E12.5 fetal liver (FL) cells from wild type embryos were cultured ex vivo in the presence of Tpo for three days. FL-derived megakaryocytes and their progenitors in the culture were separated by BSA density gradient. Megakaryocyte progenitors (“P” population) were further purified by fluorescence-activated cell sorting (FACS) for cells expressing low levels of CD41. Megakaryocytes (“M” population) were further enriched by CD41 antibody coupled with magnetic beads. Total RNA was isolated from either enriched megakaryocyte or progenitor fractions. ~5-15microgram RNA from each sample was submitted to the Dana Farber Cancer Institute Microarray Core Facility for cDNA and cRNA synthesis, labeling, and hybridization with Affymetrix Mouse Genome 430 2.0 chips according to manufacturer’s instructions. All arrays were normalized and analyzed using the dChip program. Keywords = GATA-1 Keywords = megakaryocyte Keywords = mouse model