The study investigates the mechanism by which progenitor cells of the central nervous system (CNS) can give rise to non-neuronal derivatives. By co-culturing mouse brain cells with pluripotent embryonic stem (ES) cells, the researchers identified a process of epigenetic reprogramming that allows brain cells to adopt the characteristics of ES cells. These hybrid cells, which are tetraploid and exhibit full pluripotency, can contribute to multiple lineages in chimeras. The findings suggest that the apparent plasticity of tissue stem cells may be due to spontaneous cell fusion rather than intrinsic plasticity. The study also highlights the importance of examining both donor and host cell markers in claims of cell plasticity.The study investigates the mechanism by which progenitor cells of the central nervous system (CNS) can give rise to non-neuronal derivatives. By co-culturing mouse brain cells with pluripotent embryonic stem (ES) cells, the researchers identified a process of epigenetic reprogramming that allows brain cells to adopt the characteristics of ES cells. These hybrid cells, which are tetraploid and exhibit full pluripotency, can contribute to multiple lineages in chimeras. The findings suggest that the apparent plasticity of tissue stem cells may be due to spontaneous cell fusion rather than intrinsic plasticity. The study also highlights the importance of examining both donor and host cell markers in claims of cell plasticity.