Stem cell niche expands after marrow radioablation. (A) Immunohistochemical staining of TBI versus control mice reveals an increase in 2 markers of the HSC niche: osteopontin (left) and N-cadherin (right), particularly in the metaphysis (). Scale bar (third column) represents 50 μm; scale bar (fourth column) represents 10 μm. (B) Semiquantitative RT-PCR analysis showing increased expression of osteopontin and N-cadherin in the TBI group. The negative control (Neg, without template) is shown in the middle lane. (C) Comparison of osteopontin and N-cadherin expression levels in irradiated versus nonirradiated control mice. Transcript band intensities are calculated in relation with the GAPDH levels and reported as mean percentages (± SD) of 6 measurements per group. Significant increases of osteopontin and N-cadherin are detected after irradiation (P = .03 and P < .001, respectively). (D) Double staining of TBI mice with anti-BrdU (black) and anti–N-cadherin (red) antibodies. Scale bar represents 20 μm. The typical nuclear pattern of the BrdU labeling and simultaneous N-cadherin expression () demonstrates the presence of proliferating N-cadherin–positive osteoblasts after TBI. (E) N-cadherin–positive osteoblasts (OB) in the epiphysis, metaphysis, diaphysis, and total marrow space at 48 hours after irradiation. Mean (± SD) numbers of cells per 400× microscopic field (n = 420 fields/group) are shown.