https://www.nature.com/articles/s41587-026-03015-5
John insisted that the central idea of his work — that factors in an egg can reset a differentiated nucleus to run embryogenesis again — should not feel mysterious. After all, reprogramming happens at every fertilization, when the sperm nucleus is rewritten by the oocyte. What was surprising, and what John proved with rigor in 1962, was that even nuclei from fully differentiated frog epithelial cells could be driven back to a pluripotent state by the egg. This finding was only fully embraced almost 40 years later, after the 1997 report describing Dolly the sheep — the first animal cloned from a differentiated adult mammalian cell.
This, of course, raises the question as to where the pointer is for ageing and development. One possibility is that it is in the nucleus and it can be reset. The other possibility is that it is in the cytoplasm.
I think it is in the cytoplasm. (because it is the status of the mitochondria).