Biology subjects

Masson, A.

Publications and source records attributed to Masson, A..

3 recordsLinked to original sources

bioRxiv2025

Transcription Represses Origin Activity in a Late-Replicating Fragile Site

Genome-wide analyses in vertebrates suggest that transcription can negatively regulate replication origin activation, thereby shaping the global landscape of replication initiation. In this study, we investigated how transcription and late replication influence replication origin activity by inserting an efficient minimal model origin into the avian DMD common fragile site (CFS) and a second transcriptionally silent late-replicating region. The DMD gene, which is neither transcribed nor fragile in wild-type DT40 cells, became fragile following transcriptional activation in a genetically engineered DT40 cell line. Previous molecular combing experiments have shown that transcription represses origin firing within the 500 kb 5 half of the gene. Here, we demonstrate that when a minimal origin is inserted into this repressive region, it remains partially active under basal transcription conditions but is fully inactivated upon transcriptional induction. In contrast, inserting the efficient {beta}-actin promoter/origin at the same site retains origin functionality despite transcriptional activation. Introducing these two origins into a late-replicating, transcriptionally silent locus reveals the same functional hierarchy. Notably, this contrasts with their comparable activity in a mid-late replicating region. These results define a class of replication origins capable of maintaining functionality across diverse chromosomal contexts. Our findings support the model in which CFSs arise due to transcription-dependent repression of replication origin initiation across large, late-replicating genes. Moreover, our results reinforce the idea that replication initiation in late-replicating genomic compartments is intrinsically less efficient than earlier-replicating regions.

molecular biology↗

bioRxiv2024

Deep learning detection of dynamic exocytosis events in fluorescence TIRF microscopy

Segmentation and detection of biological objects in fluorescence microscopy is of paramount importance in cell imaging. Deep learning approaches have recently shown promise to advance, automatize and accelerate analysis. However, most of the interest has been given to the segmentation of static objects of 2D/3D images whereas the segmentation of dynamic processes obtained from time-lapse acquisitions has been less explored. Here we adapted DeepFinder, a U-net originally designed for 3D noisy cryo-electron tomography (cryo-ET) data, for the detection of rare dynamic exocytosis events (termed ExoDeepFinder) observed in temporal series of 2D Total Internal Reflection Fluorescent Microscopy (TIRFM) images. ExoDeepFinder achieved good absolute performances with a relatively small training dataset of 60 cells/[~]12000 events. We rigorously compared deep learning performances with unsupervised conventional methods from the literature. ExoDeepFinder outcompeted the tested methods, but also exhibited a greater plasticity to the experimental conditions when tested under drug treatments and after changes in cell line or imaged reporter. This robustness to unseen experimental conditions did not require re-training demonstrating generalization capability of ExoDeepFinder. ExoDeepFinder, as well as the annotated training datasets, were made transparent and available through an open-source software as well as a Napari plugin and can directly be applied to custom user data. The apparent plasticity and performances of ExoDeepFinder to detect dynamic events open new opportunities for future deep-learning guided analysis of dynamic processes in live-cell imaging.

bioinformatics↗

bioRxiv2020

High mannose N-glycans on red blood cells as phagocytic ligands, mediating both sickle cell anaemia and resistance to malaria

In both sickle cell disease (SCD) and malaria, red blood cells (RBCs) are phagocytosed in the spleen, but receptor-ligand pairs mediating uptake have not been identified. Here, we report that patches of high mannose N-glycans (Man5-9GlcNAc2), expressed on diseased or oxidized RBC surfaces, bind the mannose receptor (CD206) on phagocytes to mediate clearance. Extravascular haemolysis in SCD correlates with high mannose glycan levels on RBCs. Infection of RBCs with Plasmodium falciparum expose surface mannose N-glycans on healthy RBCs, which occurred at significantly higher levels on RBCs from subjects with sickle cell trait compared to those lacking haemoglobin S. The glycans were associated with high molecular weight complexes and protease-resistant, lower molecular weight fragments containing spectrin. Recognition of surface N-linked high mannose glycans, a novel response to cellular stress, is the first molecular mechanism common to both the pathogenesis of SCD and resistance to severe malaria in sickle cell trait.

immunology↗