Pigmented and unpigmented tumors inNf1+/− mutant mice 3 months after nerve transection.A, Hindlimb portion of a fixed mutant mouse, 3 months after nerve cut (skin has been removed). An unpigmented tumor, delineated by arrows, is on the left side of the midline of the body. Pigmentation is evident in muscle lateral to the tumor.B, Hindlimb portion of an Nf1+/− mouse with a pigmented tumor, delineated by arrowheads.Arrows point to pigmented spots adjacent to the tumor.C, Toluidine blue-stained semithin plastic section showing the pigmented tumor in B, with capsule. Scale bar, 100 μm. The tumor is shown at higher magnification inE (scale bar, 50 μm) and F (scale bar, 20 μm).D, A nonpigmented tumor in paraffin section after H&E staining, showing tumor infiltration between muscles and lack of a capsule. G, Gomori's trichrome staining of an adjacent section reveals that this tumor is full of collagen-rich matrix and highlights collagen-rich bundles infiltrating nearby muscle (arrows). Scale bar, 100 μm. H, Anti-S100 staining (brown; DAB reaction product) of an adjacent section of the same tumor as D andE, at higher magnification. The section was counterstained with methyl green to show S100-negative cells.J, Anti-neurofilament staining of an adjacent section reveals the presence of axons within the tumor. Scale bars:H, J, 10 μm; I, 50 μm.