Extracellular matrix formation by chondrocytes in monolayer culture.

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Abstract
A combined effort was made to compare sequence and pattern of secretion and deposition of 3 macromolecules [type II collagen fibronectin chondroitin sulfate proteoglycan (CSPG)] in the same chondrocyte culture experiment. Immunofluorescence labeling experiments demonstrate that type II collagen, fibronectin and CSPG reappear on the cell surface after enzymatic release of chondrocytes from embryonic chick cartilage but develop different patterns in the pericellular matrix. When chondrocytes spread on the culture dish, CSPG is deposited in the extracellular space as an amorphous mass and fibronectin forms fine, intercellular strands; type II collagen disappears from the chondrocyte surface and remains absent from the extracellular space in early cultures. Only after cells in the center of chondrocyte colonies reassume spherical shape does the immunofluorescence reveal type ll collagen in the refractile matrix characteristic of differentiated cartilage. Immunofluorescence double staining of the newly formed cartilage matrix demonstrates that CSPG spreads farther out into the extracellular space than type II collagen. Fibronectin finally disappears from the cartilage matrix.