Regulation of the CYP2D6 transgene by HNF4alpha. The figure shows a Northern blot analysis of mouse liver HNF4alpha expression. Hepatic RNAs (10 mcg) from HNF4alpha wild-type:CYP2D6 +/-(lanes 1, 2); HNF4alpha liver-null CYP2D6 +/- (lanes 3, 4); HNF4alpha wild-type:- CYP2D6 -/- (lanes 5, 6); and HNF4alpha liver-null CYP2D6 -/- (lanes 7, 8) were separated on a 1 per cent agarose gel, transferred to a nylon membrane and hybridised with an HNF4alpha exons 4 and 5 cDNA probe. HNF4alpha was completely deleted after Cre-mediated recombination. Beta-actin was used as a loading control. We stern blot analysis of CYP2D6 protein expression in liver microsomal protein (40 mcg) derived from the same groups of mice as those used for RNA analysis. Deletion of HNF4alpha resulted in a loss of more than 50 per cent of CYP2D6 protein expression. The blots were re-probed with an antibody to CYP2E1 in order to verify loading and the presence of microsomal proteins in all the samples.