RNA-Seq Analysis of Gfi1b KO Hematopoietic Stem Cells

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.