With the rising incidence of obesity and type II diabetes, there is heightened interest in understanding how fat cells, or adipocytes, are produced from their precursor cells. Conventional views in the field have emphasized the notion that adipocyte differentiation is driven by extracellular inducing signals. Ross et al. challenge this notion by showing that adipogenesis is regulated by a repressive rather than an inductive mechanism. Preadipocytes in culture are maintained in an undifferentiated state by the action of the Wnt pathway, a signaling pathway already known to play a critical role in cell growth and differentiation in other tissues (see the Wnt/beta-catenin pathway). When Wnt signaling was inhibited in pre-adipocytes, the cells spontaneously differentiated into fat cells (see the fat cell differentiation movie). Disruption of Wnt signaling in muscle cell precursors, or myoblasts, also resulted in their conversion to adipocytes, which suggests that this may be a common mechanism for switching mesodermal cell fate.