Expression of MicroRNA During Tooth Development

Objectives: The genetic control of tooth development has been studied in mice. About 300 coding genes have been demonstrated to be active in the developing tooth. For a long time, molecular biologists have been focused on DNA, mRNA and proteins; whereas epigenetic factors e.g. non-coding RNAs (ncRNAs) are relatively unexplored. NcRNAs control a remarkable range of biological pathways and processes. An abundant family of short (17–25 nucleotides) ncRNAs, known as microRNAs (miRNAs), provides a example of regulatory transcripts. MiRNAs base-pair to their target mRNAs and inhibit expression by triggering either translation repression or RNA degradation. While miRNAs are known to affect cellular proliferation, differentiation, and morphological development, neither their expression nor roles in tooth development have been characterized. We therefore have investigated the miRNA expression profiles at various time points during development of the first molar mandibular tooth germ.

Methods: The first molar mandibular tooth germ were dissected from CD-1 mouse embryos and offspring, and small RNAs were isolated at embryonic day 15.5 (E15.5), E19.5 and postnatal day 5 (P5). The miRNeasy Mini Kit (Qiagen) and the flashPAGE Fractionator (Ambion) were used to isolate small RNA. Quality and RNA composition of the isolates were assessed by the Agilent-Bioanalyzer (Agilent, Palo Alto, CA). MicroRNA arrays (The Norwegian Microarray Consortium) based on the mirVana miRNAProbe Set (Ambion) were used to determine the profile of microRNAs expressed in the tooth germ. The mirVANA array represents 300 known miRNAs from human, rat and mouse. The miRNA expression profiles were validated by quantitative PCR (Applied Biosystems).

Results: Our results show that miRNA expression is abundant during tooth development. This study indicates that a significant number of miRNAs are expressed at specific stages during development of the murine first molar mandibular tooth germ.

Conclusion: This suggests that microRNAs may play an important role in tooth development.