Highlights d Single-cell-omics demonstrate megakaryocyte-biased hematopoiesis in myelofibrosis (MF) d Megakaryocyte progenitors (MkPs) show high expression of a fibrosis signature in MF d MkPs are heterogeneous in MF with aberrant metabolic and inflammatory signatures d Targeting aberrant surface G6B expression may selectively ablate the MF clone

Summary Human hematopoiesis is a dynamic process that starts in utero 18–21 days post-conception. Understanding the site- and stage-specific variation in hematopoiesis is important if we are to understand the origin of hematological disorders, many of which occur at specific points in the human lifespan. To unravel how the hematopoietic stem/progenitor cell (HSPC) compartment changes during human ontogeny and the underlying gene regulatory mechanisms, we compare 57,489 HSPCs from 5 different tissues spanning 4 developmental stages through the human lifetime. Single-cell transcriptomic analysis identifies significant site- and developmental stage-specific transitions in cellular architecture and gene regulatory networks. Hematopoietic stem cells show progression from cycling to quiescence and increased inflammatory signaling during ontogeny. We demonstrate the utility of this dataset for understanding aberrant hematopoiesis through comparison to two cancers that present at distinct time points in postnatal life—juvenile myelomonocytic leukemia, a childhood cancer, and myelofibrosis, which classically presents in older adults.