Region specific morphogenesis of tongue papillae

Abstract

The tongue of most vertebrates is muscular organ, and is used to manipulate and swallow food. It plays an important role in the digestive system and acts as the main organ of taste in the gustatory system. The human tongue is divided into the oral region of the anterior 2/3 part and the pharyngeal part of the posterior 1/3 part by the terminal sulcus, which is a V-shaped groove. The dorsal surface of the tongue is covered with a masticatory mucosa with keratinized stratified squamous epithelium. There are a number of papillae that contain taste buds and taste receptors. These lingual papillae have four forms, circumvallate, foliate, fungiform and filiform, but filiform papillae do not have a taste bud. Taste disorder associated with taste sensation occurs in various causes in life. Therefore, in this study, when the taste disorder such as decease or loss of taste occurs, it is interested in how to regenerate the taste bud in tongue in order to regain taste. To regenerate these lingual papillae, it is necessary to understand the development of lingual papillae. Regarding the development of lingual papillae, the interaction of epithelial and mesenchymal tissues, which can be observed in the development of most epithelial appendages such as feathers, lungs and teeth, is also necessary in the development process of lingual papillae. However, each of the other organs has different signaling pathways and regulatory factors for development. In the case of circumvallate papillae, morphology of embryonic day 13.5, 15.5, 17.5 (E13.5, E15.5, E17.5), post-natal 1 (PN1) and adult was confirmed by histological results. Various signaling molecules may be involved in the formation of the circumvallate papillae during the early developmental process. Among various signals, the location of Lgr5 was confirmed through in situ hybridization during the development of circumvallate papillae from E13.5 to adult, moreover, the distribution of FGF10 was confirmed in development process of circumvallate papillae through immunohistochemistry at E15.5 and E17.5. To obtain direct evidence of the interaction between epithelium Lgr5 and mesenchymal Fgf10 during the morphogenesis of circumvallate papillae, the formation of a circumvallate papillae-like structure was examined after a reverse (180-degree rotation) recombinant. It was performed after in vitro recombination assay for 72 hours using in vitro organ culture. When the epithelium of circumvallate papillae positioned to the absence of Fgf10, the structure of circumvallate was not observed. When the implanted bead soaked in FGF10 was located below the epithelium of circumvallate papillae that was the absence area of Fgf10, the form of circumvallate papillae could be formed. After 6-bromoindirubin-3′-oxime (BIO) treatment, abnormal cell proliferation and cell death were observed by a decrease in mesenchymal Fgf10. These results suggest that the communication between epithelial Lgr5 and mesenchymal Fgf10 is necessary for proper formation of circumvallate papillae in the process of tongue development.