Biology subjects

Dibsy, R.

Publications and source records attributed to Dibsy, R..

5 recordsLinked to original sources

bioRxiv2025

CARM1-mediated methylation controls interactions of ALIX with key partners important for cytokinesis

CARM1 is an arginine methyltransferase with a well-established role in regulating gene expression, but its cytoplasmic functions remain largely uncharacterized. Here, we identified ALIX, a protein acting with the ESCRT-III machinery in numerous membrane remodeling events, as a main cytoplasmic partner and a relevant substrate of CARM1. We demonstrate that CARM1 methylates arginine residues within the proline-rich motif of ALIX. At the molecular level, ALIX methylation impairs SH3-dependent association with CD2AP, CIN85, and endophilin-A2 that are required for cytokinesis. Using a mutant of ALIX that is unable to bind these proteins, we further show that these interactions are essential for ALIX functions during cytokinesis. Altogether, this work highlights the significance of arginine methylation as a regulatory post-translational modification important for the final step of cell division, by modulating interactions between proline-rich domains and their SH3-containing partners.

cell biology↗

bioRxiv2025

Cut-Detector: A Tool for Automated Temporal Analysis of Late Cytokinetic Events

Cytokinesis is the final step of cell division, resulting in the physical separation of the two daughter cells. Despite its fundamental importance in cell biology, biologists currently lack automatic tools for large-scale profiling of cytokinesis dynamics. In particular, the timing of the first microtubule cut in the intercellular bridge connecting the daughter cells is crucial, as it marks a critical step preceding abscission. Here, we introduce Cut-Detector, an open-source tool for the automatic analysis of late cytokinesis timing from time-lapse microscopy movies. Cut-Detector employs an AI approach to carry out the multiple tasks required to monitor cytokinesis: cell segmentation and tracking, detection of cell division events, localization of the intercellular bridge, and detection of the microtubule cuts. Cut-Detector will facilitate large-scale analyses to uncover new cytokinetic genes, a task that would be impractical without automation.

bioinformatics↗

bioRxiv2024

Neutrophils in People Living With HIV-1 on antiretroviral treatment conserve their cytokine and chemokine secretion capacity and display enhanced expression of Fc receptors

Neutrophils are innate immune cells with key immunomodulatory functions. In a murine retroviral model, we previously showed their essential role in promoting protective immunity during antiviral antibody therapy via Fc-Fc{gamma} receptor (Fc{gamma}R) interactions. Here, we investigated the immunomodulatory properties of neutrophils in the context of HIV-1 infection and therapy through a comprehensive analysis of their functional activation and the regulation of Fc{gamma}R expression. Neutrophils from healthy donors (HD) and people living with HIV-1 (PLWH) were stimulated with TLR ligands, free HIV-1, immune complexes (ICs) formed with broadly neutralizing antibodies (bNAbs), or pro-inflammatory cytokines (TNF, IFN{gamma}). In response, they secreted various cytokines and chemokines that can recruit and activate immune cells in a stimulus-dependent manner. Compared to TLR agonist and cytokine activation, HD neutrophils showed limited cytokine production in response to free HIV-1 or ICs alone as well as a minimal Fc{gamma}R modulation. However, PLWH neutrophils showed heightened responsiveness to microbial stimuli linked to HIV-1 pathogenesis, secreting higher levels of IFN{gamma}, CXCL1, CCL2, CCL3, and CCL4. They also expressed higher levels of two activating Fc{gamma}Rs (Fc{gamma}RI and Fc{gamma}RIIIb), as well as CD11b, CD63, CXCR4, and PD-L1, indicating an altered activation state. These findings highlight the influence of the inflammatory milieu on neutrophil function and Fc{gamma}R regulation in HIV-1 infection and mAb-based therapies.

immunology↗

bioRxiv2022

Quantification of membrane binding and diffusion using Fluorescence Correlation Spectroscopy diffusion laws

Many transient processes in cells arise from the binding of cytosolic proteins to membranes. Quantifying this membrane binding and its associated diffusion in the living cell is therefore of primary importance. Dynamic photonic microscopies, e.g. single/multiple particle tracking, fluorescence recovery after photobleaching and fluorescence correlation spectroscopy (FCS) enable noninvasive measurement of molecular mobility in living cells and their plasma membranes. However, FCS with a single beam waist is of limited applicability with complex, non Brownian, motions. Recently, the development of FCS diffusion laws methods has given access to the characterization of these complex motions, although none of them is applicable to the membrane binding case at the moment. In this study, we combined computer simulations and FCS experiments to propose an FCS diffusion law for membrane binding. First, we generated computer simulations of spot-variation FCS (svFCS) measurements for a membrane binding process combined to 2D and 3D diffusion at the membrane and in the bulk/cytosol, respectively. Then, using these simulations as a learning set, we derived an empirical diffusion law with three free parameters: the apparent binding constant KDapp, the diffusion coefficient on the membrane D2D and the diffusion coefficient in the bulk/cytosol, D3D. Finally, we monitored, using svFCS, the dynamics of retroviral Gag proteins and associated mutants during their binding to supported lipid bilayers of different lipid composition or at plasma membranes of living cells and we quantified KDapp and D2D in these conditions using our empirical diffusion law. Based on these experiments and numerical simulations, we conclude that this new approach enables correct estimation of membrane partitioning and membrane diffusion properties (KDapp and D2D) for peripheral membrane molecules.

biophysics↗

bioRxiv2021

Full assembly of HIV-1 particles requires assistance of the membrane curvature factor IRSp53.

During HIV-1 particle formation, the requisite plasma membrane curvature is thought to be solely driven by the retroviral Gag protein. Here, we reveal that the cellular I-BAR protein IRSp53 is required for the progression of HIV-1 membrane curvature to complete particle assembly. Partial gene editing of IRSp53 induces a decrease in viral particle production and a viral bud arrest at half completion. Single molecule localization microscopy at the cell plasma membrane shows a preferential localization of IRSp53 around HIV-1 Gag assembly sites. In addition, we observe the presence of IRSp53 in purified HIV-1 particles. Finally, HIV-1 Gag protein localizes preferentially to IRSp53 I-BAR domain induced curved membranes on giant unilamellar vesicles. Overall, our data reveal a strong interplay between IRSp53 I-BAR and Gag at membranes during virus assembly. This highlights IRSp53 as a crucial host factor in HIV-1 membrane curvature and its requirement for full HIV-1 particle assembly.

biophysics↗