SRA

The zinc finger protein and SNAG domain transcription factor Gfi1b is highly expressed in hematopoietic stem cells (HSC) and in megakaryocytes (MKs). Deletion of Gfi1b in mice leads to a drastic expansion of both cell types, suggesting that Gfi1b controls their proliferation. Here we present evidence that Gfi1b exerts this control by modulating the Wnt/beta-catenin signaling pathway. We can show that Gfi1b binds to beta-catenin and is part of a larger complex that contains ß-catenin co-factors. Gfi1b activates beta-catenin/TCF mediated transcription and is required for the activity of beta-catenin target gene promoter driven reporter genes in vivo. This is dependent of the ability of Gfi1b to recruit the histone modifying enzyme lysine demethylase 1 (LSD1) to ß-catenin containing complexes. Moreover, LSD1 enhances the Gfi1b-mediated activation of beta-catenin/TCF dependent transcription. Both Gfi1b deficient HSCs and MKs show de-regulation of expression of many sets on Wnt/ß-catenin target genes and Gfi1b and ß-catenin co-occupy the promoters of many common target genes. Finally, activating the Wnt/ß-catenin signaling pathway in Gfi1b deficient HSCs and MKs significantly reduces their expansion, which confirms that Gfi1b is a critical factor controlling the cellularity of HSCs and MKs and exerts this function by regulating the Wnt/ß-catenin pathway in these cells. Overall design: Hematopoietic Stem Cells isolated from Gfi1b flox/flox mice carrying ROSA-Cre or not, were analysed for differential expression by RNA-Seq. A sample of each Gfi1b wild-type and Knock-Out from each model was analyzed.