Amelogenin proteins are a major component of the developing enamel matrix, and are likely to have a key role in the control of enamel biomineralization. The heterogeneity of amelogenin is in part due to alternative splicing of the amelogenin RNA transcripts. Several patterns of alternative splicing have been described in mouse, bovine, porcine, and human enamel, with all alternatively spliced products having homologous 5' and 3' sequences within the coding regions. In these studies, we have used anchored PCR to identify alternatively spliced amelogenin cDNA sequences in the rat. We found amelogenin cDNAs that could be divided into two groups based on their 3' sequence. Group 1 cDNAs had a novel terminal sequence that has not been previously identified, while group 2 cDNAs were similar to those previously identified in other animal species. We identified a sequence, identical to the novel 3' amelogenin cDNA sequence, in rat genomic DNA downstream from the previously identified exon 7. The putative amelogenin proteins predicted for the two groups differed in their predicted isoelectric points, with the novel group 1 proteins having a more basic isoelectric point.

Polarized and unpolarized neutron-diffraction measurements have been taken to determine the magnetic structure of the Cu spins in the RBa2Cu3O6+x system as a function of temperature. Most of the results have been obtained on two (semiconducting) oxygen-deficient single crystals of composition NdBa2Cu3O6.1 and NdBa2Cu3O6.35. On cooling from the paramagnetic state, the Cu-O plane layers first order at a Néel temperature TN1 in a simple antiferromagnetic arrangement of spins, with TN1=430 K for x=0.1 and TN1=230 K for x=0.35, and with a saturated moment of 0.65B. At a lower temperature TN2 the Cu chain layer also orders, with TN2=80 and 10 K for x=0.1 and 0.35, respectively. Hence both transition temperatures decrease with increasing oxygen concentration in this range of x, and the qualitative behavior for these two samples is found to be identical. We have not, however, observed this low-T structure in polycrystalline samples of either YBa2Cu3O6+x or NdBa2Cu3O6+x, and some possible explanations for this difference in behavior are discussed. For the single crystals in the low-T phase the Cu spins in all three copper-oxygen layers are ordered in a simple antiferromagnetic arrangement, with the magnetic unit cell double the chemical unit cell along all three crystallographic directions. On the basis of the measured integrated intensities of over 40 magnetic reflections in both ordered phases, the results can be accounted for quantitatively with the assumption of a 3d magnetic form factor on the Cu ions, with no need for a significant moment on any of the oxygen ions. At low T, site-averaged moments of 0.35B and 0.8B are obtained in the chain and the plane layers, respectively. The fact that the ordered moment on the plane layers increases in the low-T phase is direct evidence that two-dimensional quantum fluctuations play an important role in the plane layers in the high-T ordered phase. The evolution of the low-T spin structure into the high-T structure involves a noncollinear configuration in which the spins rotate as a function of temperature in the plane layers, while the chain layer becomes thermally disordered. The temperature dependence of the structure indicates that competing interactions between the layers are important, and this is discussed in detail. Finally, exploratory measurements as a function of applied magnetic field indicate that the magnetic anisotropy in the tetragonal plane is much smaller than the exchange energies. © 1990 The American Physical Society.

MicroRNAs are major post-transcriptional regulators of gene expression. Here we show in the ancient protozoan Giardia lamblia a snoRNA-derived 26-nucleotide microRNA, miR3, which represses the translation of histone H2A mRNA containing an imperfect target

Alternative splicing of the amelogenin gene generates a family of proteins secreted by ameloblasts that are primarily responsible for tooth enamel formation. Here the presence of two additional exons, downstream of exon 7, which are followed by an alternate polyadenylation site, is reported. Long polymerase chain reaction was used with a rat genomic amelogenin template to amplify sequences downstream from the primary polyadenylation site. Within the amplified sequences, two exons of 45 bp (exon 8) and 110 bp (exon 9) were identified. The presence of these additional exons in the human and mouse genome was indicated by Southern blot analysis. Antibodies raised against a synthetic peptide corresponding to a sequence encoded by exon 9 positively stained ameloblasts in sections of developing murine and porcine unerupted teeth. These results suggest that an amelogenin protein(s) that includes sequences derived from exons 8 and 9 is synthesized by the ameloblasts.

This brief technique paper presents a method of reconstructing the global, time-varying distribution of some physical quantity Q that has been sparsely sampled at various locations within the magnetosphere and at different times. The quantity Q can be essentially any measurement taken on the satellite including a variety of waves (chorus, hiss, magnetosonic, and ion cyclotron), electrons of various energies ranging from cold to relativistic, and ions of various species and energies. As an illustrative example, we chose Q to be the electron number density (inferred from spacecraft potential) measured by three Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes between 2008 and 2014 and use the SYM-H index, taken at a 5 min cadence for the 5 h preceding each observed data point as the main regressor, although the predictor can also be any suitable geomagnetic index or solar wind parameter. Results show that the equatorial electron number density can be accurately reconstructed throughout the whole of the inner magnetosphere as a function of space and time, even capturing the dynamics of elementary plasmaspheric plume formation and corotation, suggesting that the dynamics of various other physical quantities could be similarly captured. For our main model, we use a simple, fully connected feedforward neural network with two hidden layers having sigmoidal activation functions and an output layer with a linear activation function to perform the reconstruction. The training is performed using the Levenberg-Marquardt algorithm and gives typical RMS errors of ~1.7 and regression of >0.93, which is considered excellent. We also present a discussion on the different applications and future extensions of the present model, for modeling various physical quantities.

Neutron-diffraction measurements have been carried out as a function of hydrostatic pressure to study the magnetic order of the Cu spins in NdBa2Cu3O6.35 and NdBa2Cu3O6.1. In the high-temperature phase, where the Cu planes order antiferromagnetically, we find that the Néel temperature TN1 is very strongly dependent on pressure, increasing at the rate of 1/423 K/kbar. We attribute this phenomenal sensitivity to the two-dimensional-like behavior of this magnetic system. In the low-temperature phase, which is associated with magnetic ordering of the chains, only a small change in the ordering temperature TN2 is observed. © 1989 The American Physical Society.

Objective

To study the mechanisms which promote the interactions of amelogenin proteins with the forming mineral to establish suitable conditions for the biomimetic synthesis of enamel in vitro.

Design

Saturated calcium phosphate solutions were used in conjunction with recombinant amelogenin proteins to induce mineral formation on glass-ceramics substrates containing oriented fluoroapatite crystals (FAP). The height of mineral layers formed on these substrates within 24 h was measured by atomic force microscopy (AFM).

Experimental variables

The effect of protein concentration, pH and degree of saturation (DS) on the growth of apatite mineral was evaluated. Mineralization experiments were performed at 0, 0.4 and 1.6 mg/ml amelogenin concentrations. Mineralization solutions were used at pH values of 6.5, 7.4, 8.0 and 8.8 and DS of calcium and phosphate between 9 and 13.

Outcome measure

Height and morphology of mineralized layer formed on glass-ceramic substrates as determined from AFM measurements.

Results

Homogeneous nucleation and crystal growth of thin layers on the FAP were observed, when calcium and phosphate ions were added. The height of these layers grown on (001) planes of FAP was strongly dependent on the protein concentration and pH. At concentrations of 0 and 0.4 mg/ml crystal grew 5-15 nm on the FAP, while they grew approximately to 200 nm at 1.6 mg/ml. The enhanced crystal growth was observed only at pH 6.5, 7.4 and 8.0, while layers only 20 nm thick were obtained at pH 8.8. An increase in DS resulted in uncontrolled growth of calcium phosphate mineral covering large areas of the substrate.

Conclusions

Protein concentration, pH and the saturation of the mineralizing solution need to be considered carefully to provide suitable conditions for amelogenin-guided growth of apatite crystals.