Cell fusion and reprogramming: resolving our transdifferences

Bone marrow-derived cells (BMDCs) can contribute to the regeneration of diverse adult tissues, including brain, liver and heart, following bone marrow transplantation. These unexpected events were initially considered a result of transdifferentiation of BMDCs, supporting the emerging idea of extended plasticity of adult stem cells. Although studies observing transdifferentiation were met with great enthusiasm, the characterization of such events was incomplete. Meanwhile, an alternative hypothesis, cell fusion, began to emerge. New studies have now clearly demonstrated that spontaneous cell fusion, rather than transdifferentiation, was the primary cause for unexpected cell fate-switches of BMDCs into hepatocytes, Purkinje cells and cardiac myocytes in vivo.