Biology subjects

Villard, L.

Publications and source records attributed to Villard, L..

5 recordsLinked to original sources

bioRxiv2020

Inoculation with highly-related mycorrhizal fungal siblings, and their interaction with plant genoptypes, strongly shapes tropical mycorrhizal fungal community structure

Arbuscular mycorrhizal fungi (AMF) have the potential to increase crop yields and all globally important crops form the mycorrhizal symbiosis. Only a few studies have investigated the impact of introduced AMF on local AMF communities and most studies have only investigated effects of one isolate. We studied the impact on AMF community structure of inoculating roots of the globally important crop cassava with highly genetically-related clonal siblings of two genetically different Rhizophagus irregularis isolates. We hypothesized that inoculation with R. irregularis siblings differentially influences the structure and the diversity of the pre-existing AMF community colonizing cassava. Alpha and beta taxonomic and phylogenetic AMF diversity were strongly and significantly altered differentially following inoculation with sibling AMF progeny. In most cases, the effects were also cassava-genotype specific. Although biomass production and AMF colonization were also both differentially affected by inoculation with sibling R. irregularis progeny these variables were not correlated with changes in the AMF community structure. The results highlight that investigations on the impact of an introduced AMF species, that use only one isolate, are unlikely to be representative of the overall effects of that AMF species and that the genetic identity of the host must be considered. The amount of inoculum added was very small and effects were observed 12 months following inoculation. That such a small amount of almost genetically identical fungal inoculum can strongly differentially influence AMF community structure 12 months following inoculation, indicates that AMF communities in tropical soils are not very resistant to perturbation.

ecology↗

bioRxiv2020

A KCNQ2 variant causing Early Onset Epileptic Encephalopathy increases spontaneous network-driven activity and excitability of pyramidal cells in the layer II/III and V of the motor cortex during a limited period of development

De novo missense variants in the KCNQ2 gene encoding the Kv7.2 subunit of the voltage-gated potassium Kv7/M channel are the main cause of Developmental and Epileptic Encephalopathy (DEE). KCNQ2 related-DEE is characterized by pharmaco-resistant neonatal seizures associated with a developmental delay. While seizures usually resolve some weeks or months after birth, cognitive/behavioral deficits persist. To better understand the cellular mechanisms underlying KCNQ2-associated network dysfunction and their progression over time, we investigated in vivo, using local field potential recordings of freely moving animals, and ex-vivo in layers II/III and V of motor cortical slices, using patch-clamp recordings, the electrophysiological properties of pyramidal cells from a heterozygous knock-in (KI) mouse model carrying the p.T274M pathogenic variant during neonatal, post-weaning and juvenile developmental stages. We found that KI mice displayed spontaneous seizures preferentially at post-weaning rather than at juvenile stages. At the cellular level, the variant led to a reduction in M current density/chord conductance and to an increase in neuronal excitability. These alterations were observed already during the neonatal period in pyramidal cells of layers II / III and during post-weaning stage in pyramidal cells of layer V. Moreover there was an increase in the frequency of spontaneous network driven events mediated by GABA receptors in the layers II/III suggesting that the excitability of some interneurons was also increased. However, all these alterations were time limited and no more observed in layers II/III and V of juvenile mice. At this stage, M-current density and neuronal excitability were not different from the measurements made in juvenile wild-type mice. Thus our data indicate that the action of the variant on neuronal activity is developmentally regulated and that some cellular mechanisms leading to the recovery of Kv7/M channels function took place during brain maturation of KI mice. These results raise the possibility that the age related seizure remission observed in KCNQ2-related DEE patient results also from a time limited alteration of Kv7 channels activity and neuronal excitability.

neuroscience↗

bioRxiv2020

It takes two to tango: M-current swings with the persistent sodium current to set the speed of locomotion.

The central pattern generator (CPG) for locomotion is set of pacemaker neurons endowed with inherent bursting driven by the persistent sodium current (INaP). How they proceed to regulate the locomotor rhythm remained unknown. Here, in neonatal rodents, we identified a persistent potassium current, critical in regulating pacemakers and locomotion speed. This current recapitulates features of the M-current (IM); a subthreshold non-inactivating outward current blocked by XE991 and enhanced by ICA73. Immunostaining and mutant mice highlight an important role of axonal Kv7.2 channels in mediating IM. Pharmacological modulation of IM regulates the emergence and the frequency regime of both pacemaker and CPG activities, and controls the speed of locomotion. Computational models captured these results and show howed an interplay between IM and INaP that endows the locomotor CPG with rhythmogenic properties. Overall, this study provides fundamental insights into how IM and INaP work in tandem to set the speed of locomotion.

neuroscience↗

bioRxiv2019

Huntington phosphorylation governs BDNF homeostasis and improves the phenotype of Mecp2 knockout mice

Mutations in the X-linked MECP2 gene are responsible for Rett syndrome (RTT), a severe neurological disorder for which there is no treatment. Several studies have linked the loss of MeCP2 function to alterations of brain-derived neurotrophic factor (BDNF) levels, but non-specific overexpression of BDNF only partially improves the phenotype of Mecp2-deficient mice. We and others have previously shown that huntingtin (HTT) scaffolds molecular motor complexes, transports BDNF-containing vesicles, and is under-expressed in Mecp2 knock-out brains. Here we demonstrate that promoting HTT phosphorylation at Ser421, either by a phospho-mimetic mutation or inhibition of the phosphatase calcineurin, restores endogenous BDNF axonal transport in vitro in the corticostriatal pathway, increases striatal BDNF availability and synaptic connectivity in vivo, and improves the phenotype and the survival of Mecp2 knockout mice--even though treatments were initiated only after the mice had already developed symptoms. Stimulation of endogenous cellular pathways may thus be a promising approach for the treatment of RTT patients.

neuroscience↗

bioRxiv2018

Within-species phylogenetic relatedness of a common mycorrhizal fungus affects evenness in plant communities through effects on dominant species

Arbuscular mycorrhizal fungi (AMF) have been shown to influence plant community structure and diversity. Studies based on single plant - single AMF isolate experiments show that within AMF species variation leads to large differential growth responses of different plant species. Because of these differential effects, genetic differences among isolates of an AMF species could potentially have strong effects on the structure of plant communities.\n\nWe tested the hypothesis that within species variation in the AMF R. irregularis significantly affects plant community structure and plant co-existence. We took advantage of a recent genetic characterization of several isolates using double-digest restriction-site associated DNA sequencing (ddRADseq). This allowed us to test not only for the impact of within AMF species variation on plant community structure but also for the role of the R. irregularis phylogeny on plant community metrics. Nine isolates of R. irregularis, belonging to three different genetic groups (Gp1, Gp3 and Gp4), were used as either single inoculum or as mixed diversity inoculum. Plants in a mesocosm representing common species that naturally co-exist in European grasslands were inoculated with the different AMF treatments.\n\nWe found that within-species differences in R. irregularis did not strongly influence the performance of individual plants or the structure of the overall plant community. However, the evenness of the plant community was affected by the phylogeny of the fungal isolates, where more closely-related AMF isolates were more likely to affect plant community evenness in a similar way compared to more genetically distant isolates.\n\nThis study underlines the effect of within AMF species variability on plant community structure. While differential effects of the AMF isolates were not strong, a single AMF species had enough functional variability to change the equilibrium of a plant community in a way that is associated with the evolutionary history of the fungus.

ecology↗