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81.
Raulin-Cerceau Florence Maurel Marie-Christine Schneider Jean 《Origins of life and evolution of the biosphere》1998,28(4-6):597-612
During the 19th and early 20th centuries, ideas related to the possible origin in space of bioorganic molecules, or seeds, or even germs and organisms (and how they reached the Earth) included the Panspermia theory. Based on the idea of the eternity of life proposed by eminent physicists – such as Arrhenius and Kelvin – Panspermia is mainly divided into two branches: lithopanspermia (transport of germs inside stones traveling in space) and radiopanspermia (transport of spores by radiative pressure of stellar light). We point out some arguments to help to understand whether Panspermia could exist nowadays as the same theory defined one century ago. And we wonder about the kind of evolution Panspermia could have undergone during only a few decades. This possible evolution of the Panspermia concept takes place in the framework of the emergence of a new field, Bioastronomy. We present how this discipline has emerged during a few decades and how it has evolved. We consider its relationship with the progression of other scientific fields, and finally we examine how it is now included in different projects of space agencies. Bioastronomy researches having become more and more robust during the last few years, we emphasize several questions about new ideas and their consequences for the current hypothesis of Panspermia and of universal life. 相似文献
82.
Thomas Lefebvre Bruno J. Gonzalez†‡ David Vaudry Laurence Desrues Antony Falluel-Morel Nicolas Aubert§ Alain Fournier¶ Marie-Christine Tonon Hubert Vaudry Hélène Castel 《Journal of neurochemistry》2009,110(3):976-989
Transient exposure to ethanol (EtOH) results in a massive neurodegeneration in the developing brain leading to behavioral and cognitive deficits observed in fetal alcohol syndrome. There is now compelling evidence that K+ channels play an important role in the control of programmed cell death. The aim of the present work was to investigate the involvement of K+ channels in the EtOH-induced cerebellar granule cell death and/or survival. At low and high concentrations, EtOH evoked membrane depolarization and hyperpolarization, respectively. Bath perfusion of EtOH (10 mM) depressed the I A (transient K+ current) potassium current whereas EtOH (400 mM) provoked a marked potentiation of the specific I K (delayed rectifier K+ current) current. Pipette dialysis with GTPγS or GDPβS did not modify the effects of EtOH (400 mM) on both membrane potential and I K current. In contrast, the reversible depolarization and slowly recovering inhibition of I A induced by EtOH (10 mM) became irreversible in the presence of GTPγS. EtOH (400 mM) induced prodeath responses whereas EtOH (10 mM) and K+ channel blockers promoted cell survival. Altogether, these results indicate that in cerebellar granule cells, EtOH mediates a dual effect on K+ currents partly involved in the control of granule cell death. 相似文献
83.
Homogalacturonan-derived partly methylated and/or acetylated oligogalacturonates were recovered after enzymatic hydrolysis (endo-polygalacturonase+pectin methyl esterase+side-chain degrading enzymes) of sugar beet pectin followed by anion-exchange and size exclusion chromatography. Around 90% of the GalA and 75% of the acetyl groups present in the initial sugar beet pectin were recovered as homogalacturonan-derived oligogalacturonates, the remaining GalA and acetyl belonging to rhamnogalacturonic regions. Around 50% of the acetyl groups present in sugar beet homogalacturonans were recovered as partly methylated and/or acetylated oligogalacturonates of degree of polymerisation 5 whose structures were determined by electrospray ionization ion trap mass spectrometry (ESI-IT-MSn). 2-O-acetyl- and 3-O-acetyl-GalA were detected in roughly similar amounts but 2,3-di-O-acetylation was absent. Methyl-esterified GalA residues occurred mainly upstream 2-O-acetyl GalA. Oligogalacturonates containing GalA residues that are at once methyl- and acetyl-esterified were recovered in very limited amounts. A tentative mapping of the distribution of acetyl and methyl esters within sugar beet homogalacturonans is proposed. Unsubstituted GalA residues are likely to be present in limited amounts (approximately 10% of total GalA residues), due to the fact that methyl and acetyl groups are assumed to be most often not carried by the same residues. 相似文献
84.
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86.
Yefimova MG Sow A Fontaine I Guilleminot V Martinat N Crepieux P Canepa S Maurel MC Fouchécourt S Reiter E Benzakour O Guillou F 《Biology of reproduction》2008,78(4):697-704
Transferrin is well known as an iron transport glycoprotein. Dimeric or tetrameric transferrin forms have recently been reported to modulate phagocytosis by human leukocytes. It is mainly synthesized by the liver, and also by other sources, such as Sertoli cells of the testis. Sertoli cells show a strong phagocytic activity toward apoptotic germ cells and residual bodies. Here, we provide evidence that purified human dimeric transferrin from commercial sources decreased residual body phagocytosis, unlike monomeric transferrin. The presence of iron appeared essential for dimeric transferrin inhibitory activity. Importantly, dimeric transferrin could be visualized by immunoblotting in Sertoli cell lysates as well as in culture media, indicating that dimeric transferrin could be physiologically secreted by Sertoli cells. By siRNA-mediated knockdown, we show that endogenous transferrin significantly inhibited residual body ingestion by Sertoli cells. These results are the first to identify dimeric transferrin in Sertoli cells and to demonstrate its implication as a physiological modulator of residual body phagocytosis by Sertoli cells. 相似文献
87.
pS2/TFF1 overexpression in breast carcinomas correlates with response to hormonotherapy. We evaluated the clinical relevance of urinary pS2/TFF1 in breast cancer patients. In healthy controls (100 cases), it represents an individual and relatively stable parameter. Although 24 out 83 pre-operative breast cancer patients showed elevated levels, both the sensitivity and specificity of the test were too low for breast cancer screening. However, neoadjuvant hormonotherapy decreased pS2/TFF1 levels in nine out of 20 patients. Furthermore, among 22 patients receiving long-term adjuvant hormonotherapy, four exhibited elevated levels, two of them at the time of relapse. Thus, urinary pS2/TFF1 quantification might be suitable as an in vivo diagnosis for tumor hormonodependency, and disease follow-up during hormonotherapy. 相似文献
88.
Jacques Ricard Jacques Vergne Jean-Luc Decout Marie-Christine Maurell 《Journal of molecular evolution》1996,43(4):315-325
A polyallylamine carrying long hydrophobic dodecyl groups and adenine residues as side chains (PALAD C12) may be able to catalyze the hydrolysis ofN-carbobenzoxy-l-alaninep-nitrophenyl ester (N-Cbz-Ala) as well asp-nitrophenyl acetate (pNPA). The progress curve of hydrolysis of the former displays a long lag and apparently no steady state.
After this transient the rate falls off due to the accumulation of the products. Conversely, the hydrolysis ofp-nitrophenyl acetate displays classical burst kinetics followed by a slow decline of the reaction rate.
Theoretical considerations show that a steady state may be expected to occur only if the concentration of the free catalyst
is very small during the reaction. This condition is sufficient to allow the rate of disappearance of the substrate to be
equal to the rate of appearance of the products, which is precisely a condition for the existence of a steady state. If the
catalyst is poorly active and has a loose affinity for its substrate and product, the measurement of a significant reaction
rate will require a much larger concentration of the catalyst. Therefore, under these conditions, one cannot expect a steady
state to occur. The mathematical expression of the error made in the steady-state assumption has been derived. This error
increases with the catalyst concentration and decreases if the affinity of the substrate for the catalyst is high. Therefore
the lack of steady state is associated with the affinity (or the dissociation) of the substrate and the product for the catalyst.
When this affinity is low, the free concentration of the catalyst during the reaction is high and one cannot expect a steady
state to occur. This is precisely what takes place with N-Cbz-Ala.
A mathematical expression of the rate of hydrolysis of N-Cbz-Ala and of any reactant that displays this type of kinetics may
be derived at the end of the transient when the rate is close to its maximum value. Under these conditions the rate cannot
follow classical Michaelis-Menten kinetics and displays positive cooperativity.
It may therefore be speculated that primordial template-like catalysts that were displaying a poor affinity for their substrates
and products were already exhibiting apparent positive cooperativity in the kinetic reactions they were able to catalyze.
Correspondence to: J. Ricard 相似文献
89.
Nisole S Said EA Mische C Prevost MC Krust B Bouvet P Bianco A Briand JP Hovanessian AG 《The Journal of biological chemistry》2002,277(23):20877-20886
The multivalent pseudopeptide HB-19 that binds the cell-surface-expressed nucleolin is a potent inhibitor of human immunodeficiency virus (HIV) infection by blocking virus particle attachment and thus anchorage in the plasma membrane. We show that cross-linking of surface-bound HB-19A (like HB-19 but with a modified template) results in aggregation of HB-19A with surface nucleolin. Consistent with its specific action, HB-19A binding to different types of cells reaches saturation at concentrations that have been reported to result in inhibition of HIV infection. By using Chinese hamster ovary mutant cell lines, we confirm that the binding of HB-19A to surface nucleolin is independent of heparan and chondroitin sulfate proteoglycans. In vitro generated full-length nucleolin was found to bind HB-19A, whereas the N-terminal part containing the acidic amino acid stretches of nucleolin did not. The use of various deletion constructs of the C-terminal part of nucleolin then permitted the identification of the extreme C-terminal end of nucleolin, containing repeats of the amino acid motif, RGG, as the domain that binds HB-19A. Finally, a synthetic peptide corresponding to the last C-terminal 63 amino acids was able to inhibit HIV infection at the stage of HIV attachment to cells, thus suggesting that this domain could be functional in the HIV anchorage process. 相似文献
90.
Létuvé S Kozhich A Arouche N Grandsaigne M Reed J Dombret MC Kiener PA Aubier M Coyle AJ Pretolani M 《Journal of immunology (Baltimore, Md. : 1950)》2008,181(7):5167-5173
YKL-40 is a chitin-binding protein that is elevated in patients with various inflammatory conditions associated with ongoing remodeling. We investigated whether the levels of YKL-40 were up-regulated in the circulation and the airways of patients with chronic obstructive pulmonary disease (COPD), and whether it promoted the production of inflammatory mediators from macrophages. Serum, bronchoalveolar lavage (BAL), bronchial biopsies, lung tissue specimens, and alveolar macrophages from never-smokers (n = 15), smokers without COPD (n = 20), and smokers with COPD (n = 30) were assessed for YKL-40 levels and immunolocalization. In addition, YKL-40-induced mediator release from alveolar macrophages was examined. We found that smokers with COPD had elevated levels of YKL-40 in serum (p = 0.027) and BAL (p = 0.007), more YKL-40-positive cells in bronchial biopsies (p = 0.03), and a greater proportion of alveolar macrophages expressing YKL-40 than smokers without COPD or never-smokers. YKL-40 levels in serum and BAL were associated with airflow obstruction (pre-beta(2) agonist forced expiratory volume in 1 s, r(s) = -0.3892, p = 0.0072 and r(s) = -0.5491, p < 0.0001, respectively) and impaired diffusion lung capacity (transfer factor of the lung for carbon monoxide, r(s) = -0.4667, p = 0.002 and r(s) = -0.3854, p = 0.0045, respectively). TNF-alpha stimulated YKL-40 synthesis in alveolar macrophages from smokers with COPD, and exposure of these cells to YKL-40 promoted the release of IL-8, MCP-1, MIP-1alpha, and metalloproteinase-9. We conclude that YKL-40 is up-regulated in COPD, in which it may contribute to tissue inflammation and remodeling by sustaining the synthesis of proinflammatory and fibrogenic chemokines and of metalloproteinases by alveolar macrophages. 相似文献