Figure 3. Schematic diagram of differentiation in human and murine in vitro models. Human primary preadipocytes grown in the absence of FGF-1 have a poor differentiation capacity. In the presence of FGF-1, phPA proliferate at a greater rate, exhibit greater levels of ERK1/2 activity, and have a greater capacity for differentiation. These cells have many properties in common with murine 3T3-L1 PA, including patterns of adipocyte gene expression and the functional and biochemical properties of mature adipocytes. A key difference is that human preadipocytes do not undergo mitotic clonal expansion (MCE).