Fig. 1.

FGF2 and TGFβ1 induce potent morphological changes in immature articular cartilage during in vitro culture. Explants were taken from adjacent sites from the same joint and cultured either in the absence (A) or continual presence (B) of 100 ng ml⁻¹ FGF2 and 10 ng ml⁻¹ TGFβ1 for 21 days in ITS containing serum-free medium. Growth factor-treated explants undergo significant resorption resulting in the disappearance of hypertrophic chondrocytes that reside in the deep zone of immature articular cartilage (bracketed in (A)]. Bar equals 500 μm. Polarising light microscopy of picro-sirius red stained sections of untreated (C) and growth factor-treated cartilage explants (D). The surface cartilage of growth factor treated cartilage displays extensive changes in collagen orientation many fibrils are anti-parallel to the surface axis (D). Also, a thin fluorescent line parallel to the surface (white arrows) delineates the lamina splendens, a collagen and lipid rich structure that is approximately 3 microns deep. This structure is absent in growth factor-treated cartilage. Bar equals 50 μm. Electron microscopy of surface chondrocytes (×7500) in untreated (E) and growth factor-treated (F) cartilage explants. Note the appearance of a thickened pericellular coat surrounding individual surface chondrocytes in growth factor-treated cartilage (black arrow in F) compared to untreated cartilage where this micro-anatomical unit of mature chondrocytes is absent (arrow in E). Also noteworthy is the increased collagen fibril density in growth factor-treated cartilage explants (F). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)