The role of ephrinB2 in hematopoietic stem/progenitor cell differentiation from an arterial hemogenic endothelium

Thesis

During development, hematopoiesis develops in temporally distinct waves in the yolk sac (YS) and embryo proper, culminating in the emergence of definitive hematopoietic stem cells (HSCs) from the hemogenic endothelium (HE) of the dorsal aorta. The close association of this aortic endothelium with definitive hematopoiesis suggests a functional relationship between arteriogenesis and blood development, but this association is not fully understood. To gain insight into this relationship, we have chosen to study the role of the “arterial” marker, EphrinB2 (EfnB2) in hematopoietic specification. EfnB2 is a transmembrane protein critical for the development of the arterial vascular system. We find that EfnB2 is expressed in the VE-Cadh⁺CD41^- HE in Day 2 BL-CFC (blast-colony forming cell) culture and Day 6 EBs (embryoid bodies), and that EfnB2 expression in ES cell differentiation enriches for endothelial cells with greater hemogenic capacity. Knock-down experiments in ES cells showed that EfnB2 is not required for endothelial cell commitment and survival. It is also not required for early hematopoietic commitment and differentiation from EBs or BL-CFCs. However, we find that EfnB2 is required for the maturation of ES cells into CD41⁺/CD45⁺ hematopoietic cells in OP9 co-culture and for definitive hematopoietic colony formation in MethoCult3434 medium. This requirement for EfnB2 expression was confirmed by peptide-mediated blocking of EfnB2 binding to its cognate receptors and by forced expression of a phospho-tyrosine signaling-deficient EfnB2. These results provide evidence for an essential role of endothelial EfnB2 in hematopoiesis.

Authors: Chen, I

• Publication date: 2014
• DOI: 10.5287/ora-vj1vv9e74
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: EphrinB2
• Subjects: Stem cells (clinical sciences)