(A) Hematopoiesis occurs first in the yolk sac (YS) blood islands and later at the aorta-gonad mesonephros (AGM) region, placenta, and fetal liver (FL). YS blood islands are visualized by LacZ staining of transgenic embryo expression GATA-1- driven LacZ. AGM and FL are stained by LacZ in Runx1-LacZ knockin mice. (Photos courtesy of Y. Fujiwara and T. North.).
(B) Hematopoiesis in each location favors the production of specific blood lineages. Abbreviations: ECs, endothelial cells; RBCs, red blood cells; LTHSC, long-term hematopoietic stem cell; ST-HSC, short-term hematopoietic stem cell; CMP, common myeloid progenitor; CLP, common lymphoid progenitor; MEP, megakaryocyte/erythroid progenitor; GMP, granulocyte/macrophage progenitor.
(C) Developmental timewindows for shifting sites of hematopoiesis.