| The growth of tooth root is the vital process in the later teeth development. The growth of root is still under strict genetic control by sequential and reciprocal interaction between epithelial and mesenchymal tissues. Nowadays it is found that some signals involve in epithelial-mesenchymal interaction by the way of signaling networks on timing, space and activity, including growth factors, transcription factors, extracellular matrix proteins and cellular membrane proteins. Its growth is postnatal, so the process owns personal characteristics. The Homeobox gene MSX-1/-2 is the specific transcription factors, which mediate the patterning of many tissues and organs during the embryogenesis. BMP-3/-4/-7 are either the growth factors or the biological signaling molecules during tooth development. Moreover apoptosis has a great value on the maintenance of histo-differentiation, organogenesis and homestasis of multicellular organ. So in our study, we took the dogs in the growth phase of permanent teeth roots as the experimenter, and observe the distribution of apoptosis and the expression of MSX-1/-2, BMP-3/-4/-7 in related tissues of teeth under three status of permanent teeth pulps (normal, inflammation, repair) by using in situ hybridization technique and TUNEL methods, then exploringthe regulatory roles of MSX-1/-2, BMP-3/-4/-7 and the significance of apoptosis. The main content and results of our researches are below: 1. The study on the expression of the related genes regulating the growth of the dog permanent tooth rootsIn this research, we .used in situ hybridization method to map out the localization of MSX-1/-2 and BMP-3/-4/-7 during the normal root morphogenesis to explore their regulatory roles and find out their physiological meaning.1. 1MSX1 is localized in dental papilla, odontobalsts, cememtoblasts, dental sac, periodontalium and alveolar bones, which suggested that transcription factors MSX1 not only mediate the differentiation of odontoblasts, but also participate in the interaction between Hertwigs epithelium root sheath (HERS) and dental sac. In addition, It still play the role in the reconstruction of alveolar bone. So we proposed that MSX1, as upstream signal, may initiate the downstream functional genes to induce the formation of roots and teeth attachment organ.1. 2 MSX2 is the master regulatory gene during the root development, which plays some roles in signaling networks regulating the root formation. MSX2 take part in the initial signal of root growth, and induce the mesenchymal cells adhesion and binding with growth factors, then making dental papilla cells differentiate into odontoblast. It still initiate the programmed cell death (PCD) of redundant odontoblasts, preodontoblasts and dental papilla cells, and keep the functional balance of cells. Moreover it participates in HERS fragment and regression by inducing PCD, then it can induce the cementogenesis andregulate the patterning of alveolar bones.1.3 BMP-7 positive signals is early found only in HERS around cervical circulus as called "developmental center" of root, which indicate that BMP-7 may be the initial signal of root growth. In addition, BMP-7 is later expressed in the secretory cementoblasts and odontoblasts, which suggests that it can induce dentinogenesis and cementogenesis. BMP-3 is found in dental sac surrounding the germs in the early course of development, and later expressed in cementoblasts on acellular cementum and periodontal cells. This suggests that BMP-3 can induce dental sac cells to differentiate into cementoblast and make the assembly of periodontal ligament fibres. BMP-4 is early confined to odontoblasts, preodontoblasts, dental papilla and osteoblasts, which indicate that it can induce the differentiation of odontoblasts and osteoblasts, and the secretion of dentin matrix. Then it still later distributed in cementoblasts upon cellular cementum, which propose that cememtoblast on cellular cementum is derived from osteogentic premier cells and BMP-4 is inducer. 2. The study on a...
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