Fig. 3. Impaired, but resumable, proliferation of the center-located chondrocytes within Pten^Co/Co;Col2a1-Cre growth plates. (A,B,D-L) BrdU labeling was performed on sections of control (A,D,G,J) or mutant (B,E,H,K) growth plates from P3 (A,B), P5 (D,E), P7 (G,H) and P38 (J,K) mice. (C) The percentage of BrdU-positive chondrocytes in the proliferating zone of P3 control (A) or mutant (B) growth plates was determined in consecutive columns, as delineated by the grids, and plotted. Mean ±s.d. of six sections from three mice of each genotype. ^*P<0.01. (E,H) The central region of mutant growth plate cartilage lost the ability to proliferate and gradually formed a neoplastic core. (F,I,L) Higher magnification of the boxed regions in E,H,K. Note the small number of BrdU-positive chondrocytes within the lower portion of the core (F,I, yellow arrowheads) and within the cartilaginous nodule (L, black arrowhead). Some balloon-like chondrocytes within the lower portion of the core also started to undergo hypertrophy (I, red arrowhead). Hours of BrdU labeling: A,B, 2; D,E, 5; G,H, 6; J,K, 2.5. Scale bar: 275 µm in A,B,J,K; 340 µm in D,E; 400 µm in G,H.