is not well understood. It sometimes seems to break down, resulting in an egg with a mixture of functional and malfunctioning mitochondria, which can result in diseases in the offspring.

Cambridge, UK