| Bone morphogenetic protein 4 (BMP-4), a member of TGF-β superfamilies, is a well-known growth factor and signal molcular. It has been proved to be involved in the development of many organs such as bone, liver, heart, eye and limbs. BMP-4 is also expressed extensively and plays an important role during odontogenesis. In early stage of tooth morphogenesis when the largest transition of tooth development takes place, odontogenetic epithelium prolifecates and extends into the mesenchyme to form tooth bud, the rudiment of tooth. However the spatiotemporal character of BMP-4 in this stage still has disputation, and its role remains unclear. Due to the lack of an efficient research model, our study on early stages of odontogenesis lags much. Thus, our research focuses on:1. Establishment of a mouse mandibular arch explant model and dynamic observation of tooth germ development in it.First of all, the feasibility and condition of mouse mandibular arch explant were groped. Mandibular arch of 11 dpc mouse embryo was dissected and cultured in 37 C culture base contained 950 mL/L air and 50 mL/L carbon dioxide, using serum-free BGJb culture medium. The explants grew well in culture. Oberserved in naked eyes, their volumes largened slightly and tounge was formed in the dorsalside, thus making the explants composed of three processes besides the two original mandibular processes. After 11 days' continious culture, the explants were checked by microscope after histological dyeing. When culture was finished, tooth development was in cap stage which was confirmed by the formation of enamel organ, dental papilla and dental sac. Merhel's cartilage was located in the middle of the mandibular process and at dorsal-lateral side of it, condenced osteoblasts and some bone matrix were seen. At the dorsal side of the mandibular arch, the tounge came into being with papillas protruding from the upper surface. The epithelium of the mandibular arch changed from monolayer to polylayer with accumulation of keratose in some arches. All of these signs indicated that the mouse mandibular arch explant model was successfully establiahed, which provided an efficient research model for the development of Merkel cartilage, jawbone, tounge and tooth.Secondly, we observed the morphological development of the tooth germ in the established model. When the culture began, no sign of tooth development was available. After 3 days' culture, thickened dental epithelium was seen at the cephalic side of oral epithelium where morlars were supposed to form, which indicated the morphological initiation of tooth development. After 7days' culture, tooth bud formed. An epithelium stick, composed of 3 to 6 layers of epithelium cells, extending into the mesenchyme with its end bulged. Mesenchyme cells about the tooth bud condensed. After 11 days' culture, the tooth bud transformed to enamel organ. Odontogenetic epithelium differentiated into three types of structures: outer enamel epithelium, stellate reticulum and inner enamel epithelium to form enamel organ. Under the enamel organ, Mesenchyme cells condensed to form tooth papilla. Surrounding the tooth papilla and enamel organ was the tooth dac. The whole process of tooth morphogenesis was observed in this model, which indicated thisexplant model can be used as an efficient research model to study the role and mechanism of growth factors and signal factors in tooth morphogenesis. 2. Expression and function of BMP-4 in tooth bud morphogenesisEmbryos of 11, 12, 13, 14 dpc mouse were used to detect the expression pattern of BMP-4 protein in early tooth morphogenesis by immunochemistry, from tooth odontogenesis initiation to tooth bud stage. Result: while in the primary epithelial band stage, first sign of tooth morphogenesis, positive dyeing located in the surfae layers of oral epithelim and the primary epithelial band. Weak dyeing was also seen in basal layer and basal membrane. When the odontogenetic epithelium thickened and extended into the mesenchyme, strong positive dyeing was seen...
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