3200 - Identification of Extrinsic Regulators of Hematopoietic Stem Cell Formation in the Embryonic Aorta Microenvironment by Tomo-Sequencing

Abstract

In all vertebrates, hematopoietic stem cell (HSC) emergence mainly occurs in the dorsal aorta of the embryo. It is now well accepted that HSCs arise from specialized endothelial cells of the aorta, named hemogenic endothelial cells, via an endothelial-to-hematopoietic transition (EHT) process. This process is tightly controlled in time and space by regulatory signals emitted by the surrounding microenvironment in all species (zebrafish, chicken, mouse and human). Nevertheless, a complete picture of the genes expressed in the surrounding tissues of the aorta that are involved during the highly regulated HSC emergence is still missing. o decipher the genes that are (differentially) expressed in specific regions of the aorta during HSC generation, we used a genome-wide RNA tomography (tomo-seq) approach (Junker 2014). Tomo-seq was applied on whole aortas (subdissected with the surrounding mesenchyme) and thick transversal embryo slices from zebrafish, chicken, mouse and human embryos. Using this approach, we provided a complete resource of the gene expression profiles around the dorsal aorta in all species. We then identified a series of genes specifically expressed either in the ventral or dorsal side of the aorta and validated their expression pattern using in situ hybridization and/or immunostainings. We further demonstrated their functional implication in HSC emergence and hematopoietic production by knocking-down these genes in zebrafish embryos. Finally, our comparative data analysis in between species unravelled conserved genes and molecular pathways involved in the regulation of the first HSC generated during embryonic development.