2 models of embryonic and adult blood formation: Figure by Ueno and Weissman
Posted by attilacsordas on May 10, 2007
If you have previously thought (in your spare time) that the conventional wisdom concerning blood formation is that the yolk sac’s embryonic blood-forming cells serve only the embryo, while the source of adult blood-forming stem cells is the region called aorta-gonad-mesonephros (AGM), it’s time to think it again due the elegant experiments of Samokhalov et al.: Cell tracing shows the contribution of the yolk sac to adult haematopoiesis Nature 446, 1056-1061 (26 April 2007)
Legend: a, The ‘separate’ model. Embryonic blood-forming cells, generated in a region called the ‘primitive streak’, proliferate in the yolk sac, migrate to the embryo proper, but eventually die out. The adult blood-forming cells, whose origin in the early-stage embryo is unknown, are separately generated in the aorta–gonad–mesonephros (AGM) region and later seed the adult bone marrow. b, The ‘common’ model. Adult blood-forming cells in the AGM regions at least partly originate from Runx1-positive progenitors in the yolk sac. Black and blue arrows show pathways of embryonic and adult blood-forming cells, respectively; bold blue arrow is the pathway described by Samokhvalov and colleagues1. Regions of cells at the primitive-streak stage: notochord (blue); somites (yellow); heart and cranial mesoderm (green); extraembryonic mesoderm (pink).
Source: Ueno-Weissman: Blood lines from embryo to adult Nature 446, 996-997 (26 April 2007)
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