Analyses of mRNA expression and enzyme activity in mouse livers. Panel (a) shows RT-PCR quantitation of mRNA levels for Abcg5, Abcg8, Hmgr, Cyp7a1, Abca1, Mdr2, Lxr, Srebp-1c and Srebp-2 in mouse livers from Abcg8+/+ (open bars), Abcg8+/- (hatched bars) and Abcg8-/- (filled bars). Knockout mice showed an ~60% reduction in mRNA for Abcg5/sterolin-1 and an 80% reduction in the message for HMG CoA reductase. Relatively no message for Abcg8/sterolin-2 was detected in the knockout mice. Panel (b) shows the enzyme activities for HMG-CoA reductase and CYP7a1 in livers from Abcg8+/+, Abcg8+/- and Abcg8-/- mice. Activities of HMG-CoA reductase and CYP7a1 were significantly reduced in the Abcg8-/- mouse liver (*P < 0.05, see text for discussion).