Biology subjects

Besse, L.

Publications and source records attributed to Besse, L..

7 recordsLinked to original sources

bioRxiv2026

Reduced tubulin polyglutamylation perturbs neuronal function and causes late-onset neurodegeneration

Microtubules are essential for neuronal functions and are involved in many neurodegenerative disorders. A posttranslational modification (PTM) of neuronal microtubules, polyglutamylation, was shown to control cargo transport, Tau protein binding to microtubules and to induce early-onset neurodegeneration when exceeding physiological levels. To determine the physiological importance of this PTM, we characterised mouse models with reduced polyglutamylation. We demonstrate that these mice develop late-onset atrophy of the olfactory bulb and frontal cortex, progressively reduced dendritic spine density, and deficits in olfaction, memory, and cognitive control. This indicates an important role of polyglutamylation in neuronal function. To test whether the observed defects are linked to neurodegeneration, we combined mice with reduced polyglutamylation with a transgenic model for tauopathy. Strikingly, reduced polyglutamylation accelerated the premature demise of mice transgenic for human Tau carrying the P301S mutation. Our work thus reveals key roles of microtubule polyglutamylation in neuronal function with implications for late-onset neurodegeneration linked to Tau pathology.

neuroscience↗

bioRxiv2025

Selective mRNA translation determines adaptative mutability of melanoma cells to anti-BRAF/MEK combination therapy

During their inevitable evolution towards acquired resistance to anti-cancer targeted therapies, cancer cells adopt distinct gene expression profiles that allow them to transiently adapt to and tolerate the treatment. Similar to bacterial cells that transiently tolerate antibiotics, cancer cells surviving therapy can increase their mutation rate, enhancing the likelihood of acquiring resistance-conferring mutations and evolving into resistant cells. This adaptive mutability has been linked to transcriptional reprogramming of DNA damage repair mechanisms and effective therapeutic strategies to target such mechanisms are currently lacking. Here we show that translational control mediates the adaptive mutability of melanoma drug-tolerant cells by regulating the translation of the error-prone non-homologous end joining (NHEJ) component 53BP1. The specific inhibition of 5UTR-driven 53BP1 mRNA translation was sufficient to impair NHEJ and mutability. We found that the eIF4A RNA helicase, a key component of the eIF4F translation complex, regulates 53BP1 mRNA translation. Consequently, targeting the eIF4A with two small molecule inhibitors significantly delays the acquisition of resistance to combination of BRAF and MEK inhibitors (BRAFi/MEKi) in BRAFV600-mutant melanoma xenograft models and cell lines by reducing the mutability of drug-tolerant cells. Our results demonstrate that a standard-of-care therapy for melanoma, by engaging non-genetic adaptation driven at the translational level, contributes to the evolution of drug-tolerant melanoma cells toward acquired resistance.

cancer biology↗

bioRxiv2025

MAFA Phosphorylation Controls Beta-Cell Identity and Sex-Specific Pancreatic Disease Outcomes

Mafa is a critical transcription factor in pancreatic beta-cell biology, orchestrating insulin expression in response to glucose elevations. As a member of the large MAF protein family, MAFAs stability and activity are intricately regulated by GSK3-mediated phosphorylation. To decipher the functional roles of these phosphorylations, we engineered knock-in mice (Mafa4A/+) in which MAFA is rendered non-phosphorylatable. In all Mafa4A/+ animals, MAFA stability was markedly enhanced. Under high-fat diet (HFD) conditions, Mafa4A/+ males rapidly developed glucose intolerance, which was attributed to impaired glucose-stimulated insulin secretion. Bulk RNA sequencing revealed disrupted beta- cell identity, characterized by increased expression of MODY-associated genes and a delta-cell signature, suggesting beta-to-delta cell reprogramming, a hypothesis supported by lineage- tracing experiments. Conversely, Mafa4A/+ females exhibited hypoglycemia and, with age, developed pronounced inflammatory cystic ducts including mucinous cystic neoplasms (MCNs). Strikingly, MAFA protein was also detected in MCN biopsies from female patients, linking our findings to human pathology. Our results unveil a sex-biased impact of GSK3-mediated MAFA phosphorylation. The male phenotype closely parallels the MODY-like diabetes observed in patients with MAFA S64F mutations, implicating defective phosphorylation in disease etiology. The emergence of MCNs in female mice suggests a novel role for MAFA stability or mutations in the pathogenesis of these enigmatic neoplasms, providing a fresh molecular hypothesis with clinical relevance.

cell biology↗

bioRxiv2024

The fission yeast SUMO-targeted Ubiquitin Ligase Slx8 functionally associates with clustered centromeres and the silent mating type region at the nuclear periphery

The SUMO-targeted Ubiquitin ligase (STUbL) family is involved in multiple cellular processes via a wide range of mechanisms to maintain genome stability. One of the evolutionarily conserved functions of STUbL is to promote changes in the nuclear positioning of DNA lesions, targeting them to the nuclear periphery. In Schizossacharomyces pombe, the STUbL Slx8 is a regulator of SUMOylated proteins and promotes replication stress tolerance by counteracting the toxicity of SUMO conjugates. In order to study the dynamic dialectic between Ubiquitinylation and SUMOylation in the nuclear space of the S. pombe genome, we analyzed Slx8 localization. Unexpectedly, we did not detect replication stress-induced Slx8 foci. However, we discovered that Slx8 forms a single nuclear focus, enriched at the nuclear periphery, which marks both clustered centromeres at the spindle pole body and the silent mating type region. The formation of this single Slx8 focus requires the E3 SUMO ligase Pli1, poly-SUMOylation and the histone methyl transferase Clr4 that is responsible for the heterochromatin histone mark H3-K9 methylation. Finally, we established that Slx8 promotes centromere clustering and gene silencing at heterochromatin domains. Altogether, our data highlight evolutionarily conserved and functional relationships between STUbL and heterochromatin domains to promote gene silencing and nuclear organization. HighlightsO_LIThe S. pombe STUbL Slx8 forms a single nuclear focus enriched at the nuclear periphery in a SUMO-chain-dependent manner. C_LIO_LISlx8 foci mark clustered centromeres and the silenced mating type region but not telomeres. C_LIO_LIH3-K9 methylation by Crl4 promotes the single nuclear Slx8 focus C_LIO_LISlx8 promotes centromere clustering and gene silencing. C_LI

cell biology↗

bioRxiv2023

SUMO protease and proteasome recruitment at the nuclear periphery differently affect replication dynamics at arrested forks.

Nuclear pores complexes (NPCs) are genome organizers, defining a particular nuclear compartment enriched for SUMO protease and proteasome activities, and acting as docking sites for DNA repair. In fission yeast, the anchorage of perturbed replication forks to NPCs is an integral part of the recombination-dependent replication restart mechanism (RDR) that resumes DNA synthesis at terminally dysfunctional forks. By mapping DNA polymerase usage, we report that SUMO protease Ulp1-associated NPCs ensure efficient initiation of restarted DNA synthesis, whereas proteasome-associated NPCs sustain the progression of restarted DNA polymerase. In contrast to Ulp1-dependent events, this last function occurs independently of SUMO chains formation. By analyzing the role of the nuclear basket, the nucleoplasmic extension of the NPC, we reveal that the activities of Ulp1 and the proteasome cannot compensate for each other and affect RDR dynamics in distinct ways. Our work probes the mechanisms by which the NPC environment ensures optimal RDR. Highlights[bullet] Ulp1-associated NPCs ensure efficient initiation of restarted DNA synthesis, in a SUMO chain-dependent manner [bullet]Proteasome-associated NPCs foster the progression of restarted DNA synthesis, in a SUMO chain-independent manner [bullet]The nucleoporin Nup60 promotes the spatial sequestration of Ulp1 at the nuclear periphery [bullet]Ulp1 and proteasome activities are differently required for optimal recombination-mediated fork restart.

molecular biology↗

bioRxiv2021

Defining the cell surface proteomic landscape of multiple myeloma reveals immunotherapeutic strategies and biomarkers of drug resistance

The myeloma cell surface proteome ("surfaceome") not only determines tumor interaction with the microenvironment but serves as an emerging arena for therapeutic development. Here, we use glycoprotein capture proteomics to first define surface markers most-enriched on myeloma when compared to B-cell malignancy models, revealing unexpected biological signatures unique to malignant plasma cells. We next integrate our proteomic dataset with existing transcriptome databases, nominating CCR10 and TXNDC11 as possible monotherapeutic targets and CD48 as a promising co-target for increasing avidity of BCMA-directed cellular therapies. We further identify potential biomarkers of resistance to both proteasome inhibitors and lenalidomide including changes in CD53, EVI2B, CD10, and CD33. Comparison of short-term treatment with chronic resistance delineates large differences in surface proteome profile under each type of drug exposure. Finally, we develop a miniaturized version of the surface proteomics protocol and present the first surface proteomic profile of a primary myeloma patient plasma cell sample. Our dataset provides a unique resource to advance the biological, therapeutic, and diagnostic understanding of myeloma.

cancer biology↗

bioRxiv2019

Dynamic measurement of cytosolic pH and uncovers the role of the vacuolar transporter AtCLCa in the control of cytosolic pH.

Ion transporters are key players of cellular processes. The mechanistic properties of ion transporters have been well elucidated by biophysical methods. Meanwhile the understanding of their exact functions in the whole cell homeostasis is limited by the difficulty to monitor their activity in vivo. The development of biosensors to track subtle changes in intracellular parameters provides an invaluable key to tackle this challenging issue. Here, we adapted the use of a dual biosensor using guard cells as experimental model to visualize the impact on the cytosol of anion transport from intracellular compartments. To image the activity of AtCLCa, a vacuolar NO3-/H+ exchanger regulating stomata aperture in Arabidopsis thaliana, we expressed a genetically encoded biosensor, ClopHensor allowing monitoring the dynamics of cytosolic anion concentration and pH. We first show that ClopHensor is not only a Cl- but also a NO3- sensor. We were then able to unravel and quantify the variations of NO3- and pH in the cytosol. Our data show that AtCLCa activity modifies cytosolic pH and NO3-, demonstrating that the transport activity of a vacuolar exchanger has a profound impact on cytosolic homeostasis. We propose that a major function of this endomembrane transporter is to adjust cytosolic conditions to cellular needs. This opens a novel perspective on the function of intracellular transporters of the CLC family in eukaryotes: not only controlling the intra organelle lumen but also actively modifying cytosolic conditions.\n\nSignificanceIntracellular transporters are key actors in cell biological processes. Their disruption causes major physiological defects. The role of intracellular ion transporters is usually seen through an \"intra organelle\" lens, meanwhile their potential action on cytosolic ion homeostasis is still a black box. The case of a plant CLC is used as a model to uncover the missing link between the regulation of conditions inside the vacuole and inside the cytosol. The development of an original live imaging workflow to simultaneously measure pH and anion dynamics in the cytosol reveals the role of an Arabidopsis thaliana CLC, AtCLCa, in the modification of cytosolic pH. Our data highlight an unsuspected function of endomembrane transporters in the regulation of cytosolic pH.

plant biology↗