Growth and dedifferentiation of a heterogeneous mouse chondrocyte population, prepared from epiphyses of mouse embryos (day 17 of gestation), were studied in primary monolayer culture. At different times of culture, light and electron microscopic investigations were carried out and the change of collagen types was shown by immunofluorescence microscopy. During the first four days in culture, chondrocytes express their typical phenotype. Round or polygonal cells are embedded in a metachromatically staining matrix and produce type II collagen. After four to eight days in vitro most of the chondrocytes lose their matrix capsule and alter to fibroblast-like cells. Simultaneously, a switch of collagen synthesis to type III and type I collagen occurs, whereas the type II collagen synthesis is stopped. Altered cells and transitional stages have intracellular glycogen like typical chondrocytes, but show phagocytosis and indications of cell migration like fibroblasts. It is proposed that these cells, originating from a subpopulation of epiphyseal cartilage, are able to differentiate and dedifferentiate in vitro.
