The transcriptional landscape of hematopoietic stem cell ontogeny

Transcriptome analysis of adult hematopoietic stem cells (HSC) and their progeny has informed our understanding of blood differentiation and leukemogenesis, but a similarly transformative analysis of the embryonic origins of hematopoiesis is lacking. To address this issue, we acquired gene expression profiles of developing HSC purified from over 2500 dissected murine embryos and adult mice, and applied a network biology-based analysis to reconstruct the gene regulatory networks of sequential stages of HSC development. We found that embryonic hematopoietic elements clustered into three distinct transcriptional states characteristic of the definitive yolk sac, HSCs emerging from hemogenic endothelium, and definitive HSCs. We functionally validated several candidate transcriptional regulators of HSC ontogeny by morpholino-mediated knock-down in zebrafish embryos, confirming changes in the expression of HSC markers runx1 and c-myb in the aorta-gonads-mesonephros (AGM), the site of definitive HSC specification. Moreover, we found that HSCs derived from differentiating embryonic stem cells in vitro (ESC-HSC) most closely resemble definitive HSC, yet lack a signature indicative of specification by Notch signaling, which likely accounts for their deficient lymphoid development. Our analysis and accompanying web resource will accelerate the characterization of regulators of HSC ontogeny, facilitate efforts to direct hematopoietic differentiation and cell fate conversion, and serve as a model to study the origins of other adult stem cells.

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McKinney-Freeman S, Cahan P, Li H, Lacadie SA, Huang HT, Curran M, Loewer S, Naveiras O, Kathrein KL, Konantz M, Langdon EM, Lengerke C, Zon LI, Collins JJ, Daley GQ