Regulated expression of neurogenic basic helix-loop-helix transcription factors during differentiation of the immortalized neuronal progenitor cell line HC2S2 into neurons

Expression of nine neurogenic basic helix-loop-helix (bHLH) transcription factors was examined in an immortalized neuronal progenitor cell line HC2S2, which differentiates into neurons after suppression of the v-myc expression with tetracycline. Expression of MASH-1, NeuroD, NeuroD-related factor (NDRF) and HES-1 was demonstrated in HC2S2 cells by Northern blot analysis using total RNA. Expression of MASH-1 mRNA was downregulated upon differentiation of HC2S2 cells into mature neurons. In contrast, NeuroD and NDRF mRNA expression was maintained all through the differentiation. The expression of HES-1, a negative regulator of the neuronal differentiation, was upregulated temporarily in accordance with the suppression of the v-myc expression and was downregulated upon the differentiation of HC2S2 cells into neurons. The reduced expression of HES-1 mRNA in undifferentiated HC2S2 cells may be explained by the transcriptional suppression of HES-1 by the myc oncoprotein. The above data imply that both HES-I and MASH-1 need to be downregulated at the time of accomplishment of the terminal differentiation into mature neurons and that NeuroD and NDRF participate in the regulatory process of the terminal differentiation in combination.