Abstract
Despite much work studying ex vivo multipotent stromal cells (MSCs), the identity and characteristics of MSCs in vivo are not well defined. Here, we generated a CD73-EGFP reporter mouse to address these questions and found EGFP+ MSCs in various organs. In vivo, EGFP+ mesenchymal cells were observed in fetal and adult bones at proliferative ossification sites, while in solid organs EGFP+ cells exhibited a perivascular distribution pattern. EGFP+ cells from the bone compartment could be clonally expanded ex vivo from single cells and displayed trilineage differentiation potential. Moreover, in the central bone marrow CD73-EGFP+ specifically labeled sinusoidal endothelial cells, thought to be a critical component of the hematopoietic stem cell niche. Purification and molecular characterization of this CD73-EGFP+ population revealed an endothelial subtype that also displays a mesenchymal signature, highlighting endothelial cell heterogeneity in the marrow. Thus, the CD73-EGFP mouse is a powerful tool for studying MSCs and sinusoidal endothelium.