S862 THE ROLE OF GATA2 IN HSC GENERATION THROUGH ENDOTHELIAL‐TO‐HEMATOPOIETIC TRANSITION.

Abstract

Background:GATA2 is the most frequently mutated gene in childhood AML. These patients have germline mutations in one allele of GATA2 and have a high predisposition for MDS/AML. Also, in mouse, Gata2 is required for embryonic HSC generation and survival and complete deletion of Gata2 is lethal at embryonic day (E)10, while Gata2 haploinsufficiency results in a severe reduction in the formation of HSCs. The first HSCs are formed at E10.5 through a process called endothelial‐to‐hematopoietic transition (EHT) from specialized hemogenic endothelial cells of the dorsal aorta in the aorta‐gonad‐mesonephros (AGM) region.Aims:As all patients suffering from GATA2 haploinsufficiency syndromes have innate GATA2 mutations, our hypothesis is that embryonic haploinsufficiency of GATA2 is responsible for the phenotype of the patients. Therefore, we want to understand how Gata2 haploinsufficiency affects the generation of HSCs through EHT.Methods:We sorted phenotypic HSPCs (CD31+cKit+ cells) from WT and Gata2 +/‐ E11 AGMs and performed transcriptome analysis. Also, with whole‐mount antibody staining performed on the WT and Gata2 +/‐ AGMs, we analysed CD31+cKit+ cell populations.Results:Surprisingly, we found that the hematopoietic transcriptional program is not abrogated in Gata2 +/‐ mouse E11 CD31+cKit+ cells. However, Gata2 +/‐ HSPCs still express the endothelial program indicating that the hematopoietic cells are stuck in the endothelium and cannot complete EHT. We found that Gfi1b is downregulated in Gata2 +/‐ HSPCs. As Gfi1b is known to be required for downregulation of the endothelial program for EHT during primitive hematopoiesis, we hypothesize that Gata2 directly regulates Gfi1b and that this regulation is required for normal EHT.Summary/Conclusion:In conclusion, we showed Gata2 +/‐ HSPCs are transcriptionally different from WT HSPCs. We are currently studying if a specific HSPC subtype can overcome Gata2 haploinsufficiency and will still undergo EHT as this may have implications for the hematopoietic cells that eventually populate the hematopoietic tissues.