Differential regulation of N-myc and c-myc expression in F9 teratocarcinoma cells.

Previous work has shown that the members of the myc protooncogene family are differentially regulated during murine development (Zimmerman et al., 1986). In this study, we have used the F9 mouse teratocarcinoma cell line to investigate the expression of two members of this family, the N- and c-myc genes. We demonstrate here that both N-myc and c-myc RNAs are unstable in these cells, but that they are clearly differentially regulated during a variety of cellular processes. Following retinoic acid addition, N-myc expression declines but then returns to initial levels as the cells undergo endodermal differentiation. c-myc RNA levels decrease more slowly and remain low in the differentiated cells. Additionally, we find that serum starvation and serum stimulation, treatments that alter c-myc RNA levels, do not have a significant effect on N-myc expression. These results provide further support for a role of c-myc expression in growth control but demonstrate that N-myc levels are not correlated with proliferative state of the cell.