Discrete Notch signaling requirements in the specification of hematopoietic stem cells

Abstract

Hematopoietic stem cells (HSCs) require multiple molecular inputs for proper specification, including activity of the Notch signaling pathway. A requirement for the Notch1 and dispensability of the Notch2 receptor has been demonstrated in mice, but the role of the remaining Notch receptors has not been investigated. Here, we demonstrate that three of the four Notch receptors are independently required for the specification of HSCs in the zebrafish. The orthologues of the murine Notch1 receptor, Notch1a and Notch1b, are each required intrinsically to fate HSCs, just prior to their emergence from aortic hemogenic endothelium. By contrast, the Notch3 receptor is required earlier within the developing somite to regulate HSC emergence in a non-cell-autonomous manner. Epistatic analyses demonstrate that Notch3 function lies downstream of Wnt16, which is required for HSC specification through its regulation of two Notch ligands, dlc and dld. Collectively, these findings demonstrate for the first time that multiple Notch signaling inputs are required to specify HSCs and that Notch3 performs a novel role within the somite to regulate the neighboring precursors of hemogenic endothelium.

Osteopontin attenuates aging‐associated phenotypes of hematopoietic stem cells

“…It was also previously reported that a decrease in OPN‐positive cells in the endosteal niche of diabetic mice correlates with decreased expression levels of N‐cadherin and β‐catenin on LT‐HSCs (Chiba et al , 2013). Upon aging, a switch in Wnt‐signaling in aged HSCs occurs (Roozen et al , 2012; Florian et al , 2013; Kim et al , 2014) which thus raises the possibility that the reduction in stromal OPN upon aging might likely contribute to or at least further enhance aging‐related Wnt pathway dysregulation. Analysis of the cytokine/chemokine composition of the BM extracellular fluid upon aging confirmed a previously published increase in the pro‐inflammatory protein RANTES in BM upon aging (Fig EV1E).…”

Gata2b is a restricted early regulator of hemogenic endothelium in the zebrafish embryo

“…Notch signaling regulates HSC formation through both direct and indirect mechanisms (Clements et al, 2011;Hadland et al, 2004;Kim et al, 2014;Kobayashi et al, 2014). Our data demonstrate that Notch signaling is required for the expression of gata2b in hemogenic endothelium.…”

“…Both cell-autonomous and non-cell-autonomous Notch signaling is required for the formation of vertebrate HSCs (Hadland et al, 2004;Kim et al, 2014). Notch signaling is required for both arterial specification and HSC formation from arterial vasculature.…”

“…Gata2 is a direct Notch target in the mouse DA (Robert-Moreno et al, 2005) and is regulated by hematopoietic, rather than arterial, Notch signaling (Robert-Moreno et al, 2008). Somitic Wnt16 is required upstream of both somite-intrinsic and somite-to-PLM Notch signaling without affecting arterial specification (Clements et al, 2011;Kim et al, 2014;Kobayashi et al, 2014), demonstrating that the Notch requirements of arterial and HSC development are separable in zebrafish. Surprisingly, gata2a expression in the aortic endothelium is unaffected by knockdown of wnt16 (Clements et al, 2011), which led us to investigate whether Notch signaling is required for the expression of gata2b in hemogenic endothelium.…”

“…HSCs emerge from ventral endothelium of the DA (Bertrand et al, 2010;Boisset et al, 2010;Chen et al, 2009;Kissa and Herbomel, 2010;Lam et al, 2010;Taoudi and Medvinsky, 2007). Several signaling pathways, including Hedgehog, VEGF and multiple Notch inputs, are important for the formation of hemogenic endothelium upstream of runx1 expression (Gering and Patient, 2005;Kim et al, 2014). Owing to a paucity of markers for the early detection of hematopoietic specification within endothelium, we lack a full understanding of how these cues drive the establishment of HSC fate.…”