Control of Muscle Differentiation by Mitogens: A Rationale for Multiple Restriction Points in the Cell Cycle

In this chapter, the authors summarize their observations on the control of muscle differentiation by mitogens and suggests from these observations that fibroblast growth factor and other mitogenic molecules can control cell differentiation in the absence of cell growth. They focus on the important biological consequences that are derived from these observations. Normally, the commitment of fused myoblasts to the differentiation program is irreversible, and this precludes a detailed study of the role of mitogens in the control of their differentiation program. The existence of two restriction points, G_1q and G_1d, is compatible with the long-term survival of quiescent cells, allowing them to easily move from a differentiation incompetent state to a differentiation competent state. Movement of the cells through the cell cycle is associated with changes in the pattern of protein synthesis, and the expression of different proteins, often of unknown function, is associated with particular phases of the cell cycle.