HOXB4 target genes in ES cell-derived embryoid bodies (EBs)

To unravel the molecular mechanism by which HOXB4 promotes the expansion of early hematopoietic progenitors within differentiating ES cells, we analzed the gene expression profiles of embryoid bodies (EBs) in which transcription of HOXB4 had been induced or not induced. A substantial number of the identified HOXB4 target genes are involved in signaling pathways important for controlling self-renewal, maintenance and differentiation of stem cells. Furthermore, we demonstrate that HOXB4 activity and FGF-signaling are intertwined. HOXB4-mediated expansion of ES cell-derived early progenitors was enhanced by specific and complete inhibition of FGF-receptors. In contrast, the expanding activity of HOXB4 on hematopoietic progenitors in day4-6 embryoid bodies was blunted in the presence of basic FGF (FGF2) indicating a dominant negative effect of FGF-signaling on the earliest hematopoietic cells. Taken together, we show that modulation of FGF signaling is an essential feature of HOXB4 activity in the context of embryonic hematopoiesis. Keywords: plus/minus induction of HOXB4 gene expression by treatment with doxycycline (Dox) The Hoxb4i ES cell line (Kyba et al. 2002, Cell 109:29-37) contains an integrated “tet-on” cassette that allows induction of HOXB4 expression upon treatment with doxycycline. These ES cells can be used to produce hematopoietic cells through the formation of embryoid bodies (EBs). Hematopoiesis starts in these EBs at day 4 and the differentiation into hematopoietic fates can be quantified by colony assays on methyl-cellulose using cells dissociated from EBs at day 6 of incubation. The induction of HOXB4 by incubation with doxycycline increases the production of hematopoietic progenitors within EBs by day 6. Using this specific ES cell line, we compared the transcriptome between embryoid bodies (EBs) in which transcription of HOXB4 had been induced or not induced from day 4 to day 6 (48hours). Biological replicates: 3