Differential Gene Expression in the Periodontal Ligament of the Mouse Molar and Incisor

Objectives: The periodontal ligament (PDL) is a viscoelastic tissue that is critical for anchorage of teeth to alveolar bone, and in physiologic and orthodontic tooth movement (OTM). Adult mice possess rooted molars like humans, but their incisors continuously renew throughout life. We hypothesize that comparison of PDL gene expression in the mouse incisor vs. molar will identify important genes involved in OTM. Ultimately, these genes may then be targeted to optimize and accelerate OTM during treatment.
Methods: We isolated and purified total RNA from 3 distinct PDL populations from adult mouse mandibles: 1) right incisor (control incisor, CI); 2) right molar (control molar, CM); and 3) left incisor with accelerated renewal (experimental incisor, EI). To induce accelerated incisor renewal, we clipped the distal tip of the left incisor so that it was out of occlusion. All specimens were collected and analyzed after 24h. We performed histology, real-time qPCR, and RNA-seq (UCSF SABRE Center Functional Genomics Core Facility)
Results: Using qPCR, we observed statistically significant, differential expression of numerous genes in distinct PDL populations. For example, bone morphogenic protein 4 (Bmp4), periostin (Postn), and osterix (Osx) were up-regulated in CI compared to CM; scleraxis (Scx) expression was up-regulated and Postn was down-regulated in EI compared to CI; and Bmp4 and Osx were up-regulated and smooth muscle actin alpha 2 (Acta2) was down-regulated in EI compared to CM. RNA-seq experiments are currently being performed and differentially expressed genes of interest will be confirmed by qPCR.
Conclusions: The candidate gene approach using qPCR determined that Postn, Osx, Bmp4, and Scx expression patterns in the continuously renewing mouse incisor are similar to that observed when molars are put under tension during OTM. Our study demonstrates that the PDL in continuously renewing mouse incisors possess similar expression profiles to molars undergoing OTM.