Novel roles for Notch, Wnt and Hedgehog in hematopoesis derived from human pluripotent stem cells.

Human pluripotent stem cells (PSCs) derived from a number of different sources, including reprogrammed adult somatic cells, provide a powerful cellular system to study signaling pathways implicated in cell fate decisions, and generate new sources of cells for regenerative medicine. To realize this potential, it is essential to control the direction and efficiency of human PSC differentiation. Although Notch, Wnt and Hedgehog (HH) signaling pathways have been implicated in the self-renewal/proliferation of hematopoietic stem/progenitor cells, both in vitro and in vivo, their roles in differentiation processes remain poorly explored. This review describes the role(s) of these pathways in the adult and embryonic hematopoietic system of mice and humans, with a particular emphasis on our recent studies on the hematopoietic development of human embryonic stem cells (hESCs). Understanding the individual and collective contributions of Notch, Wnt and HH signaling to the initial development of hematopoiesis is critical for achieving successful ex vivo expansion and differentiation of hematopoietic stem cells (HSCs) from human PSCs that will retain bona fide function comparable to adult-derived HSCs.