Intestinal and liver samples from Ire1b+/+ (+/+; white bars) and Ire1b−/− (−/−; black bars) mice (n = 3 per group) fed a cholesterol-enriched or fat-enriched diet were used for MTP activity assays (A, E, I, and M). RNA was used to measure MTP (B, F, J, and N), apoB (C, G, K, and O), GAPDH (D, H, L, and P), and ARPp0 mRNA in triplicate. The ratio between the gene of interest and ARPp0 in Ire1b+/+ mice was used to normalize mRNA levels in all samples. Values are mean ± SD. **p < 0.01, ***p < 0.001 compared to Ire1b+/+. Data are representative of two experiments.