Determining the Structural and Functional Characteristics of Enamelin in Enamel Formation.

Enamelin (Enam) is essential for proper dental enamel formation. In Enam null mice the mineralization front associated with the secretory surface of the ameloblast membrane fails to initiate and elongate enamel mineral ribbons, so no true enamel forms. The mineralization front is a complex of enamel proteins that cannot be reconstituted in vitro. The main purpose of this dissertation was to develop an in vivo assay to study the structural and functional characteristics of enamelin in enamel formation by establishing a range of enamelin transgene expression that recovers the enamel phenotype of Enam knockout mice. A mouse expression vector was constructed using 4.6 kb of 5’ amelogenin gene up to the translation initiation codon, the 3.8 kb Enam cDNA, and 1.1 kb of amelogenin 3’ noncoding sequence. This construct was assembled and used to generate enamelin transgenic mice. The expression level of Enam gene in different transgenic mice lines varies from very little to as high as around 5 times as the amount of endogenous gene expression. Using these transgenic mice to breed with Enam knockout mice, we found that appropriate transgene expression level can fully recover the defective phenotype of Enam knockout mice. In one transgenic mouse line, which has a moderate expression level, the transgene successfully rescued the defective phenotype of Enam knockout mice. The enamel thickness and microstructure of enamel is the same as wild-type mouse in this transgene expressed in knockout background mice. Other transgenic mouse lines have a normal enamel thickness and normal decussation pattern when the transgene is expressed in heterozygous background. The teeth appear yellowish and smooth, which is similar to that of the wild-type mouse. We also found in moderate to high expression level enamelin transgenic mouse lines, the enamel started to have defective phenotypes: with moderate expression level, the teeth show protrusive structure on the surface of enamel; with high transgene expression, the enamel layer is almost lost. This is the first time in the literature that described the effect of over-expression of enamelin in developing enamel.Ph.D.Oral Health SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/78884/1/yuhel_1.pd

Advances of MnO2 nanomaterials as novel agonists for the development of cGAS-STING-mediated therapeutics

As an essential micronutrient, manganese plays an important role in the physiological process and immune process. In recent decades, cGAS-STING pathway, which can congenitally recognize exogenous and endogenous DNA for activation, has been widely reported to play critical roles in the innate immunity against some important diseases, such as infections and tumor. Manganese ion (Mn2+) has been recently proved to specifically bind with cGAS and activate cGAS-STING pathway as a potential cGAS agonist, however, is significantly restricted by the low stability of Mn2+ for further medical application. As one of the most stable forms of manganese, manganese dioxide (MnO2) nanomaterials have been reported to show multiple promising functions, such as drug delivery, anti-tumor and anti-infection activities. More importantly, MnO2 nanomaterials are also found to be a potential candidate as cGAS agonist by transforming into Mn2+, which indicates their potential for cGAS-STING regulations in different diseased conditions. In this review, we introduced the methods for the preparation of MnO2 nanomaterials as well as their biological activities. Moreover, we emphatically introduced the cGAS-STING pathway and discussed the detailed mechanisms of MnO2 nanomaterials for cGAS activation by converting into Mn2+. And we also discussed the application of MnO2 nanomaterials for disease treatment by regulating cGAS-STING pathway, which might benefit the future development of novel cGAS-STING targeted treatments based on MnO2 nanoplatforms

In situ poling X-ray diffraction studies of lead-free BiFeO3–SrTiO3 ceramics

The origin of the large electrostrain in BiFeO3-BaTiO3 (BF-BT) ceramics is controversial and has been attributed to either a field-induced transition to a long-range ferroelectric (FE) state or to multi-symmetry, polar nanoregions within a pseudocubic matrix whose vectors approximately align with the direction of the applied field. The (1-x)BiFeO3-xSrTiO3 (BF-xST) solid solution is structurally and microstructurally similar to BF-BT and provides a further case study to assess the origin of electrostrain. In BF-xST, electrostrain is optimized at x = 0.4 (0.15%) which zero field, room temperature full-pattern X-ray diffraction (XRD) Rietveld refinement and scanning/transmission electron microscopy suggest is composed of 15% rhombohedral (R) cores, surrounded by 85% pseudocubic (PC) shells. In-situ poling synchrotron XRD reveals that all peaks remain singlet and exhibit no change in full width half maximum up to 100 kV cm−1, confirming the absence of long-range FE order and the retention of short-range polar order, despite the large applied field. Strain anisotropy (calculated from individual peaks) of ε220 > ε111 > ε200 and the associated strain orientation distribution however, indicate the existence of local orthorhombic (O), R and tetragonal (T) symmetries. The data therefore imply the existence under poling of multi-symmetry polar nanoregions in BF-0.4ST rather than a long FE phase, supporting the model described by Wang and co-workers (2019) for BF-BT compositions

Signal Transduction Pathways in the Pentameric Ligand-Gated Ion Channels

The mechanisms of allosteric action within pentameric ligand-gated ion channels (pLGICs) remain to be determined. Using crystallography, site-directed mutagenesis, and two-electrode voltage clamp measurements, we identified two functionally relevant sites in the extracellular (EC) domain of the bacterial pLGIC from Gloeobacter violaceus (GLIC). One site is at the C-loop region, where the NQN mutation (D91N, E177Q, and D178N) eliminated inter-subunit salt bridges in the open-channel GLIC structure and thereby shifted the channel activation to a higher agonist concentration. The other site is below the C-loop, where binding of the anesthetic ketamine inhibited GLIC currents in a concentration dependent manner. To understand how a perturbation signal in the EC domain, either resulting from the NQN mutation or ketamine binding, is transduced to the channel gate, we have used the Perturbation-based Markovian Transmission (PMT) model to determine dynamic responses of the GLIC channel and signaling pathways upon initial perturbations in the EC domain of GLIC. Despite the existence of many possible routes for the initial perturbation signal to reach the channel gate, the PMT model in combination with Yen's algorithm revealed that perturbation signals with the highest probability flow travel either via the β1-β2 loop or through pre-TM1. The β1-β2 loop occurs in either intra- or inter-subunit pathways, while pre-TM1 occurs exclusively in inter-subunit pathways. Residues involved in both types of pathways are well supported by previous experimental data on nAChR. The direct coupling between pre-TM1 and TM2 of the adjacent subunit adds new insight into the allosteric signaling mechanism in pLGICs. © 2013 Mowrey et al

Enamelin Is Critical for Ameloblast Integrity and Enamel Ultrastructure Formation

Mutations in the human enamelin gene cause autosomal dominant hypoplastic amelogenesis imperfecta in which the affected enamel is thin or absent. Study of enamelin knockout NLS-lacZ knockin mice revealed that mineralization along the distal membrane of ameloblast is deficient, resulting in no true enamel formation. To determine the function of enamelin during enamel formation, we characterized the developing teeth of the Enam−/− mice, generated amelogenin-driven enamelin transgenic mouse models, and then introduced enamelin transgenes into the Enam−/− mice to rescue enamel defects. Mice at specific stages of development were subjected to morphologic and structural analysis using β-galactosidase staining, immunohistochemistry, and transmission and scanning electron microscopy. Enamelin expression was ameloblast-specific. In the absence of enamelin, ameloblasts pathology became evident at the onset of the secretory stage. Although the aggregated ameloblasts generated matrix-containing amelogenin, they were not able to create a well-defined enamel space or produce normal enamel crystals. When enamelin is present at half of the normal quantity, enamel was thinner with enamel rods not as tightly arranged as in wild type suggesting that a specific quantity of enamelin is critical for normal enamel formation. Enamelin dosage effect was further demonstrated in transgenic mouse lines over expressing enamelin. Introducing enamelin transgene at various expression levels into the Enam−/− background did not fully recover enamel formation while a medium expresser in the Enam+/− background did. Too much or too little enamelin abolishes the production of enamel crystals and prism structure. Enamelin is essential for ameloblast integrity and enamel formation

Enamelin is critical for ameloblast integrity and enamel ultrastructure formation

Mutations in the human enamelin gene cause autosomal dominant hypoplastic amelogenesis imperfecta in which the affected enamel is thin or absent. Study of enamelin knockout NLS-lacZ knockin mice revealed that mineralization along the distal membrane of ameloblast is deficient, resulting in no true enamel formation. To determine the function of enamelin during enamel formation, we characterized the developing teeth of the Enam-/- mice, generated amelogenin-driven enamelin transgenic mouse models, and then introduced enamelin transgenes into the Enam-/- mice to rescue enamel defects. Mice at specific stages of development were subjected to morphologic and structural analysis using β-galactosidase staining, immunohistochemistry, and transmission and scanning electron microscopy. Enamelin expression was ameloblast-specific. In the absence of enamelin, ameloblasts pathology became evident at the onset of the secretory stage. Although the aggregated ameloblasts generated matrix-containing amelogenin, they were not able to create a well-defined enamel space or produce normal enamel crystals. When enamelin is present at half of the normal quantity, enamel was thinner with enamel rods not as tightly arranged as in wild type suggesting that a specific quantity of enamelin is critical for normal enamel formation. Enamelin dosage effect was further demonstrated in transgenic mouse lines over expressing enamelin. Introducing enamelin transgene at various expression levels into the Enam -/- background did not fully recover enamel formation while a medium expresser in the Enam+/- background did. Too much or too little enamelin abolishes the production of enamel crystals and prism structure. Enamelin is essential for ameloblast integrity and enamel formation. © 2014 Hu et al

Three dimensional CBCT analysis of morphology in patients with chin deviation

PLEASE NOTE: This work is protected by copyright. Downloading is restricted to the BU community: please click Download and log in with a valid BU account to access. If you are the author of this work and would like to make it publicly available, please contact [email protected] (MSD) --Boston University, Henry M. Goldman School of Dental Medicine, 2013 (Department of Orthodontics and Dentofacial Orthopedics).Includes bibliographic references: leaves 33-36.Introduction: Facial symmetry is defined as the correspondence in size, form, and arrangement of the facial features on opposite sides of the median sagittal plane. Although mild facial asymmetry is the norm, significant facial asymmetry is not uncommon. Mandibular asymmetry, in which the chin position deviates from the midsagittal plane, is one of the largest contributors to facial asymmetry. Seeking a reliable measurement for evaluation of facial asymmetry with chin deviation is a difficult task. Radiographically, 2-dimensional films such as posteroanterior cephalogram, submentalvertex views and panoramic films have been used by different investigators for diagnosis of facial and mandibular asymmetry. Objective: The purpose of this study is to investigate which anatomic areas contribute to asymmetry in patients with chin deviation. Material and Methods: 31 adult patients were divided into facial symmetry (n=16) and chin deviation groups (n=15), with asymmetry being defined as at least a 2 degree deviation between Me-ANS and the midfacial plane. Patients included had no history of trauma, temporomandibular disease, or craniofacial tumors. Three-dimensional cone-beam computed tomography (CBCT) scans were used to locate surface landmarks that represented condylar, coronoid, gonial angle, body and chin units. This method has been used in a recent study. These landmarks were used to calculate the lengths and widths of each mandibular component. For each measurement, the difference between the two sides in the chin deviation group was compared to the difference between the two sides in the control group. Student's t-test was used to test the differences between the 2 groups for significance. Results: The difference in mandibular body unit length and chin unit length between the right and left sides was significantly greater in the chin deviation group (P = 0.03 and p =0.001, respectively) than in the control group. The measurements of condylar length, coronoid length, and condylar width, angular unit width, ramal heights between the chin deviation and control groups were not found to be statistically significant. Within the chin deviation group, the side from which the chin was deviated had a statistically significant longer body unit length and chin unit length. Conclusion: Asymmetry in the mandibular body unit length and chin length seem to be a consistent feature in patients with chin deviation. The heterogeneity of facial asymmetry with chin deviation may explain the lack of consistent asymmetry in other areas such as mandibular condylar length, coronoid length, ramal length, angular width, and condylar width. Comparison of unit volumes between the two groups will be investigated. A larger sample size may be needed to see other differences

Tax Burden and Corporate Investment Efficiency

Using A-share listed companies in Shanghai and Shenzhen from 2015 to 2021 as the research sample, a fixed-effects model was used to examine the effect of the reduction of corporate tax burden on investment efficiency under the tax reduction policy, as well as the role of tax avoidance and financing constraints in the mechanism. The results of the study show that the reduction of tax burden can effectively improve the efficiency of corporate investment, and this positive effect is reflected in the alleviation of corporate under-investment and discouragement of over-investment. The paper also analyses the mechanism through which tax burden affects the efficiency of corporate investment, and finds that tax reduction can discourage inefficient investment by reducing corporate tax avoidance and alleviating corporate financing constraints. In further analysis, it is found that the effect of tax cuts on investment efficiency is more significant in the sample of non-state enterprises, low corporate governance and low marketisation. The findings of the study support the positive significance of the current tax reduction policy. We provide a reference of tax reduction benefits to curb tax avoidance behavior, and provide a basis for relevant policy departments to further accelerate the implementation of tax reduction policies

Tax Burden and Corporate Investment Efficiency

Using A-share listed companies in Shanghai and Shenzhen from 2015 to 2021 as the research sample, a fixed-effects model was used to examine the effect of the reduction of corporate tax burden on investment efficiency under the tax reduction policy, as well as the role of tax avoidance and financing constraints in the mechanism. The results of the study show that the reduction of tax burden can effectively improve the efficiency of corporate investment, and this positive effect is reflected in the alleviation of corporate under-investment and discouragement of over-investment. The paper also analyses the mechanism through which tax burden affects the efficiency of corporate investment, and finds that tax reduction can discourage inefficient investment by reducing corporate tax avoidance and alleviating corporate financing constraints. In further analysis, it is found that the effect of tax cuts on investment efficiency is more significant in the sample of non-state enterprises, low corporate governance and low marketisation. The findings of the study support the positive significance of the current tax reduction policy. We provide a reference of tax reduction benefits to curb tax avoidance behavior, and provide a basis for relevant policy departments to further accelerate the implementation of tax reduction policies