APC colocalizes with lamin B1 in human colonic tissue. (A) Confocal immunofluorescence microscopy of cryosections from normal human colon tissues triple-labeled with APC-M2 pAb (green), anti-lamin B1 (red) and DNA dye topro-3 (blue). Arrows point to stromal cells in which lamin B1 staining is more intense compared to adjacent epithelial cells within crypts. In contrast, less APC staining is detected in stromal cells compared to crypt epithelial cells. Tissues are oriented such that luminal surfaces are at the top of the images. (b) and (c) Enlarged images of two regions indicated in (a). (B) APC colocalizes with β-catenin in the cytoplasm and cell junctions of human colonic crypts. (b) Enlarged image of a region at the base a colonic crypt shown in (a). (C) Immunofluorescence microscopy using preimmune sera and purified mouse IgG to probe consecutive tissue sections revealed only minimal signal. Scale bars, 20 μm.