Cell-specific induction of mouse Cyp1a1 mRNA during development.

The dioxin-inducible cytochrome P(1)450 (Cyp1a1 gene) and P(3)450 (Cyp1a2 gene) enzymes have been implicated in the metabolism of numerous polycyclic hydrocarbons and arylamines, respectively. The prototypic inducer 3-methylcholanthrene was given to the pregnant mouse, and the intrauterine response was examined with the use of in situ hybridization. During the early postimplantation stage, inducible Cyp1a1 mRNA is detected in specific cell types in the extraembryonic tissues only. This selective expression along with the lack of detectable constitutive Cyp1a1 and constitutive or inducible Cyp1a2 gene transcripts between 5.3 and 14.5 days of gestation suggest that (i) these two genes appear to play no endogenous role during differentiation and (ii) the metabolic activity of the inducible Cyp1a1 enzyme may be important to the embryo and fetus from the standpoint of protection against toxic foodstuff and other environmental chemicals.