Fig. 7.

Analysis of mouse neocartilage ultrastructure. A–D, ultrathin sections of 3-week mouse neocartilage cultures were examined by transmission electron microscopy after standard fixation in Karnovsky's reagent. E–I, TEM analysis of 3-week neocartilage after fixation in 0.7% safranin O. Low power micrographs display chondrocytes with a rounded or ovoid morphology (A, C, E, and H). Most chondrocytes are surrounded by a pericellular capsule (pc), defined at the outer boundary by a dense band of collagen fibrils (open arrows), which also appears to form a boundary with the territorial matrix (tm). Preservation of proteoglycans and glycosaminoglycans by fixation in safranin O reveals a dense proteoglycan network (pgn) that, at high magnification, can be observed in direct contact with the plasma membrane (I, *). Although generally smooth, finger-like protrusions are also observed projecting from the plasma membrane (B, arrowheads). Other distinctive features include abundant glycogen granules (gly), large secretory vesicles (sv), and rough endoplasmic reticulum (rer).