Fig. 2. Characterization of BMSSCs in vivo. (A) Light microscopic examination of cytospins representing freshly sorted STRO-1^BRIGHT/VCAM-1⁺ marrow cells (1000x) counterstained with heamatoxylin. (B) Transmission electron micrograph depicting the ultrastructure of freshly sorted STRO-1^BRIGHT/VCAM-1⁺ cells (15000x). Immunohistochemical staining of cytospin preparations of the sorted STRO-1^BRIGHT/VCAM-1⁺ cells (1000x) with collagen type I (C) and -SMA (D). (E) Dual-color flow cytometric analysis of Ki67 (FITC) expression by STRO-1⁺ (PE) marrow cells isolated by MACS. The majority of the STRO-1^BRIGHT marrow cells lack detectable binding of Ki67 relative to that of the isotype-matched control antibody, indicated by the vertical quad-stat marker. (F) Telomerase activity in different sorted cell populations was examined using a modified TRAP assay. TRAP products derived from CHAPS extracts of non-denatured (-) and denatured (+) total BM (lanes 1), STRO-1^BRIGHT/VCAM-1⁺ cells sorted fraction (lanes 2) and CD34⁺-sorted BM cells (lanes 3). TRAP products were resolved on a 12% polyacrylamide gel, stained with SYBR green fluorescent dye, and visualised using a fluorescence scanning system. (G) A typical light microscopic view of a single purified STRO-1^BRIGHT/VCAM-1⁺ cell, allowed to adhere to fibronectin-coated culture plates (400x). (H) A representative example of a day 14 CFU-F colony stained with toluidine blue is shown (200x). (I) Immunohistochemical staining showing all the cells that comprise the CFU-F colony express collagen type I (200x).