The origin of the first blood cell

In mouse development, the first blood cell activity appears in the yolk sac at E7.5(embryonic day 7.5). However,this blood cell activity (primitive hematopoiesis)is restricted to red blood cells (primitive erythrocytes). The pluripotent hematopoietic stem cells which are able to differentiate into all kinds of peripheral blood cell (including lymphocytes)are initially identified in the AGM (aorta-gonad -mesonephros)region at E10.5(definitive hematopoiesis).In vitro studies suggest the presence of hemangioblasts,which can differentiate into both blood and endothelial cells. However, until recently, direct evidence of the presence of these hemangioblasts in vivo was not available, and the precise mechanism of the differentiation of hematopoietic cells from hemangioblasts was totally unknown. Recent progress in this field of study indicates that the first hematopoietic stem cells are generated through the hemogenic endothelium stage and are anatomically derived from the hemogenic endothelium in the dorsal aorta floor of the AGM region.7KJ00007510662PReview articledepartmental bulletin pape