The timing of insulin/c-Ras signal is critical for its effect upon the differentiation of C3H10T1/2-derived preadipocytes

The effect of the peptide hormone insulin upon the differentiation of a 10T1/2-derived preadipocytic line was found to display a potent time-dependence. Insulin addition before cell confluence strongly enhanced differentiation, while addition after confluence had no effect. In keeping with the role of c-Ras as a downstream effector of insulin, c-ras downregulation before confluence abolished differentiation, while it was ineffective once the process of differentiation was underway. These data suggest that the insulin signal is effective during an early window of time before cell confluence, while normal c-Ras levels are required for its transmission.