Avian myelocytomatosis virus immortalizes differentiated quail chondrocytes

Quail embryo chondrocytes in culture display two morphological phenotypes: polygonal epithelial-like and floating cells. Both cell populations synthesize cartilage extracellular matrix proteins (type II collagen and specific proteoglycans), whereas type X collagen, which appears to be a marker of later stages of chondrocyte differentiation, is expressed only by the epithelial-like cells. Avian myelocytomatosis virus strain MC29 does not induce morphological transformation in quail embryo chondrocytes but stimulates these cells to proliferate with a progressively reduced doubling time. MC29-infected chondrocytes can be established in culture as a continuous cell line, whereas control (uninfected) cultures only survive a few months. Rapidly dividing MC29-infected chondrocytes still express type II collagen and cartilage proteoglycans but do not synthesize type X collagen.