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61.
Loiseau C Zoorob R Garnier S Birard J Federici P Julliard R Sorci G 《Ecology letters》2008,11(3):258-265
Genes of the Major Histocompatibility Complex ( Mhc ) play a fundamental role during the immune response because MHC molecules expressed on cell surface allow the recognition and presentation of antigenic peptides to T-lymphocytes. Although Mhc alleles have been found to correlate with pathogen resistance in several host-parasite systems, several studies have also reported associations between Mhc alleles and an accrued infection risk or an accelerated disease progression. The existence of these susceptibility alleles is puzzling, as the cost generated by the infection should rapidly eliminate them from the population. Here, we show that susceptibility alleles may be maintained in a population of house sparrows ( Passer domesticus ) if they have antagonistic effects on different malaria parasites. We found that one Mhc class I allele was associated with a 2.5-fold increase in the risk to be infected with a Plasmodium strain, but with a 6.4-fold reduction in the risk to harbour a Haemoproteus strain. We suggest that this antagonistic effect might arise because Mhc genes can alter the competitive interactions between malaria parasites within the host. 相似文献
62.
Nomi Kreif Oleg Sofrygin Julie A. Schmittdiel Alyce S. Adams Richard W. Grant Zheng Zhu Mark J. van der Laan Romain Neugebauer 《Biometrics》2021,77(1):329-342
In studies based on electronic health records (EHR), the frequency of covariate monitoring can vary by covariate type, across patients, and over time, which can limit the generalizability of inferences about the effects of adaptive treatment strategies. In addition, monitoring is a health intervention in itself with costs and benefits, and stakeholders may be interested in the effect of monitoring when adopting adaptive treatment strategies. This paper demonstrates how to exploit nonsystematic covariate monitoring in EHR‐based studies to both improve the generalizability of causal inferences and to evaluate the health impact of monitoring when evaluating adaptive treatment strategies. Using a real world, EHR‐based, comparative effectiveness research (CER) study of patients with type II diabetes mellitus, we illustrate how the evaluation of joint dynamic treatment and static monitoring interventions can improve CER evidence and describe two alternate estimation approaches based on inverse probability weighting (IPW). First, we demonstrate the poor performance of the standard estimator of the effects of joint treatment‐monitoring interventions, due to a large decrease in data support and concerns over finite‐sample bias from near‐violations of the positivity assumption (PA) for the monitoring process. Second, we detail an alternate IPW estimator using a no direct effect assumption. We demonstrate that this estimator can improve efficiency but at the potential cost of increase in bias from violations of the PA for the treatment process. 相似文献
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In central neurons, the threshold for spike initiation can depend on the stimulus and varies between cells and between recording sites in a given cell, but it is unclear what mechanisms underlie this variability. Properties of ionic channels are likely to play a role in threshold modulation. We examined in models the influence of Na channel activation, inactivation, slow voltage-gated channels and synaptic conductances on spike threshold. We propose a threshold equation which quantifies the contribution of all these mechanisms. It provides an instantaneous time-varying value of the threshold, which applies to neurons with fluctuating inputs. We deduce a differential equation for the threshold, similar to the equations of gating variables in the Hodgkin-Huxley formalism, which describes how the spike threshold varies with the membrane potential, depending on channel properties. We find that spike threshold depends logarithmically on Na channel density, and that Na channel inactivation and K channels can dynamically modulate it in an adaptive way: the threshold increases with membrane potential and after every action potential. Our equation was validated with simulations of a previously published multicompartemental model of spike initiation. Finally, we observed that threshold variability in models depends crucially on the shape of the Na activation function near spike initiation (about −55 mV), while its parameters are adjusted near half-activation voltage (about −30 mV), which might explain why many models exhibit little threshold variability, contrary to experimental observations. We conclude that ionic channels can account for large variations in spike threshold. 相似文献
66.
Bouyoucos Ian A. Romain Martin Azoulai Lorine Eustache Kim Mourier Johann Rummer Jodie L. Planes Serge 《Coral reefs (Online)》2020,39(5):1209-1214
Coral Reefs - Sharks play important functional roles in coral reef ecosystems. Studying reef shark populations’ spatial ecology also contributes important data for effective conservation... 相似文献
67.
Endocrine control of follicular growth was determined by observing the left ovary of prepubertal calves previously treated with a potent GnRH agonist for 13 days. The ovarian response to hormonal stimulation was determined using the right ovaries of the same animals. Three-month-old crossbred calves were assigned to one of the two following treatment groups: 1) saline control for 13 days, with purified porcine FSH for the last 3 days (n = 5); and 2) GnRHa for 13 days, with purified porcine FSH for the final 3 days (n = 5). The left ovaries were removed from all calves after 10 days, and the right ovaries were removed at the end of treatment. Plasma concentrations of FSH, LH and oestradiol-17 beta were followed up during the GnRHa and pFSH treatments. The maximum macroscopic diameter of the F1 follicle, as determined by daily ultrasonography, did not differ between GnRHa-treated calves (from 6.6 to 10.4 mm) and the saline control calves (from 6.7 to 10.3 mm). Histological analysis of the ovaries showed that the number of follicles > 0.40 mm in diameter varied greatly for calves of the two groups (from 11 to 220 at 10 days). GnRHa significantly increased the mean number of follicles (total and nonatretic) of size class > 5.4 mm as compared to saline control calves (P < 0.05). The FSH treatment significantly increased the mean number of follicles 3.00-5.4 and > 5.4 mm in diameter (P < 0.05), with no change in the number of follicles smaller than 3.00 mm. The rate of atresia of large follicles (3.01-5.40 mm) was significantly reduced by purified porcine FSH treatment in both groups (P < 0.05). In no case did the GnRHa induce ovulation or luteinization of follicles. The LH and FSH concentrations increased transiently after GnRHa treatment on the first day, but afterwards, both hormones increased to only one sixth of what was observed after the initial GnRHa injection treatment. This increase in LH and FSH was observed 1 h after GnRHa treatment on each consecutive day of the experiment and were significantly different in the control group (0 h versus 1 h versus 2 h x saline control versus GnRH agonists groups; P < 0.01). During the superovulatory treatment, FSH concentrations peaked at around 0.70 ng.mL-1 in both saline- and GnRHa-treated groups on the first day but on the last day of surovulatory treatment, FSH concentrations were higher in GnRHa agonist-treated calves than in the control calves (day 11 versus day 12 versus day 13 x saline control versus GnRH agonist treatment groups; P < 0.01). LH profiles were unchanged by surovulatory treatment. Concentrations of oestradiol-17 beta increased significantly over the three days (P < 0.001) of the superovulatory treatments in both groups (P < 0.01). These results indicate that GnRH agonist treatment allows recruited antral follicles to pursue their growth during the early selection process via sustained FSH and LH secretion allowing more than a single large follicle to maintain their growth without going to atresia. 相似文献
68.
Romain Vullo Eric Buffetaut Didier Néraudeau Jean Le Lœuff Jean-François Heil Michèle Dunand 《Annales de Paléontologie》2012
The “Megalosaur” remains from Saint-Agnant (Charente-Maritime, France), reported as early as 1881 by Boissellier, are here described and figured for the first time. These bones, as well as a few additional specimens from the nearby locality of Soubise, belong in fact to an indeterminate sauropod. The stratigraphical position of these remains unambiguously indicates an infra-Cenomanian age. However, the presence in this area of continental deposits with Purbeckian and Wealden facies does not allow to decide between an earliest or late Early Cretaceous age. 相似文献
69.
Dominique Dorin-Semblat Claudia Demarta-Gatsi Romain Hamelin Florence Armand Teresa Gil Carvalho Marc Moniatte Christian Doerig 《PloS one》2015,10(12)
Casein kinase 1 (CK1) is a pleiotropic protein kinase implicated in several fundamental processes of eukaryotic cell biology. Plasmodium falciparum encodes a single CK1 isoform, PfCK1, that is expressed at all stages of the parasite’s life cycle. We have previously shown that the pfck1 gene cannot be disrupted, but that the locus can be modified if no loss-of-function is incurred, suggesting an important role for this kinase in intra-erythrocytic asexual proliferation. Here, we report on the use of parasite lines expressing GFP- or His-tagged PfCK1 from the endogenous locus to investigate (i) the dynamics of PfCK1 localisation during the asexual cycle in red blood cells, and (ii) potential interactors of PfCK1, so as to gain insight into the involvement of the enzyme in specific cellular processes. Immunofluorescence analysis reveals a dynamic localisation of PfCK1, with evidence for a pool of the enzyme being directed to the membrane of the host erythrocyte in the early stages of infection, followed by a predominantly intra-parasite localisation in trophozoites and schizonts and association with micronemes in merozoites. Furthermore, we present strong evidence that a pool of enzymatically active PfCK1 is secreted into the culture supernatant, demonstrating that PfCK1 is an ectokinase. Our interactome experiments and ensuing kinase assays using recombinant PfCK1 to phosphorylate putative interactors in vitro suggest an involvement of PfCK1 in many cellular processes such as mRNA splicing, protein trafficking, ribosomal, and host cell invasion. 相似文献
70.
Romain Boulho Christel Marty Yolanda Freile-Pelegrín Daniel Robledo Nathalie Bourgougnon Gilles Bedoux 《Journal of applied phycology》2017,29(5):2219-2228
Carrageenan yield, physicochemical properties, and antiviral activity of the carrageenan from Solieria chordalis (Rhodophyceae, Solieriaceae) harvested at the Brittany coast (France) were investigated. S. chordalis carrageenan was extracted by conventional and the microwave-assisted extraction (MAE) methods. The effect of different parameters during MAE extraction such as alkali concentration (0, 0.5 and 1% KOH), extraction time (10, 20, and 25 min) and temperature (90 and 105 °C) were evaluated. Native carrageenan extracted by MAE had the highest yield (29.3%) after 10 min at 90 °C. After alkali treatment, carrageenan yield ranged from 10.7 to 18.4%. No significant differences in the carrageenan yield were observed between MAE and conventional method under alkaline conditions. Chemical analysis and FTIR spectra revealed the presence of a predominant iota-carrageenan. Evaluation of the antiviral activity of S. chordalis carrageenan against HSV-1 (Herpes simplex virus type 1) showed a EC50 of the iota-carrageenans fractions in the range of 3.2 to 54.4 μg mL?1 (MOI 0.01 ID50 mL?1) without cytotoxicity in that range of concentrations. 相似文献