Biology subjects

Fournier, J.

Publications and source records attributed to Fournier, J..

10 recordsLinked to original sources

bioRxiv2025

Rhizobial motility preference in root colonization of Medicago truncatula

O_LITunnel-like infection thread (IT) structures support root colonization by symbiotic nitrogen-fixing rhizobia bacteria in most legume species. These tip-grown structures are key to direct rhizobia from root hairs to developing nodules, where they are hosted to fix nitrogen. Rhizobia likely progress inside ITs by combining growth and motility, by modes not yet defined. Here, we tackled this question by combining mathematical modeling, live cell imaging, and bacterial mutant phenotyping in Medicago truncatula. C_LIO_LIModeling the motion of fluorescently-labeled Sinorhizobium meliloti inside early root hair IT compartments estimated slow movement (2 to 6 {micro}m/h), compatible with passive rather than active motility. Consistent with this model, flagella-less fliF and fliF-fliRdel S. meliloti mutants were impaired in active swimming motility in vitro, yet could colonize host roots and nodules in planta. In contrast, mutation in the rhizobactin 1021 siderophore rhbE biosynthesis gene affected both surface motility in vitro, and host root and nodule colonisation. This mutation also promoted the formation of branched ITs in root hairs, which ultimately resulted in impaired nodule development and infection. C_LIO_LIOur findings support the model estimation and suggest that S. meliloti prioritises flagella-independent surface translocation, partially by secreting rhizobactin 1021 surfactants to reach developing nodules in M. truncatula. C_LI

plant biology↗

bioRxiv2024

Template-driven dynamic functional network connectivity predicts medication response for major depression and bipolar disorders

The process of finding reliable treatment for major depression and bipolar disorder can be arduous. The myriad behavioral symptoms presented by patients and resistance to treatment from particular medication classes complicate standard diagnostic and prescription methodologies, often requiring multiple attempted treatments during which symptoms may still be present. Physiological information such as neuroimaging scans may help to alleviate some of the uncertainty surrounding diagnosis and treatment when incorporated into a clinical setting. Changes in functional magnetic resonance imaging show particular promise, as the incorporation of dynamical information may provide insights into physiological changes prior to static, structural changes. In this work, we present a novel method for generating robust and replicable dynamic functional network connectivity (dFNC) features from neuroimaging data using a template of dynamic states derived from a large, non-affected data set. We demonstrate that this template-driven dFNC approach expands on standard dFNC approaches by allowing for the derivation of a continuous state-contribution time series. We demonstrate that the derived biomarkers can support high predictive performance for the identification of medication class and non-responders while also expanding the set of biomarkers available for studying differences in mood disorder medication response.

neuroscience↗

bioRxiv2024

Annexin and calcium-regulated priming of legume root cells for endosymbiotic infection

Legumes establish endosymbioses with arbuscular mycorrhizal (AM) fungi or rhizobia bacteria to improve mineral nutrition. Symbionts are hosted in privileged habitats, root cortex (for AM fungi) or nodules (for rhizobia) for efficient nutrient exchange. To reach these habitats, plants form cytoplasmic bridges, which are key to predicting and guiding the cellular route of entry of fungal hyphae or rhizobia-filled infection threads (ITs). However, the underlying mechanisms are poorly studied. Here we show that unique ultrastructural changes and Ca2+ spiking signatures, closely linked to MtAnn1 annexin accumulation, accompany rhizobia-associated bridge formation. Loss of MtAnn1 function in M. truncatula affects Ca2+ spike amplitude, cytoplasmic configuration and rhizobia infection efficiency, consistent with a role of MtAnn1 in regulating infection priming. MtAnn1, which evolved in species establishing intracellular symbioses, is also AM-symbiosis-induced and required for proper arbuscule formation. Together, we propose that MtAnn1 is part of an ancient Ca2+-regulatory module for transcellular endosymbiotic infection.

plant biology↗

bioRxiv2023

The penetration of sunflower root tissues by the parasitic plant Orobanche cumana Wallr. is intracellular

O_LIParasitic plants cause yield losses for important crops. Among these, Orobanche cumana Wallr, sunflower broomrape, is one of the major pests for sunflower. Previous studies stated that in most cases, the haustorium, a specific parasitic plant organ, penetrates host roots intercellularly. However, host cellular mechanisms involved during the parasitic cells penetration remained poorly described. C_LIO_LIWe investigated sunflower root cellular behavior during haustorium penetration using various microscopy approaches including live cell imaging of inoculated transgenic fluorescent sunflower roots. C_LIO_LIWe showed that the haustorium of O. cumana penetrated living sunflower root tissues, as a result of the degradation of the host cell wall and the formation of a new host trans-cellular apoplastic compartment for haustorium accommodation. Moreover, broomrape induced cell divisions in outer root tissues at very early stages of the interaction, leading to localized hypertrophy at the site of broomrape attachments. C_LIO_LIThese findings are a change of paradigm in the research field of parasitic plants. They extend host root intracellular accommodation mechanisms initially shown for symbiotic and pathogenic biotrophic fungi to parasitic plants. It paves the way for future understanding and development of resistance to parasitic plants. C_LI Key messageCombination of in vivo confocal, large field and transmission electron microscopy approaches revealed how intimate the relationship between the parasitic plant broomrape (Orobanche cumana Wallr.) and its sunflower host (Helianthus annus L.) is at very early stages of their interaction.

plant biology↗

bioRxiv2023

Establishment and maintenance of two sand fly colonies (Phlebotomus perniciosus and Phlebotomus papatasi) to implement experimental infections

Sand flies are vectors of Leishmania and Phlebovirus, pathogens responsible for public health concerns in numerous countries. Sand fly colonies are essential for research on vector-pathogen interactions. Methods for establishing and maintaining sand fly colonies have been well described in the literature. However, very few colonies of these considerable vectors currently exist. In order to encourage the creation of new colonies, we provide a timeline for researchers who want to implement colonies of Phlebotomus perniciosus and Phlebotomus papatasi. In this study, we set up colonies of both species to test and optimize their breeding conditions. For Ph. perniciosus, we reached a stable production of 800 individuals per week, one year after the start of the colony. For Ph. papatasi, a stable production of 400 individuals per week was reached 11 months after establishing the colony. Moreover, we have successfully conducted experiments within a year of establishing the colonies. In conclusion, our data on these two species showed that colonies could be established without difficulty with 1000-1500 eggs. It is possible to reach a stable weekly production of 800 individuals one year after starting the colony. We also describe colony settings and breeding recommendations to facilitate this procedure for other laboratories.

ecology↗

bioRxiv2023

The cerebellum promotes sequential foraging strategies and contributes to the directional modulation of hippocampal place cells

The cerebellum contributes to goal-directed navigation abilities and place coding in the hippocampus. Here we investigated its contribution to foraging strategies. We recorded hippocampal neurons in mice with impaired PKC-dependent cerebellar functions (L7-PKCI) and in their littermate controls while they performed a task where they were rewarded for visiting a subset of hidden locations. We found that L7-PKCI and control mice developed different foraging strategies: while control mice repeated spatial sequences to maximize their rewards, L7-PKCI mice persisted to use a random foraging strategy. Sequential foraging was associated with more place cells exhibiting theta-phase precession and theta rate modulation. Recording in the dark showed that PKC-dependent cerebellar functions controlled how self-motion cues contribute to the selectivity of place cells for both position and direction. Thus, the cerebellum contributes to the development of optimal sequential paths during foraging, possibly by controlling how self-motion and theta signals contribute to place cells coding. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/526971v1_ufig1.gif" ALT="Figure 1"> View larger version (52K): org.highwire.dtl.DTLVardef@1a4e344org.highwire.dtl.DTLVardef@449ab8org.highwire.dtl.DTLVardef@9aa45org.highwire.dtl.DTLVardef@89c110_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2021

Biologging of emperor penguins - attachment techniques and associated deployment performance

An increasing number of marine animals are equipped with biologgers, to study their physiology, behaviour and ecology, often for conservation purposes. To minimise the impacts of biologgers on the animals welfare, the Refinement principle from the Three Rs framework (Replacement, Reduction, Refinement) urges to continuously test and evaluate new and updated biologging protocols. Here, we propose alternative and promising techniques for emperor penguin (Aptenodytes forsteri) capture and on-site logger deployment that aim to mitigate the potential negative impacts of logger deployment on these birds. We equipped adult emperor penguins for short-term (GPS, Time-Depth Recorder (TDR)) and long-term (i.e. planned for one year) deployments (ARGOS platforms, TDR), as well as juvenile emperor penguins for long-term deployments (ARGOS platforms) in the Weddell Sea area where they had not yet been studied. We describe and qualitatively evaluate our protocols for the attachment of biologgers on-site at the colony, the capture of the animals and the recovery of the devices after deployment. We report unprecedented recaptures of long-term equipped adult emperor penguins (50% of equipped individuals recaptured after 290 days). Our data demonstrate that the traditional technique of long-term attachment by gluing the biologgers directly to the back feathers is detrimental to the birds. It causes excessive feather breakage and the loss of the devices at an early stage. We therefore propose an alternative method of attachment for back-mounted devices. This technique led to successful year-round deployments on 37.5% of the equipped juveniles. Finally, we also disclose the first deployments of leg-bracelet mounted TDRs on emperor penguins. Our findings highlight the importance of monitoring potential impacts of biologger deployments on the animals and the need to remain critical towards established and new protocols.

ecology↗

bioRxiv2020

Multiscale PHATE Exploration of SARS-CoV-2 Data Reveals Multimodal Signatures of Disease

1The biomedical community is producing increasingly high dimensional datasets, integrated from hundreds of patient samples, which current computational techniques struggle to explore. To uncover biological meaning from these complex datasets, we present an approach called Multiscale PHATE, which learns abstracted biological features from data that can be directly predictive of disease. Built on a continuous coarse graining process called diffusion condensation, Multiscale PHATE creates a tree of data granularities that can be cut at coarse levels for high level summarizations of data, as well as at fine levels for detailed representations on subsets. We apply Multiscale PHATE to study the immune response to COVID-19 in 54 million cells from 168 hospitalized patients. Through our analysis of patient samples, we identify CD16hi CD66blo neutrophil and IFN{gamma}+GranzymeB+ Th17 cell responses enriched in patients who die. Further, we show that population groupings Multiscale PHATE discovers can be directly fed into a classifier to predict disease outcome. We also use Multiscale PHATE-derived features to construct two different manifolds of patients, one from abstracted flow cytometry features and another directly on patient clinical features, both associating immune subsets and clinical markers with outcome.

bioinformatics↗

bioRxiv2019

Modulation of visual cortex by hippocampal signals

Neurons in primary visual cortex (V1) are influenced by the animals position in the environment and encode positions that correlate with those encoded by hippocampus (CA1). Might V1s encoding of spatial positions be inherited from hippocampal regions? If so, it should depend on non-visual factors that affect the encoding of position in hippocampus, such as the physical distance traveled and the phase of theta oscillations. We recorded V1 and CA1 neurons while mice ran through a virtual corridor and confirmed these predictions. Spatial representations in V1 and CA1 were correlated even in the absence of visual cues. Moreover, similar to CA1 place cells, the spatial responses of V1 neurons were influenced by the physical distance traveled and the phase of hippocampal theta oscillations. These results reveal a modulation of cortical sensory processing by non-sensory estimates of position that might originate in hippocampal regions.

neuroscience↗

bioRxiv2017

Coherent representations of subjective spatial position in primary visual cortex and hippocampus

A major role of vision is to guide navigation, and navigation is strongly driven by vision1-4. Indeed, the brains visual and navigational systems are known to interact5, 6, and signals related to position in the environment have been suggested to appear as early as in visual cortex6, 7. To establish the nature of these signals we recorded in primary visual cortex (V1) and in the CA1 region of the hippocampus while mice traversed a corridor in virtual reality. The corridor contained identical visual landmarks in two positions, so that a purely visual neuron would respond similarly in those positions. Most V1 neurons, however, responded solely or more strongly to the landmarks in one position. This modulation of visual responses by spatial location was not explained by factors such as running speed. To assess whether the modulation is related to navigational signals and to the animals subjective estimate of position, we trained the mice to lick for a water reward upon reaching a reward zone in the corridor. Neuronal populations in both CA1 and V1 encoded the animals position along the corridor, and the errors in their representations were correlated. Moreover, both representations reflected the animals subjective estimate of position, inferred from the animals licks, better than its actual position. Indeed, when animals licked in a given location - whether correct or incorrect - neural populations in both V1 and CA1 placed the animal in the reward zone. We conclude that visual responses in V1 are tightly controlled by navigational signals, which are coherent with those encoded in hippocampus, and reflect the animals subjective position in the environment. The presence of such navigational signals as early as in a primary sensory area suggests that these signals permeate sensory processing in the cortex.

neuroscience↗