Function
The most significant function of the aorta gonad mesonephros region is its role in definitive haematopoiesis. Definitive haematopoiesis is the second wave of embryonic haematopoiesis and give rise to all hematopoietic stem cells in the adult hematopoietic system. The aorta gonad mesonephros region has been shown to harbour multipotent hematopoietic colony-forming unit-spleen (CFU-S) progenitor cells and pluripotential long-term repopulating hematopoietic stem cells (LTR-HSCs). In contrast to the yolk sac, the extra-embryonic haematopoietic site, the number of CFU-S was much greater in the aorta gonad mesonephros region. LTR-HSC activity was also found in the aorta gonad mesonephros region at a slightly earlier time than in the yolk sac and foetal liver. Thus indicating the potency of definitive haematopoiesis from this region. Furthermore, isolated organ cultures of the AGM from mice embryos can autonomously initiate hematopoietic stem cell activity, without influence from the yolk sac or liver. At 10 days post coitus (d.p.c.) the aorta gonad mesonephros region was able to initiate and expand definitive haematopoietic stem cell activity, whereas no haematopoietic activity was seen in the yolk sac until 11 d.p.c. This is the same case in human embryos, where they are first detected at day 27 in the aorta gonad mesonephros region, expand rapidly at day 35, then disappear at day 40. This “disappearance” correlates to the migration of these hematopoietic stem cells to the foetal liver, where it becomes the subsequent site of haematopoiesis.
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