Asymmetric division in a two-cell-like state rejuvenates embryonic stem cells

A fundamental question in biology is whether all cells age. Embryonic stem cells (ESCs) defy the norm as rare normal cells capable of indefinite in vitro passage. However, the mechanisms underlying ESC lineage immortality remain unresolved. Using long-term live-cell imaging to follow the fates of single ESCs, we show that ESC lineage renewal is achieved through sporadic entry into a state characterized by the expression of two-cell embryo-specific markers. During this state, cells undergo asymmetric fate divisions, enriching accumulated DNA damage into one daughter lineage that is destined for elimination, while producing a second lineage that reverts to the pluripotent state. Importantly, the latter lineage exhibits signs of rejuvenation, including reduced DNA damage and enhanced chimeric efficiency. These findings underscore the crucial role of asymmetric cell division in maintaining the long-term health of the ESC lineage against mounting damage within individual cells and provide a potential model for studying cellular aging and rejuvenation in mammalian cells.