Morphological changes in response to retinoic acid treatment. Cell lines grown in standard conditions (A-F) or treated with retinoic acid (G-L). Only NTERA-2 cells (A vs. G) and D283 cells (B vs. H) showed a morphological response to retinoic acid. PC12 cells treated with NGF developed a complex network of cellular processes (I inset). Scale bar in L = 100 μm.