The ARID Family Transcription Factor Bright Is Required for both Hematopoietic Stem Cell and B Lineage Development

Bright/Arid3a has been characterized both as an activator of immunoglobulin heavy-chain transcription and as a proto-oncogene.Although Bright expression is highly B lineage stage restricted in adult mice, its expression in the earliest identifiable hematopoietic stem cell (HSC) population suggests that Bright might have additional functions.We showed that >99% of Bright ؊/؊ embryos die at midgestation from failed hematopoiesis.Bright ؊/؊ embryonic day 12.5 (E12.5)fetal livers showed an increase in the expression of immature markers.Colony-forming assays indicated that the hematopoietic potential of Bright ؊/؊ mice is markedly reduced.Rare survivors of lethality, which were not compensated by the closely related paralogue Bright-derived protein (Bdp)/Arid3b, suffered HSC deficits in their bone marrow as well as B lineage-intrinsic developmental and functional deficiencies in their peripheries.These include a reduction in a natural antibody, B-1 responses to phosphocholine, and selective T-dependent impairment of IgG1 class switching.Our results place Bright/Arid3a on a select list of transcriptional regulators required to program both HSC and lineage-specific differentiation.