Mesenchymal lineage potentials of aorta-gonad-mesonephros stromal clones.

BACKGROUND AND OBJECTIVES The characterization of stem cell microenvironments throughout ontogeny is of fundamental interest in the field of stem cell biology. Within the adult blood system, hematopoietic stem cells (HSC) are supported in the osteoblastic and endothelial bone marrow microenvironments. During mouse mid-gestation, the first HSC emerge autonomously in the aorta-gonad-mesonephros (AGM) region. However, little is known about this microenvironment. To study the cellular complexity of the AGM hematopoietic microenvironment and its relationship to HSC, we examined the potential of AGM stromal clones to differentiate into several mesenchymal lineages. DESIGN AND METHODS Stromal cell clones from the mid-gestation mouse were cultured in appropriate conditions known to support osteogenic, adipogenic, chondrogenic and endothelial differentiation. Potentials of the stromal cells were scored by morphological examination of the cultures, specific staining and gene expression profile. RESULTS We show that most clones possess uni/bilineage osteogenic, adipogenic and/or endothelial potential. The differentiation potential of the stromal clones appears to relate to their site of origin but not to their ability to support hematopoiesis. Moreover, we show that AGM HSC activity is unaffected by the osteogenic differentiation of UG26.1B6 stromal cells. INTERPRETATION AND CONCLUSIONS These results confirm the existence of mesenchymal stem/progenitor cells in the AGM region and suggest that the AGM hematopoietic microenvironment is highly complex, containing stromal cells with various mesenchymal lineage potentials.