aorta-gonad-mesonephros

The aorta-gonad-mesonephros (AGM) is a transient region in the developing embryo composed of the dorsal aorta, the developing gonads (genital ridges), and the embryonic kidney (mesonephros). Located in the embryonic mesoderm, this structure is recognized as the primary site for the de novo generation of definitive hematopoietic stem cells (HSCs) during embryogenesis.

The AGM region is located in the trunk of the developing embryo, within the embryonic mesoderm. It corresponds to the region of the future abdomen, where the dorsal aorta runs alongside the developing gonads and mesonephric ridges. In human embryos, AGM-type hematopoiesis is active around the 4th to 6th week of development.

The AGM is involved in generating the definitive hematopoietic stem cells that will ultimately populate the fetal liver, spleen, and bone marrow to sustain lifelong hematopoiesis. Clusters of hematopoietic cells bud from the floor of the dorsal aorta within this region—a process known as aortic hematopoiesis—establishing the HSC pool for the organism.

Disruptions to the molecular signals governing AGM hematopoiesis—such as mutations in transcription factors like RUNX1 or defects in Notch signaling—may be associated with failure to establish a normal HSC pool. Research on AGM hematopoiesis is relevant to understanding hematological malignancies that originate from defects in early stem cell specification.

The AGM region is examined primarily in embryonic specimens using histological sections stained with hematoxylin and eosin, which reveal hematopoietic cell clusters in the aortic floor. Immunohistochemistry with markers such as CD34, CD31, and c-Kit identifies hematopoietic progenitors. In vitro colony-forming assays and transplantation experiments assess the hematopoietic activity of AGM-derived cells.