Establishment of crown–root domain borders in mouse incisor

Teeth are composed of two domains, the enamel-covered crown and the enamel-free root. The understanding of the initiation and regulation of crown and root domain formation is important for the development of bioengineered teeth. In most teeth the crown develops before the root, and erupts to the oral cavity whereas the root anchors the tooth to the jawbone. However, in the continuously growing mouse incisor the crown and root domains form simultaneously, the crown domain forming the labial and the root domain the lingual part of the tooth. While the crown–root border on the incisor distal side supports the distal enamel extent, reflecting an evolutionary diet adaptation, on the incisor mesial side the root-like surface is necessary for the attachment of the interdental ligament between the two incisors. Therefore, the mouse incisor exhibits a functional distal–mesial asymmetry. Here, we used the mouse incisor as a model to understand the mechanisms involved in the crown–root border formation. We analyzed the cellular origins and gene expression patterns leading to the development of the mesial and distal crown–root borders. We discovered that Barx2, En1, Wnt11, and Runx3 were exclusively expressed on the mesial crown–root border. In addition, the distal border of the crown–root domain might be established by cells from a different origin and by an early Follistatin expression, factor known to be involved in the root domain formation. The use of different mechanisms to establish domain borders gives indications of the incisor functional asymmetry.     

Monte Carlo Simulation of the β-Sheet–Random Coil Transition of a Homopolypeptide. I. Equilibrium Study

Abstract

Monte Carlo simulation of the β-sheet – random coil conversion of a homopolypeptide chain was carried out on the basis of a model where successive two amino acid residues were assumed to change their states simultaneously and hence constituted a basic unit. Only three states were considered for each unit: extended, turn and coil. The conversion exhibited a transition between two states, random coil (C) and the β-sheet (B). In the transition region, two population maxima were always found, each corresponded to the local minimum of the free energy and there was an energy barrier between them. This behavior is characteristic of the all-or-none type transition. We have found that the nature of the first-order transition is retained in the case of a small system consisting of 100 units. The size of the cooperative unit was evaluated. According to the analytical theory of Kanô, a transition curve was obtained which was very close to the present one. This consistent result has suggested that equilibrium properties of the β-sheet-random coil transition are well evaluated with the mean field approximation. The matrix method of Mattice is also discussed.     

Proton NMR studies of 5'-d-(TC)(3) (CT)(3) (AG)(3)-3'--a paperclip triplex: the structural relevance of turns

In this study, we present the results of structural analysis of an 18-mer DNA 5'-T(1)C(2)T(3)C(4)T(5)C(6)C(7)T(8)C(9)T(10)C(11)T(12)A(13)G(14)A(15)G(16)A(17)G(18)-3' by proton nuclear magnetic resonance (NMR) spectroscopy and molecular modeling. The NMR data are consistent with characteristics for triple helical structures of DNA: downfield shifting of resonance signals, typical for the H3(+) resonances of Hoogsteen-paired cytosines; pH dependence of these H3(+) resonance; and observed nuclear Overhauser effects consistent with Hoogsteen and Watson-Crick basepairing. A three-dimensional model for the triplex is developed based on data obtained from two-dimensional NMR studies and molecular modeling. We find that this DNA forms an intramolecular "paperclip" pyrimidine-purine-pyrimidine triple helix. The central triads resemble typical Hoogsteen and Watson-Crick basepairing. The triads at each end region can be viewed as hairpin turns stabilized by a third base. One of these turns is comprised of a hairpin turn in the Watson-Crick basepairing portion of the 18-mer with the third base coming from the Hoogsteen pairing strand. The other turn is comprised of two bases from the continuous pyrimidine portion of the 18-mer, stabilized by a hydrogen-bond from a purine. This "triad" has well defined structure as indicated by the number of nuclear Overhauser effects and is shown to play a critical role in stabilizing triplex formation of the internal triads.     

Plakophilin-1, a Novel Wnt Signaling Regulator,Is Critical for Tooth Development and Ameloblast Differentiation

Tooth morphogenesis is initiated by reciprocal interactions between the ectoderm and neural crest-derived mesenchyme, and the Wnt signaling pathway is involved in this process. We found that Plakophilin (PKP)1, which is associated with diseases such as ectodermal dysplasia/skin fragility syndrome, was highly expressed in teeth and skin, and was upregulated during tooth development. We hypothesized that PKP1 regulates Wnt signaling via its armadillo repeat domain in a manner similar to β-catenin. To determine its role in tooth development, we performed Pkp1 knockdown experiments using ex vivo organ cultures and cell cultures. Loss of Pkp1 reduced the size of tooth germs and inhibited dental epithelial cell proliferation, which was stimulated by Wnt3a. Furthermore, transfected PKP1-emerald green fluorescent protein was translocated from the plasma membrane to the nucleus upon stimulation with Wnt3a and LiCl, which required the PKP1 N terminus (amino acids 161 to 270). Localization of PKP1, which is known as an adhesion-related desmosome component, shifted to the plasma membrane during ameloblast differentiation. In addition, Pkp1 knockdown disrupted the localization of Zona occludens 1 in tight junctions and inhibited ameloblast differentiation; the two proteins were shown to directly interact by immunoprecipitation. These results implicate the participation of PKP1 in early tooth morphogenesis as an effector of canonical Wnt signaling that controls ameloblast differentiation via regulation of the cell adhesion complex.     

Effects of polyamines on the thermal stability and formation kinetics of DNA duplexes with abnormal structure

The effects of ions (i.e. Na⁺, Mg²⁺ and polyamines including spermidine and spermine) on the stability of various DNA oligonucleotides in solution were studied. These synthetic DNA molecules contained sequences that mimic various cellular DNA structures, such as duplexes, bulged loops, hairpins and/or mismatched base pairs. Melting temperature curves obtained from the ultraviolet spectroscopic experiments indicated that the effectiveness of the stabilization of cations on the duplex formation follows the order of spermine > spermidine > Mg²⁺ > Na⁺ > Tris–HCl buffer alone at pH 7.3. Circular dichroism spectra showed that salts and polyamines did not change the secondary structures of those DNA molecules under study. Surface plasmon resonance (SPR) observations suggested that the rates of duplex formation are independent of the kind of cations used or the structure of the duplexes. However, the rate constants of DNA duplex dissociation decrease in the same order when those cations are involved. The enhancement of the duplex stability by polyamines, especially spermine, can compensate for the instability caused by abnormal structures (e.g. bulged loops, hairpins or mismatches). The effects can be so great as to make the abnormal DNAs as stable as the perfect duplex, both kinetically and thermodynamically. Our results may suggest that the interconversion of various DNA structures can be accomplished readily in the presence of polyamine. This may be relevant in understanding the role of DNA polymorphism in cells.     

Retrograde intrabiliary injection of amphipathic materials causes phospholipid secretion into bile. Taurocholate causes phosphatidylcholine secretion, 3-[(3-cholamidopropyl)dimethylammonio]-propane-1-sulphonate (CHAPS) causes mixed phospholipid secretion.

The control of biliary phospholipid and cholesterol secretions by bile acid was studied by using the technique of retrograde intrabiliary injection. Taurocholate (TC), a moderately hydrophobic bile acid, taurodehydrocholate (TDHC), a hydrophilic non-micelle-forming bile acid, and 3-[(3-cholamidopropyl)-dimethylammonio]propane-1-sulphonate (CHAPS), a detergent, were individually administered by retrograde intrabiliary injection (RII) into the biliary tree, and bile acids, phospholipids and cholesterol subsequently appearing in the bile were measured. TC (1.3 mumol; 45 microliters) injected retrogradely provoked a 3.5-fold increase in biliary phospholipid output for 40 min, as compared with the saline control. Injection of 2.7 mumol of TC (90 microliters) caused a 7.5-fold increase in phospholipid output, which reached a peak at 12 min after RII, and phospholipid output continued for 40 min. Cholesterol output was also elicited under these conditions, showing both dose-dependency and extended secretion. Injection of 1.8 mumol of TDHC caused very little increase in either biliary phospholipid or cholesterol. Injection of 0.9 mumol of CHAPS (45 microliters) provoked a single substantial peak of phospholipid output in the 3 min bile sample. T.l.c. analysis of the phospholipid extracts of the bile collected after each compound showed, for TC, a single compound which co-migrated with the phosphatidylcholine standard, whereas for CHAPS substantial amounts of other phospholipids were present.     

胺碘酮致甲状腺功能异常的诊治进展

胺碘酮是治疗心律失常的常用药物。但由于其富含碘及自身固有的特性,可导致一系列甲状腺功能的紊乱,甚至引发明显的甲状腺功能减退(甲减)或甲状腺功能亢进(甲亢)。对于胺碘酮所致甲减(AIH)的诊断和治疗目前比较清晰,但对胺碘酮所致甲亢(AIT)的诊断、鉴别其亚型及治疗有一定的难度。