Figure 5.

An increased frequency of tumor formation in (Col2A1-Gli2); Ift88+/− mice is associated with changes in chondrocyte proliferation and apoptosis during growth plate development, Developing limbs from early postnatal mice were compared for changes in proliferation (PCNA) and apoptosis (TUNEL). (a) Growth plate chondrocytes from the distal femur show an increase in proliferation in Col2A1-Gli2 and Ift88+/− limbs compared to WT littermates, which is further increased in Col2A1-Gli2; Ift88+/− limbs. The section shows the junction of the resting and proliferating zones of the growth plate ‘P' labels a positively stained cells for PCNA, and ‘N' labels a cell that has not stained (negative for staining). Graphically the resting and proliferating zones were analyzed separately, and the percentage of PCNA stained cells is shown as the mean and 95% confidence interval for each zone. (b) At the cartilage-bone interface, terminal hypertrophic chondrocytes undergo programmed cell death that is identified by TUNEL-positive cells. There was no change in the number of TUNEL-positive cells detected in Col2A1-Gli2 and Ift88+/− limbs compared to WT littermates, however, WT compared with Col2A1-Gli2; Ift88+/− limbs show a significant reduction in apoptosis. (c) Col2A1-Gli2; Ift88+/− mice show a significant increase in the length of their proliferative zone compared with WT mice. Hypertrophic zone lengths were reduced in Col2A1-Gli2 and Ift88+/− limbs compared with WT littermates, but no further differences were observed in double transgenic Col2A1-Gli2; Ift88+/−. All error bars represent 95% confidence intervals, with the asterisk indicating a statistical significance of P<0.05.