Fig. 5. Abnormal cellularity and Col II properties in Pten^Co/Co;Col2a1-Cre growth plates. (A,B) Immunohistochemistry (IHC) for type II collagen (Col II) proteins performed on mouse P5 proximal humeral growth plate sections. The neoplastic core was clearly distinguishable by its abnormal cellularity and Col II properties (B). (C-F) Electron microscopy images of chondrocytes and surrounding matrix from resting zone (C) and proliferating zone (E) control growth plate, or from the periphery (D) and central region (F) of the core. The insets show higher magnification views from positions indicated in A or B. The ER of the abnormal cells was extremely distended and fragmented (D,F, asterisks) compared with the normal ER (C,E). Note the premature `string-bead' fibrils implanted inside the deformed ER (F, red arrowhead), which were similar to those surrounding the resting chondrocytes (C, red arrowhead). (G-J) IHC for Col II proteins of wild-type (G,I) and mutant (H,J) chondrocytes cultured under normoxic (G,H) or hypoxic (I,J) conditions. Note that Pten mutant chondrocytes were detached from each other and were swollen by pools of Col II fibrils within the cytoplasm under hypoxic conditions (J, red arrowheads). (K) Col2a1 mRNA expression in control and mutant primary chondrocytes cultured under hypoxic conditions as evaluated by northern blot. Scale bar: 500 µm in A,B; 2 µm in C; 2.5 µm in D; 2.9 µm in E; 3.1 µm in F; 90 µm in insets, C-F; 120 µm in G-J.