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Biomedical subjects

B Senger

Publications and source records attributed to B Senger.

At least 19 recordsLinked to original sources
PubMed2000

[Leukocyte adhesion on a fibrinogen-coated surface under static conditions: experimentation and creation of a model].

The adhesion of polymorphonuclear leukocytes (PMNs) on the vascular endothelium is a complex process that occurs during different biological and pathological events and involves numerous molecules. The adhesion cascade is induced after PMN stimulation by various molecular or cellular signals. Fibrinogen is one of the substrates for CD11b/CD18 B2-integrins expressed at the PMN surface; fibrinogen-neutrophil binding is induced by inflammatory reactions. In order to understand this process, we have carried out studies on the basis of preliminary experiments on red blood cells and synthetic particles. The modelization of quiescent PMNs adhesion on a fibrinogen substrate was investigated with a sedimentation cell chamber. Two different physiological conditions were tested: the activated state of PMN by a synthetic pro-inflammatory activator (FMLP). The activated state of PMNs was both quantified by flow cytometry and controlled by fluorescence microscopy. The results suggest that quiescent neutrophils deposit in accordance with the ballistic deposition model. This random adsorption model differs from random sequential adsorption (RSA) in that the cells arriving at the surface are able to roll along cells previously adsorbed introducing the notion of gravitational attraction of cells. The preliminary results obtained with stimulated PMN do not allow to choose between one of this two deposition models. Nevertheless, the qualitative and quantitative effects of FMLP on neutrophils were demonstrated by modifications of adhesion molecules expression.

Antigens, CD↗
PubMed1999

Extended random sequential adsorption model of irreversible deposition processes: from simulations to experiments.

An experimental study of the irreversible deposition of colloidal particles of various radii R on a solid surface is presented over a wide range of the Péclet number, Pe, or reduced radius R* (Pe = R*(4)). The experimental data are analyzed by means of a new generalized random sequential adsorption model that takes explicitly the diffusion of the particles during the deposition into account. It allows description of the continuous transition from a random sequential adsorption-like to a ballistic-like deposition behavior. It depends on three parameters: d(s), related to the diffusion of the particles before adhesion; n(s), related to the number of allowed adhesion trials of a particle; and R(e), representing the effective particle radius. The model allows accounting for all of the experimental observations relative to the radial distribution functions and the number density fluctuations over the whole coverage range and all investigated values of R*. In addition, it is found that d(s)/R is proportional to R*(-2) as expected for a diffusional process. Moreover, the parameters d(s) and n(s) appear to be connected through the empirical relation (d(s)/R)n(s)(2/3) = C, where C is found to be of the order of 50. This unique statistical model allows an accurate description of the irreversible deposition process, whatever the influence of gravity with respect to diffusion.

Journal Article↗
PubMed1999

Adhesion Probability of Colloidal Particles with Repulsive Soft Interaction.

Computer simulations of the irreversible adhesion of charged colloidal particles at a solid/liquid interface are performed to determine whether the distribution of particles in the vicinity of a preadsorbed (also charged) one follows the Boltzmann law applied to an a priori uniform adhesion probability, as first assumed by Adamczyk et al. (J. Colloid Interface Sci. 140, 123 (1990)). If true, this would indicate that the whole information on the deposition process is contained in the potential energy distribution on the adsorbing surface. In general, diffusion in a field of force and the irreversibility of the process induce significant deviations from the Boltzmann-weighted uniform adhesion density. Nevertheless, it is shown that for particles characterized by a small gravitational energy this procedure leads to a reasonable first approximation of the distribution of the particles over the adsorbing surface. This observation thus demonstrates the validity of Adamczyk's assumption and extends its range of applicability to the case of a weak gravitational field. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Dynamic and cyclic fatigue of engine-driven rotary nickel-titanium endodontic instruments.

The absence of adequate testing standards for engine-driven nickel-titanium (NiTi) instruments necessitates further study of these instruments in all areas. This study examined three groups of engine-driven rotary NiTi endodontic instruments (Profile, Hero, and Quantec) and assessed the times for dynamic fracture in relation to the radius of curvature to which the instruments were subjected during preparation, with the instrument diameter determined by size and taper and the mode by which the fracture occurred. Ten instruments were randomly selected representing each size and taper for each group and for each radius of curvature: 600 in total. The instruments were rotated at 350 rpm and introduced into a tempered steel curve that simulated a canal. Two radii of curvature of canals were used: 5 and 10 mm. Time at fracture was noted for all files, and the fracture faces of each file were analyzed with scanning electron microscopy. Radius of curvature was found to be the most significant factor in determining the fatigue resistance of the files. As radius of curvature decreased, fracture time decreased. Taper of files was found to be significant in determining fracture time. As diameter increased, fracture time decreased. In all cases, fracture was found to be of a ductile nature, thus implicating cyclic fatigue as a major cause of failure and necessitating further analyses and setting of standards in this area.

Dental High-Speed Technique↗
PubMed1999

Initial features of the inner dental epithelium histo-morphogenesis in the first lower molar in mouse.

First lower molar development in the mouse was investigated from the cap to early bell stage using histology, morphometry, TEM and 3D reconstructions. This period was characterized by the histogenesis of the enamel organ (EO), folding of the epithelio-mesenchymal junction and growth of the tooth. The histogenesis of the EO and appearance of the enamel knot (EK) were initiated at the early cap stage (ED14). From ED14 to ED15, the anterior and posterior extension of the EK was very prominent whilst the length of the enamel organ did not substantially change. The EK appeared as a dynamic and transitory histological structure including dying and replacement cells. At ED16, the folding of the IDE, which extended over the anterior two thirds of the molar, was the first sign of cuspidogenesis. It was accompanied by a local remodeling of the basement membrane (BM): IDE cells involved in this folding transitorily lost contact with the BM which formed a loop in the mesenchyme. During this period, the growth of the lower M1 along the antero-posterior axis was restricted to the posterior part of the molar. Histogenesis occurred in the whole EO, whilst initial cuspidogenesis was limited to the anterior part of the tooth. Distinct cell populations were thus involved in different contemporary processes leading to changes in the cell density in the mesenchyme, in the mitotic activity, in cell-shape, and cell-matrix interactions in the IDE, and remodeling of the BM where both epithelium and mesenchyme might participate.

Animals↗
PubMed1999

Mechanical effects and volatile sulfur compound-reducing effects of chewing gums: comparison between test and base gums and a control group.

OBJECTIVE: Chewing gum may act as a masking or a therapeutic agent against the different chemical compounds that are responsible for oral malodor. An open-label exploratory study investigated the effect of mastication and aromatic components of chewing gum on reducing oral volatile sulfur compounds. METHOD AND MATERIALS: Twelve dental students (5 males and 7 females) acted as their own controls. Toothbrushing stopped 12 hours before observations. Measurements included organoleptic and volatile sulfur compound scores and the pH of the anterior and posterior zones of the dorsal tongue. Measurements were made at 9 AM and 12 PM on 1 day for 3 successive weeks; week 1, no gum (control); week 2, test gum; week 3, unsweetened gum base. This open-label study was then completed by an observer-blind study, according to the same schedule; the recorded measurement was the plaque index. RESULTS: The pH, volatile sulfur compounds, and organoleptic scores were similar for all groups. The pH was more basic in the posterior part than in the anterior zone of the dorsal tongue, irrespective of time and presence or absence of chewing gum. In addition, the volatile sulfur compound score rose transiently immediately after the test gum, and the organoleptic score fell in the first hour only after the test gum. The two chewing gum groups seemed to have a greater reduction in plaque index than did the control (no gum) group. CONCLUSION: Chewing gum may have a valuable mechanical role in cleaning dental surfaces, and the test gum may temporarily control bad breath. After 3 hours, similar volatile sulfur compound scores were observed for subjects who chewed either test or unsweetened gum base and control subjects.

Analysis of Variance↗
PubMed1999

Modelisation of leukocyte adhesion on a fibrinogen coated surface in static conditions.

The adhesion of polymorphonuclear leukocytes (PMNs) on the vascular endothelium is a complex process that occurs during biological and pathological events and involves a large family of molecules. This phenomenom could be approached by a modelisation study of the adhesion of PMNs on a biological substrate, fibrinogen. Two different physiological conditions were tested such as the activated state of PMNs with a synthetic pro-inflammatory activator (N-Formyl-Methionyl-Leucyl-Phenylalanine, FMLP). The activated state of PMNs was both quantified by flow cytometry and controlled by fluorescence microscopy. The results suggest that quiescent PMNs deposit in accordance with the ballistic deposition model. The preliminary results obtained with FMLP-stimulated PMNs show a different deposit process compared to quiescent PMNs but do not allow to determine exactly a deposition model.

Activated-Leukocyte Cell Adhesion Molecule↗
PubMed1998

Mtr10p functions as a nuclear import receptor for the mRNA-binding protein Npl3p.

MTR10, previously shown to be involved in mRNA export, was found in a synthetic lethal relationship with nucleoporin NUP85. Green fluorescent protein (GFP)-tagged Mtr10p localizes preferentially inside the nucleus, but a nuclear pore and cytoplasmic distribution is also evident. Purified Mtr10p forms a complex with Npl3p, an RNA-binding protein that shuttles in and out of the nucleus. In mtr10 mutants, nuclear uptake of Npl3p is strongly impaired at the restrictive temperature, while import of a classic nuclear localization signal (NLS)-containing protein is not. Accordingly, the NLS within Npl3p is extended and consists of the RGG box plus a short and non-repetitive C-terminal tail. Mtr10p interacts in vitro with Gsp1p-GTP, but with low affinity. Interestingly, Npl3p dissociates from Mtr10p only by incubation with Ran-GTP plus RNA. This suggests that Npl3p follows a distinct nuclear import pathway and that intranuclear release from its specific import receptor Mtr10p requires the cooperative action of both Ran-GTP and newly synthesized mRNA.

Amino Acid Sequence↗
PubMed1998

Structural requirements for enzymatic formation of threonylcarbamoyladenosine (t6A) in tRNA: an in vivo study with Xenopus laevis oocytes.

We have investigated the specificity of the eukaryotic enzymatic machinery that transforms adenosine at position 37 (3' adjacent to anticodon) of several tRNAs into threonylcarbamoyladenosine (t6A37). To this end, 28 variants of yeast initiator tRNAMet and yeast tRNAVal, devoid of modified nucleotide, were produced by in vitro transcription with T7 polymerase of the corresponding synthetic tRNA genes and microinjected into the cytoplasm of Xenopus laevis oocytes. Threonylcarbamoyl incorporation was analyzed in tRNA transcripts mutated in the anticodon loop by substitution, deletion, or Insertion of nucleotides, or in the overall 3D structure of the tRNA by altering critical tertiary interactions. Specifically, we tested the effects of altering ribonucleotides in the anticodon loop, changes of the loop size, perturbations of the overall tRNA 3D structure due to mutations disruptive of the tertiary base pairs, and truncated tRNAs. The results indicate that, in addition to the targeted A37, only U36 was absolutely required. However, A38 in the anticodon loop considerably facilitates the quantitative conversion of A37 into t6A37 catalyzed by the enzymes present in X. laevis. The anticodon positions 34 and 35 were absolutely "neutral" and can accept any of the four canonical nucleotides A, U, C, or G. The anticodon loop size may vary from six to eight nucleotides, and the anticodon stem may have one mismatch pair of the type AxC or GxU at location 30-40 without affecting the efficiency of t6A37 formation and still t6A37 is efficiently formed. Although threonylcarbamoylation of A37 occurred with tRNA having limited perturbations of 3D structure, the overall L-shaped architecture of the tRNA substrate was required for efficient enzymatic conversion of A37 to t6A37. These results favor the idea that unique enzymatic machinery located in the oocyte cytoplasm catalyzes the formation of t6A37 in all U36A37-containing tRNAs (anticodon NNU). Microinjection of the yeast tRNAMeti into the cytoplasm of X. laevis oocytes also revealed the enzymatic activities for several other nucleotide modifications, respectively m1Gg, m2G10, m(2)2G26, m7G46, D47, m5C48/49, and m1A58.

Adenosine↗
PubMed1997

The modified wobble base inosine in yeast tRNAIle is a positive determinant for aminoacylation by isoleucyl-tRNA synthetase.

Earlier work by two independent groups has established the fact that anticodons GAU and LAU of Escherichia coli tRNAIle isoacceptors play a critical role in the tRNA identity. Yeast possesses two isoleucine transfer RNAs, a major one with anticodon IAU and a minor one with anticodon PsiAPsi which are derived from the post-transcriptional modification of AAU and UAU gene sequences, respectively. We present direct evidence which reveals that inosine is a positive determinant for yeast isoleucyl-tRNA synthetase. We also show that yeast tRNAMet with guanosine at the wobble position becomes aminoacylated with isoleucine while methionine acceptance is lost. As inosine and guanosine share the 6-keto and the N-1 hydrogen groups, this suggests that these hydrogen donor and acceptor groups are determinants for isoleucine specificity. The role of the minor tRNAIle anticodon pseudouridines in tRNA isoleucylation could not be tested directly but was deduced from a 40-fold decrease in the activity of the unmodified transcript. The presence of the NHCO structure in guanosine, inosine, pseudouridine, and lysidine suggests a unifying model of wobble base recognition by the yeast and E. coli isoleucyl-tRNA synthetase. In contrast to lysidine which switches the identity of the tRNA from methionine to isoleucine [Muramatsu, T., Nishikawa, K., Nemoto, F., Kuchino, Y., Nishimura, S., Miyazawa, T., & Yokoyama, S. (1988) Nature 336, 179-181], pseudouridine-34 does not modify the specificity of the yeast minor tRNAIle since U-34 is a strong negative determinant for yeast MetRS. Therefore, the major role of Psi-34 (in combination with Psi-36 or not) is likely in isoleucine AUA codon specificity and translational fidelity.

Acylation↗
PubMed1997

Influence of different parameters on bone heating and drilling time in implantology.

The influence of various parameters on bone heating during drilling and drilling time was studied in vitro in a bovine cortical femur model. Drilling using a standard, a surgical or a laboratory motor unit did not affect bone temperature elevation. For a given speed, low 1/40 reduction contra-angle was more effective in moderating temperature elevation when compared to 1/10 reduction; but drilling time in this case (1/40) had to be doubled. Enhancing the drilling load from 0.8 kg to 2 kg had little effect on temperature elevation at 400 rpm and 800 rpm (< 3 degrees C). Drilling time drastically decreased and was inversely proportional to the square of the load. Predrilling did not affect temperature elevation, but decreased drilling time. From 400 rpm to 10,000 rpm, temperature elevation was positively correlated with drilling speed. It further decreased up to 24,000 rpm and then was constant up to 40,000 rpm. Drilling time was proportionally reduced with increased rotation speed. Strikingly, heat was largely dissipated within 10 s at high rotation speed. The use of a cryogenic spray at 24,000 rpm allowed the reduction of temperature elevation. Finally, protection from temperature elevation according to above parameters is suggested.

Animals↗
PubMed1997

Importance of structural features for tRNA(Met) identity.

We showed previously that the tRNA tertiary structure makes an important contribution to the identity of yeast tRNA(Met) (Senger B, Aphasizhev R, Walter P, Fasiolo F, 1995, J Mol Biol 249:45-58). To learn more about the role played by the tRNA framework, we analyzed the effect of some phosphodiester cleavages and 2'OH groups in tRNA binding and aminoacylation. The tRNA is inactivated provided the break occurs in the central core region responsible for the tertiary fold or in the anticodon stem/loop region. We also show that, for tRNA(Met) to bind, the anticodon loop, but not the anticodon stem, requires a ribosephosphate backbone. A tertiary mutant of yeast tRNA(Met) involving interactions from the D- and T-loop unique to the initiator species fails to be aminoacylated, but still binds to yeast methionyl-tRNA synthetase. In the presence of 10 mM MgCl2, the mutant transcript has a 3D fold significantly stabilized by about 30 degrees C over a wild-type transcript as deduced from the measure of their T(m) values. The k(cat) defect of the tRNA(Met) mutant may arise from a failure to overcome an increase of the free energetic cost of distorting the more stable tRNA structure and/or a tRNA based MetRS conformational change required for formation of transition state of aminoacylation.

Anticodon↗
PubMed1996

Red blood cell adhesion on a solid/liquid interface.

Red blood cells (RBCs), previously fixed with glutaraldehyde, adhere to glass slides coated with fibrinogen. The RBC deposition process on the horizontal glass surface is investigated by analyzing the relative surface covered by the RBCs, as well as the variance of this surface coverage, as a function of the concentration of particles. This study is performed by optical microscopy and image analysis. A model, derived from the classical random sequential adsorption model, has been developed to account for the experimental results. This model highlights the strong influence of the hydrodynamic interactions during the deposition process.

Adsorption↗
PubMed1996

Conservation in evolution for a small monomeric phenylalanyl-tRNA synthetase of the tRNA(Phe) recognition nucleotides and initial aminoacylation site.

We previously showed that yeast mitochondrial phenylalanyl-tRNA synthetase (MSF protein) is evolutionarily distant to the cytoplasmic counterpart based on a high degree of divergence in protein sequence, molecular mass, and quaternary structure. Using yeast cytoplasmic tRNA(Phe) which is efficiently aminoacylated by MSF protein, we report here the tRNA(Phe) primary site of aminoacylation and the identity determinants for MSF protein. As for the cytoplasmic phenylalanyl-tRNA synthetase (Sampson, J. R., Di Renzo, A. B., Behlen, L. S., & Uhlenbeck, O. C. (1989) Science 243, 1363-1366), MSF protein recognizes nucleotides from the anticodon and the acceptor end including base A73 and, as shown here, adjacent G1-C72 base pair or at least C72 base. This indicates that the way of tRNA(Phe) binding for the two phenylalanine enzymes is conserved in evolution. However, tRNA(Phe) tertiary structure seems more critical for the interaction with the cytoplasmic enzyme than with MSF protein, and unlike cytoplasmic phenylalanyl-tRNA synthetase, the small size of the monomeric MSF protein probably does not allow contacts with residue 20 at the top corner of the L molecule. We also show that MSF protein preferentially aminoacylates the terminal 2'-OH group of tRNA(Phe) but with a catalytic efficiency for tRNA(Phe)-CC-3'-deoxyadenosine reduced 100-fold from that of native tRNA(Phe), suggesting a role of the terminal 3'-OH in catalysis. The loss is only 1.5-fold when tRNA(Phe)-CC-3'-deoxyadenosine is aminoacylated by yeast cytoplasmic PheRS (Sprinzl, M., & Cramer, F. (1973) Nature 245, 3-5), indicating mechanistic differences between the two PheRS's active sites for the amino acid transfer step.

Amino Acid Sequence↗
PubMed1996

Yeast tRNA(Met) recognition by methionyl-tRNA synthetase requires determinants from the primary, secondary and tertiary structure: a review.

The primordial role of the CAU anticodon in methionine identity of the tRNA has been established by others nearly a decade ago in Escherichia coli and yeast tRNA(Met). We show here that the CAU triplet alone is unable to confer methionine acceptance to a tRNA. This requires the contribution of the discriminatory base A73 and the non-anticodon bases of the anticodon loop. To better understand the functional communication between the anticodon and the active site, we analysed the binding and aminoacylation of tRNA(Met) based anticodon and acceptor-stem minihelices and of tRNA(Met) chimeras where the central core region of yeast tRNA(Met) is replaced by that of unusual mitochondrial forms lacking either a D-stem or a T-stem. These studies suggest that the high selectivity of the anticodon bases in tRNA(Met) implies the L-conformation of the tRNA and the presence of a D-stem. The importance of a L-structure for recognition of tRNA(Met) was also deduced from mutations of tertiary interactions known to play a general role in tRNA(Met) folding.

Amino Acid Sequence↗
PubMed1995

The presence of a D-stem but not a T-stem is essential for triggering aminoacylation upon anticodon binding in yeast methionine tRNA.

Dissection of the yeast cytoplasmic initiator tRNA(Met) into two helical domains, the T psi C acceptor and anticodon minihelices, failed to show anminoacylation and binding of the acceptor minihelix by the yeast methionyl-tRNA synthetase (MetRS) even in the presence of the anticodon minihelix. In contrast, based on the measure of the inhibition constant Ki, the anticodon minihelix carrying the methionine anticodon CAU is specifically bound to the synthetase and with an affinity comparable to that of the full-length tRNA. The yeast tRNA(Met) acceptor and anticodon minihelices were covalently linked using the central core sequences of either bovine mitochondrial tRNA(Ser) (AGY) lacking a D-stem or initiator tRNA(Met) from Caenorhabditis elegans lacking a T-stem. Based on modeling studies of analogous constructs performed by others, we assume that the folding and distance between the anticodon and acceptor ends of these hybrid tRNAs are identical to that of canonical tRNA. The three-quarter molecule, which includes the T-stem, has aminoacylation activity significantly more than an acceptor minihelix, while the acceptor stem/anticodon-D stem biloop has near wild-type aminoacylation activity. These results suggest that the high selectivity of the anticodon bases in tRNA(Met) depends upon the tRNA L-shape conformation and the presence of a D-arm. Protein contacts with the D-arm phosphate backbone are required for connecting anticodon recognition with the active site. These interactions probably contribute to fine tune the position of the acceptor end in the active site, allowing entry into the transition state of aminoacylation upon anticodon binding. The importance of an L structure for recognition of tRNA(Met) by yeast MetRS was also deduced from mutations of tertiary interactions known to play a general role in tRNA folding.

Acylation↗