Expression of the mouse P(1)450 gene during differentiation without foreign chemical stimulation.

Transcriptional activation of the P(1)450 and P(3)450 genes, mRNA accumulation, and induction of the P(1)450 and P(3)450 enzymes are known to be stimulated by foreign chemicals such as tetrachlorodibenzo-p-dioxin and 3-methylcholanthrene. It has been established that this induction process is dependent on trans-acting factor(s) that include a complex between the environmental chemical inducer and the aromatic hydrocarbon (Ah) receptor. In this report we show that constitutive P(1)450 mRNA but not P(3)450 mRNA is elevated in 7-day-old mouse embryos and following retinoic acid-induced differentiation of F9 embryonal carcinoma cells. In both instances it is shown that P(1)450 gene activation can occur in the absence of a foreign chemical stimulus. These data suggest that the P(1)450 gene may serve an important developmental function during differentiation.