Requirements for GATA-1 in megakaryocyte gene expression. (A) Affymetrix probe set hybridization results for 16 representative genes that were differentially affected by the absence of GATA-1. Highest levels of expression are depicted as yellow squares; the lowest levels or no expression are represented by black squares. (B) Quantitative real-time RT-PCR validation of 16 genes selected from the array data. Data were divided into the following groups: genes that were not significantly affected (P > .05, upper left), ones that were down-regulated 2- to 3-fold (P ranged from < .002 to .02, upper right), those that were reduced more than 5-fold (P < .001, lower left), and genes that were induced in the absence of GATA-1 (GATA-2 and Ets-1, P < .001; myc P < .05; myb P < .5; lower right). Fold changes of gene expression in the GATA-1 knockdown cells (yellow bars) are shown relative to the levels detected in wild-type cells (black bars: wild-type expression was set to 1). Means ± SD for 3 experiments are shown.