Previously, a small molecule, reversine, was identified that reverses lineage-committed murine myoblasts to a more primitive multipotent state. Here, we show that reversine can increase the plasticity of C2C12 myoblasts at the single-cell level and that reversinetreated cells gain the ability to differentiate into osteoblasts and adipocytes under lineage-specific inducing conditions. Moreover, reversine is active in multiple cell types, including 3T3E1 osteoblasts and human primary skeletal myoblasts. Biochemical and cellular experiments suggest that reversine functions as a dual inhibitor of nonmuscle myosin II heavy chain and MEK1, and that both activities are required for reversine's effect. Inhibition of MEK1 and nonmuscle myosin II heavy chain results in altered cell cycle and changes in histone acetylation status, but other factors also may contribute to the activity of reversine, including activation of the PI3K signaling pathway.myoblasts ͉ multipotent ͉ small molecule ͉ osteoblast ͉ adipocyte A growing body of evidence suggests that lineage-restricted somatic cells are capable of gaining increased plasticity. This can occur through somatic cell nuclear transfer, cell fusion, ectopic gene expression, and/or treatment with exogenous factors. For example, somatic cells can be reprogrammed to a state of developmental totipotency or pluripotency, respectively, by somatic cell nuclear transfer (1, 2) or fusion with ES cells (3, 4). More recently, it has been shown that the combined expression of four transcription factors, i.e., Oct3/4, Sox2, c-Myc, and Klf4, is sufficient to reprogram primary mouse embryonic and adult fibroblast culture to pluripotent cells, which can express pluripotency markers and contribute to teratomas (5). In addition, enforced expression of C/EBP␣ and C/EBP in differentiated B cells leads to their rapid and efficient reprogramming into macrophages (6); and ectopic expression of Msx1 (7) or treatment with newt regeneration extract (8) has been reported to induce dedifferentiation of terminally differentiated myotubes.The identification of small molecules that increase the cellular plasticity of mammalian cells would provide further insights into the mechanisms that control this complex process and may ultimately provide chemical reagents that make it possible to use healthy, abundant, and easily accessible adult cells to generate different types of stem/progenitor cells for therapeutic applications. Previously, myoseverin, a small molecule, was shown to convert myotubes to proliferative myoblast-like cells by disrupting microtubule assembly (9, 10). More recently, a purine derivative, reversine (Fig. 1A), was discovered in a cell-based screen, which can increase the plasticity of lineage-committed murine C2C12 myoblasts. The reversine-treated cells gained the ability to redifferentiate into osteoblasts and adipocytes, respectively, under lineage-specific inducing conditions (LSICs) (11). In addition, it was reported that reversine treatment reprograms primary murine and human dermal ...