The Expression Of CBFA1 And Mineral-Associated Proteins In Tooth Development Of Postnatal Mice

Cbfa1 is an essential transcription factor for osteoblast differentiation and bone formation and also a positive regulator of chondrocyte and odontogenic lineage. Besides osteoblast and bone, Cbfa1 also plays an important role in tooth development. Cbfa1 can regulate many factors, including several mineral-associated proteins that play crucial role in tooth germ, such as bone sialoprotein(BSP)N osteopontin(OPN), osteocalcin(OC), alkaline phosphatase(ALP)and et al. Recent data shows that Cbfa1 is highly expressed in early stages of tooth development and is involved in crown morphogenesis and cytodifferentiation of odontoblasts. But there is few research about Cbfa1 in later stage of tooth germ. So we adopted immunohistochemical technique to study the expression of Cbfa1 and mineral-associated proteins in developing tooth of postnatal mice.Objectives:(1) To establish a postnatal mice tooth developing model.(2) To study the expression of Cbfa1 and mineral-associated proteins in postnatal mice tooth development.Methods:For tissues preparation, mandibles including the first molars were removed form the postnatal BALB/c mice at various stages of tooth development and fixed with 4% paroformaldehyde overnight at 4℃.Thendecalcidied with formic acid-sodium formate compound solution for 1-30 days. Decalcified specimens were dehydrate with increasing concentrations of ethanol and embedded in paraffin and 5um sections were made. The sections were subjected to build postnatal mice tooth developing model histologically and determine the expression of Cbfa1 and mineral-associated proteins in the tooth development by immunohistochemical technique. Results:(1) Tooth development of postnatal mice: At 5^th day, tooth germ was at later bell stage, the epithelial root sheath had already innerly folded, but the root still could not be seen. This was the symbol of initiation for root development. With the development of the germ, at 11^th day, dental follicle cells at root region differentiated into periodontal tissues, the outline of tooth root was formed. The root kept on extending, when to 27^th day, the apical foramen was becoming narrowed; there was much cellular cementum around the apical zone. The tooth development was completed.(2) Expression of Cbfa1 in tooth development of postnatal mice: Cbfa1 was merely present in predentin and developing alveolar bone matrix in the exact and before 11^th day's postnatal stages; meanwhile, it was positively located in odontoblasts and dental pulp cells in root region while negatively in coral part, and also in periodontal ligament cells, cementoblasts, osteoblasts and osteocytes except the alveolar bone matrix.(3) Expression of mineral-associated proteins in tooth development of postnatal mice: OPN and BSP was merely present in predentin and developing alveolar bone matrix in the exact and before 11^th day's postnatal stages; meanwhile, it was positively located only in periodontal ligament cells and cementum at the later stage and OPN is earlier than BSP. OC and ALP were expressed in papilla cells\pulp cells odontolblast and periodontal ligament cells, but not in cementum. All of them were in ameloblasts, but not in dentin, and weaker in alveolar bone.Conclusions:(1) The span of the developing periodontal tissue of the first molar in mandible is from 5lh day to 27th day.(2) Cbfal may play an important role in the deposition of tooth dentim the differentiation of odontoblasts n pulp cells ■> cementoblasts and osteoblasts -> and the formation of periodontal tissues during tooth development.(3) OPN> BSP. OC\ ALP are all involved in tooth development. OPN and BSP may play an important role in the formation of cementum. As ALP and OC are two essential factors for the formation of the hard tissues related to tooth, the expression of them indicate that most of the tooth cells own the ability to mineralize.(4)Data indicate that Cbfal is the up-stream regulator of OP1SU BSP> OC and ALP. We study also confirm that during late stage of tooth development expression of Cbfal is earlier than OPNn BSP ,but OC is found earlier than Cbfal, perhaps the difference is from technique. The detail mechanism between them still needs further study.