Hematopoietic stem cells (HSCs) are the therapeutic component of bone marrow transplants, but finding immune-compatible donors limits treatment availability and efficacy. Recapitulation of endogenous specification during development is a promising approach to directing HSC specification in vitro, but current protocols are not capable of generating authentic HSCs with high efficiency. Across phyla, HSCs arise from hemogenic endothelium in the ventral floor of the dorsal aorta concurrent with arteriovenous specification and intersegmental vessel (ISV) sprouting, processes regulated by Notch and Wnt. We hypothesized that coordination of HSC specification with vessel patterning might involve modulatory regulatory factors such as R-spondin 1 (Rspo1), an extracellular protein that enhances β-catenin-dependent Wnt signaling and has previously been shown to regulate ISV patterning. We find that Rspo1 is required for HSC specification through control of parallel signaling pathways controlling HSC specification: Wnt16/DeltaC/DeltaD and Vegfa/Tgfβ1. Our results define Rspo1 as a key upstream regulator of two crucial pathways necessary for HSC specification.
The authors declare no competing or financial interests.
J.R.G. and W.K.C.: Conception and design of research; interpretation of results of experiments; editing and revision of manuscript. J.R.G.: Performed experiments and analyzed data; prepared figures and drafted manuscript. W.K.C.: approved final version of manuscript.
This work was supported by the National Heart, Lung, and Blood Institute (grant R00HL097150 to W.K.C.) and March of Dimes Foundation Basil O'Connor Starter Scholar Research Award (#5-FY14-42 to W.K.C.). Deposited in PMC for release after 12 months.
Supplementary information available online at http://dev.biologists.org/lookup/doi/10.1242/dev.139956.supplemental
- Received May 17, 2016.
- Accepted December 22, 2016.