bStudies of proteins involved in microRNA (miRNA) processing, maturation, and silencing have indicated the importance of miRNAs in skeletogenesis, but the specific miRNAs involved in this process are incompletely defined. Here, we identified miRNA 665 (miR-665) as a potential repressor of odontoblast maturation. Studies with cultured cell lines and primary embryonic cells showed that miR-665 represses the expression of early and late odontoblast marker genes and stage-specific proteases involved in dentin maturation. Notably, miR-665 directly targeted Dlx3 mRNA and decreased Dlx3 expression. Furthermore, RNA-induced silencing complex (RISC) immunoprecipitation and biotin-labeled miR-665 pulldown studies identified Kat6a as another potential target of miR-665. KAT6A interacted physically and functionally with RUNX2, activating tissue-specific promoter activity and prompting odontoblast differentiation. Overexpression of miR-665 reduced the recruitment of KAT6A to Dspp and Dmp1 promoters and prevented KAT6A-induced chromatin remodeling, repressing gene transcription. Taken together, our results provide novel molecular evidence that miR-665 functions in an miRNA-epigenetic regulatory network to control dentinogenesis. D entinogenesis is the process by which dentin, the major mineralized tissue of teeth, is formed through progressive cytodifferentiation of progenitor cells to mature odontoblasts (1). Multiple layers of gene regulation, including those by microRNA (miRNA), orchestrate the physiologic process of dentinogenesis in a stage-specific manner (2). Progenitor cells, including dental papilla cells or dental follicle cells, derived from the ectomesenchyme of the cranial neural crest, differentiate into preodontoblasts and produce predentin. Predentin stimulates further differentiation of the cells it surrounds, giving rise to mature odontoblasts that produce dentin. Odontoblast secretion of dentin extracellular matrix proteins, including dentin sialophosphoprotein (DSPP) and dentin matrix protein 1 (DMP1), aids in the process of mineralization that forms primary dentin. However, the mechanisms of odontoblast-specific gene regulation by miRNA during dentinogenesis are not clearly understood.miRNAs are endogenous, noncoding RNAs implicated in posttranscriptional RNA silencing (3-9). The importance of miRNAs in skeletogenesis has been shown in mice by loss-offunction analysis of proteins involved in miRNA processing (Drosha and DGCR8), maturation (Dicer), and silencing (argonaute 2; AGO2), which revealed embryonic lethality and severe developmental defects upon loss of these proteins (10-15). Furthermore, cartilage-specific deletion of Dicer led to accelerated differentiation and subsequent cell death (11), whereas osteoblast-and osteoclast-specific deletion increased bone mass (13,16). Current studies on miRNA regulation of gene expression indicate a key role for this process in tooth development (17)(18)(19)(20) and in controlling cellular signaling (18,(21)(22)(23)(24)(25) and differentiation (2,26). However, ...