Chapter category: Stem Cells
Hematopoiesis in Fetal Liver
Chapter authors:
Masaki Takeuchi and Atsushi Miyajima
Hematopoiesis is a complex cellular process to generate a huge number of mature blood cells. In the steady state condition, hematopoiesis in the adult takes place in the bone marrow (BM) microenvironment, where a rare population of slowly cycling pluripotent hematopoietic stem cells (HSCs) is programmed to self renew or to differentiate into lymphoid or myeloid progenitors. HSCs produce more than one billion blood cells each day throughout life. This process occurs in a specialized environment in BM, where HSCs are compartmentalized and maintained in certain niches by adhesive interactions with other cells and the extracellular matrix. During the development, hematopoiesis takes place in several distinct tissues1,2,3 (Fig. 1). In mammals, initial hematopoietic activity known as primitive hematopoiesis appears in the blood island of the yolk sac (YS) where nucleated primitive erythrocytes are generated. Adult-type definitive HSCs emerge in the aorta-gonad-mesonephros (AGM) region and rapidly shift to the fetal liver (FL) where the massive production of various hematopoietic cells occurs. Along with the development of the hematopoietic system, liver acquires the characteristics of the metabolic organ. Then, hematopoiesis shifts to BM and spleen, and the liver becomes the hub of metabolism. Therefore, FL is the major, but transient, hematopoietic organ during the embryonic period.
