14 research outputs found
Contributions des effets directs et indirects du broutement et de la compétition à la performance des plants de sapin baumier
Une augmentation considĂ©rable de lâabondance des grands herbivores a des rĂ©percussions majeures sur la composition, la structure et le fonctionnement des Ă©cosystĂšmes forestiers ce qui peut entraĂźner des Ă©checs de rĂ©gĂ©nĂ©ration chez de nombreuses espĂšces d'arbres. Cependant, la rĂ©duction de lâabondance des herbivores ne garantit pas le rĂ©tablissement d'espĂšces sensibles au broutement. Dans un tel contexte, la plantation dâarbres peut ĂȘtre utilisĂ©e afin de restaurer le couvert forestier. Le succĂšs des plantations avec des espĂšces dâorigines vulnĂ©rables au broutement est potentiellement contraint Ă la fois par le broutement rĂ©siduel et la compĂ©tition pour les ressources par la rĂ©gĂ©nĂ©ration naturelle dâautres espĂšces. Notre objectif principal Ă©tait d'Ă©valuer les relations directes et indirectes entre le broutement par le cerf de Virginie (Odocoileus virginianus; Zimm.) et les changements dans la compĂ©tition sur la performance du sapin baumier en plantation dans un contexte de rĂ©duction de la densitĂ© des grands herbivores. Ă l'aide d'une expĂ©rience contrĂŽlĂ©e, nous avons dĂ©montrĂ© que le cerf de Virginie induit simultanĂ©ment un effet direct nĂ©gatif par le broutement des flĂšches apicales et un effet indirect positif sur les plants en diminuant la compĂ©tition pour la lumiĂšre induite par les espĂšces compagnes. Les effets directs nĂ©gatifs, cependant, l'emportent sur les avantages d'une disponibilitĂ© accrue en lumiĂšre. Contrairement Ă nos prĂ©dictions, la prĂ©paration de terrain et le dĂ©gagement mĂ©canique nâont pas eu dâeffets positifs sur la performance et la survie des plants et nâont pas diminuĂ© de maniĂšre significative la compĂ©tition pour les ressources Ă moyen terme. Nous proposons de poursuivre les recherches afin de cibler une densitĂ© de cerfs qui maximise les effets positifs du broutement tout en minimisant les effets nĂ©gatifs et que, dans ce contexte, la prescription pour la prĂ©paration du terrain et le dĂ©gagement mĂ©canique devrait reposer sur d'autres considĂ©rations que la promotion de la croissance des plants.High abundance of large herbivores has major impacts on the composition, structure and functioning of forest ecosystems, which can result in regeneration failures of many tree species. Reduction of the large herbivore, however, does not warrant successful recovery of species sensitive to browsing. In such contexts, planting in combination with silvicultural treatments can be used to restore forest cover over large areas. Our main objective was to evaluate the direct and indirect relationships between white-tailed deer browsing, changes in biotic and abiotic factors induced by site preparation and mechanical release at the tree level on survival and performance of planted balsam fir under reduced deer density. Using a controlled experiment, we demonstrated that white-tailed deer induces both a direct negative effect by browsing on apical shoots of fir, and a positive indirect effect on planted seedlings by decreasing competition for light from palatable species. The magnitude of direct negative effects, however, outweighs the benefits of increased light availability. Contrary to predictions, site preparation as well as mechanical release did not have a positive effect on seedling performance and survival and did not significantly reduce competition for resources. We propose to continue research to find a target deer density that maximizes positive effects of browsing and minimize its negative effects. In this context, prescription for site preparation and mechanical release should be based on considerations other than promoting seedlings growth
Relationship between salivary/pancreatic amylase and body mass index: a systems biology approach
Evidence of disruptive selection in the adaptation of two closely related species of tropical trees
International audienc
Escherichia coli O157:H7 Survives within Human Macrophages: Global Gene Expression Profile and Involvement of the Shiga Toxinsâż
Escherichia coli O157:H7 is an important food-borne pathogen that specifically binds to the follicle-associated epithelium in the intestine, which rapidly brings this bacterial pathogen in contact with underlying human macrophages. Very little information is available about the interaction between E. coli O157:H7 and human macrophages. We evaluated the uptake and survival of strain EDL933 during infection of human macrophages. Surprisingly, EDL933 survived and multiplied in human macrophages at 24 h postinfection. The global gene expression profile of this pathogen during macrophage infection was determined. Inside human macrophages, upregulation of E. coli O157:H7 genes carried on O islands (such as pagC, the genes for both of the Shiga toxins, and the two iron transport system operons fit and chu) was observed. Genes involved in acid resistance and in the SOS response were upregulated. However, genes of the locus of enterocyte effacement or genes involved in peroxide resistance were not differentially expressed. Many genes with putative or unknown functions were upregulated inside human macrophages and may be newly discovered virulence factors. As the Shiga toxin genes were upregulated in macrophages, survival and cytotoxicity assays were performed with isogenic Shiga toxin mutants. The initial uptake of Shiga toxins mutants was higher than that of the wild type; however, the survival rates were significantly lower at 24 h postinfection. Thus, Shiga toxins are implicated in the interaction between E. coli O157:H7 and human macrophages. Understanding the molecular mechanisms used by E. coli to survive within macrophages may help in the identification of targets for new therapeutic agents
A 3âweek nonalcoholic steatohepatitis mouse model shows elafibranor benefits on hepatic inflammation and cell death
International audienceThe long duration of animal models represents a clear limitation to quickly evaluate the efficacy of drugs targeting nonalcoholic steatohepatitis (NASH). We, therefore, developed a rapid mouse model of liver inflammation (i.e., the mouse fed a high-fat/high-cholesterol diet, where cyclodextrin is co-administered to favor hepatic cholesterol loading, liver inflammation, and NASH within 3 weeks), and evaluated the effects of the dual peroxisome proliferator-activated receptor alpha/delta agonist elafibranor (ELA). C57BL6/J mice were fed a 60% high-fat, 1.25% cholesterol, and 0.5% cholic acid diet with 2% cyclodextrin in drinking water (HFCC/CDX diet) for 3 weeks. After 1 week of the diet, mice were treated orally with vehicle or ELA 20 mg/kg q.d. for 2 weeks. Compared with vehicle, ELA markedly reduced liver lipids and nonalcoholic fatty liver disease activity scoring, through steatosis, inflammation, and fibrosis (all P < 0.01 vs. vehicle). Flow cytometry analysis showed that ELA significantly improved the HFCC/CDX diet-induced liver inflammation by preventing the increase in total number of immune cells (CD45+), Kupffer cells, dendritic cells, and monocytes population, as well as the reduction in natural killer and natural killer T cells, and by blocking conversion of T cells in regulatory T cells. ELA did not alter pyroptosis (Gasdermin D), but significantly reduced necroptosis (cleaved RIP3) and apoptosis (cleaved caspase 3) in the liver. In conclusion, ELA showed strong benefits on NASH, including improvement in hepatic inflammation, necroptosis, and apoptosis in the 3-week NASH mouse. This preclinical model will be useful to rapidly detect the effects of novel drugs targeting NASH
Microgeographic local adaptation and ecotype distributions: The role of selective processes on early lifeâhistory traits in sympatric, ecologically divergent Symphonia populations
International audienceTrees are characterized by the large number of seeds they produce. Although most of those seeds will never germinate, plenty will. Of those which germinate, many die young, and eventually, only a minute fraction will grow to adult stage and reproduce. Is this just a random process? Do variations in germination and survival at very young stages rely on variations in adaptations to microgeographic heterogeneity? and do these processes matter at all in determining tree species distribution and abundance?We have studied these questions with the Neotropical Symphonia tree species. In the Guiana shield, Symphonia are represented by at least two sympatric taxa or ecotypes, Symphonia globulifera found almost exclusively in bottomlands, and a yet undescribed more generalist taxon/ecotype, Symphonia sp1. A reciprocal transplantation experiment (510 seeds, 16 conditions) was set up and followed over the course of 6 years to evaluate the survival and performance of individuals from different ecotypes and provenances.Germination, survival, growth, and herbivory showed signs of local adaptation, with some combinations of ecotypes and provenances growing faster and surviving better in their own habitat or provenance region. S. globulifera was strongly penalized when planted outside its home habitat but showed the fastest growth rates when planted in its home habitat, suggesting it is a specialist of a highârisk highâgain strategy. Conversely, S. sp1 behaved as a generalist, performing well in a variety of environments.The differential performance of seeds and seedlings in the different habitats matches the known distribution of both ecotypes, indicating that environmental filtering at the very early stages can be a key determinant of tree species distributions, even at the microgeographic level and among very closely related taxa. Furthermore, such differential performance also contributes to explain, in part, the maintenance of the different Symphonia ecotypes living in intimate sympatry despite occasional gene flow
Relationship between salivary/pancreatic amylase and body mass index: a systems biology approach
International audienceBackgroundSalivary (AMY1) and pancreatic (AMY2) amylases hydrolyze starch. Copy number of AMY1A (encoding AMY1) was reported to be higher in populations with a high-starch diet and reduced in obese people. These results based on quantitative PCR have been challenged recently. We aimed to re-assess the relationship between amylase and adiposity using a systems biology approach.MethodsWe assessed the association between plasma enzymatic activity of AMY1 or AMY2, and several metabolic traits in almost 4000 French individuals from D.E.S.I.R. longitudinal study. The effect of the number of copies of AMY1A (encoding AMY1) or AMY2A (encoding AMY2) measured through droplet digital PCR was then analyzed on the same parameters in the same study. A Mendelian randomization analysis was also performed. We subsequently assessed the association between AMY1A copy number and obesity risk in two case-control studies (5000 samples in total). Finally, we assessed the association between body mass index (BMI)-related plasma metabolites and AMY1 or AMY2 activity.ResultsWe evidenced strong associations between AMY1 or AMY2 activity and lower BMI. However, we found a modest contribution of AMY1A copy number to lower BMI. Mendelian randomization identified a causal negative effect of BMI on AMY1 and AMY2 activities. Yet, we also found a significant negative contribution of AMY1 activity at baseline to the change in BMI during the 9-year follow-up, and a significant contribution of AMY1A copy number to lower obesity risk in children, suggesting a bidirectional relationship between AMY1 activity and adiposity. Metabonomics identified a BMI-independent association between AMY1 activity and lactate, a product of complex carbohydrate fermentation.ConclusionsThese findings provide new insights into the involvement of amylase in adiposity and starch metabolism
Clinico-biological features and clonal hematopoiesis in patients with severe covid-19
International audienceAdvanced age or preexisting comorbidities have been characterized as risk factors for severe coronavirus disease 2019 (COVID-19) cases requiring hospitalization and intensive care. In recent years, clonal hematopoiesis (CH) of indeterminate potential (CHIP) has emerged as a risk factor for chronic inflammatory background and subsequent aging-associated diseases. The purpose of this study was to identify biological factors (particularly leukocyte subtypes and inflammatory markers) associated with a risk of clinical deterioration (i.e., orotracheal intubation (OTI)) and to determine whether CH was likely to influence clinical and biological behavior in patients with severe COVID-19 requiring hospitalization. Here, we describe clinical and biological features, including the screening of CHIP mutants in a well-annotated cohort of 122 hospitalized patients with a laboratory-confirmed diagnosis of COVID-19 (55% requiring OTI). We showed that elevated white blood cell counts, especially neutrophils and high C-reactive protein (CRP) levels at admission, were associated with an increased requirement of OTI. We noticed a high prevalence of CH (25%, 38%, 56%, and 82% of patients aged 80 years) compared to a retrospective cohort of patients free of hematological malignancy explored with the same pipelines (10%, 21%, 37%, and 44%). However, the existence of CH did not significantly impact clinical outcome, including OTI or death, and did not correlate with other laboratory findings
AubinEtAl_CoVitas_ITV
Trait data collected for the CoVitas project that was used in the publication. Please see Metadata file for more details (in xlsx format