Northern blot analysis for MBP, gp91^phox, neutrophil elastase, GATA-1, GATA-2, GATA-3, C/EBP, C/EBPβ, PU.1 (Spi-1), and β-actin mRNA expression in HT93A cells treated with RA. Lane 1, untreated HT93A cell; lanes 2 through 5, HT93A cells treated with 2 μmol/L RA for 1, 3, 5, and 7 days, respectively. Each lane contained 4 μg of poly(A)⁺ RNA. The blot was probed sequentially with each cDNA probe and the β-actin probe to control for equivalent loading.