Cytokines & Cells Online Pathfinder Encyclopaedia
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abbr. AGM region. This region, which extends from the umbilicus to the anterior limb bud of the embryo, has been identified in embryonic mice, humans, and birds. It is part of the para-aortic splanchnopleural mesoderm, an anterior lateral region that later contributes to the future aorta, gonads and mesonephros.
The aorta-gonad-mesonephros region is an important intra-embryonic site of primitive hematopoiesis and serves as the first supportive microenvironment supporting hematopoietic stem cell development. It is thought that the microenvironment of this region plays an important role in the ontogeny hematopoietic stem cells that have the capacity of long-term repopulating bone marrow of lethally irradiated animals (see also: long-term repopulaqting cells). Some stem cells present in the AGM region have been identified as hemangioblasts, which are bipotential stem cells that can differentiate into hematopoietic cells and endothelial cells (Hamaguchi et al, 1999). These cells cannot be identified by morphological criteria but can be identified by their expression of a set of characteristic genes common to both cell types.
Nishikawa et al (2001) have used mouse AGM explant cultures and found that hematopoiesis is enhanced in such cultures by the presence of the combination cytokines (SCF, bFGF, LIF, oncostatin M). These cultures, however, do not allow expansion of hematopoietic stem cells capable of long-term reconstitution of hematopoiesis in irradiated mice (see also: LTRC). Rather, these culture conditions provide a favorable microenvironment for hematogenic angioblasts (see: hemangioblasts) that are precursors of both endothelial and hematopoietic cells. Human and murine cells that can reconstitute irradiated bone marrow have been expanded by Nishikawa et al (2001) in cultures containing the stromal cell line AGM-S3. In this system, maintenance of these cells appears to mediated by a mechanism other than SCF signaling through its receptor (Kit).
Durand et al (2007) have reported that the aorta-gonad-mesonephros expresses the neurotrophic factor beta-NGF, the chemokine MIP-1-gamma (CCL9) and BMP4 (a TGF-beta family member). When these three factors are added to aorta-gonad-mesonephros region explant cultures, enhance the in vivo repopulating ability of AGM hematopoietic stem cells.
See also: Angiogenesis Dictionary section of this encyclopedia for other entries directly bearing on factors and processes involved in the generation of new blood vessels. For other entries pertaining to hematopoiesis see also the Hematology Dictionary section of this encyclopedia.
LAST MODIFIED: March 2008
See REFERENCES for entry aorta-gonad-mesonephros region
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