Mandibular condylar cartilage (MCC) is classified as secondary cartilage, the histologic structure of which is unique from that of primary cartilage. MicroRNA (miRNA) is a small noncoding RNA that binds to the messenger RNA (mRNA) target to repress its translation and plays an important role in cell differentiation, proliferation, and death. Microarray analysis revealed that miR-200a was characteristically expressed during embryonic development. We hypothesized that miR-200a may be involved in regulating the formation of cartilage during MCC growth. We investigated the function of miR-200a by transfecting an inhibitor or mimic into MCC organ and cell cultures. A histologic examination revealed the localized inhibitory effects of the miR-200a mimic and widespread enhancing effects of the inhibitor on chondrocytic differentiation in the MCC organ culture system. An immunohistochemical examination and gene expression analysis demonstrated that the miR-200a inhibitor enhanced chondrogenesis, while the mimic had the opposite effect by enhancing cell proliferation. Quantitative reverse transcription polymerase chain reaction analysis revealed that miR-200a downregulated the gene expression of chondrocyte markers. Moreover, transfection of the miR-200a mimic into ATDC5 cells repressed the formation of the cartilaginous matrix. These results indicate that miR-200a contributed to chondrogenesis in developing MCC by controlling proliferation and differentiation in MCC cells.
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