mAb labeling of histological sections. Cryosections (20 μm) from formaldehyde-fixed planarians processed as indicated. (A) Sections labeled with secondary antibody only. (B) mAb 3F11 labels the intestine (arrows). (C) 2G4 labels the apical regions of intestinal cells (arrows) and epidermis. (D) 2H3 labels enteric (yellow arrows) and body wall (magenta arrows) muscles. Schematics illustrating orientation of cross sections and tissues labeled (green) are to located the right of each set of panels. All planarians were treated with HCl or NAc, and fixed in formaldehyde/Triton X-100 (20 min). Bleaching in 6% H2O2/PBS (12 hr) (middle column) was conducted prior to cryosectioning. Antigen retrieval was conducted after sectioning. Dorsal is to the top in all images. Conditions yielding the highest signal-to-noise for each mAb are indicated with an asterisk. Scale bars: 100 μm.