MOUSE EMBRYONIC HEMATOPOIESIS

The hematopoietic system of vertebrates is derived from the mesodermal germ layer in early embryogenesis. Various animal models have been us ed for the study of hematopoiesis, from early stages in the visceral y olk sac or its analog, to the later stages where hematopoiesis is obse rved in intraembryonic areas surrounding the aorta, genital ridge and pro/mesonephros. Using the mouse as a model, we describe what is known about mammalian embryonic hematopoiesis and put it in the context of hematopoietic cell formation in avian, amphibian and fish embryos. Evo lutionary comparisons and recent experimental evidence show that there are two embryonic sites of developing hematopoietic activity is the m ouse before fetal liver hematopoiesis and suggest that, during ontogen y, two successive waves of hematopoietic activity may contribute to th e blood system of the adult.