Immature BMSSCs express higher levels of SDF-1 than more mature populations. (A) The dot plot represents dual flow cytometric analysis of single-cell suspensions of ex vivo–expanded BMSSCs, grown under standard culture condition media, based on the cell surface expression of STRO-1 and AP antigens. The different sorted STRO-1/AP subpopulations were isolated by FACS according to the sorting regions R1, R2, R3, and R4. (B) The graph depicts semiquantitative RT-PCR analysis of the relative expression of SDF-1 in respect to GAPDH expression in total RNA prepared from unsorted and FACS-isolated cultured BMSSC populations according to their cell surface expression of STRO-1 and AP. The most immature osteogenic precursor population (STRO-1⁺/AP^-) expressed higher levels than preosteoblasts (STRO-1⁺/AP⁺), followed by more mature osteoblast (STRO-1^-/AP⁺) and osteocyte (STRO-1^-/AP^-) populations. The data represent the mean values ± standard errors of 2 independent experiments, using secondary BMSSC cultures established from 2 different healthy bone marrow donors.