Phenotypic characterization of the ROSA cell lines. ROSA^{KIT WT} cells were stained by (A-B) MGG or (C) toluidine blue. (D) The ultrastructure of ROSA^{KIT WT} cells was analyzed by transmission electron microscopy. In addition, ROSA^{KIT WT} cells were treated with an antibody against (E) tryptase or (F) KIT (CD117). Positivity was revealed by indirect immunocytochemistry as described in “Material and methods.” (G) Cytospin preparations or (H-I) glass smears of ROSA^{KIT D816V} cells were stained by MGG. (G) Note the presence of many granules in ROSA^{KIT D816V} cells and of apoptotic cells, a phenomenon likely to be related to terminal maturation induced by the introduction of the KIT D816V mutant. (H) On glass smear, a significant proportion of the ROSA^{KIT D816V} cells presented with spindle-shaped appearance, which was not noticed for (I) ROSA^{KIT WT} cells. Magnification: A and C, ×200; B, E, G, H, and I ×500; D, ×2000; F, ×1000.