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Much is now known of the molecular signalling and genetic determinants for tooth development. Here, we discuss the current understanding of the cellular origin of teeth, the early patterning that determines where a tooth is positioned in the mouth, how the tooth initiates, and the number of the teeth that will form in mouse. The genes that are important for regulating the tooth shape are also discussed.

Investigation of chemically synthesized inositol 1,4,5-trisphosphate analogs has led to the isolation of a novel protein with a molecular size of 130 kDa, characterized as a molecule with domain organization similar to phospholipase C (PLC)-ζ1 but lacking enzymatic activity; therefore the molecule was named PRIP (PLC-related, but catalytically inactive protein). Yeast two-hybrid screening of a brain cDNA library identified GABA_A receptor-associated protein (GABARAP) and protein phosphatase 1(PP1), which led us to examine the possible involvement of PRIP in neuroscience, particularly in GABA_A receptor signaling. PRIP knock-out (KO) mice were analyzed for GABA_A receptor function with special reference to the action of benzodiazepines whose target is the γ subunit of the receptors; sensitivity to benzodiazepine was reduced as assessed by biochemical, electrophysiological, and behavioral analyses of KO mice, suggesting the dysfunction of γ2 subunit-containing GABA_A receptors. The mesencephalic trigeminal nucleus, which mediates perceptions from periodontal mechanoreceptors and jaw-closer muscle spindles, receives many synaptic inputs, including those from GABA_A receptors, indicating that PRIP might indirectly be involved in rhythmical jaw movement. In the present article, we summarize our current reach and the perspective of the functional significance of PRIP.

Synthetic hydroxyapatite, in the usual case, of a macroscopic size, exhibits excellent osteoconductivity. However, it is not substituted with natural bone and remains permanently in the body; therefore it is suitable for using as an implant. It is well known that natural bone is composed of collagen and nanocrystallites of apatite with the size of approximately 50 nm. When the composite with collagen and nanoapatite synthesized in the biomimetic aspects is implanted, phagocytosis and inflammation are induced. Osteoclasts and osteoblasts are then differentiated and activated. The bone resemblant material and its phagocytizable nanometer size provide the conditions that composite is biologically degradable through phagocytosis by osteoclasts, and new bone formation by osteoblasts is simultaneously activated and proceeded. As a result, nanocomposite leads to the bone substitutional properties. Thus the conversion of functions is attained for apatite by nanosizing—from osteoconductivity in macroscopic size to bone substitutional properties in nano/micro scale. This tendency is more enhanced for carbonated hydroxyapatite. The mineralization surrounding collagen fibrils determines the crystallization of apatite for their size and orientations. Nanoparticles cause the reaction of cells/tissue and stimulate the occurrence of inflammation, which works as a stimulus in most cases or pronounces the conversion of functions leading to the bioactive properties for some cases, depending on the situation. Nano structure is essential for these stages to be processed.

The structure of eukaryotic cells is controlled by a dynamic balance of mechanical forces. The mechanical force is exerted by the cytoskeleton on the extracellular matrix attachments, neighboring cells, and the substratum. Living bone is continually undergoing remodeling processes, which allow for continuous fine-tuning of the amount and spatial organization of the tissue in response to mechanical strain. The properties of osteocytes have been difficult to study and analyze because they are surrounded by mineralized tissue. Our successful isolation and maintenance of bone cells, especially osteocytes, facilitated the real-time analysis of osteocytes and osteoblasts in isolated culture. To identify the phenotype of osteocytes in the same field as that analyzed by calcium imaging, we used OB7.3, a chicken osteocyte-specific monoclonal antibody. We examined flow-induced calcium transients in primary chick osteocytes and osteoblasts, and analyzed the micro-elasticity of osteocyte and osteoblast to examine their stiffness measured with atomic force microscope (AFM) which is a powerful tool for measuring the micro-mechanics of the cells. We also examined the relationship among focal adhesion formation, calcium transients, and the micro-elasticity. It was concluded that focal adhesion formation and micro-elasticity are very important for bone cells to interact with cells and/or extracellular matrix for remodeling in response to mechanical stress.

Chondrocyte differentiation has been known to be affected by shearing stress, compressive or expansive force in vivo and in vitro. In the present study, we investigated the transient phosphorylation of extracellular signal-regulated kinase (ERK)-1/2 under stretch stimulation, and this ERK-1/2 phosphorylation mediates mechanical stretch signaling during chondrogenesis. Dissociated embryonic E12 rat limb bud cells were assembled to micromass culture on a silicon bottom plate. After 4 days, micromass cultures were stretched prior to the isolation of protein samples. Stretch stimulation was also loaded with or without MEK-1 or MEK-1/2 inhibitor. Western blot analysis revealed that phosphorylation of ERK-1/2 increased and peaked at 1.0 h after stretch loaded. Alcian blue staining and semi-quantitative reverse transcription-polymerase chain reaction analysis for type II collagen gene expression revealed that inhibited chondrogenesis by mechanical stretch stimulation was rescued by inhibiting MEK-1 and MEK-2 activities. It was concluded that signaling through ERK-1/2 was activated by stretch stimulation in micromass cultures and was involved in the inhibition of chondrogenesis by stretch stimulation.

Cytoskeleton is thought to undergo remodeling in response to mechanical stimuli such as compression (hydrostatic pressure or direct platen contact), tensile strain, and fluid shear stress. Despite the wealth of information as to effect of these mechanical stimuli on the structure and function of their cells, there is a paucity of information as to whether mechanical stimuli may facilitate cell differentiation regarding the quality and quantity of the strain and the timing applied. The present study was designed to investigate whether the deformation of scaffold affects the differentiation of chondrogenic cells. We developed a culture system that induces the mechanical stimuli to the inoculated cells with quantitative gradient strain. The culture systems previously developed were reviewed and compared to the present system in designing the mode to load the deformation.

Wnt/β-catenin signaling plays an important role in developing the skeletal system. However, the exact mechanisms by which Wnt/β-catenin signaling regulates bone remodeling remain to be elucidated. Our previous studies demonstrated that canonical Wnt signaling inhibited the ability of bone morphogenetic protein (BMP)-2 to induce myotubes in the C2C12 cell line, and that this inhibition was mediated by Id-1. We also showed that BMP-2 induced β-catenin-mediated lymphoid enhancer factor 1/T cell factor (Lef1/Tcf)-dependent transcription in this cell line. Here, we examined the role of intracellular signaling by Wnt/β-catenin and BMP-2 in the regulation of expression of osteoprotegerin ( OPG ) and receptor activator of NFκB ligand ( RANKL ) in osteoblasts. OPG expression was induced by overexpression of activated β-catenin in C2C12 cells and caused an increased OPG concentration in the culture supernatant. Silencing of glycogen synthase kinase-3β (GSK-3β) by sgRNA (tRNaseZL-utilizing gene silencing) also increased OPG concentration in the culture supernatant. BMP-2 acted synergistically with Wnt3a to enhance OPG expression. In contrast, Wnt3a suppressed RANKL expression. Transient transfection analyses using murine OPG gene promoter constructs revealed that activated β-catenin induced transcription activity, and that this induction might be mediated by the Lef1/Tcf response element in the OPG gene promoter. These results show that both Wnt/β-catenin and BMP-2 signaling regulate OPG and RANKL expression.

Gene transfer by electroporation in combination with mandibular explant culture is expected to give better understanding of the molecular mechanisms during maxillofacial development. In the present study, we attempted to analyze the gene transfer efficiency of mandibular explant in relation with vector size or the magnitude of electroporation voltage in comparison with gene transfer using lipofection method. Ectopic expression of enhanced green fluorescent protein (EGFP) was accomplished in the mesenchymal area where the gene was transferred in electroporation group, whereas the lipofection group showed minimal transfection efficiency. We established a method for in vitro electroporation, which induced transient gene delivery without tissue damage.

This study investigated the effect of initially light and gradual increases in force on tooth movement using the attractive force of magnets in an experimental rat model. The distance between the magnets incrementally decreased from an initial light force in the experimental group, in contrast to no tooth displacement in the control group. There were significant differences in the number of osteoclasts and in the relative hyalinized area on the pressure side of the periodontal tissue between the control group and the experimental group. The application of gradual incremental increases in force induced effective tooth movement in rats, and recruitment of osteoclasts and inhibition of hyalinization.

The purpose of this study was to compare the biomechanical effects of the incisor movement in three different types of traction by the miniscrew implants as an anchorage using 2D finite element method (FEM). The FEM model was made by tracing the maxilla including tooth, the wire, and the bracket. Three different types of hooks were set up in the model. We suggested that controlled incisor retraction is possible by changing the length and the position of the hooks soldered to the archwire when using miniscrew implants.