FIGURE 2.
HNF4α is required for XBP1 expression in vivo. Hnf4αfloxed/floxed mice under the control of a ubiquitously expressed CAGGCreERT promoter were treated with tamoxifen to induce Hnf4α deletion. A, pancreatic islets were isolated 28 days after beginning tamoxifen treatment (see “Experimental Procedures”) and their RNA harvested. Expression of Xbp1, Hnf4α, and the downstream XBP1 target, Edem1, was assayed by qRT-PCR. B, expression of other unfolded protein response pathway transcripts, Chop, Bip, and Atf4 was assayed as for A. C, immunofluorescent images of the ER marker Calregulin reveal altered ER structure in ΔHnf4α mouse islets. Scale bars = 20 μm (white box shown at higher magnification immediately below). D, mean fluorescent intensity (arbitrary units from 16-bit images) of non-nuclear, β-cell-specific Calregulin staining in mouse islets was determined after normalizing each tissue section to neighboring acinar Calregulin mean fluorescence. Data represent means ± S.E. from three mice/condition, significance determined by one-tailed Student's t test. E, total β-cell area in the pancreas was quantified by anti-insulin immunofluorescence from sections by completely sectioning through whole tissue blocks of the entire embedded pancreata from ΔHnf4α and controls. (Means ± S.E. from 6 mice/condition, significance determined by one-tailed Student's t test.)