Relationship between localization of annexins and dentinogenesis during rat tooth development

Annexins (ANXAs) are a calcium-dependent, membrane-bound protein superfamily involved in the transport of matrix vesicle ion channels and Ca²⁺ ions, which are essential for early hard tissue calcification. However, the localization of ANXAs in dentin calcification is unknown. To analyze the localization and function of ANXA1, 2, 5, and 6 in odontoblast differentiation and dentin calcification, we examined the immunohistochemical localization of ANXAs in developing rat molars. During the bud (E15) and cap (E17) stages, ANXA-positive cells were not observed in the dental mesenchyme or dental papillae. In the early bell stage (E20), many ANXA1-, 2-, 5-, 6-, and CD31-positive cells were observed around the blood vessels of the dental papillae. In the late bell stage (P2), CD31, ANXA1, and ANXA2 immunoreactivity was observed around blood vessels in the vicinity of odontoblasts, but little ANXA5 and ANXA6 immunoreactivity was observed. ANXA2 immunoreactivity was observed in the cytoplasm and plasma membrane of the odontoblast. Furthermore, the immunoreactivity of plasma membrane calcium-ATPase (PMCA-ATPase), one of the Ca²⁺ ion efflux systems in odontoblasts, was observed to be co-localized with ANXA2. On postnatal Day 7 (P7), PMCA-ATPase immunoreactivity in odontoblasts decreased compared with P2. At P7 and 5 weeks of age (P35), little immunoreactivity for ANXAs was observed in odontoblasts and perivascular areas close to odontoblasts. ANXA1-, 2-, 5-, and 6-positive cells may be involved in vascular induction in the developing dental papillae, and ANXA2 may be involved in early dentin calcification.