Signaling axis involving Hedgehog, Notch, and Scl promotes the embryonic endothelial-to-hematopoietic transition

Abstract

During development, the hematopoietic lineage transits through hemogenic endothelium, but the signaling pathways effecting this transition are incompletely characterized. Although the Hedgehog (Hh) pathway is hypothesized to play a role in patterning blood formation, early embryonic lethality of mice lacking Hh signaling precludes such analysis. To determine a role for Hh signaling in patterning of hemogenic endothelium, we assessed the effect of altered Hh signaling in differentiating mouse ES cells, cultured mouse embryos, and developing zebrafish embryos. In differentiating mouse ES cells and mouse yolk sac cultures, addition of Indian Hh ligand increased hematopoietic progenitors, whereas chemical inhibition of Hh signaling reduced hematopoietic progenitors without affecting primitive streak mesoderm formation. In the setting of Hh inhibition, induction of either Notch signaling or overexpression of Stem cell leukemia (Scl)/T-cell acute lymphocytic leukemia protein 1 rescued hemogenic vascular-endothelial cadherin + cells and hematopoietic progenitor formation. Together, our results reveal that Scl overexpression is sufficient to rescue the developmental defects caused by blocking the Hh and Notch pathways, and inform our understanding of the embryonic endothelial-to-hematopoietic transition.

Transmembrane protein 88: a Wnt regulatory protein that specifies cardiomyocyte development

“…6A). In addition to upregulation of HHEX (a hemato-endothelial specific homeobox gene) and OTX1 (a homeobox gene involved in hematopoiesis and neural development), we found that SCL (TAL1), encoding a master transcription factor that drives hemato-endothelial specification and represses cardiomyogenesis (Gering et al, 1998;Van Handel et al, 2012;Kim et al, 2013), was significantly increased in TMEM88 KD cohorts. SOX17, also greater than twofold upregulated in TMEM88 KD cells, has recently been shown to be expressed in hemogenic endothelium and emerging hematopoietic stem cells (HSCs) and is functionally required for HSC development (Clarke et al, 2013).…”

“…Development 140 (18) Bioinformatics analysis of gene ontology show that gene clusters greater than twofold upregulated in the TMEM88 KD cells included the Notch signaling pathway (Kim et al, 2013), EGF signaling (Doan et al, 2013), regulation of cell proliferation, mesenchymal and mesodermal developmental, and, most interestingly, genes involved in hematopoiesis and blood vessel development (supplementary material Table S6). The endothelial potential of these cells was validated by qPCR of specific genes involved in development of hemato-endothelial lineages (Fig.…”

Flow-induced protein kinase A–CREB pathway acts via BMP signaling to promote HSC emergence

“…3 H). However, when we treated VEcadherin  cells, which includes CD41 + /CD45 + hematopoietic precursors (North et al, 2002;Kim et al, 2013), the treatment had no effect, suggesting that the effect is specific to VE-cadherin + cells (Fig. 3 I).…”

“…CFU assays. Cells were plated into 1.5-2 ml of methylcellulose media containing interleukin-3 (IL-3), IL-6, erythropoietin (Epo), and SCF (M3434; StemCell Technologies) as described (Kim et al, 2013 Transplantation and peripheral blood analysis. B6.SJL-Ptprca mice were used at 6-10 wk of age.…”

Adenosine signaling promotes hematopoietic stem and progenitor cell emergence

“…We first used an mESC hematopoietic differentiation system, an accessible in vitro model which recapitulates mouse embryonic hematopoiesis (Kim et al, 2013). In this model, mESCs are aggregated into embryoid bodies (EBs) and differentiated into primitive streak-like mesoderm on day 2, hemangioblasts on day 3.25, and hematopoietic precursors after day 5.…”