PubMed Health⌕ Search

Biomedical subjects

C Chapon

Publications and source records attributed to C Chapon.

At least 19 recordsLinked to original sources
PubMed2007

Evaluating SPIO-labelled cell MR efficiency by three-dimensional quantitative T2* MRI.

An in vitro MR-assay for superparamagnetic iron oxide (SPIO) particle cell labelling assessment via three-dimensional quantitative T(2) (*) MR microscopy was proposed. On high-resolution images, and due to the high susceptibility difference between the particles and the surrounding medium, SPIO internalized in cells induces signal loss which may be counted and measured on T(2) (*) maps. The increase in both labelled cell percentage and the average perturbation volume with an added amount of iron in the incubation medium proved that intracellular iron uptake is dependent upon the initial concentration of incubation iron. It also proved that the observed increases in total cellular iron uptake measured by inductively coupled plasma optical emission spectroscopy are due to both an increase in the iron mass per cell and also an increase in labelled cell concentration. MR results were compared with Prussian blue staining histology. The sensitivity of the MR methodology was then used to distinguish labelling differences for two different types of particle coating. The MRI-assay we proposed is a compulsory tool to optimize labelling efficiency in order to improve in vivo cell detection. Key parameters for detection, such as the percentage of cell labelling, the effect on the image for a given amount of internalized iron and labelling distribution among a cell population, are easily obtained. The comparison of different contrast agents for labelling one cell type, the assessment of one type of contrast agent for labelling different cell types and/or the evaluation of labelling strategies, are possible without having recourse to classical methods, and provide improved accuracy, since the principle is based on intracellular relaxivity.

Animals↗
PubMed2005

Volumetric assessment of myocardial viability in rats using 3D double contrast enhanced T1 and T2-weighted MRI.

OBJECTIVE: Volumetric evaluation of the myocardial viability post-infarction in rats using 3D in vivo MR imaging at 7 T using injection of an extracellular paramagnetic contrast agent and intravascular superparamagnetic iron oxide nanoparticles in the same imaging session. MATERIALS AND METHODS: Five hours after induction of permanent myocardial infarction in rats (n=6), 3D in vivo T1- and T2-weighted MR Imaging was performed prior to and after Gd-DOTA injection (0.2 mmol/kg) and prior to and after nanoparticle injection (5 mg Fe/kg) to assess infarct size and myocardial viability. RESULTS: 3D MR Imaging using a successive contrast agent injection showed a difference of infarct size after Gd-DOTA injection on T1-weighted images compared to the one measured on T2-weighted images after Gd-DOTA and nanoparticle injection. CONCLUSION: The use of 3D T1- and T2-weighted MR Imaging using a double contrast agents protocol made possible the accurate characterization of myocardial infarction volume and allowed the detection of myocardial viability post-infarction in rats.

Analysis of Variance↗
PubMed2005

Prenatal evaluation of kidney function in mice using dynamic contrast-enhanced magnetic resonance imaging.

Glomerular differentiation starts as soon as embryonic stage 12 in mice and suggests that kidneys may be functional at this stage. Dynamic contrast-enhanced magnetic resonance microscopy, a noninvasive imaging technique, was used to assess renal function establishment in utero. Indeed, in adults (n = 3), an intravenous injection of gadolinium-DOTA induced in a first step a massive and rapid drop in kidney signal intensity followed, in a second step, by a drop in bladder signal intensity. The delay in signal changes between kidney and bladder reflected glomerular filtration. Pregnant mice underwent anatomical and dynamic contrast-enhanced magnetic resonance microscopy on postcoital days 12-13 (n = 2), 13-14 (n = 1), 14-15 (n = 3), 15-16 (n = 2), 16-17 (n = 3), 17-18 (n = 3), and 18-19 (n = 1). Kidneys and bladder were unambiguously depicted prior to contrast agent injection on stage 15-16 embryos. Contrast agent injection allowed kidney, detection as early as stage 12-13 but not bladder. Kinetics of signal changes demonstrated that glomerular filtration is established at embryonic stage 15-16 in mice. Thus, anatomical and dynamic contrast-enhanced magnetic resonance microscopy may be a powerful noninvasive method for in vivo prenatal developmental and functional studies.

Animals↗
PubMed2005

Structure and deformations of Pd-Ni core-shell nanoparticles.

Homogeneous collections of Pd-Ni core-shell nanoparticles have been prepared by decomposition of metal-organic compounds and studied by several electron microscopy techniques: transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), energy-filtered microscopy (EFTEM), and by X-ray photoelectron spectroscopy (XPS). The physical and chemical properties of the Pd shell are supposed to depend on its electronic properties, which are influenced by the presence of the Ni core and by the deformation in the Pd lattice. Here, the interfacial structure of Pd/Ni and the lattice deformations in the core and the shell are studied in detail. The catalytic properties of the pure metal and the bimetallic particles, toward CO oxidation, have been investigated.

Journal Article↗
PubMed2003

High field magnetic resonance imaging evaluation of superparamagnetic iron oxide nanoparticles in a permanent rat myocardial infarction.

RATIONALE AND OBJECTIVES: The purpose of this study was to evaluate superparamagnetic iron oxide (SPIO) nanoparticles to discriminate infarcted from normal tissue after myocardial infarction using high field MR imaging (7 tesla). MATERIALS AND METHODS: Permanent myocardial infarction was induced in rats. SPIO nanoparticles (1 mg Fe/kg) were assessed with T1-weighted gradient echo sequence to visualize the myocardial infarction 48 hours after ligature (n = 6). Furthermore, MR Imaging was performed using a T2-weighted RARE sequence and nanoparticles were injected (5 or 10 mg Fe/kg) on 36 rats 5, 24 or 48 hours after infarction. RESULTS: No changes in contrast between normal and infarcted myocardium was observed after nanoparticle injection on T1-weighted images. However, nanoparticles induced a significant contrast increase between normal and infarcted myocardium on T2-weighted images whatever the delay between infarction and imaging (2.99 +/- 1.66 preinjection vs. 7.82 +/- 1.96 after SPIO injection at a dose of 5 mg Fe/kg 5 hours postinfarction, P = 0.0001). CONCLUSIONS: Nanoparticle injection made it possible to discriminate normal from infarcted myocardium on T2-weighted images. However, the high magnetic field prevented the visualization of the T1 effect of SPIO nanoparticles.

Analysis of Variance↗
PubMed2002

In utero time-course assessment of mouse embryo development using high resolution magnetic resonance imaging.

Magnetic resonance microscopy, a non-invasive imaging technique was used for a longitudinal follow-up of mouse embryonic development in utero and for the assessment of embryonic kidney function using 50 nm magnetite dextran particles. Even though the morphologic proton images obtained were still far from classical histological slices quality, an in-plan resolution of 195 microm was achieved for a slice thickness of 800 microm. Mouse embryos sub-structures such as the fourth ventricle, the mesencephalic vesicle, the aorta or the liver can be revealed as early as E11/12. Heart, diaphragm, spinal cord, third, fourth and lateral ventricles were unambiguously seen at E13/14; whereas skeleton, tail, kidney and digit can only be seen from E15/16. Kidney and bladder were certainly identified from E16 on. MR microscopy offers a possibility for in utero phenotyping of mice and can therefore be a powerful tool for post-genomic applications.

Animals↗
PubMed2002

Quantitative MR renography using a calibrated internal signal (ERETIC).

To measure MR renograms, cortical and medullary kidney signal intensity evolution is followed after contrast agent injection. To obtain an accurate quantitative signal measurement, the use of a reference signal is necessary to correct the potential MRI system variations in time. The ERETIC method (Electronic Reference To access In vivo Concentrations) provides an electronic reference signal. It is synthesized as an amplitude modulated RF pulse applied during the acquisition. The ERETIC method was as precise as the external tube reference method but presents major advantages like its free adjustability (shape, location and magnitude) to the characteristics of the organ studied as well as its not taking room inside the magnet. Even though ERETIC showed a very good intrinsic stability, systems' variations still affect its signal in the same way as real NMR signals are affected. This method can be easily implemented on any imaging system with two RF channels.

Animals↗
PubMed1997

Polyadenylation of telomerase RNA in budding yeast.

Telomerase RNA is a subunit of a stable ribonucleoprotein particle required for telomere replication. We find that, at steady state, 5-10% of the telomerase RNA in Saccharomyces cerevisiae and Kluyveromyces lactis contains a poly(A) tail of about 80 nt. In S. cerevisiae, the poly(A)+ fraction quickly disappeared when a conditional pap1 or rna15 mutant was shifted to the nonpermissive temperature, indicating that polyadenylation is accomplished by the same machinery that polyadenylates mRNAs. Potential cis-acting polyadenylation elements were identified in the telomerase RNA sequence; when they were mutagenized, the polyadenylation pattern shifted, but was not eliminated. The corresponding mutants displayed wild-type growth. By putting the RNA under the control of an inducible promoter, we were able to show that synthesis of the poly(A)+ RNA precedes that of the poly(A)- fraction. This supports, but does not prove, a model in which all telomerase RNA is first polyadenylated and then rapidly processed to give the stable poly(A)-form. Cell cycle arrest experiments showed an increase in the poly(A)+ form between G1 and S phase, consistent with an induction of telomerase RNA transcription at the time of DNA replication.

Base Sequence↗
PubMed1996

Cloning and characterization of PET100, a gene required for the assembly of yeast cytochrome c oxidase.

The biogenesis of cytochrome c oxidase in Saccharomyces cerevisiae requires a protein encoded by the nuclear gene, PET100. Cells carrying a recessive mutation (pet100-1) in PET100 are respiratory deficient and have reduced levels of cytochrome c oxidase activity. The PET100 gene has been cloned by complementation of pet100-1, sequenced and disrupted. PET100 is located adjacent to the PDC2 gene on chromosome IV and contains an open reading frame of 333 base pairs. The PET100 protein contains a possible membrane-spanning segment and a putative mitochondrial import sequence at its NH2 terminus. A strain carrying a null mutation in PET100 lacks cytochrome c oxidase activity and assembled cytochromes a and a3, but the other respiratory chain carriers are present. The respiratory-deficient phenotype of this strain is not rescued by added hemin or heme A. These findings indicate that the mutation is specific for cytochrome c oxidase and does not affect the biosynthesis of heme A. In addition, mitochondria from the strain carrying a null mutation in PET100 contain each of the subunit polypeptides of cytochrome c oxidase. Together, these findings suggest that PET100p is not required for the synthesis or localization of cytochrome c oxidase subunits to mitochondria, but is required at a later step in their assembly into an active holoenzyme.

Amino Acid Sequence↗
PubMed1995

Failure of pristinamycin treatment in a case of pneumococcal pneumonia.

A case of pneumonia caused by Streptococcus pneumoniae occurring in a patient receiving pristinamycin is reported. Despite empirical treatment with pristinamycin, 2 g/day for five days, the patient's condition worsened. Protected brush specimen and blood cultures permitted isolation of Streptococcus pneumoniae. MIC testing indicated that the strain was susceptible to pristinamycin and resistant to erythromycin and penicillin. Streptococcus pneumoniae was eradicated by cefotaxime, and pneumonia resolved. This case underlines the fact that pristinamycin may not be suitable for the treatment of multiresistant pneumococcal infections.

Aged↗
PubMed1994

The Saccharomyces cerevisiae SPT8 gene encodes a very acidic protein that is functionally related to SPT3 and TATA-binding protein.

Mutations in the Saccharomyces cerevisiae SPT8 gene were previously isolated as suppressors of retrotransposon insertion mutations in the 5' regions of the HIS4 and LYS2 genes. Mutations in SPT8 confer phenotypes similar to those caused by particular mutations in SPT15, which encodes the TATA-binding protein (TBP). These phenotypes are also similar to those caused by mutations in the SPT3 gene, which encodes a protein that directly interacts with TBP. We have now cloned and sequenced the SPT8 gene and have shown that it encodes a predicted protein of 602 amino acids with an extremely acidic amino terminus. In addition, the predicted SPT8 amino acid sequence contains one copy of a sequence motif found in multiple copies in a number of other eukaryotic proteins, including the beta subunit of heterotrimeric G proteins. To investigate further the relationship between SPT8, SPT3 and TBP, we have analyzed the effect of an spt8 null mutation in combination with different spt3 and spt15 mutations. This genetic analysis has shown that an spt8 deletion mutation is suppressed by particular spt3 alleles. Taken together with previous results, these data suggest that the SPT8 protein is required, directly or indirectly, for TBP function at particular promoters and that the role of SPT8 may be to promote a functional interaction between SPT3 and TBP.

Amino Acid Sequence↗
PubMed1993

Interaction between PRP11 and SPP91 yeast splicing factors and characterization of a PRP9-PRP11-SPP91 complex.

Several proteins are involved in the early steps of the spliceosome assembly pathway. Protein-protein interactions have been identified between two Saccharomyces cerevisiae yeast splicing factors, PRP9 and SPP91. Here it is demonstrated that protein-protein interactions occur between SPP91 and PRP11. The combination of the prp9-1 mutant and a truncated prp11 mutant exhibits a synthetic lethal phenotype, suggestive of a common biochemical defect. The PRP9 and PRP11 proteins do not interact directly, but the PRP9 and PRP11 molecules can simultaneously bind SPP91 to form a three-molecule complex. Structurally and functionally related proteins are found in mammalian cells and are associated in a single biochemical fraction. This strongly suggests that the PRP9-SPP91-PRP11 complex is a key element of the splicing machinery.

Fungal Proteins↗
PubMed1993

Interactions between PRP9 and SPP91 splicing factors identify a protein complex required in prespliceosome assembly.

The PRP9 protein is a yeast splicing factor implicated in the early steps of spliceosome assembly whose sequence contains an amino-terminal putative leucine zipper structure and two carboxy-terminal motifs reminiscent of zinc fingers. Here, we show that the deletion of the second carboxy-terminal motif results in a dominant lethal phenotype. This observation, combined with an in vivo-binding assay for protein-protein interactions, reveals the presence of two distinct binding sites on the PRP9 protein. The carboxy-terminal region contributes to the PRP9 homodimerization, whereas the amino-terminal region binds the SPP91 splicing factor. Further experiments suggest that other factors bind to PRP9 and SPP91 proteins. Finally, we demonstrate that the PRP9 protein acts after the formation of the U1 snRNP-pre-mRNA complex. The existence of a protein complex including the PRP9 factor is discussed.

Binding Sites↗
PubMed1992

A novel gene, spp91-1, suppresses the splicing defect and the pre-mRNA nuclear export in the prp9-1 mutant.

Processing and export of nuclear pre-mRNA are believed to be competing processes in the nucleus. In order to identify factors which are involved in these processes, we isolated suppressors that relieve the growth defect of a prp9-1 temperature-sensitive mutant strain of Saccharomyces cerevisiae. The prp9-1 mutation was previously shown to abolish splicing and to target pre-mRNA to the cytoplasm. One of the suppressors, spp91-1, corrects the prp9-1 growth defect through partial restoration of splicing and by a complete reversion of the pre-mRNA escape phenotype. This suppressor is specific for two prp9 alleles and cannot substitute for PRP9 function. The mutant and wild-type alleles of SPP91 were cloned and sequenced. SPP91 encodes a novel protein essential for mitotic growth whose sequence contains motifs indicative of a nuclear localization. In vivo depletion of SPP91 in a prp9-1 genetic background is lethal and is associated with reduced amounts of spliced mRNA and accumulation of pre-mRNA. This observation strongly supports the hypothesis that SPP91 encodes a PRP factor. We suggest that spp91-1 increases pre-mRNA retention in the nucleus by improving the formation of the spliceosome and thereby allowing a larger proportion of the pre-mRNA molecules to be spliced.

Alleles↗
PubMed1991

Cloning of the two essential yeast genes, PRP6 and PRP9, and their rapid mapping, disruption and partial sequencing using a linker insertion strategy.

In the yeast Saccharomyces cerevisiae, some thermosensitive (ts) mutants have been shown to be impaired in pre-mRNA splicing (prp mutants). From a yeast genomic library, we have isolated plasmids that complement prp6 or prp9 ts mutations. These plasmids also complement the ts growth defect of additional independent mutants identified as new prp6 and prp9 ts alleles, indicating that the cloned DNAs encode PRP6 and PRP9 genes, respectively. Here, we describe the restriction maps of these loci which are localized on chromosome II and IV, respectively. The limits of open reading frames (ORFs) within the cloned inserts have been determined using a linker insertion strategy combined with the ts complementation assay. Double-strand DNA sequencing was also performed directly on the yeast expression vector from the inserted linkers. Gene disruption experiments demonstrate that both genes are essential for viability.

Base Sequence↗
PubMed1987

Export and secretion of the lipoprotein pullulanase by Klebsiella pneumoniae.

Pullulanase, a secreted lipoprotein of Klebsiella pneumoniae, is initially localized to the outer face of the outer membrane, as shown by protease and substrate accessibility and by immunofluorescence tests. Freeze-thaw disruption of these cells released both membrane-associated and apparently soluble forms of pullulanase. Membrane-associated pullulanase co-fractionated with authentic outer membrane vesicles upon isopycnic sucrose-gradient centrifugation, whereas the quasi-soluble form had the same equilibrium density as inner membrane vesicles and extracellular pullulanase aggregates. The latter also contained outer membrane maltoporin, but were largely devoid of other membrane components including LPS and lipids. K. pneumoniae carrying multiple copies of the pullulanase structural gene (pulA) produced increased amounts of cell-associated and secreted pullulanase, but a large proportion of the enzyme was neither exposed on the cell surface nor released into the medium, even after prolonged incubation. This suggests that factors necessary for pullulanase secretion were saturated by the over-produced pullulanase. When pulA was expressed under lacZ promotor control, the pullulanase which was produced was not exposed on the cell surface at any time, suggesting that pullulanase secretion genes are not expressed constitutively, and raising the possibility that they, like pulA, may be part of the maltose regulon.

Cell Membrane↗