Biology subjects

Gautier, J.

Publications and source records attributed to Gautier, J..

10 recordsLinked to original sources

bioRxiv2025

Laser-driven VHEE pulsed fast fractionation (PFF): second-scale inter-pulse timing differentially modulates normal tissue and tumour toxicity

Radiotherapy (RT) is constrained by the narrow therapeutic window between tumour control and normal-tissue toxicity. While FLASH RT has been reported to reduce normal-tissue toxicity at ultra-high dose rates (UHDR) while preserving tumour control in several preclinical models, the radiobiological potential of intermediate temporal regimes between conventional fractionation and FLASH remains largely unexplored. Here, we show that temporal separation of ultrashort (fs-ps) dose-delivery pulses delivered at ultra-high instantaneous dose rate, with second-scale inter-pulse intervals, can differentially modulate biological response in vitro and in vivo. Samples were irradiated with very high-energy electrons (VHEEs, 50 MeV to 300 MeV) generated by a laser-plasma accelerator (LPA), using a temporal irradiation modality we term pulsed fast fractionation (PFF), with instantaneous dose rates exceeding 10^12 Gy/s. Varying the inter-pulse interval from 1 s to 10 s while maintaining dose per pulse and total dose constant modulated biological response in both in vitro and in vivo models. At the shortest investigated inter-pulse interval ({theta} = 1s), MRC5-hTERT human fibroblasts showed higher viability, whereas HCT116 colorectal carcinoma cells showed lower viability under matched dose conditions. In vivo, the same interval was associated with reduced radiation-induced growth impairment in zebrafish embryos, consistent with the response pattern observed in the non-tumour cell model and extending this timing-dependent response to a whole-organism context. These findings identify second-scale pulse timing as a biologically active degree of freedom for VHEE delivery, positioning PFF as a distinct temporal irradiation regime with the potential to complement spatial dose modulation through temporal optimisation and extend the current fractionation-FLASH framework.

cell biology↗

bioRxiv2025

Comparative analysis of the radiobiological effects of laser-driven VHEE vs. conventional electrons using in vitro, ex vivo, and in vivo models

PurposeThis study systematically investigates the radiobiological effects of Very High Energy Electrons (VHEE) generated by a laser-plasma accelerator (LPA), in comparison with Conventional Intermediate Energy Electrons (CIEE) from a conventional linear accelerator (LINAC). Using in vitro, ex vivo, and in vivo models, we evaluate and compare their potential toxicity on healthy tissues. Methods and MaterialsCell survival, tissue response, and developmental toxicity were assessed across three biological models. In vitro, human fibroblasts (MRC5-hTERT) were used to generate post-irradiation survival curves. Ex vivo, precision-cut lung slices (PCLS) from mice were analyzed for radiation-induced inhibition of cell proliferation. In vivo, zebrafish embryos were used to evaluate developmental toxicity through body length and spinal curvature measurements. VHEE irradiations were performed using a broadband electron beam spanning 50-300 MeV, using the Salle Jaune LPA (Laboratoire dOptique Appliquee, France), while CIEE exposures were performed with a 7 MeV conventional LINAC (Institut Curie, France). ResultsIn vitro, MRC5-hTERT cells showed no significant difference in radiosensitivity between VHEE and CIEE, with comparable D10 values (p-value = 0.7). In the ex vivo model, both beams induced a dose-dependent decrease in cell division with no significant inter-beam differences at any dose level (p-value > 0.99). In vivo, zebrafish embryos exhibited dose-dependent body shortening and increased spinal curvature following both VHEE and CIEE exposure. No significant differences were observed between the two modalities at matched doses for any measured metric (p-value[≥] 0.5). ConclusionThis study presents the first comprehensive radiobiological evaluation of a laser-driven VHEE beam across multiple biological models. Under the investigated conditions, VHEE and CIEE irradiations exhibit similar biological toxicity. These findings support the feasibility and potential of VHEE generated with LPA for future clinical applications.

cell biology↗

bioRxiv2025

The Optimal Retinal Locus for High-Resolution Vision in Space and Time

Humans exhibit machine-like eye-movement behavior in space and time while performing challenging visual resolution tasks. Fewer microsaccades occur as stimulus presentation is imminent. Drifts and microsaccades combine to confine the landing location of an anticipated visual stimulus to a tiny retinal region: the preferred retinal locus (PRL). We find that this location confers the best visual acuity despite it being offset from the anatomical fovea (the location of maximum cone density). We also find that acuity is best when the last microsaccade occurs 400msec or longer before stimulus presentation. The machine-like eye movements are involuntary and not perceived. Our findings thus reveal a highly evolved oculomotor system such that gaze direction during fixation is rarely far enough from the PRL to cause a decline in visual resolution. TeaserHumans exhibit machine-like eye-movement behavior during fine visual tasks that rarely deviates from an optimal retinal location.

neuroscience↗

bioRxiv2023

Foveal drusen increase fixation instability: fixational eye movements as biomarkers for pre-symptomatic AMD

PurposeThis study aims at linking subtle changes of fixational eye movements (FEM) in controls and in patients with foveal drusen using adaptive optics retinal imaging in order to find anatomo-functional markers for pre-symptomatic Age-related Macular Degeneration (AMD). MethodsWe recruited 7 young controls, 4 older controls and 16 presymptomatic AMD patients with foveal drusen from the Silversight Cohort. A high speed research-grade adaptive optics flood illumination ophthalmoscope (AO-FIO) was used for monocular retinal tracking of fixational eye movements. The system allows for sub-arcminute resolution, high-speed and distortion-free imaging of the foveal area. Foveal drusen position and size were documented using gaze-dependent imaging on a clinical-grade AO-FIO. ResultsFEM were measured with high precision (RMS-S2S=0.0015{degrees} on human eyes) and small foveal drusen (median=60{micro}m) were detected with high contrast imaging. Microsaccade amplitude, drift diffusion coefficient and ISOline Area (ISOA) were significantly larger for patients with foveal drusen compared with controls. Among the drusen participants, microsaccade amplitude was correlated to drusen eccentricity from the center of the fovea. ConclusionsA novel high-speed high-precision retinal tracking technique allowed for the characterization of FEM at the microscopic level. Foveal drusen altered fixation stability, resulting in compensatory FEM changes. Particularly, drusen at the foveolar level seemed to have a stronger impact on microsaccade amplitudes and ISOA. The unexpected anatomo-functional link between small foveal drusen and fixation stability opens up a new perspective of detecting oculomotor signatures of eye diseases at the presymptomatic stage.

neuroscience↗

bioRxiv2023

Transcription Coupled Repair of DNA Interstrand Crosslinks by UVSSA

DNA interstrand crosslinks (ICLs) are covalent bonds between bases on opposing strands of the DNA helix which prevent DNA melting and subsequent DNA replication or RNA transcription. Here, we show that Ultraviolet Stimulated Scaffold Protein A (UVSSA) participates in transcription-coupled repair of ICLs in human cells. Inactivation of UVSSA sensitizes human cells to ICL-inducing drugs, and delays ICL repair. UVSSA is required for transcription-coupled repair of a single ICL in a fluorescence- based reporter assay. UVSSA localizes to chromatin following ICL damage, and interacts with transcribing Pol II, CSA, CSB, and TFIIH. Specifically, UVSSA interaction with TFIIH is required for ICL repair. Finally, UVSSA expression positively correlates with ICL chemotherapy resistance in human cancer cell lines. Our data strongly suggest that transcription-coupled ICL repair (TC-ICR) is a bona fide ICL repair mechanism that contributes to crosslinker drug resistance independently of replication-coupled ICL repair.

molecular biology↗

bioRxiv2022

Mechanisms of insertions at a DNA double-strand break

Insertions and deletions (indels) are common sources of structural variation, and insertions originating from spontaneous DNA lesions are frequent in cancer. We developed a highly sensitive assay in human cells (Indel-Seq) to monitor rearrangements at the TRIM37 acceptor locus which reports indels stemming from experimentally-induced and spontaneous genome instability. Templated insertions derive from sequences genome-wide and are enriched within 100 kb of donor regions flanking a DSB. Insertions require contact between donor and acceptor loci as well as DNA-PK catalytic activity. Notably, these templated insertions originate from actively transcribed loci, underscoring transcription as a critical source of spontaneous genome instability. Transcription-coupled insertions involve a DNA/RNA hybrid intermediate and are stimulated by DNA end-processing. Using engineered Cas9 breaks, we establish that ssDNA overhangs at the acceptor site greatly stimulate insertions. Indel-Seq revels that insertions are generated via at least three distinct pathways. Our studies indicate that insertions result from movement and subsequent contact between acceptor and donor loci followed invasion or annealing, then by non-homologous end-joining at the acceptor site.

molecular biology↗

bioRxiv2021

ARP2/3- and resection-coupled genome reorganization facilitates translocations

DNA end-resection and nuclear actin-based movements orchestrate clustering of double-strand breaks (DSBs) into homology-directed repair (HDR) domains. Here, we analyze how actin nucleation by ARP2/3 affects damage-dependent and -independent 3D genome reorganization and facilitates pathologic repair. We observe that DNA damage, followed by ARP2/3-dependent establishment of repair domains enhances local chromatin insulation at a set of damage-proximal boundaries and affects compartment organization genome-wide. Nuclear actin polymerization also promotes interactions between DSBs, which in turn facilitates aberrant intra- and inter-chromosomal rearrangements. Notably, BRCA1 deficiency, which decreases end-resection, DSB mobility, and subsequent HDR, nearly abrogates recurrent translocations between AsiSI DSBs. In contrast, loss of functional BRCA1 yields unique translocations genome-wide, reflecting a critical role in preventing spontaneous genome instability and subsequent rearrangements. Our work establishes that the assembly of DSB repair domains is coordinated with multiscale alterations in genome architecture that enable HDR despite increased risk of translocations with pathologic potential.

molecular biology↗

bioRxiv2021

Fixational Eye Movements Depend on Task and Target

Human fixational eye movements are so small and precise that they require high-speed, accurate tools to fully reveal their properties and functional roles. Where the fixated image lands on the retina and how it moves for different levels of visually demanding tasks is the subject of the current study. An Adaptive Optics Scanning Laser Ophthalmoscope (AOSLO) was used to image, track and present Maltese cross, disk, concentric circles, Vernier and tumbling-E letter fixation targets to healthy subjects. During these different passive (static) or active (discriminating) fixation tasks under natural eye motion, the landing position of the target on the retina was tracked in space and time over the retinal image directly. We computed both the eye motion and the exact trajectory of the fixated targets motion over the retina. We confirmed that compared to passive fixation, active tasks elicited a partial inhibition of microsaccades, leading to longer drifts periods compensated by larger corrective saccades. Consequently the fixation stability during active tasks was larger overall than during passive tasks. The preferred retinal locus of fixation was the same for each task and did not coincide with the location of the peak cone density.

neuroscience↗

bioRxiv2020

Distinct pathways of homologous recombination controlled by the SWS1-SWSAP1-SPIDR complex

Homology-directed repair (HDR), a critical DNA repair pathway in mammalian cells, is complex, leading to multiple outcomes with different impacts on genomic integrity. However, the factors that control these different outcomes are often not well understood. Here we show that SWS1-SWSAP1-SPIDR controls distinct types of HDR. Despite their requirement for stable assembly of RAD51 recombinase at DNA damage sites, these proteins are not essential for intra-chromosomal HDR, providing insight into why patients and mice with mutations are viable. However, SWS1-SWSAP1-SPIDR is critical for inter-homolog HDR, the first mitotic factor identified specifically for this function. Furthermore, SWS1-SWSAP1-SPIDR drives the high level of sister-chromatid exchange, promotes long-range loss of heterozygosity often involved with cancer initiation, and impels the poor growth of BLM helicase-deficient cells. The relevance of these genetic interactions is evident as SWSAP1 loss prolongs Blm-mutant embryo survival, suggesting a possible druggable target for the treatment of Bloom syndrome.

molecular biology↗

bioRxiv2018

Evaluating FAIR-Compliance Through an Objective, Automated, Community-Governed Framework

With the increased adoption of the FAIR Principles, a wide range of stakeholders, from scientists to publishers, funding agencies and policy makers, are seeking ways to transparently evaluate resource FAIRness. We describe the FAIR Evaluator, a software infrastructure to register and execute tests of compliance with the recently published FAIR Metrics. The Evaluator enables digital resources to be assessed objectively and transparently. We illustrate its application to three widely used generalist repositories - Dataverse, Dryad, and Zenodo - and report their feedback. Evaluations allow communities to select relevant Metric subsets to deliver FAIRness measurements in diverse and specialized applications. Evaluations are executed in a semi-automated manner through Web Forms filled-in by a user, or through a JSON-based API. A comparison of manual vs automated evaluation reveals that automated evaluations are generally stricter, resulting in lower, though more accurate, FAIRness scores. Finally, we highlight the need for enhanced infrastructure such as standards registries, like FAIRsharing, as well as additional community involvement in domain-specific data infrastructure creation.

scientific communication and education↗