3137 – IKBA IS REQUIRED FOR HSC GENERATION

Abstract

Despite long-lasting efforts to generate transplantable Haematopoietic Stem Cells (HSCs) from Embryonic Stem Cells and more recently, to reprogram skin/endothelial cells into HSCs, the results have been limited. The main pitfall is still our only limited understanding of HSC generation during development. The first HSCs trans differentiate from endothelial cells in the ventral part of the Dorsal Aorta (vDA). Here, the HSCs are organized as Intra-Aortic-Haematopoietic Cluster (IAHC) in the region where the aorta, gonads and mesonephros (AGM) meet and express haematopoietic marker c-KIT, CD41 and CD45 and endothelial markers CD31 and CDH5. Next to key transcription factors, cytokines and inflammatory signals contribute to the generation of these IAHCs. Here we present data, that loss of Ikba, a member of the NfkB signalling family, leads to not only alterations of the blood lineages in the adult bone marrow as previously described, but negatively impacts the frequency of Long term HSC (LT-HSC, LSKCD48-CD150+). Through analysis of the E14.5 fetal liver with FACS and transplantation assays, demonstrate a dramatic loss of this population. RNA sequencing of sorted LT-HSC population from wild type or Ikba KO embryos was performed to investigate the molecular impact of this loss. Furthermore, we traced the origin of this defect to a cell population within the E11.5 vDA and show an altered notch signaling as a cause for this specific loss of LT-HSCs.