Incomplete methylation reprogramming in SCNT embryos

The cloning of Dolly the sheep was a remarkable demonstration of the oocyte's ability to reprogram a specialized nucleus. However, embryos derived from such somatic cell nuclear transfer (SCNT) very rarely result in live births-a fate that may be linked to observed epigenetic defects. A new genome-wide study shows that epigenetic reprogramming in SCNT embryos does not fully recapitulate the natural DNA demethylation events occurring at fertilization, resulting in aberrant methylation at some promoters and repetitive elements that may contribute to developmental failure.