Regulation of C/EBPε expression in U937 cells by ATRA. Northern blot of total RNA (30 μg/lane) of U937 cells exposed for various lengths of time to ATRA (5 × 10⁻⁷ mol/L). The top panel shows the hybridization with full-length C/EBPε cDNA probe, and the bottom panel shows the hybridization with β-actin cDNA probe as assessment of RNA quantities in each lane.