Identification of gene targets of Meis1

The homeodomain protein Meis1 is essential for definitive hematopoiesis and vascular patterning in the mouse embryo. Our present study suggested it exerts two distinguishable effects in differentiating ES cells. First, it increases the numbers of hematopoietic progenitors and extends their persistence in culture. Second, Meis1 skews hematopoietic differentiation by suppressing erythroid while enhancing megakaryocytic progenitor differentiation. To identify the underlying transcriptional bases of these actions, we carried out microarray analysis to compare the various populations of cells developing in ES differentiation cultures in the presence and absence of Meis1 induction. ES cells with dox-inducible Meis1 (A2lox.Meis1) were differentiated as embryoid bodies (EBs) for 6 days before plating on OP9-GFP cell monolayers and cytokines, and treated with (+) or without (-) doxycycline (dox). Cells were purified by cell sorting on day 7 or 8 into various populations based on levels of CD41 expression: GFP-CD41-, GFP-CD41+ (day 7) and GFP-CD41-,GFP-CD41int, and GFP-CD41hi (day 8). Gene expression of these purified populations was determined by microarray analysis.