Biology subjects

Robert, T.

Publications and source records attributed to Robert, T..

9 recordsLinked to original sources

bioRxiv2023

TOPOVIBL function in meiotic DSB formation: new insights from its biochemical and structural characterization.

The TOPOVIL complex catalyzes the formation of DNA double strand breaks (DSB) that initiate meiotic homologous recombination, an essential step for chromosome segregation and genetic diversity during gamete production. TOPOVIL is composed of two subunits (SPO11 and TOPOVIBL) and is evolutionarily related to the archaeal TopoVI topoisomerase complex. SPO11 is the TopoVIA subunit orthologue and carries the DSB formation catalytic activity. TOPOVIBL shares homology with the TopoVIB ATPase subunit. TOPOVIBL is essential for meiotic DSB formation, but its molecular function remains elusive, partly due to the lack of biochemical studies. Here, we purified TOPOVIBL{Delta}C25 and characterized its structure and mode of action in vitro. Our structural analysis revealed that TOPOVIBL{Delta}C25 adopts a dynamic conformation in solution and our biochemical study showed that the protein remains monomeric upon incubation with ATP, which correlates with the absence of ATP binding. Moreover, TOPOVIBL{Delta}C25 interacted with DNA, with a preference for some geometries, suggesting that TOPOVIBL senses specific DNA architectures. Altogether, our study identified specific TOPOVIBL features that might help to explain how TOPOVIL function evolved toward a DSB formation activity in meiosis.

molecular biology↗

bioRxiv2023

Learning modifies attention during bumblebee visual search

The role of visual search during bee foraging is relatively understudied compared to the choices made by bees. As bees learn about rewards, we predicted that visual search would be modified to prioritise rewarding flowers. To test this, we ran an experiment testing how bee search differs in the initial and later part of training as they learn about flowers with either higher-or lower-quality rewards. We then ran an experiment to see how this prior training with reward influences their search on a subsequent task with different flowers. We used the time spent inspecting flowers as a measure of attention and found that learning increased attention to rewards and away from distractors. Higher quality rewards led to decreased attention to non-flower regions, but lower quality rewards did not. Prior experience of lower rewards also led to more attention to higher rewards compared to distractors and non-flower regions. Our results suggest that flowers would elicit differences in bee search behaviour depending on the sugar content of their nectar. They also demonstrate the utility of studying visual search and have important implications for understanding the pollination ecology of flowers with different qualities of reward. Significance StatementStudies investigating how foraging bees learn about reward typically focus on the choices made by the bees. How bees deploy attention and visual search during foraging is less well studied. We analysed flight videos to characterise visual search as bees learn which flowers are rewarding. We found that learning increases the focus of bees on flower regions. We also found that the quality of the reward a flower offers influences how much bees search in non-flower areas. This means that a flower with lower reward attracts less focussed foraging compared to one with a higher reward. Since flowers do differ in floral reward, this has important implications for how focussed pollinators will be on different flowers. Our approach of looking at search behaviour and attention thus advances our understanding of the cognitive ecology of pollination.

animal behavior and cognition↗

bioRxiv2023

Responses of the hyper-diverse community of canopy-dwelling Hymenoptera to oak decline

O_LIForest decline and dieback are growing phenomena worldwide, resulting in severe, large-scale degradation of the canopy. This can profoundly alter the provision of trophic resources and microhabitats for canopy-dwelling arthropods. C_LIO_LIIn 2019, we assessed the effect of oak decline on the community of canopy-dwelling Hymenoptera. We selected 21 oak stands, and 42 plots, located in three forests in France, presenting contrasting levels of decline. Insects were sampled at the canopy level with green multi-funnel and flight-interception traps. C_LIO_LIWe collected a particularly diverse community of 19,289 insect individuals belonging to 918 taxa, ten larval trophic guilds and five nesting guilds. C_LIO_LIOak decline had no effect on the abundance or richness of the overall community, but significantly reshaped the community assemblages. Decline had contrasting effects depending on the taxa and guilds considered. Specialist parasitoids were more abundant at intermediate levels of decline severity while generalists were negatively affected. Taxa depending on ground-related resources and microhabitats were promoted. Saproxylic taxa were more abundant while xylophagous insects were negatively impacted. C_LIO_LIReduced leaf area index promoted several guilds, and the diversity of the overall community. While an increasing tree mortality rate enhanced the abundance and diversity of deadwood resources, it had negative impacts on several Hymenoptera guilds. Our results suggest that micro-environmental changes at the ground-level due to canopy decline have major cascading effects on the communities of canopy-dwelling Hymenoptera. C_LIO_LIOur study highlights the relevance of studying Hymenoptera communities to investigate the outcomes of disturbances on forest biodiversity. C_LI

ecology↗

bioRxiv2023

Cue Disparity and Visual Selective Attention in Praying Mantises

External cues bias human attention and the perception of subsequent targets. Little is known about how cue properties, such as depth, influence insect attention. One robust cue to depth is stereoscopic disparity, the difference in the position of an object in the views of the two eyes. Praying mantises are known to use disparity to judge the distance to prey and are therefore ideal insect models to investigate its role in attention. We investigated how three cue propertiesposition, duration and stereoscopic disparity affect mantis selective attention towards subsequent targets. We fitted mantises with 3D glasses and presented them with a cue in 2D or in 3D, followed by two 3D stimuli: a high contrast target and a distractor at different contrasts. Our results show that cue position and distractor contrast had the most influence on responses to targets, with no strong effect of disparity. Compared to the Uncued condition, cues in two of our disparity conditions reduced target responses if presented on the opposite side of the screen, when the distractor was absent. The cues affected subsequent selective attention even when they did not themselves attract head saccades, suggesting covert but not overt attention to the cues. Our results show that the position of prior cues can affect mantis selective attention and add further evidence for the complexity of attention-like processes in insects. Summary StatementCue position and, to a lesser extent, disparity affect praying mantises responses to a subsequent target. This adds further evidence for the complexity of attention-like processes in insects.

animal behavior and cognition↗

bioRxiv2022

Accuracy of a markerless motion capture system for balance related quantities

BackgroundBalance studies usually focus on quantities describing the global body motion, such as the position of the whole-body centre of mass (CoM), its associated extrapolated centre of mass (XCoM) and the whole-body angular momentum (WBAM). Assessing such quantities using classical marker-based approach can be tedious and modify the participants behaviour. The recent development of markerless motion capture methods could bypass the issues related to the use of markers. Research questionCan we use markerless motion capture systems to study quantities that are relevant for balance studies? MethodsSixteen young healthy participants performed four different motor tasks: walking at self-selected speed, balance loss, walking on a narrow beam and countermovement jumps. Their movements were recorded simultaneously by marker-based and markerless motion capture systems. Videos were processed using a commercial markerless pose estimation software, Theia3D. The position of their CoM was computed, and the associated XCoM and WBAM were derived. Bland-Altman analysis was performed and root mean square error and coefficient of determination were computed to compare the results obtained with marker-based and markerless methods across all participants and tasks. ResultsBias remained of the magnitude of a few mm for CoM and XCoM position, and RMSE of CoM and XCoM was around 1 cm. Confidence interval for CoM and XCoM was under 2 cm except for one task in one direction. RMSE of the WBAM was less than 8% of the total amplitude in any direction, and bias was less than 1%. SignificanceResults suggest that the markerless motion capture system can be used in balance studies as the measured errors are in the range of the differences found between different models or populations in the literature. Nevertheless, one should be careful when assessing dynamic movements such as jumping, as they displayed the biggest errors. HighlightsO_LIMarkerless motion capture could bypass issues from classical marker-based approaches C_LIO_LIWe compared balance related quantities computed from both approaches C_LIO_LIMean differences were about 1cm on the position of the whole-body center of mass C_LIO_LIObtained differences are acceptable for most applications C_LI

bioengineering↗

bioRxiv2022

Description, Development and Dissemination of Two Consistent Marker-based and Markerless Multibody Models

In human movement analysis, multibody models are an indispensable part of the process both for marker-based and video-based markerless approaches. Constituents (segments, joint constraints, body segment inertial parameters etc.) of such models and modelers choice play an important role in the accuracy of estimated results (segmental and joint kinematics, segmental and whole-body center of mass positions etc.). For marker-based method, although standard models exist, particularly for the lower extremity (e.g., Conventional Gait Model or models embedded in OpenSim), there seems to be a lack of consolidated explanation on the constituents of the whole-body model. For the markerless approach, multibody kinematic models (e.g., the Theia3D model) have been in use lately. However, there is no clear explanation on the estimated quantities (e.g., joint centers, body surface landmarks etc.) and their relation to the underlying anatomy. This also motivates the need for a description of the markerless multibody model. Moreover, comparing markerless results to those of classical marker-based method is currently the most commonly used approach for evaluation of markerless approaches. This study first aims to develop and describe a whole-body marker-based model ready to be used for human movement analysis. Second, the markerless multibody model embedded in Theia3D is described and inertial parameters are redefined. We also report assessment of the markerless approach compared to marker-based method for a static T-pose performed by 15 subjects. Finally, we disseminate the marker-based and markerless multibody models for their use in Visual3D.

bioengineering↗

bioRxiv2022

How bumblebees coordinate path integration and body orientation at the start of their first learning flight

The start of a bumblebees first learning flight from its nest provides an opportunity to examine the bees learning behaviour on its initial view of the nests unfamiliar surroundings. Bumblebees like many other ants, bees and wasps learn views of their nest surroundings while facing their nest. A bumblebees first fixation of the nest is a coordinated manoeuvre in which the insect faces the nest with its body oriented towards a particular visual feature within its surroundings. The manoeuvres utility is that during return flights after foraging bees, when close to the nest, adopt the same preferred body-orientation (Hempel de Ibarra et al., 2009; Robert et al., 2018). A translational scan oriented orthogonally to the bees body-orientation helps the bee reach the preferred conjunction of nest-fixation and body-orientation. How does a bee, unacquainted with its surroundings, know when it is facing its nest? The details of nest-fixation argue that, like desert ants (Fleischmann et al., 2018), the bee relies on path integration. Path integration gives bees continuously updated information about the current direction of their nest and enables them to fixate the nest when the body points in the appropriate direction. We relate the three components of the coordinated manoeuvre to events in the central complex, noting that nest fixation is in egocentric coordinates, whereas body orientation and flight direction within the visual surroundings of the nest are in geocentric coordinates.

animal behavior and cognition↗

bioRxiv2021

TOPOVIBL-REC114 interaction regulates meiotic DNA double-strand breaks

Meiosis requires the formation of programmed DNA double strand breaks (DSBs), essential for fertility and for generating genetic diversity. DSBs are induced by the catalytic activity of the TOPOVIL complex formed by SPO11 and TOPOVIBL. To ensure genomic integrity, DNA cleavage activity is tightly regulated, and several accessory factors (REC114, MEI4, IHO1, and MEI1) are needed for DSB formation in mice. How and when these proteins act is not understood. Here, we show that REC114 is a direct partner of TOPOVIBL, and identified their conserved interacting domains by structural analysis. We then analysed the role of this interaction by monitoring meiotic DSBs in female and male mice carrying point mutations in TOPOVIBL that decrease or disrupt its binding to REC114. In these mutants, DSB activity was strongly reduced genome-wide in oocytes, and only in sub-telomeric regions in spermatocytes. In addition, in mutant spermatocytes, DSB activity was delayed in autosomes. These results provide evidence that REC114 is a key member of the TOPOVIL catalytic complex, and that the REC114/TOPOVIBL interaction ensures the efficiency and timing of DSB activity.

molecular biology↗

bioRxiv2018

Anticipatory adjustments of posture allow elderly fallers to achieve a balance recovery performance equivalent to elderly non-fallers

BackgroundIn an important number of laboratory-based perturbation experiments, differences in the balance recovery performance of elderly fallers and non-fallers are moderate or absent. This performance may be affected by the subjects adjusting their initial posture in anticipation of the perturbation.\n\nResearch questionsDo elderly fallers and non-fallers adjust their posture in anticipation of externally-imposed perturbations in a laboratory setting, and how does this impact their balance recovery performance?\n\nMethods21 elderly non-fallers, 18 age-matched elderly fallers and 11 young adults performed both a forward waist-pull perturbation task and a Choice Stepping Reaction Time (CSRT) task. Whole-body kinematics and ground reaction forces were recorded. For each group, we evaluated the balance recovery performance in the perturbation task, change in initial center of mass (CoM) position between the CSRT and the perturbation task, and the influence of initial CoM position on task performance.\n\nResultsThe balance recovery performance of elderly fallers was equivalent to elderly non-fallers (p > 0.5 Kolmogorov-Smirnov test). All subject groups anticipated forward perturbations by shifting their CoM backward compared to the CSRT task (young: 2.1% of lower limb length, elderly non-fallers: 2.7%, elderly fallers: 2.2%, Hodges-Lehmann estimator, p < 0.001 Mann-Whitney U). This backward shift increases the probability of resisting the traction without taking a step.\n\nSignificanceThe ability to anticipate perturbations is preserved in elderly fallers and may explain their preserved balance recovery performance in laboratory-based perturbation tasks. Therefore, future studies aimed at predicting fall risk in elderly adults should carefully control for this postural strategy, by interleaving perturbations of different directions for example.

neuroscience↗