The Role of the IGFs in Myogenic Differentiation

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Abstract
Myogenesis is an important aspect of developmental biology that has been actively investigated in cultured cells for nearly three decades. Interest has been heightened and activity more sharply focussed during the past few years by the discovery of a family of myogenesis controlling genes, which appear to play major roles in the aspect of myogenesis to be considered here: the terminal differentiation of proliferating myoblasts to form postmitotic myotubes in which a number of muscle-specific genes are expressed. Most attention on the control of this process has been concentrated on its negative regulation by medium components initially characterized loosely as „mitogens,“ but subsequently identified as Fibroblast Growth Factor (FGF) and Transforming Growth Factor-beta (TGF-ft). This laboratory has shown that the Insulinlike Growth Factors (IGFs), in contrast, are stimulators of myogenesis, and recent work suggests that autocrine/paracrine actions of the IGFs may play an important role in differentiation in low serum medium even when the exogenous growth factors are not added. Thus, initiation of myogenic differentiation in vitro requires not only the removal of inhibitors present in serum, but also the secretion or addition of stimulators of this process.