Unknown,Transcriptomics,Genomics,Proteomics

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The transcriptional landscape of hematopoietic stem cell ontogeny

ABSTRACT: 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. Hematopoietic stem cells and their precursors were isolated from mouse embryos and distinct stages and sites during development, purified by fluorescence activated cell sorting, and gene expression profiled on Affymetrix arrays. We also profiled HSCs and their precurors derived by in vitro differentitation of embryonic stem cells [expression data from GSE16925 and GSE14012 was used for mESCs, available at http://hsc.hms.harvard.edu/].

ORGANISM(S): Mus musculus

SUBMITTER: Patrick Cahan

PROVIDER: E-GEOD-37000 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:The cellular ontogeny of hematopoietic stem cells (HSCs) remains poorly understood because their isolation from and their identification in early developing small embryos are difficult. We attempted to dissect early developmental stages of HSCs using an in vitro mouse embryonic stem cell (ESC) differentiation system combined with inducible HOXB4 expression. Here we report the identification of pre-HSCs and an embryonic type of HSCs (embryonic HSCs) as intermediate cells between ESCs and HSCs. Both pre-HSCs and embryonic HSCs were isolated by their c-Kit+CD41+CD45- phenotype. Pre-HSCs did not engraft in irradiated adult mice. After co-culture with OP9 stromal cells and conditional expression of HOXB4, pre-HSCs gave rise to embryonic HSCs capable of engraftment and long-term reconstitution in irradiated adult mice. Blast colony assays revealed that most hemangioblast activity was detected apart from the pre-HSC population, implying the early divergence of pre-HSCs from hemangioblasts. Gene expression profiling suggests that a particular set of transcripts closely associated with adult HSCs is involved in the transition of pre-HSC to embryonic HSCs. Experimental strategy consisted of EB formation, co-culture with OP9 cells, and functional assays. iHOXB4 ESCs were allowed to differentiate spontaneously into EBs for 6 days without HOXB4 expression. We decided to fractionate EB6 cells mainly because by day 6 of culture the number of multipotent progenitors reaches a plateau and several surface markers become detectable. CD41 is known as a marker for the initiation of definitive hematopoiesis. CD41 appeared in a significant proportion of EB cells on day 6 of culture. Induced HOXB4 expression during EB formation did not affect the generation of colony forming cells and repopulating cells in the OP9 and iHOXB4 system or the appearance of surface markers in EB cells. EB6 cells were analyzed and sorted by flow cytometry. Sorted EB6 cells were co-cultured with OP9 cells for various days under HOXB4-on or -off conditions. The minimal requirement of the co-culture period appeared to be only 4 days, which is much shorter than previously thought. After a second analysis and fractionation by flow cytometry, cells were subjected to in vivo repopulating assays under HOXB4-on or -off conditions.

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The transcriptional landscape of hematopoietic stem cell ontogeny

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