Fig 5.

PCNA-immunohistochemistry of the femoral diaphysis. (A) At 2 weeks old, many immunoreactive cells (arrowheads) are detected in the osteonal cavity (OC) of incomplete (ICPO) and complete primary osteons (CPO); however, only a few are detected in the periosteum (PeO). (B) At 7 weeks old, the immunoreactive cells (arrowheads) are detected mainly in the ICPO and CPO in the outermost region of the cortical bone (CB). (C) At 3 months old, no immunoreactive cells are detected. (D–F) Double-labeling immunohistochemistry for PCNA (green) and Runx2 (red) shows PCNA-immunoreactive spindle cells (arrow) and cuboidal osteoblasts (arrowhead) express Runx2. CB, cortical bone. Scale bars: 20 μm. (G) The panel shows the PCNA labeling index in the osteonal cavity and osteogenic layer at 2, 4, 7 weeks and 3 months old. Data represent mean ± SD. Significant differences were analyzed by Student's t-test (osteonal cavity vs. osteogenic layer; N.S. not significant, *P < 0.05, **P < 0.01).