<b>Developmental changes in primary cilia in the mouse tooth germ and oral </b><b>cavity </b>

Abstract

The primary cilium, a sensory apparatus, functions as both a chemical and mechanical sensor to receive environmental stimuli. The present study focused on the primary cilia in the epithelialmesenchymal interaction during tooth development. We examined the localization and direction of projection of primary cilia in the tooth germ and oral cavity of mice by immunohistochemical observation. Adenylyl cyclase 3 (ACIII)-immunolabeled cilia were visible in the inner/outer enamel epithelium of molars at the fetal stage and then conspicuously developed in the odontoblast layer postnatally. The primary cilia in ameloblasts and odontoblasts-shown by the double staining of acetylated tubulin and γ-tubulin-were regularly arranged from postnatal Day12, projecting apart from each other. The periodontal ligament possessed ACIII-positive cilia, which gathered on both sides of the dentin/cement and alveolar bone in postnatal days. In the oral cavity, numerous long primary cilia immunoreactive for ACIII were condensed at subepithelial stromal cells in the oral processes in fetuses, while postnatally a small number of short cilia were dispersed throughout the stroma of the oral cavity. These findings suggest that the primary cilia showing stage-and regionspecific morphology are involved in the epithelial-mesenchymal interaction during tooth development via mechano-and/or chemoreception for growth factors.

Role of Primary Cilia in Odontogenesis

“…In the E16.5 mouse molar, numerous short cilia were found in the inner and outer enamel epithelium, while fewer cilia were found in the stellate reticulum (Hisamoto et al 2016). Cilia are also present on the cells of the enamel knot.…”

“…Cilia are also present on the cells of the enamel knot. In the mesenchyme, there are primary cilia widely distributed in areas surrounding the tooth germ as well as in the dental papilla (Hisamoto et al 2016).…”

“…In odontoblasts, primary cilia are aligned parallel to the dentin walls, and their axonemes are oriented toward the pulp core (Thivichon-Prince et al 2009;Hisamoto et al 2016). The regular arrangement of cilia in odontoblasts first appears near the root apex and then extends along the odontoblast layer.…”

“…Cilia on the ameloblasts project toward the outer enamel epithelium. Thus, the cilia of ameloblasts and odontoblasts are oriented in opposite directions out of the area where the hard tissue is produced (Hisamoto et al 2016). Ameloblasts seem to have shorter cilia compared with odontoblasts, but a detailed quantitative analysis of cilia length has not been performed yet.…”

“…Cilia were located in periodontal ligament cells between the dentin/cement and the alveolar bone. In early postnatal and adult mice, cilia were detected on the edges of the periodontal ligament adjacent to both the tooth and alveolar bone; however, there were few ciliated cells in the medial region of the periodontal ligament (Hisamoto et al 2016). In contrast to the aligned cilia of ameloblasts and odontoblasts, where the odontoblast axoneme points toward the pulp cavity and the ameloblast axoneme points to the outer enamel epithelium, the mesenchymal primary cilia do not show an orderly arrangement in the fetal dental follicle or in the neonatal and adult periodontal ligament (Hisamoto et al 2016).…”