Notch signaling in mandibular condylar cartilage developmemt

Objective: The purpose of this study was to investigate the expression pattern of Notch signaling in mandibular condylar cartilage, as a type of secondary cartilage. Methods: Mandibular condyle of ddY mice were fixed from embryonic day 14 (E14) through just after birth (equivalent to E19). Samples were cut into 4 μ serial sections through the central area of the mandibular condyle at the sagittal plane. Serial sections were examined using histological, immunohistochemical (IHC) and in situ hybridization (ISH) techniques. Results: At E14, there were no developmental features of mandibular condyle. At the distal upper portion of developmental mandibular bone, mesenchymal cell proliferation and condensation without metacholomatic reaction to toluidine blue (TB) were seen. At E15, mandibular condylar cartilage was clearly evident, as TB metacholomasia. In IHC specimens at E14, expression of Notchl intracellular domain (NICD) was observed in the nuclei of coagulating mesenchymal cells. After E15, NICD appeared in the nuclei and the cytoplasms of cells. In ISH examination at E14, expressions of Notch1 mRNA appeared in cytoplasm of proliferating chondrocytes. From E15 to E19, Notch1 mRNA was detected throughout almost all cytoplasm in all layers. Conclusion: These IHC and ISH results suggest that Notch signaling plays an essential role for mandibular condylar cartilage morphogenesis and development.