[P3-3-19] Molecular mechanism governing tongue morphogenesis in embryonic mice
Keywords:舌形態、発生、分子制御機構
Objectives: Tongue morphogenesis first forms tongue primordium, the lateral lingual swellings, on the dorsal surface of the mandibular arches, which changes into the shape of the tongue with the differentiation of tongue muscle cells. In this study, we focused on the signaling molecules that act in tongue morphogenesis and investigated their molecular regulatory mechanisms. Materials & Methods: Serial sections containing tongue primordia were prepared from ICR embryonic mice (embryonic 9.0-18.5 days; E9.0-18.5) and analyzed by immunohistochemistry using specific antibodies. In the search for signaling molecules involved in tongue morphogenesis, gene expression was analyzed by real-time PCR on microdissected samples of tongue primordia. Additionally, the analyses using knockdown of signaling molecules and gene deletion animal models were performed. Results: Tongue morphogenesis began with the formation of the lateral lingual swellings by cell proliferation in the non-muscle mesenchyme at E11.5. Tongue morphogenesis began with the formation of the lateral lingual swellings by cell proliferation in the non-muscle mesenchyme at E11.5. At E12.5, the epithelial invagination occurred at the marginal tongue primordium. The lateral lingual swellings transitioned to the shape of tongue by proliferation and arrangement of tongue muscle cells from E13.5 onward. In the search for signaling molecules, expression of Shh, Patched1, Igf1, and Bmp4 was upregulated during the formation of the lateral lingual swellings. Endothelin-1 (ET-1) signaling was found to be an upstream molecule of Shh, Bmp4, and Fgf8 expressed in the epithelium of the lateral lingual swellings. 100% of ET-1-deficient mice developed microtia. This phenotype was thought to be due to the inability of muscle progenitor cells to make contact with the epithelium (expressed ET-1) of the medial mandibular arches, resulting in a non-muscle lineage mesenchymal cell population that lost proliferative activity and suppressed the formation of the lateral lingual swellings. In Shh knockdown with the Shh inhibitor jervine in an organ culture system of the mandibular process, proliferative activity only in the non-muscle lineage mesenchymal cells of the lateral lingual swellings were significantly reduced compared to the no-treatment group. This indicates that Shh regulates non-muscle mesenchyme cell proliferation and contributes to the morphogenesis of tongue primordium. Conclusion: Taken together, these findings reveal molecular regulatory mechanisms that operate in the cell-to-cell interactions among the coating epithelium, tongue muscle and non-muscle mesenchyme in the morphogenesis of tongue. Supported by JSPS KAKENHI Grant numbers 18K09530 & 21K09822. Non-member co-author: Kensuke Toyoda, Dept Nat Sci, Nippon Dent Univ Sch Life Dent at Tokyo.