Site-specific differentiation of human eGFP-MSCs in the murine BM compartment. The engraftment and differentiation of transplanted eGFP-MSCs were determined by eGFP fluorescence and immunofluorescence staining for lineage-specific antigens. eGFP-cells were located on the abluminal side of endothelial cells (A) or lined the sinus wall (D). Those vasculature-associated eGFP-cells express α-SM actin (red in panels B and E, and merged in panels C and F). (A-F) eYFP-cells reside next to eGFP-cells. (G) An elongated cell in the endosteal hematopoietic cord interacts with eYFP-cells. eGFP-reticular cells (H) with ALP⁺ (red) cytoplasmic extensions (I), which haphazardly radiate into the hematopoietic parenchyma, interact with eYFP-cells. An eGFP-cell in the bone exhibits the morphology of authentic osteocytes with filopodial processes surrounded by bone matrix and extending into the canaliculi (J), and expresses osteocalcin (red, K-L). A bone-lining eGFP-cell (M) expresses N-cadherin (red, N-O). N-cadherin is localized to the cell surface. Vasculature-associated eGFP-cells (P,S) express CD31 (red, Q-R) and CD34 (red, T-U). Interactions between eGFP-cells (arrows) and eYFP-cells (arrowheads in A-I) are seen in the specimens from mice in which eGFP-MSCs and eYFP-CBCD34 were cotransplanted. All bars represent 10 μm.