Immunohistochemical localization of Opn and correlation with CFSE⁺ donor cells in a longitudinal section of a murine femur. (A) Opn expression was highly restricted to the endosteum of the marrow cavity (dotted arrows) and correlated with the localization of 2 CFSE⁺ donor LSK cells (solid arrows). (B) Isotype control for Opn expression with 1 CFSE⁺ donor LSK cell (arrows). Counterstained with DAPI (4′, 6-diamino-2-phenylindole). Bars = 30 μm.