Fig. 7. Different impacts of the absence of Mpl signaling during establishment of definitive hematopoiesis in the mouse embryo. The anatomical locations involved in the generation of the pool of HSCs are shown, together with the timing of their activity on a timescale of embryonic days. AGM and placenta are the sites of production of the first HSCs (Emergence). These cells (red) migrate to the FL, where they mature further and expand (Maturation/expansion). The FL is also colonized by HSCs coming from the YS (yellow) and placenta (purple). Ultimately, HSCs establish steady-state levels in the bone marrow, where balance between self-renewal, quiescence and differentiation is tightly regulated. The absence of Mpl leads to a delayed and defective production of HSCs by the AGM region, and to a defect in amplification and self-renewal/survival of HSCs in the FL, which in turn results in the HSC defect described for the adult bone marrow.