Blood Induction and Embryonic Formation

Vertebrate blood derives from mesoderm. Blood formation (hematopoiesis) occurs in successive waves. The primitive wave predominantly generates red cells to transiently provide oxygen for the rapidly growing embryo. The definitive wave produces hematopoietic stem cells (HSCs) that ultimately differentiate into all the blood lineages in the adult. Hematopoiesis is tightly regulated by complex interactions between extrinsic and intrinsic factors. Transcription factors play intrinsic roles to define HSC generation and lineage differentiation. The process of hematopoiesis is highly conserved throughout vertebrate evolution. The genetic manipulation of animal models, such as mouse and zebrafish, has identified many essential genes controlling normal and malignant hematopoiesis.