MicroRNAs (miRNAs) are known to regulate a variety of gene functions in many tissues and organs, but their expression and function in tooth development are not well-understood. A specific miRNA, miR-135a, was determined to be highly expressed at the bud stage. Interestingly, after the cap stage, miR-135a was expressed in the epithelium and mesenchyme but not in the inner enamel epithelium. To identify the relationship between miR-135a and its putative target genes, Bmpr-Ia and Bmpr-Ib, in early tooth development, miR-135a was ectopically overexpressed with a lentivirus. This overexpression resulted in the repression of Bmpr-Ia and Bmpr-Ib. Furthermore, miR-135a inhibited both Bmpr-Ia and Bmpr-Ib transcription. BMP2 proteins were expressed ectopically in tooth germs during the cap stage to determine the relationship between miR-135a and BMP signaling in early tooth development. When miR-135a was ectopically expressed, no tooth formation was observed after 4 wk of incubation in the kidney capsule. This study suggested that Bmp signaling, specifically Bmpr-Ia and Bmpr-Ib, regulates tooth formation via miR-135a.
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