Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.07.17.208678v1?rss=1 Authors: Blokzijl-Franke, S., Ponsioen, B., Schulte-Merker, S., Herbomel, P., Kissa, K., Choorapoikayil, S., den Hertog, J. Abstract: Hematopoietic Stem and Progenitor Cells (HSPCs) are multipotent cells giving rise to all blood lineages during life. HSPCs emerge from the ventral wall of the dorsal aorta (VDA) during a specific timespan in embryonic development through endothelial hematopoietic transition (EHT). We investigated the ontogeny of HSPCs in mutant zebrafish embryos lacking functional pten, an important tumor suppressor with a central role in cell signaling. Through in vivo live imaging, we discovered that in pten mutant embryos a proportion of the HSPCs died upon emergence from the VDA, an effect rescued by inhibition of phosphatidylinositol-3 kinase (PI3K). Surprisingly, inhibition of PI3K in wild type embryos also induced HSPC death. Surviving HSPCs colonized the caudal hematopoietic tissue (CHT) normally and committed to all blood lineages. Single cell RNA sequencing indicated that inhibition of PI3K enhanced survival of multi-potent progenitors, whereas the number of HSPCs with more stem-like properties was reduced. At the end of the definitive wave, loss of Pten caused a shift to more restricted progenitors at the expense of HSPCs. We conclude that PI3K signaling tightly controls HSPCs survival and both up- and downregulation of PI3K signaling reduces stemness of HSPCs. 2 Key pointsO_LILoss of Pten and inhibition of PI3K induced apoptosis of hematopoietic stem/progenitor cells upon endothelial to hematopoietic transition C_LIO_LISurviving hematopoietic stem/progenitor cells committed to all blood lineages but displayed reduced stemness C_LI Copy rights belong to original authors. Visit the link for more info