Showing papers by "Braunschweig University of Technology published in 1994"

Pax-3 is required for the development of limb muscles: a possible role for the migration of dermomyotomal muscle progenitor cells

Abstract: Limb muscles in vertebrates originate from dermomyotomal cells, which during early development migrate from the ventrolateral region of somites into the limb buds. These progenitor cells do not express any muscle-specific marker genes or myogenic transcription factors until they reach their destination in the limbs. Here, we demonstrate by in situ hybridization that myogenic cells in somites and a population of presumably migratory muscle precursor cells in somatopleural tissue as well as myoblasts in the developing limbs express Pax-3. Significantly, in homozygous splotch mutant mice, which synthesize altered Pax-3 mRNA but make no normal protein, no cells positive for Pax-3 transcripts can be detected in the region of migrating limb muscle precursors or in the limb itself. In contrast, myotomal precursor cells and axial skeletal muscles contain Pax-3 transcripts also in the mutant. Interestingly, these animals fail to develop limb musculature as demonstrated by the lack of hybridization with various probes for myogenic transcription factors (Myf-5, myogenin, MyoD) but make apparently normal axial muscles. These observations suggest that Pax-3 is necessary for the formation of limb muscles, affecting either the generation of myogenic precursors in the somitic dermomyotome or the migration of these cells into the limb field.

Analysis of vectorial mode fields in optical waveguides by a new finite difference method

Abstract: An important class of dielectric optical waveguides has stepped refractive index profiles. For these waveguides we present a new finite-difference approach free of spurious modes. The coupled difference equations are formulated in terms of the transverse magnetic field components H/sub x/ and H/sub y/. We show how the boundary conditions can be formulated and included in the finite difference scheme to obtain a unique set of equations. For a step-index fiber a comparison of the numerical results with the analytical solution shows that the relative error in the propagation constant is as low as 4.4/spl times/10/sup /spl minus/7/ for an index difference of 7.3%. For a rib waveguide, we compare our results with previously published data based on other methods. Field plots of the dominant and the weak transverse field components of the magnetic field for the fundamental mode of a buried rib waveguide are also given. >

On the inference of configuration structures from source code

Abstract: We apply mathematical concept analysis to the problem of inferring configuration structures from existing source code. Concept analysis has been developed by German mathematicians over the last years; it can be seen as a discrete analogon to Fourier analysis. Based on this theory, our tool will accept source code, where configuration-specific statements are controlled by the preprocessor. The algorithm will compute a so-called concept lattice, which - when visually displayed - allows remarkable insight into the structure and properties of possible configurations. The lattice not only displays fine-grained dependencies between configuration threads, but also visualizes the overall quality of configuration structures according to software engineering principles. The paper presents a short introduction to concept analysis, as well as experimental results on various programs. >

Domain structure and conserved epitopes of Sfb protein, the fibronectin-binding adhesin of Streptococcus pyogenes.

Abstract: Summary Streptococcus pyogenes expresses a fibronectin-binding surface protein (Sfb protein) which mediates adherence to human epithelial cells. The nucleotide sequence of the sfb gene was determined and the primary sequence of the Sfb protein was analysed. The protein consists of 638 amino acids and comprises five structurally distinct domains. The protein starts with an N-terminal signal peptide followed by an aromatic domain. The central part of the protein is formed by four proline-rich repeats which are flanked by non-repetitive spacer sequences. A second repeat region, consisting of four repeats that are distinct from the proline repeats and have been shown to form the fibronectin-binding domain, is located in the Cterminal part of the protein. The protein ends with a typical cell wall and membrane anchor region. Comparative sequence analysis of the N-terminal aromatic domain revealed similarities with carbohydrate-binding sites of other proteins. The proline repeat region of the Sfb protein shares characteristic features with proline-rich repeats of functionally distinct surface proteins from pathogenic Gram-positive cocci. Immunoelectron microscopy revealed an even distribution of the fibronectin-binding domain of Sfb protein on the surface of streptococcal cells. Analyses of 38 sfb genes originating from different S. pyogenes isolates revealed primary sequence variability in regions coding for the N-termini of mature Sfb proteins, whereas sequences coding for the central and C-terminal repeats were highly conserved. The repeat sequences are postulated to act as target sites for intragenic recombination events that result in variable numbers of repeats within the different sfb genes. A model of the Sfb protein is presented.

Cloning of human and mouse genes homologous to RAD52, a yeast gene involved in DNA repair and recombination

Abstract: The RAD52 gene of Saccharomyces cerevisiae is required for recombinational repair of double-strand breaks. Using degenerate oligonucleotides based on conserved amino acid sequences of RAD52 and rad22, its counterpart from Schizosaccharomyces pombe, RAD52 homologs from man and mouse were cloned by the polymerase chain reaction. DNA sequence analysis revealed an open reading frame of 418 amino acids for the human RAD52 homolog and of 420 amino acid residues for the mouse counterpart. The identity between the two proteins is 69% and the overall similarity 80%. The homology of the mammalian proteins with their counterparts from yeast is primarily concentrated in the N-terminal region. Low amounts of RAD52 RNA were observed in adult mouse tissues. A relatively high level of gene expression was observed in testis and thymus, suggesting that the mammalian RAD52 protein, like its homolog from yeast, plays a role in recombination. The mouse RAD52 gene is located near the tip of chromosome 6 in region G3. The human equivalent maps to region p13.3 of chromosome 12. Until now, this human chromosome has not been implicated in any of the rodent mutants with a defect in the repair of double-strand breaks.

Quantitative transient gene expression: Comparison of the promoters for maize polyubiquitin1, rice actin1, maize-derived Emu and CaMV 35S in cells of barley, maize and tobacco

Abstract: The particle gun approach was used for the quantification of promoter efficiency in a test system for transient gene expression. β-Glucuronidase was used as reporter gene for determining promotote strength. The variability inherent in this gene transfer system was considerably reduced by calculating a transformation efficiency factor given by the expression of a cotransferred second reporter gene (firefly luciferase). The calibration of β-glucuronidase activity by the transformation efficiency factor caused a lower statistical variance of the values and allowed reliable results to be obtained with a smaller set of repetitions. The CaMV 35S promoter (as a control) and the monocot-specific promoters for maize polyubiquitin1, rice actin 1 and the maize-derivedEmu were characterized and compared with respect to expression strength, as tested under identical conditions in suspension cell cultures of maize, barley and tobacco. Compared to the 35S promoter, the monocot-specific promoters show up to 15-fold higher expression in maize and barley but give only weak expression in tobacco. No expression was found for the rice actin 1 promoter in tobacco. The level of reporter gene expression is influenced by the osmotic potential in the agar medium. For theEmu promoter, the calibrated β-glucuronidase activities remained mearly constant at low sucrose concentrations. Above 8% sucrose, the calibrated activities increased steadily with increasing osmotic conditions, reaching a three-to four-fold higher level at the highest sucrose concentration (32%) as compared to the standard concentration (4% sucrose) in the medium.

Initial steps of myogenesis in somites are independent of influence from axial structures

Abstract: Formation of paraxial muscles in vertebrate embryos depends upon interactions between early somites and the neural tube and notochord. Removal of both axial structures results in a complete loss of epaxial myotomal muscle, whereas hypaxial and limb muscles develop normally. We report that chicken embryos, after surgical removal of the neural tube at the level of the unsegmented paraxial mesoderm, start to develop myotomal cells that express transcripts for the muscle-specific regulators MyoD and myogenin. These cells also make desmin, indicating that the initial steps of axial skeletal muscle formation can occur in the absence of the neural tube. However, a few days following the extirpation, the expression of MyoD and myogenin transcripts gradually disappears, and becomes almost undetectable after 4 days. From these observations we conclude that the neural tube is not required for the generation of the skeletal muscle cell lineage, but may support the survival or maitenance of further differentiation of the myotomal cell compartment. Notochord transplanted medially or laterally to the unsegmented paraxial mesoderm leads to a ventralization of axial structures but does not entirely prevent the early appearance of myoblasts expressing MyoD transcripts. However, the additional notochord inhibits subsequent development and maturation of myotomes. Taken together, our data suggest that neural tube promotes, and notochord inhibits, the process of myogenesis in axial muscles at a developmental step following the initial expression of myogenic bHLH regulators.

Statistical analysis of diffuse ion events upstream of the Earth's bow shock

Abstract: A statistical study of diffuse energetic ion events and their related waves upstream of the Earth's bow shock was performed using data from the Active Magnetospheric Particle Tracer Explorers/Ion Release Module (AMPTE/IRM) satellite over two 5-month periods in 1984 and 1985. The data set was used to test the assumption in the self-consistent model of the upstream wave and particle populations by Lee (1982) that the particle acceleration through hydromagnetic waves and the wave generation are directly coupled. The comparison between the observed wave power and the wave power predicted on the observed energetic particle energy density and solar wind parameters results in a high correlation coefficient of about 0.89. The intensity of diffuse ions falls off approximately exponentially with the distance upstream from the bow shock parallel to the magnetic field with e-folding distances which vary from approximately 3.3 R(sub E) to approximately 11.7 R(sub E) over the energy range from 10 keV/e to 67.3 keV/e for both protons and alpha particles. After normalizing the upstream particle densities to zero bow shock distance by using these exponential variations, a good correlation (0.7) of the density of the diffuse ions with the solar wind density was found. This supports the suggestion that the solar wind is the source of the diffuse ions. Furthermore, the spectral slope of the diffuse ions correlates well with the solar wind velocity component in the direction of the interplanetary magnetic field (0.68 and 0.66 for protons and alpha particles) which concurs with the notion that the solar wind plays an important role in the acceleration of the upstream particles.

Microbial production of propionic acid and vitamin B12 using molasses or sugar.

Abstract: With a cell concentration of 125 g dry biomass 1−1 and a dilution rate of 0.1 h−1,Propionibacterium acidipropionici produces 30 g propionic acid 1−1 from sugar with a productivity of 3 g 1−1 h−1. The yield of propionic acid is approx. 0.36–0.45 g propionic acid g−1 sucrose and is independent of the dilution rate and cell concentration. Acetic acid is an unwanted by-product in the production of propionic acid. The concentration of acetic acid only increases slightly when the cell concentration is increased. A two-stage fermentation process was developed for the conversion of sugar or molasses of various types to propionic acid and vitamin B12. By fermentation of blackstrap molasses (from sugar beet and sugar cane) in the first fermentation stage 17.7 g propionic acid 1−1 with a yield of 0.5 g propionic acid g−1 carbohydrate was produced with a dilution rate of 0.25 h−1. In the second stage 49 mg vitamin B12 1−1 was produced at a dilution rate of 0.03 h−1.

Simulation of anisotropic chemical etching of crystalline silicon using a cellular automata model

Abstract: Anisotropic chemical etching of crystalline silicon in aqueous KOH is simulated at the atomic level using a cellular automata model. Experimental etch-rate ratios as well as the influence of temperature and concentration of the etchant are taken into account by introducing a stochastic component. With the help of two examples, the underetching of a convex mask corner and mask-corner compensation for mesa-type corners, the capabilities of this model are demonstrated.

Interaction of plant profilin with mammalian actin

Abstract: The mode of interaction of birch and bovine profilins with actin was compared using a number of techniques. Birch profilin was purified from pollen or as a recombinant protein from Escherichia coli, using poly(l-proline) affinity chromatography and a monoclonal antibody for the identification of the isolated product. On two-dimensional gels, the genuine and recombinant proteins were identical in molecular mass and isoelectric point and revealed that birch profilin, in contrast to the basic profilins found in mammals, is an acidic protein, analogous to maize profilins. Bovine profilin was obtained from calf thymus. In viscometric assays, the birch protein was seen to modulate actin filament formation analogous to animal profilin. Birch profilin increased the critical concentration required for muscle and brain actin polymerization in a concentration-dependent manner, supporting the notion of the formation of a heterologous complex between the plant protein and animal actin. The effect was Mg2+-sensitive, as had been described for homologous complexes. The dissociation constants obtained for the plant/vertebrate and the vertebrate/vertebrate system were both in the micromolar range. The affinity of birch profilin for muscle actin was slightly lower than that for nonmuscle (brain) actin. A binary complex of birch profilin and skeletal muscle actin could be isolated by gel chromatography. Cross-linking experiments with actin, birch profilin, the G-actin binding peptide thymosin β4 and gelsolin segment 1, the N-terminal fragment of an actin capping protein, showed that profilin competed with thymosin β4, but had no effect on segment 1 binding to actin. These data indicate that the actin-binding domains in plant and animal profilins are functionally highly conserved, although the overall sequence similarity is less than 25%.

New spin filters for interferometric fringe patterns and grating patterns.

Abstract: The basic spin filter for interferometric fringe patterns is improved and developed into several new versions for different applications. These spin filters can filter off random noise efficiently and have almost no blurring effect and phase distortion for the fringe patterns. First, they find the local fringe tangent direction, and then they apply a one-dimensional low-pass filter on this direction. In this way the spin filters can separate easily and clearly high-frequency noise from a real fringe signal with nearly zero frequency. The new spin filters are suitable not only for various fringe patterns but also for wrapped-phase, line-grating, and cross-grating patterns, which are impossible by common filters.

Local 1-D interpretation of magnetotelluric B-polarization impedances

Abstract: SUMMARY It is shown that magnetotelluric impedances from the B-polarization (magnetic field in the strike direction of a 2-D resistivity structure) share a number of properties with 1-D impedances: all B-polarization impedances satisfy the same phase constraints as 1-D data, i.e. the impedance phase always lies between 0° and 90°. As a consequence the B-polarization impedances are minimum phase and thus allow conversions between apparent resistivity and phase. The constraints hold for an arbitrary 2-D topography of the air–earth interface. By examining the spectral function it is found that the B-polarization impedances for a number of models admit an exact 1-D interpretation. For two quarter-spaces this holds for all points and resistivity contrasts. The resulting 1-D model gives the correct resistivity down to a depth of half the distance to the interface. For the dyke model as the next complicated structure, 1-D interpretability requires that the host resistivity does not exceed the dyke resistivity by more than a factor of 60. B-polarization data of more complex structures investigated in this paper show either no, or only a marginal, violation of 1-D interpretability. A necessary condition constraining the frequency dependence of B-polarization and 1-D data in terms of their Mellin transform is derived in the final section.

Synthesis of Silver(I) Complexes with the Bis(diphenylphosphanyl)‐o‐carborane Ligand. Crystal Structure of [Ag(phen){(PPh2)2C2B10H10}]ClO4 and [Ag{(SPPh2)2CH2}{(PPh2)2C2B10H10}]ClO4 · CH2Cl2

Abstract: Silver(I) perchlorate or nitrate react readily with bis(di-phenylphosphanyl)-o-carborane to give the complexes [AgX{(PPh2)2C2B10H10}] [X = ClO4 (1), NO3, (2)]. The perchlorate ligand is weakly bound to the silver atom and thus can be displaced by other ligands affording the three-coordinated complexes [AgL{(PPh2)2C2B10H10}]ClO4 [L = PPh3 (3), PPh2Me (4), AsPh3 (5), C5H4NCOOH (6), C9H6NCOOH (7), SPPh3 (8)]. Compounds 3 and 4 can also be obtained by reaction of [Ag(OClO3)PR3] with the diphosphane. Treatment of complex 1 with bidentate ligands leads to the cationic four-coordinated [Ag(LL){(PPh2)2C2B10H10}]ClO4 [LL = (PPh2)2C2B10H10 (9), bipy (10), phen (11), (SPPh2)2CH2 (12)] or to the neutral [Ag(S2CNR2){(PPh2)2C2B10H10}] [NR2 = NEt2 (13), NC4H8 (14)]. The crystal structures of 11 and 12 have been established by X-ray crystallography. In both complexes the silver(I) atoms exhibit tetrahedral coordination by two phosphorus and two nitrogen or two sulfur atoms, respectively.

Exploitation of microfilament proteins by Listeria monocytogenes: microvillus-like composition of the comet tails and vectorial spreading in polarized epithelial sheets

Abstract: Effective cell-to-cell spreading of the facultative intracellular pathogen Listeria monocytogenes requires the interaction between bacteria and the microfilament system of the host cell. By recruiting actin filaments into a 'comet tail' localized at one pole of the bacterial cell wall, Listeria become mobile and propel themselves through the cytoplasm. They create protrusions at the plasma membrane that can invaginate adjacent cells. In this work, we have analysed the structural composition of Listeria-recruited microfilaments in various epithelial cell lines by immunofluorescence microscopy. The microfilament-crosslinking proteins alpha-actinin, fimbrin and villin were localized around bacteria as soon as actin filaments could be detected on the bacterial surface. Surprisingly, the same was found for ezrin/radixin, proteins involved in linking microfilaments to the plasma membrane. We found that in a polarized cell line derived from brush border kidney epithelium (LLC-PK1), the actin filaments surrounding intracytoplasmic motile bacteria show the same immunoreactivity as the brush border-like microvilli, when analysed by a specific actin antibody. The successful invasion of polarized LLC-PK1 islets is vectorial, i.e. it progresses predominantly from the periphery of the islets towards the centre. Infection of the peripheral cells is sufficient for infiltration of the entire cellular islets, without any further contact with the extracellular milieu. This is in contrast to nonpolarized epithelial sheets, which can be invaded from the apical surface of any individual cell. The importance of active bacterial motility in this vectorial spreading is emphasized by our finding that an isogenic Listeria mutant that is unable to recruit actin filaments cannot colonize polarized epithelial layers but accumulates in the peripheral cells of the islets.

Adaptation of partitioning and high-level synthesis in hardware/software co-synthesis

Abstract: Previously, we had presented the system COSYMA for hardware/software co-synthesis of small embedded controllers. Target system of COSYMA is a core processor with application specific co-processors. The system speedup for standard programs compared to a single 33MHz RISC processor solution with fast, single cycle access RAM was typically less than 2 due to restrictions in high-level co-processor synthesis, and incorrectly estimated back end tool performance, such as hardware synthesis, compiler optimization and communication optimization. Meanwhile, a high-level synthesis tool for high-performance co-processors in co-synthesis has been developed. This paper explains the requirements and the main features of the high-level synthesis sytem and its integration into COSYMA. The results show a speedup of 10 in most cases. Compared to the speedup, the co-processor size is very small.

A general stochastic model for the description of surface reaction systems

Abstract: In this paper we introduce a stochastic ansatz which can be used to model surface reaction systems. The systems may include mono- and bimolecular steps (i.e. adsorption, desorption, reaction and diffusion steps). We take advantage of the Markovian behaviour of these systems by using master equations for their description. The resulting infinite chain of equation is truncated at a certain level: In a small lattice region we solve the exact lattice equations and connect their solution to continuous functions which represent the behaviour of the system for large distances from a reference point. The stochastic ansatz is used to model different surface reaction systems such as the oxidation of CO on a Pt surface and on a Pt/Sn alloy. Also the formation of NH3 is discussed.

Fine structure of field-aligned current sheets deduced from spacecraft and ground-based observations: Initial FREJA results

Abstract: Due to its special orbit—over large segments tangential to the auroral oval and at altitudes around 1600 km—FREJA provides measurements from a sparsely sampled region. Here we will introduce initial results from the magnetic field experiment. For one event occurring about an hour after midnight we investigate the fine structure of the field-aligned currents associated with a westward electrojet. From simultaneous ground-based observations we deduce the orientation and the spatial and temporal variations of the electrojet. Space-borne magnetic field measurements provide estimates of the field-aligned current density. We deduce a lower limit of 1.75 km for the thickness of field-aligned current filaments. The comparison between electric and magnetic field recordings on FREJA suggests a poor correlation of these quantities for this event.