Wikipedia
The aorta-gonad-mesonephros (AGM) is a region of embryonic mesoderm that develops during embryonic development from the para-aortic splanchnopleura in chick, mouse and human embryos. It has been suggested that this area, in particular the ventral wall of the dorsal aorta, is one of the primary origins of the definitive haematopoietic stem cell.
The aorta-gonad-mesonephros (AGM) region is an area derived from splanchnopleura mesoderm identified in embryonic humans, mice, and non-mammalian vertebrates such as birds and zebrafish. It contains the dorsal aorta, genital ridges and mesonephros and lies between the notochord and the somatic mesoderm, extending from the umbilicus to the anterior limb bud of the embryo. The AGM region plays an important role in embryonic development, being the first autonomous intra-embryonic site for definitive haematopoiesis. Definitive haematopoiesis produces hematopoietic stem cells that have the capacity to differentiate any blood cell lineage in the adult circulation. Specialised endothelial cells on the dorsal aorta of the AGM region, identified as haemogenic endothelium differentiate into haematopoietic stem cells.