Smed-6G10 and -2G3 label different populations of muscle fibers. (A-D) Whole-mount immunostaining of intact planarians with 6G10 (magenta) and 2G3 (green). (A) 6G10 and 2G3 staining in the head region of the animal showing partial co-labeling. (B) 6G10 predominantly labels the circular and diagonal fibers, whereas 2G3 strongly labels circular, longitudinal, and diagonal fibers in the body wall musculature. Arrows indicate circular fibers. Closed arrowheads mark diagonal fibers. Open arrowheads highlight an example of a longitudinal fiber weakly labeled with 6G10. Insets show zoomed in regions marked by dashed white and yellow boxes. (C) Image of the anterior intestinal branches showing that 6G10 labels the intestinal musculature and transverse muscle fibers (marked by arrows and closed arrowheads, respectively). Open arrowhead highlights a transverse fiber in the parenchyma, which is co-labeled by 6G10 and 2G3. (D) 6G10 labels the circular muscle fibers of the body wall, mouth, and the pharynx; 2G3 labels circular, longitudinal, and diagonal fibers and the exterior portion of the mouth. Images are maximum intensity projections of optical sections. Anterior of the animal is to the top in A-C, and to the left in D. Scale bars: (A, D) 100 μm; (B, D) 10 μm.