CHANGES IN PHENOTYPIC GENE-EXPRESSION IN RAT MANDIBULAR CONDYLAR CARTILAGE CELLS DURING LONG-TERM CULTURE

Gene expression patterns have been investigated in prolonged cultures of rat mandibular condylar cartilage (MCC) cells to examine the possib ility of culture-induced phenotypic changes, MCC cells were isolated f rom newborn rats and grown in the presence of 10% fetal bovine serum ( FBS) and basic fibroblast growth factor (bFGF). MCC cells were passage d and cultured in the presence of 10% FBS and bFGF until confluent. Af ter confluence, the medium was changed to that supplemented with 10% F BS, ascorbate, and beta-glycerophosphate (day 1). Mineralization and g ene expression of MCC cells have been investigated. Mineralization, vi sualized by staining with Alizarin red, was observed to begin at day 1 3 in culture, and increased up to day 22 in culture, which was the len gth of this study. Type II collagen and aggrecan mRNAs were highly exp ressed at the start of culture (day 1-4) and decreased in a time-depen dent manner. Type I collagen, alkaline phosphatase, and osteopontin mR NAs expressed biphasic patterns that peaked at the start of culture an d the beginning of mineralization (day 13-16), Osteonectin mRNA was ex pressed throughout the culture period. Osteocalcin mRNA was expressed before the beginning of mineralization peaking at day 7. These observa tions suggest that the gene expression patterns of MCC cells can be ca tegorized into two different periods in prolonged culture: maturation (day 1-10) and mineralization (day 13-22). The cell culture system of MCC represents a new model system in which the differentiation of embr yonic MCC cells can be examined.