Biomedical subjects

E Cornel

Publications and source records attributed to E Cornel.

8 recordsLinked to original sources

PubMed1997

Overexpression of c-src and n-src in the developing Xenopus retina differentially impairs axonogenesis.

To compare the roles of the nonreceptor tyrosine kinase c-src and its neuronal splice form n-src in developing neurons, Xenopus retinal precursors were transfected in vivo with c-src, n-src, or constitutively active mutants. Axonogenesis of retinal ganglion cells was markedly impaired by the expression of constitutively active c-src and only mildly affected by the expression of constitutively active n-src. This differential phenotype could not be accounted for by raised levels of intracellular tyrosine phosphorylation alone because the average anti-phosphotyrosine staining intensity of retinal neurons expressing mutant n-src was almost twofold greater than that of neurons expressing mutant c-src. The expression of either constitutively active isoform inhibited photoreceptor differentiation by 72% but did not influence other cell fates. These results suggest that c-src and n-src have both overlapping and distinct activities in differentiating retinal neurons.

Animals↗

PubMed1996

Inhibition of FGF receptor activity in retinal ganglion cell axons causes errors in target recognition.

Native fibroblast growth factor receptor (FGFR) function was inhibited in developing Xenopus retinal ganglion cells (RGCs) by in vivo transfection of a dominant negative FGFR. Axons expressing the dominant negative protein advanced at 60% of the normal speed, but nevertheless navigated appropriately in the embryonic optic pathway. When they neared the optic tectum, however, many axons made erroneous turns, causing them to bypass rather than enter their target. By contrast, RGC axons expressing nonfunctional FGFR mutants entered the tectum correctly. These findings demonstrate a role for FGFR signaling in the extension and targeting of RGC axons and suggest that receptor tyrosine kinase/growth factor interactions play a critical function in establishing initial connectivity in the vertebrate visual system.

Animals↗

PubMed1996

Cadherin function is required for axon outgrowth in retinal ganglion cells in vivo.

The cell-cell adhesion molecule N-cadherin strongly promotes neurite outgrowth in cultured retinal neurons. To test whether cadherins regulate process outgrowth in retinal neurons in vivo, we have blocked cadherin function in single cells by expression of a dominant negative N-cadherin mutant. We report that when cadherin function is inhibited, axon and dendrite outgrowth are severely impaired, particularly in retinal ganglion cells. Laminar migration and cell type specification, by contrast, appear unaffected. Further, expression of the catenin-binding domain of N-cadherin, which blocks cadherin-mediated adhesion in early embryos, does not affect axon outgrowth, suggesting that outgrowth and adhesion are mediated by distinct regions of the cytoplasmic domain. These findings indicate that cadherins play an essential role in the initiation and extension of axons from retinal ganglion cells in vivo.

Animals↗

PubMed1995

[Phenotypes of resistance to antibiotics of the most frequently isolated strains in five specialized hospital centers. Multicenter study].

Antibiotic susceptibility of 948 bacterial strains isolated from varied samples essentially proceeding from urinary infections in five Paris psychiatric Hospitals was determined by disk diffusion method. E. coli, P. mirabilis, Klebsiella spp., P. aeruginosa et S. aureus are the predominant bacteria. 40% of S. aureus are methicilline resistant. Enterobacteriaceae are progressively becoming resistant to aminopenicillines, but remain sensitive to third generation cephalosporines. They are still susceptible to first generation quinolones. At least, if no resistance of P. aeruginosa to imipeneme has been reported, 30% of strains are resistant to ciprofloxacine. Resistance phenotypes to antibiotics of the strains isolated in patients from psychiatric Hospitals are located between those observed in out patients and in patients from general Hospitals. However, we noticed a worrying evolution of resistance to those encontered in psychiatric Hospitals. Therefore, a multiresistant strains emergence monitoring must be carried out regulary.

4-Quinolones↗

PubMed1992

Precocious pathfinding: retinal axons can navigate in an axonless brain.

The developing axons of retinal ganglion cells follow a stereotyped trajectory through the diencephalon to the optic tectum. In Xenopus, this trajectory closely parallels that of a preexisting fiber tract, the tract of the postoptic commissure (TPOC). This tract comprises part of the early CNS scaffold and has been proposed to play a critical role in guiding the later growing optic axons. We have tested this possibility using heterochronic and xenoplastic transplants of eye primordia to force optic axons to enter the brain before scaffold tracts have arisen in the forebrain. We show that optic axons can navigate appropriately in the absence of the TPOC or any other axons, indicating that axonal pathfinding cues are present in the axonless neuroepithelial sheet. We suggest that molecularly distinct heterogeneities within the neuroepithelium are used for pathfinding by early and late developing axons alike in normal development.

Ambystoma↗

PubMed1990

Lipofection of cDNAs in the embryonic vertebrate central nervous system.

Neurons from the embryonic brain of Xenopus were transfected in vivo with a vector expressing luciferase cDNA using a simple lipofection procedure. Luciferase activity was monitored quantitatively, and the protein was immunolocalized in whole-mount embryonic brains. Luciferase-expressing neurons were often intensely labeled, displaying a Golgi-like filling of their dendrites, axons, and growth cones. Luciferase expression could be targeted to the retina by simply removing the skin epidermis covering the area and exposing the whole embryo to the DNA-lipofectin mixture. Luciferase activity in transfected embryos rose to peak values during the first 48 hr posttransfection and was still detectable 28 days later. Cotransfection experiments in which embryonic nervous tissue was exposed simultaneously to two different genes, luciferase and chloramphenicol acetyl-transferase, showed that transfected cells coexpressed the two genes at an extremely high frequency (85%-100%). This offers the possibility of targeting functionally significant genes along with benign reporter genes in the developing CNS.

Animals↗

PubMedDate not supplied

[Beta-lactamases of ampicillin-resistant Salmonella].

One hundred and five strains of Salmonella, including 103 clinical isolates, were examined for resistance to beta-lactams (ampicillin, carbenicillin). The resistance frequency was 5.9 and 40.6%, respectively, according to the geographical source: France or Senegal. The mechanism of resistance to beta-lactam antibiotics was always related to the biosynthesis of one constitutive beta-lactamase (beta la+). By analytical isoelectric focusing on gel of all crude sonic extracts, four types of enzymes were identified: TEM-1, TEM-2, OXA-1 and SHV -1. TEM-1, the most prevalent, was observed among 17 serotypes, TEM-2 among 3 including S. poona , and OXA-1 among 2 serotypes. SHV -1 was detected in all isolates of S. ordonez (38) but only among strains of this serotype. Among others factors involved in their distribution, differences were reported according to the geographical origin of the studied strains. In France, the three types, TEM-1, TEM-2 and OXA-1, were isolated only in the north. Moreover, the resistance frequency was 4-fold higher (7.3%) than in the south (1.8%). In Africa (Senegal), three types were individualized: TEM-1, TEM-2 and SHV -1. The SHV -1 type was only detected in clinical isolates of S. ordonez from Senegal, all of which were multi-resistant to other antibiotics (chloramphenicol, sulfonamides and tetracyclines).

Ampicillin↗

PubMedDate not supplied

[Rapid determination of the synergy of clavulanic acid and beta lactams by measuring the intracellular ATP by bioluminescence].

Twenty clinical isolates of ampicillin- and carbenicillin-resistant or susceptible (two strains) Gram-negative rods, producing at least one beta-lactamase, were examined for susceptibility to a combination of ampicillin or carbenicillin with clavulanic acid (enzymatic inhibitor). Synergy was evaluated by the reduction of the beta-lactam agar dilution MIC and by the measurement of intracellular AYP using firefly bioluminescence. The potentiation effect of clavulanic acid was variable, depending on resistance levels, species and types of beta-lactamase (TEM, SHV-1, CARB, OXA, MAL and Cpase). The synergy was significant, with 10 mg/l of inhibitor for all the strains producing TEM-1, TEM-2 and Carb-2 except for one strain of Serratia marcescens (TEM-2). The synergy was weak for Levinea strains (Citrobacter diversus biotype b), biosynthesizing specific penicillinases as MAL-1. No potentiation effect was observed for strains producing a cephalosporinase, such as Escherichia coli and Pseudomonas aeruginosa. This effect appeared to be variable for strains producing the oxacillin-hydrolysing enzyme (OXA-1), such as E. coli and P. aeruginosa. A positive correlation was clearly demonstrated between the MIC values and the intracellular ATP concentration in bacteria within 2 h. The opportunity of using the firefly assay for the rapid determination of synergy between beta-lactam antibiotics and clavulanic acid is discussed.

Adenosine Triphosphate↗