Biology subjects

Mahou, P.

Publications and source records attributed to Mahou, P..

9 recordsLinked to original sources

bioRxiv2026

Persistent and recyclable myosin II minifilaments drive cortical contractility in the early C. elegans embryo

Non-muscle myosin II is a key regulator of cell and tissue morphogenesis, yet the cortical dynamics of myosin minifilaments in vivo remain poorly understood. Here, we combine SIM-TIRF and single-molecule TIRF microscopy to characterize the structure and dynamics of myosin minifilaments in an early developing embryo. High-temporal-resolution SIM-TIRF imaging revealed diverse minifilament behaviors, including partition-like events, long-range alignment of multiple minifilaments into collective structures we called proto-stress fibers, partial unbinding, and sequential unbinding and rebinding to the cortex. Photoconversion experiments showed that minifilaments persist as intact units after cortical unbinding, diffuse through the cytoplasm, and can be recycled over long distances rather than disassembling upon detachment. Despite these dynamic behaviors, minifilaments are predominantly stationary when bound to actin. Numerical simulations demonstrated that this static behavior is essential to sustain cortical stress within a continuously remodeling actin network. Using myosin motor-domain mutants, we further investigated the contribution of motor activity to these behaviors. Together, our results reveal that myosin minifilaments can persist as stable units while cycling between the cortex and cytoplasm, and that their predominantly static behavior when bound to actin enables sustained force generation in a continuously renewing cortical network. These findings provide new insights into myosin organization, recycling, and force generation during early embryonic development.

cell biology↗

bioRxiv2026

High-throughput serial two-photon tomography with BakingTray and BrainSaw

Volumetric imaging is increasingly important in fields such as neuroscience, where quantifying structure and mapping features are inherently three-dimensional problems. Block-face serial two-photon tomography (STPT) has emerged as a powerful approach for high-resolution, whole-organ volumetric imaging. STPT avoids complex sample preparation and balances image quality, speed, and scalability. However, STPT remains niche, in part because of the absence of flexible, general-purpose control software. Here we present BakingTray, an open-source software platform for STPT that extends ScanImage. BakingTrays modular framework accommodates diverse hardware configurations and allows users to build systems customised to their needs. Twelve such systems, which we call BrainSaws, have been constructed worldwide since 2016, with more under construction, and have so far contributed to 35 research papers. The three systems at the Sainsbury Wellcome Centre alone have acquired over 7,000 samples in a busy multi-user facility. We demonstrate the platform across its core neuroscience applications: electrode track localisation, brain-wide cell counting, and bulk projection mapping. Beyond these, we map the cell-type-specific synaptic output of inhibitory neurons in the ventral lateral geniculate nucleus and, with whole-mount staining, amyloid plaques brain-wide in a mouse model of Alzheimers disease. BakingTray is a mature platform for groups or facilities needing a customised volumetric imaging solution, whether built new or converted cheaply from an existing two-photon microscope.

neuroscience↗

bioRxiv2026

Advanced Optical Microscopy Reveals Spatio-Temporal Dynamics of Cervix Remodeling during Gestation

Collagen remodeling in the uterine cervix is a vital process in pregnancy that allows for timely fetal delivery, yet its spatio-temporal details are still not fully understood. In this study, we measured collagen reorganization at different stages of murine gestation and at various cervical depths. We used polarization-resolved Second Harmonic Generation microscopy to specifically detect fibrillar collagen and assess its orientation with sub-micrometer resolution. We imaged large cervical areas using automated mosaicking and implemented an analysis pipeline that showed significant region-dependent changes in collagen quantity, porosity, and orientation disorder. Notably, we found that collagen disorganization begins in the lower cervix at gestation day 12 and extends throughout the entire cervix by day 15. Additionally, we demonstrated that the temporal dynamics of disorganization, without spatial sensitivity, can also be tracked using Mueller Matrix imaging, which is a clinically deployable method. These findings should improve understanding and diagnosis of gestation-related issues such as premature birth.

biophysics↗

bioRxiv2024

G-quadruplexes in Haloferax volcanii

Archaea, a domain of microorganisms found in diverse environments including the human microbiome, represent the closest known prokaryotic relatives of eukaryotes. This phylogenetic proximity positions them as a relevant model for investigating the evolutionary origins of nucleic acid secondary structures such as G-quadruplexes (G4s), which play regulatory roles in transcription and replication. Although G4s have been extensively studied in eukaryotes, their presence and function in archaea remain poorly characterized. In this study, a genome-wide analysis of the halophilic archaeon Haloferax volcanii identified over 5, 800 potential G4-forming sequences. Biophysical validation confirmed that many of these sequences adopt stable G4 conformations in vitro. Using G4-specific detection tools and super-resolution microscopy, G4 structures were visualized in vivo in both DNA and RNA across multiple growth phases. Comparable findings were observed in the thermophilic archaeon Thermococcus barophilus. Functional analysis using helicase-deficient H. volcanii strains further identified candidate enzymes involved in G4 resolution. These results establish H. volcanii as a tractable archaeal model for G4 biology.

molecular biology↗

bioRxiv2022

Apical size and deltaA expression predict adult neural stem cell decisions along lineage progression

The maintenance of neural stem cells (NSCs) in the adult brain depends on their activation frequency and division mode. We use long-term intravital imaging of NSCs in the zebrafish adult telencephalon to link activation and division mode with predictive cellular and molecular parameters. We reveal that apical surface area and expression of the Notch ligand DeltaA predict NSC activation frequency, while deltaA expression marks NSC commitment to neurogenesis. We also find that deltaA-negative NSCs constitute the bona fide self-renewing NSC pool and systematically engage in asymmetric divisions generating a self-renewing deltaAneg and a neurogenic deltaApos NSC. Finally, modulation of Notch signaling during imaging indicates that the prediction of activation frequency by apical size, and the asymmetric divisions of deltaAneg NSCs, are functionally independent of Notch. These results provide dynamic qualitative and quantitative readouts of NSC lineage progression in vivo and support a hierarchical organization of NSCs in differently fated sub-populations.

neuroscience↗

bioRxiv2022

Spatial modeling of telomere intra-nuclear distribution reveals non-random organization that varies during cell cycle and depends on LAP2 and BAF

Genome organization within the 3D nuclear volume influences major biological processes but is completely lost during mitosis, which represents a major challenge to maintain cellular identity and cell fate. To restore a functional G1 nucleus for the next cell cycle, it is imperative to reestablish genome organization during post-mitotic nuclear assembly. Importantly, the configuration of linear chromosomes has been shown to directly impact spatial genome architecture. Both centromeres and telomeres are known to associate with nuclear structures, such as the nuclear envelope, and support chromatin distribution. Here, using high-resolution 3D imaging combined with 3D spatial statistics and modeling, we showed that telomeres generally followed a regular distribution compared to what is expected under a random organization. While the preferential localization of telomeres at nuclear periphery was restricted to early G1, we found a strong clustering of centromeres in addition to their predominant peripheral localization at all cell cycle stages. We then conducted a targeted screen using MadID to identify the molecular pathways driving or maintaining telomere anchoring to the nuclear envelope. Among these factors, we could show that LAP2 transiently localizes to telomeres in anaphase, at a stage where LAP2 initiates the reformation of the nuclear envelope. Moreover, co-depletion of LAP proteins and their partner BAF impacted telomere redistribution in the next interphase. There results suggest that in addition to their crucial role in genome protection, telomeres also participate in reshaping functional G1 nuclei after mitosis.

cell biology↗

bioRxiv2021

The TPLATE complex mediates membrane bending during plant clathrin-mediated endocytosis

Clathrin-mediated endocytosis in plants is an essential process but the underlying mechanisms are poorly understood, not least because of the extreme intracellular turgor pressure acting against the formation of endocytic vesicles. In contrast to other models, plant endocytosis is independent of actin, indicating a mechanistically distinct solution. Here, by using biochemical and advanced microscopy approaches, we show that the plant-specific TPLATE complex acts outside of endocytic vesicles as a mediator of membrane bending. Cells with disrupted TPLATE fail to generate spherical vesicles, and in vitro biophysical assays identified protein domains with membrane bending capability. These results redefine the role of the TPLATE complex as a key component of the evolutionarily distinct mechanism mediating membrane bending against high turgor pressure to drive endocytosis in plant cells. One Sentence SummaryWhile plant CME is actin independent, we identify that the evolutionarily ancient octameric TPLATE complex mediates membrane bending against high turgor pressure in plant clathrin-mediated endocytosis.

cell biology↗

bioRxiv2020

Dynamic spatiotemporal coordination of neural stem cell fate decisions through local feedback in the adult vertebrate brain

Neural stem cell (NSC) populations persist in the adult vertebrate brain over a life time, and their homeostasis is controlled at the population level. The nature and properties of these coordination mechanisms remain unknown. Here we combine dynamic imaging of entire NSC populations in their in vivo niche over weeks, pharmacological manipulations, mathematical modeling and spatial statistics, and demonstrate that NSCs use spatiotemporally resolved local feedbacks to coordinate their decision to divide. These involve a Notch-mediated inhibition from transient neural progenitors, and a dispersion effect from dividing NSCs themselves, exerted with a delay of 9-12 days. Simulations from a stochastic NSC lattice model capturing these interactions demonstrate that they are linked by lineage progression and control the spatiotemporal distribution of output neurons. These results highlight how local and temporally delayed interactions occurring between brain germinal cells generate self-propagating dynamics that maintain NSC population homeostasis with specific spatiotemporal correlations.

neuroscience↗

bioRxiv2020

Balancing signal and photoperturbation in multiphoton light-sheet microscopy by optimizing laser pulse frequency

Improving the imaging speed of multiphoton microscopy is an active research field. Among recent strategies, light-sheet illumination holds distinctive advantages for achieving fast imaging in vivo. However, photoperturbation in multiphoton light-sheet microscopy remains poorly investigated. We show here that the heart beat rate of zebrafish embryos is a sensitive probe of linear and nonlinear photoperturbations. By analyzing its behavior with respect to laser power, pulse frequency and wavelength, we derive guidelines to balance signal and photoperturbation. We then demonstrate one order-of-magnitude signal enhancement over previous implementations by optimizing the laser pulse frequency. These results open new opportunities for fast live tissue imaging.

biophysics↗