Objectives: The Order Rodentia is characterized, in part, by their continuously erupting or renewing incisors. Since little is known about the attachment of the incisors to alveolar bone, we aim to identify differentially expressed genes in the periodontal ligament (PDL)-like tissue of the mouse incisor during normal and accelerated renewal. We confirmed that mouse incisors grow faster when out of occlusion. We hypothesize that this accelerated renewal is associated with changes in gene expression within the PDL-like tissue on the lingual surface of the mouse incisor that allows for increased turnover of tooth-bone attachment. Global profiling of gene expression during periods of accelerated incisor renewal will identify genes and genetic networks that will advance understanding of PDL turnover, and ultimately, may allow us to accelerate orthodontic tooth movement (OTM) in mouse molars and human teeth.Methods: Sample groups consisted of 6-week-old control (n=3) and experimental (n=3) FVB/NJ mice. Experimental mice had one incisor cut at the tip (2-3mm), and incisor renewal was allowed for 24 hours. Control mice were unaltered. Mice were euthanized, mandibular incisors were extracted, soft tissues attached to the extracted incisors were collected, and total RNA was isolated to perform global profiling of gene expression using bulk RNAseq analysis. The total number of samples (n=9) include control (n=3), the non-cut incisor from experimental mice (n=3), and the cut incisor from experimental mice (n=3). From a list of differentially expressed genes, three specific genes were selected for further evaluation using quantative in situ hybridization (RNAscope).
Results: Bulk RNAseq revealed a significant increase (p<.01) in the expression of 365 genes in cut incisors and non-cut contralateral incisors relative to control (CTRL). Lgals7, Ovol1, and Stx19 were selected for potential promising roles during accelerated incisor renewal. RNAscope analysis confirmed the upregulation of these genes in soft tissue associated with the cut experimental incisor but expression was specific to gingival tissue.
Conclusion: We identified three up-regulated genes, Lgals7, Ovol1, and Stx19, that were associated with the mouse incisor undergoing accelerated renewal. These genes may play key roles in gingival remodeling during tooth movement, such as tooth eruption, drift, and OTM. Further experiments will be performed to determine the roles of these candidate genes in gingival homeostasis during OTM, and to isolate differentially expressed genes specifically expressed in PDL-like tissue. We envision that the accelerated mouse incisor model will be valuable in advancing cellular and molecular understanding of soft tissue turnover (PDL and gingiva) during OTM.