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Biomedical subjects

E Bertrand

Publications and source records attributed to E Bertrand.

At least 19 recordsLinked to original sources
PubMed2006

Acceleration of the recognition rate between grafted ligands and receptors with magnetic forces.

When ligands and receptors are both attached on surfaces, because of the restriction of configurational freedom, their recognition kinetics may be substantially reduced as compared with freely diffusing species. In nature, this reduction may influence the efficiency of the capture and adhesion of circulating cells. Here we show that similar consequences are observed for colloids grafted with biomolecules that are used as probes for diagnostics. We exploit Brownian magnetic colloids that self-assemble into linear chains to show also that the resulting one-dimensional confinement considerably accelerates the recognition rate between grafted receptors and their ligands. We propose that because confinement significantly augments the colliding frequency, it also causes a large increase in the attempt frequency of the recognition. This work gives the basis of a rapid, homogeneous, and highly sensitive bioanalysis method.

Antibodies↗
PubMed2006

ART outcome in HIV-infected patients.

BACKGROUND: To assess assisted reproductive technique (ART) outcome in couples affected by human immunodeficiency virus (HIV). METHODS: Intrauterine insemination (IUI), IVF and ICSI were performed in 85 couples affected by HIV between January 2000 and June 2005. RESULTS: In 33 of the 85 couples, women were HIV positive-the clinical pregnancy rate (CPR) and cancellation rate (CR) after 34 IUI cycles were, respectively, 25 and 18%. The CPR after 26 IVF and 30 ICSI cycles were, respectively, 37.5 and 18.8% with CRs of 38.5 and 46.7%, respectively. In 38 couples, men were infected-the CPR and CR after 85 IUI cycles were, respectively, 14.7 and 20%; 62 ICSI cycles were performed leading to CPR of 23.4% with a CR of 25%. In 14 couples, the two partners were infected: none of the four IUI cycles carried out was successful (CR, 20%); the CPR and CR after 35 ICSI cycles were, respectively, 12.5% with 31%. All children born had a negative HIV test. CONCLUSION: In couples affected by HIV, an acceptable pregnancy rate was obtained. The worst results were obtained when both partners were infected. The CR was elevated among HIV-infected couples.

Adult↗
PubMed2006

Irreversible shear-activated aggregation in non-Brownian suspensions.

We have studied the effect of shear on the stability of suspensions made of non-Brownian solid particles. We demonstrate the existence of an irreversible transition where the solid particles aggregate at remarkably low volume fractions (phi approximately 0.1). This shear-induced aggregation is dramatic and exhibits a very sudden change in the viscosity, which increases sharply after a shear-dependent induction time. We show that this induction time is related exponentially to the shear rate, reflecting the importance of the hydrodynamic forces in reducing the repulsive energy barrier that prevents the particles from aggregating.

Journal Article↗
PubMed2005

Magnetic force probe for nanoscale biomolecules.

We present a new technique to measure the mechanical properties of small biomolecules. This technique uses long range repulsive colloidal forces together with magnetic attraction as a force probing tool. The biomolecules are grafted between superparamagnetic particles, which are regularly spaced within long chains maintained by an external magnetic field. Varying the magnetic field results in compression or extension of the molecules between the particles. In order to demonstrate this technique we use, as a size controlled model molecule, a short double stranded DNA (151 base pairs) for which the force-extension law is determined and found in agreement with existing predictions.

Biopolymers↗
PubMed2005

Spreading dynamics of chain-like monolayers: a molecular dynamics study.

Using large-scale molecular dynamics simulations, we have shown previously that the spreading dynamics of sessile drops on solid surfaces can be described in detail using the molecular-kinetic theory of dynamic wetting. Here we present our first steps in extending this approach to investigate the spreading dynamics of Langmuir-Blodgett monolayers. We make use of a monolayer model originally developed by Karaborni and Toxvaerd, but somewhat simplified to facilitate large-scale simulations. Our preliminary results are in good agreement with recent experimental observations and also support a molecular-kinetic interpretation in which the driving force for spreading is the lateral pressure in the monolayer. Away from equilibrium, initial spreading rates are constant and logarithmically dependent on pressure. However, near equilibrium, spreading is pseudo-diffusive and follows the square root of time. In both regimes the controlling factor is the equilibrium frequency of molecular displacements within the monolayer.

Journal Article↗
PubMed2003

Flexible magnetic filaments as micromechanical sensors.

We propose a new micromechanical approach to probe bending rigidity at molecular scale. Long flexible filaments made of magnetic colloids and linkers are shown to adopt under magnetic field a hairpin configuration. Measuring the hairpin curvature as a function of the field intensity and the linker length from diffracted light allows us to deduce the linker bending rigidity kappa. The technique is presented for two types of linkers: a spontaneously adsorbing polymer and a grafted biomolecular.

Acrylic Resins↗
PubMed2001

Box C/D small nucleolar RNA trafficking involves small nucleolar RNP proteins, nucleolar factors and a novel nuclear domain.

Nucleolar localization of box C/D small nucleolar (sno) RNAs requires the box C/D motif and, in vertebrates, involves transit through Cajal bodies (CB). We report that in yeast, overexpression of a box C/D reporter leads to a block in the localization pathway with snoRNA accumulation in a specific sub-nucleolar structure, the nucleolar body (NB). The human survival of motor neuron protein (SMN), a marker of gems/CB, specifically localizes to the NB when expressed in yeast, supporting similarities between these structures. Box C/D snoRNA accumulation in the NB was decreased by mutation of Srp40 and increased by mutation of Nsr1p, two related nucleolar proteins that are homologous to human Nopp140 and nucleolin, respectively. Box C/D snoRNAs also failed to accumulate in the NB, and became delocalized to the nucleoplasm, upon depletion of any of the core snoRNP proteins, Nop1p/fibrillarin, Snu13p, Nop56p and Nop5p/Nop58p. We conclude that snoRNP assembly occurs either in the nucleoplasm, or during transit of snoRNAs through the NB, followed by routing of the complete snoRNP to functional sites of ribosome synthesis.

Active Transport, Cell Nucleus↗
PubMed2001

Terminal minihelix, a novel RNA motif that directs polymerase III transcripts to the cell cytoplasm. Terminal minihelix and RNA export.

Determining the cis-acting elements controlling nuclear export of RNA is critical, because they specify which RNA will be selected for transport. We have characterized the nuclear export motif of the adenoviral VA1 RNA, a small cytoplasmic RNA transcribed by RNA polymerase III. Using a large panel of VA1 mutants in both transfected COS cells and injected Xenopus oocytes, we showed that the terminal stem of VA1 is necessary and sufficient for its export. Surprisingly, we found that the nucleotide sequence within the terminal stem is not important. Rather, the salient features of this motif are its length and its relative position within the RNA. Such stems thus define a novel and degenerate cytoplasmic localization motif that we termed the minihelix. This motif is found in a variety of polymerase III transcripts, and cross-competition analysis in Xenopus oocytes revealed that export of one such RNA, like hY1 RNA, is specifically competed by VA1 or artificial minihelix. Taken together these results show that the minihelix defines a new cis-acting export element and that this motif could be exported via a novel and specific nuclear export pathway.

Animals↗
PubMed2001

A short cytoplasmic domain of the amyloid precursor protein induces apoptosis in vitro and in vivo.

The amyloid precursor protein presents several cleavage sites leading to the release of its entire C-terminal domain into the cytoplasm. During apoptosis, this C-terminal domain can be cleaved at amino acid 664 by caspases 3, 6, and 8 and can thus generate two peptides N- and C-terminal to amino acid 664 (C31). Recently, it was shown that the C31 induces apoptosis after transfection into N2A and 293 T cell lines. We have analyzed here, by internalization into neurons, the physiological consequences of the entire C-terminal domain (APP-Cter) and of its membrane proximal sequence corresponding to the N-terminal peptide unmasked after caspase cleavage. We find that whereas micromolar concentrations of APP-Cter are harmless, the peptide extending from the membrane (amino acid 649) to the caspase cleavage site (amino acid 664) in the same range of concentrations induces DNA fragmentation, cleavage of actin at a caspase-sensitive site, and activates caspase 3. A mutated version of this sequence (tyrosine 653 replaced by an aspartate) abolishes the effect in vitro and in vivo. Taken together, this report suggests the existence of a new mechanism contributing to Alzheimer's Disease-associated cell death.

Alzheimer Disease↗
PubMed2001

A well-connected and conserved nucleoplasmic helicase is required for production of box C/D and H/ACA snoRNAs and localization of snoRNP proteins.

Biogenesis of small nucleolar RNA-protein complexes (snoRNPs) consists of synthesis of the snoRNA and protein components, snoRNP assembly, and localization to the nucleolus. Recently, two nucleoplasmic proteins from mice were observed to bind to a model box C/D snoRNA in vitro, suggesting that they function at an early stage in snoRNP biogenesis. Both proteins have been described in other contexts. The proteins, called p50 and p55 in the snoRNA binding study, are highly conserved and related to each other. Both have Walker A and B motifs characteristic of ATP- and GTP-binding and nucleoside triphosphate-hydrolyzing domains, and the mammalian orthologs have DNA helicase activity in vitro. Here, we report that the Saccharomyces cerevisiae ortholog of p50 (Rvb2, Tih2p, and other names) is required for production of C/D snoRNAs in vivo and, surprisingly, H/ACA snoRNAs as well. Point mutations in the Walker A and B motifs cause temperature-sensitive or lethal growth phenotypes and severe defects in snoRNA accumulation. Notably, depletion of p50 (called Rvb2 in this study) also impairs localization of C/D and H/ACA core snoRNP proteins Nop1p and Gar1p, suggesting a defect(s) in snoRNP assembly or trafficking to the nucleolus. Findings from other studies link Rvb2 orthologs with chromatin remodeling and transcription. Taken together, the present results indicate that Rvb2 is involved in an early stage of snoRNP biogenesis and may play a role in coupling snoRNA synthesis with snoRNP assembly and localization.

Adenosine Triphosphatases↗
PubMed2001

Lewy body variant of Alzheimer's disease and Alzheimer's disease: a comparative immunohistochemical study.

Immunohistochemistry (IHC) and ultrastructural study were performed on 19 demented autopsy cases of sporadic Alzheimer's disease (AD). Semiquantitative IHC assessment of the pathological changes, according to the criteria of the Consortium to Establish a Registry of Alzheimer's Disease (CERAD) and the Consortium on Dementia with Lewy Bodies, showed morphological hallmarks of AD in 18 demented patients. It was found that 11 of these cases fulfilled criteria for "pure" AD, whereas the remaining 7 cases, with mixed findings, Lewy bodies (LBs) and Lewy-related dystrophic neurites, neuritic plaques (NP) and sometimes neurofibrillary tangles (NFT), met the criteria for Lewy body variant of Alzheimer's disease (LBV). One case with brain stem and cortical LBs but without NP and NFT was finally diagnosed as a pure form of dementia with Lewy bodies (DLB). Regional distribution and semiquantitative assessment frequency of alpha-synuclein-immunoreactive LBs, tau-immunoreactive NFT and beta-amyloid immunoreactive senile plaques, were compared between LBVand AD. Ultrastructural examination confirmed the filamental structure of cortical LBs. In conclusion, IHC study including antibody to alpha-synuclein, the sensitive marker for Lewy bodies, revealed the coexistence of brain stem and cortical LBs and pathological features of AD in a great part of dementia cases. Patients with mixed, LBs, NP and sometimes NFT pathology, fulfilled neuropathological CERAD criteria for LBV. Semiquantitative comparative IHC study, according to LBs- and NFT-scores and CERAD NP-scores showed in the LBV group a significantly lower frequency of NFT coexisting with neocortical LBs than in the group with pure form of AD.

Aged↗
PubMed2001

Neuropathological analysis of pathological forms of astroglia in Wilson's disease.

A neuropathological study of Alzheimer type I (Alz I) and Alzheimer type II (Alz II) as well as Opalski (Opl) cells was performed serially on brain tissue from nine autopsied Wilson's disease (WD) cases. Conventional staining methods (Kluver-Barrera, HE, PAS) and immunocytochemical techniques (anti-GFAP and anti-Metallothionein-MT) were used. On conventional staining, each of the studied abnormal cell types retained common morphological characteristics of astroglia, and concurrently demonstrated its own distinctive features, specific only for a given cell type. Anti-GFAP staining revealed positive immunoreactivity of Alz I and Opl cells, and its absence in Alz II cells. On anti-MT staining both the cytoplasm and nucleus of Alz I and Opl cells showed positivity whereas in Alz II cells the cytoplasm was positive in contrast to the negative nucleus. The results of our study confirm the hypothesis of the astroglial origin of all three types of cells. The lack of immunoreactivity for GFAP and similar immunocytochemical staining patterns for MT in Alz II cells and protoplasmic astrocytes may suggest that Alz II cells originate from the protoplasmic type of astroglia. The fact that Alz I and Opl cells resemble fibrous astrocytes in their immunoreactive positivity for GFAP may lead to a supposition that they originate from the fibrous type of astroglia. MT-positive expression by the three abnormal cell types suggests that they may be involved in the process of copper detoxification in WD.

Adolescent↗
PubMed2001

Neurones and microglia in central nervous system immune response to degenerative processes. Part 1: Alzheimer's disease and Lewy body variant of Alzheimer's disease. Quantitative study.

The quantitative correlation between neurone loss and brain immune response, assessed by intensity of microglia inflammatory reaction in cortical association area and limbic cortex, was investigated and compared in previously immunohistochemistry (IHC) and ultrastructural confirmed 11 cases of Alzheimer's disease (AD), 7 cases mixed form of Dementia with AD findings and Lewy bodies (AD/DLB) reported, in accordance with Consortium on Dementia, as Lewy body variant of AD (LBV) and 6 non-demented autopsy control cases from 63 to 86 years old. In the present work we investigated association and limbic cortical areas linked with memory mechanisms; there are regions characterised by early distribution of IHC confirmed AD and DLB/AD (LBV) markers, as well as a substantial physiological stability of neurone pool regardless of age. The results indicated that AD and LBV differ in their neurone loss intensity and inflammatory reaction, with much higher intensity in AD. In Alzheimer's disease, neurone loss in association temporal cortex made up 51% of control values with simultaneous 8-fold increase in the density of MHC II-positive activated microglia, whereas in LBV, both the loss of neurone density and the increase in activated microglia density, was not so high (up to 41% and 4-5-fold, respectively). Changes in the limbic cortex were less pronounced. A strong correlation in the clinical material between neurone loss and microglia activation in both processes, especially in AD (r = 0.73), speaks in favour of the hypothesis on the neuronal immune surveillance and arousal of immune brain response in conditions of declining control, due to significant neurone loss in the neurodegenerative process. The inflammatory reaction of MHC II-immunoreactive microglia, concomitant with neurodegenerative process, seems to be a consequence of increased immune response due to loss of neurones and weakening of their control upon immunosurveillance in central nervous system.

Aged↗
PubMed2000

A CBF5 mutation that disrupts nucleolar localization of early tRNA biosynthesis in yeast also suppresses tRNA gene-mediated transcriptional silencing.

In the budding yeast, Saccharomyces cerevisiae, actively transcribed tRNA genes can negatively regulate adjacent RNA polymerase II (pol II)-transcribed promoters. This tRNA gene-mediated silencing is independent of the orientation of the tRNA gene and does not require direct, steric interference with the binding of either upstream pol II factors or the pol II holoenzyme. A mutant was isolated in which this form of silencing is suppressed. The responsible point mutation affects expression of the Cbf5 protein, a small nucleolar ribonucleoprotein protein required for correct processing of rRNA. Because some early steps in the S. cerevisiae pre-tRNA biosynthetic pathway are nucleolar, we examined whether the CBF5 mutation might affect this localization. Nucleoli were slightly fragmented, and the pre-tRNAs went from their normal, mostly nucleolar location to being dispersed in the nucleoplasm. A possible mechanism for tRNA gene-mediated silencing is suggested in which subnuclear localization of tRNA genes antagonizes transcription of nearby genes by pol II.

Cell Nucleolus↗
PubMed2000

First-order and critical wetting of alkanes on water

Ellipsometry measurements of the wetting behavior of different alkanes on water show a sequence of two wetting transitions: a first-order (discontinuous) transition followed by a critical (continuous) one. We report temperature-induced wetting transitions for different alkanes and a novel pressure-induced wetting transition for an alkane mixture. The experiments enable us to determine the global wetting phase diagram as a function of chain length and temperature which we subsequently calculate theoretically. The two transition lines are found to be approximately parallel, in accordance with basic theoretical arguments.

Journal Article↗