Figure 4. Immunocytochemical analysis of neuronal and photoreceptor cell markers in ARPE-19 cells after treatment with dimethyl sulfoxide or fenretinide. A-K: ARPE-19 cells were treated with 3 μM fenretinide or DMSO and processed for immunocytochemistry. The nuclei of cells are stained with 4',6-diamidino-2-phenylindole (blue) with the exception of cells where protein expression was detected within the nucleus (OPN4, CRX, and PAX6). Staining is indicated by the text color. L: Staining was not detected in control plates where only secondary antibodies were used. M: Final cell density did not affect cell morphology or changes in protein expression. ARPE-19 cells were seeded at various densities (i, 0.5×10³; ii, 1×10³; and iii, 2×10³ cells/dish) and cultured for 7 days in DMSO-containing medium before staining for CALB2 (red). All scale bars are 50 μm.