The idea that the demethylation enzyme targets paternal DNA is supported by work done on a second gene that starts out heavily methylated in both sperm and egg. The question now is to work out how the egg controls this new weapon, he says. It may be part of a system that strikes a balance between maternal and paternal imprints so that neither dominates, he says. Understanding demethylation will also be critical for cloning research, Wolffe says. As cells specialise, their methylation patterns change.
Cloning can only work when the recipient egg somehow resets the donor DNA to an embryonic state.
One of the main causes of failure in cloning is overgrowth of the embryo, as if paternal imprints were winning out. This story first appeared in New Scientist magazine.