Background MicroRNAs are non-coding small RNA molecules that regulate various cellular functions. In this study, we analyzed the function of microRNA-200a (miR-200a) during the development of primary and secondary cartilages in the mandible during the embryonic stage. Materials and methods Mandibular processes were excised from ICR mouse embryos. Meckel's cartilage and the complex of condylar and angular cartilages were examined as primary and secondary cartilages, respectively. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) and in situ hybridization were performed to examine the expression of miR-200a during normal mandibular development. Transfection of a miR-200a-mimic and -inhibitor were performed to analyze the effect of miR-200a on mandibular cartilage formation. Prior to transfection, DiI labeling was performed to detect the transfection sites and examine the effect of miR-200a on Meckel's and condylar cartilage formation. Nine days after transfection, Alcian blue staining and quantification were performed to analyze the formation of the cartilage. Results The expression levels of miR-200a gradually increased from embryonic day 9–14 in mandibular processes. However, the expression levels of miR-200a in Meckel's cartilage were nearly identical from embryonic day 12–16. The positive hybridization signals were observed in Meckel's cartilage and mesenchymal condensation of mandibular condylar cartilage. Alcian blue analysis showed a significant decrease in the complex of condylar and angular cartilage formation in the lateral-anterior-miR-200a-mimic transfected samples compared to miR-200a-inhibitor-transfected and control samples. Conclusion miR-200a negatively regulates the formation of condylar cartilage in early mandibular development.
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