Early B Cell Factor 2 Regulates Hematopoietic Stem Cell Homeostasis in a Cell-Nonautonomous Manner. Mus musculus

Hematopoiesis requires the interaction of hematopoietic stem cells (HSCs) with various stromal microenvironments. Here, we examine the role of early B cell factor 2 (Ebf2), a transcription factor expressed in a subset of immature osteoblastic cells. Ebf2-/- mice show decreased frequencies of HSCs and lineage-committed progenitors. This defect is cell nonautonomous, as shown by the fact that transplantation of Ebf2-deficient bone marrow into wild-type hosts results in normal hematopoiesis. In coculture experiments, Ebf2 Ebf2-/-osteoblastic cells have reduced potential to support short-term proliferation of HSCs. Expression profiling of sorted Ebf2-/- osteoblastic cells indicated that several genes implicated in the maintenance of HSCs are downregulated relative to Ebf2+/- cells, whereas genes encoding secreted frizzled-related proteins are upregulated. Moreover, HSCs from Ebf2-/- mice and wild-type HSCs cocultured with Ebf2-/- osteoblastic cells show reduced Wnt responses. Thus, Ebf2 acts as a transcriptional determinant of an osteoblastic niche that regulates the maintenance of hematopoietic progenitors, in part by modulating Wnt signaling. Overall design: Osteoblastic cells from tibia and femur of Ebf2 heterozygous and knockout mice (n=3 each) were loaded with FDG, FACS sorted and total RNA was isolated. cDNA was synthesised using the One-Cycle cDNA Synthesis Kit (Affymetrix), and labeled cRNA was synthesized by transcription in vitro, using the IVT labelling kit (Affymetrix). The labeled RNA was fragmented and hybridized to GeneChip® Mouse genome 430 2.0 arrays (GPL1261), according to the manufacturer’s instructions.