Temporal and spatial changes in marrow SDF-1 following sublethal radiation. (A) Representative images of radioactive in situ hybridization with SDF-1 antisense probe (red pseudocolor indicates SDF-1 transcripts) on femoral marrow sections from (left to right panels): unirradiated (0 Gy), and days 1, 2, and 3 post-4 Gy TBI. Dotted lines delineate the endosteal region. Images were acquired and processed as described in the “RNA in situ hybridization.” (B) Expression of SDF-1 transcripts by qPCR in flushed marrow cells from unirradiated mice (black) and days 1, 2, and 3 post-4 Gy TBI (green). SDF-1 transcripts increase in the marrow following TBI. (C) Ratio of SDF-1 transcript area in the endosteal region (between 0-100 μm from the endosteal surface within the diaphysis) compared to an immediately adjacent region of the same size (between 100-200 μm from the endosteal surface) for each biologic replicate of unirradiated mice (black), and days 1, 2, and 3 post-4 Gy TBI (green). An endosteal gradient of SDF-1 transcript is apparent at day 2, but is lost at day 3. Error bars represent standard error of the mean of ≥3 independent experiments (n = 3-7 total mice per group). Statistical analyses either comparing irradiated samples to unirradiated control (B) or indicated samples (C) were performed using a 2-tailed Student’s t test. Bar represents 100 μm (A). *P < .02; **P < .007.