Abstract:

BACKGROUND: The process consists of primitive hematopoiesis and definitive hematopoiesis in mammalian. It has been approved that primitive hematopoiesis emergence from yolk sac. However, the original sites of definitive hematopoiesis have been a controversial issue in the field of hematopoiesis.
OBJECTIVE: To explore embryonic origins of definitive hematopoiesis.
METHODS: The first author retrieved PubMed database for articles published from January 2000 to March 2010. The key words were “hematopoietic stem cell, hematopoiesis, yolk sac, aorta-gonad-mesonephros (AGM) region”. Simultaneously, China National Knowledge Infrastructure database was also retrieved for relevant articles published from January 2000 to March 2010. The key words were “hematopoietic stem cell, hematopoiesis, yolk sac, AGM region”. A total of 682 articles were obtained, and the literature of repetitive content was excluded. Finally, 42 articles were included.
RESULTS AND CONCLUSION: Traditional opinions thought the definitive hematopoiesis origins from yolk sac of extra-embryo. However, a series of studies showed that the definitive hematopoiesis come from AGM region of intra-embryo first. The placenta is a newly discovered site which may generate hematopoietic cells during period from AGM region to fetal liver. In the yolk sac and PSp/AGM region, the progenitor cell of hematopoietic cell presents two different models. The hematopoietic cells and endothelial cells are normally derived from the hemangioblast in the yolk sac. However, in the AGM region, hematopoietic stem cells come from haemogenic endothelium of the dorsal aorta ventral wall. In addition, hematopoitic development process is regulated by several signal pathways.