Biology subjects

Morel, E.

Publications and source records attributed to Morel, E..

7 recordsLinked to original sources

bioRxiv2025

Vimentin intermediate filaments support autophagosome biogenesis at ER-endosomes contact sites in response to starvation

Macroautophagy (autophagy) is a fundamental catabolic process requiring the biogenesis of the autophagosome to support cell survival during stress. While the roles of F-actin and microtubule cytoskeleton in autophagy are well established, the contribution of intermediate filaments (IFs) remains poorly understood. Here, we investigated the role of the type III IF vimentin in supporting the early steps of starvation-induced autophagy. We demonstrate that starvation triggers a rapid, perinuclear compaction of vimentin IFs, correlating with transient phosphorylation at serine 56 and enhanced overlap with the endoplasmic reticulum (ER). We reveal that autophagic proteins accumulate at the vimentin/ER interface, physically connecting the autophagosome biogenesis machinery to the vimentin IF network. Knock-out or pharmacological perturbation of vimentin-IFs dynamics using Withaferin-A significantly impairs starvation-induced autophagic flux. Mechanistically, we reveal that vimentin IFs are essential coordinators for the mobilization of endosome-ER-membrane contact sites (EERCS), a critical hub for autophagosome nucleation. Together, our findings uncover a novel role for vimentin IFs as a dynamic cytoskeletal coordinator that spatially organizes membrane contact sites to promote the efficient initiation of autophagosome biogenesis in response to nutrient stress. Summary statementThis study reveals that vimentin intermediate filaments rapidly reorganize to mobilize ER-endosome contact sites, establishing a critical spatial platform for starvation-induced autophagy initiation.

cell biology↗

bioRxiv2025

Keratin intermediate filaments mechanically position melanin pigments for genome photoprotection

Melanin pigments block genotoxic agents by positioning on the sun-exposed side of human skin keratinocytes nucleus. How this position is regulated and its role in genome photoprotection remains unknown. By developing a model of human keratinocytes internalizing extracellular melanin into pigment organelles, we show that keratin 5/14 intermediate filaments mechanically control the 3D perinuclear position of pigments, shielding DNA from photodamage. Imaging and microrheology in human disease-related model identify structural keratin cages surrounding pigment organelles to stiffen their microenvironment and maintain their 3D position. Optimum pigment spatialization is required for DNA photoprotection and rely on the interplay between intermediate filaments and microtubules bridged by plectin cytolinkers. Thus, the mechanically-driven proximity of pigment organelles to the nucleus is a key photoprotective parameter. Uncovering how human skin counteracts solar radiation by positioning the melanin microparasol next to the genome anticipates that dynamic spatialization of organelles is a physiological UV stress response. Short summaryMelanin pigments shield DNA from photodamage by positioning atop nuclei in skin keratinocytes. We show keratin 5/14 intermediate filaments control this 3D spatialization, forming protective cages around pigments. This positioning, together with microtubule function, optimizes genome protection, revealing cytoskeletons and organelle dynamics as a UV stress response.

cell biology↗

bioRxiv2024

Influenza A virus-induced production of PI4P at the endoplasmic reticulum involves ATG16L1 and promotes the egress of viral ribonucleoproteins

The genomic RNAs of influenza A viruses (IAVs) are replicated in the nucleus of infected cells in the form of viral ribonucleoproteins (vRNP) before being exported to the cytoplasm. The small GTPase RAB11A is involved in the transport of vRNPs to the sites of viral assembly at the plasma membrane, but the molecular mechanisms involved remain largely unknown. Here we show that IAV infection remodels the architecture of the endoplasmic reticulum (ER) sheets, where vRNPs tend to accumulate in the absence of RAB11A. To decipher the interplay between RAB11A, vRNPs and the ER, we investigated viral-induced perturbations of RAB11A proximity interactome. To this end, we generated cells stably expressing a TurboID-RAB11A fusion protein and performed biotin-based proximity labeling upon viral infection. We found that cellular regulators of phophatidylinositol-4-phosphate (PI4P) homeostasis, including the autophagic and stress response protein ATG16L1, are significantly enriched at the vicinity of RAB11A in infected cells. Infection induces an increase in cellular PI4P levels in an ATG16L1-dependent manner, while ATG16L1 relocalizes to ER membranes upon infection. Depletion of ATG16L1 decreases the co-distribution of vRNPs with PI4P punctae on ER membranes, and reduces the accumulation of vRNPs at the plasma membrane as well as the production of IAV infectious particles. Our data extend to IAVs the notion that viruses can modulate the metabolism and localization of phosphoinositides to control host membrane dynamics and point to the ER as an essential platform for vRNP transport. They provide evidence for a pivotal role of ATG16L1 in regulating the identity of endomembranes and coordinating RAB11A and PI4P-enriched membranes to ensure delivery of vRNPs to the plasma membrane.

microbiology↗

bioRxiv2024

The fate of pollen in two morphologically contrasting buzz-pollinated Solanum flowers

Pollen transfer efficiency (PTE) and pollen deposition patterns on a pollinators body significantly influence plant reproductive success. However, studies on pollen fates (i.e., the destination of pollen grains after anther dehiscence) in animal-pollinated species offering pollen as the sole reward are limited. This study investigated pollen fates in two nectarless, buzz-pollinated Solanum species with contrasting floral morphology. Experimental trials were conducted involving one pollen donor and four recipient flowers of Solanum rostratum Dunal or S. dulcamara L., using captive Bombus terrestris L. as pollinator. The number of pollen grains remaining in the anthers, deposited on stigmas, placed on the pollinator, and falling to the ground was quantified. Both species produced a relatively high number of pollen grains as expected for buzz-pollinated plants. Pollen deposition curves followed exponential decay patterns, with a higher number of pollen grains deposited for S. dulcamara, and a similar rate of decline for both species. PTE was similar between species (0.86 % vs. 1.00 %, for S. rostratum and S. dulcamara, respectively) but these values could be 25 % higher if we were to measure pollen deposition in 20 recipients rather than four as in the present study. Although both species had similar PTE values, their pollen fates differed: pollen was mainly lost on the ground in S. rostratum and due to bee grooming in S. dulcamara, potentially explained by their different floral architectures. These findings suggest that species with different flower morphology could exhibit different pollen fates without impacting pollen transfer to conspecific stigmas.

plant biology↗

bioRxiv2024

Birnaviral Hijacking of Endosomal Membranes

Birnaviruses are a group of double-stranded RNA (dsRNA) viruses infecting birds, fish and insects. Early endosomes (EE) constitute the platform for viral replication. Here, we study the mechanism of birnaviral targeting of EE membranes. Using the Infectious Bursal Disease Virus (IBDV) as a model, we validate that the viral protein 3 (VP3) binds to phosphatidylinositol-3-phosphate (PI3P) present in EE membranes. We identify the domain of VP3 involved in PI3P-binding, named P2 and localized in the core of VP3, and establish the critical role of the arginine at position 200 (R200), conserved among all known birnaviruses. Mutating R200 abolishes viral replication. Moreover, we propose a two-stage modular mechanism for VP3 association with EE. Firstly, the carboxy-terminal region of VP3 adsorbs on the membrane, and then the VP3 core reinforces the membrane engagement by specifically binding PI3P through its P2 domain, additionally promoting PI3P accumulation. Significance StatementBirnaviruses are a family of viruses unique among the group of dsRNA viruses. Here, we show that VP3 seizes the endosomes by anchoring to the PI3P lipids in the luminal side of the EE membrane, in order to organize the viral replication factory. We propose a two-stage modular mechanism for VP3 association with PI3P-enriched EE. The significance of this work resides in the biochemical and biophysical insights on the mechanism of association of VP3 with EE and its role in the viral life cycle, which represents a substantial contribution toward understanding the replication strategy of these "non-canonical" viruses.

microbiology↗

bioRxiv2023

YAP-dependent autophagy is controlled by AMPK, SIRT1 and flow intensity in kidney epithelial cells.

Shear stress generated by the urinary fluid flow is an important regulator of renal function. Its dysregulation is observed in various chronic and acute kidney diseases. Previously, we demonstrated that primary cilium-dependent autophagy allows kidney epithelial cells to adapt their metabolism in response to fluid flow. Here, we show that nuclear YAP/TAZ negatively regulates autophagy machinery in kidney epithelial cells subjected to fluid flow. This crosstalk is supported by a primary cilium-dependent activation of AMPK and SIRT1, independently of the Hippo pathway. We confirmed the relevance of the YAP/TAZ-autophagy molecular dialog in vivo using a zebrafish model of kidney development and a unilateral ureteral obstruction mouse model. In addition, an in vitro assay simulating the pathological flow observed at early stages of chronic kidney disease (CKD) activated YAP, leading to a primary cilium-dependent inhibition of autophagy. Our findings demonstrate the importance of YAP/TAZ and autophagy in the translation of fluid flow into cellular and physiological responses. Dysregulation of this pathway is associated with the early onset of CKD.

cell biology↗

bioRxiv2021

EPAC1 Inhibition Protects the Heart from Doxorubicin-Induced Toxicity

Anthracyclines, such as doxorubicin (Dox), are widely used chemotherapeutic agents for the treatment of solid tumors and hematologic malignancies. However, they frequently induce cardiotoxicity leading to dilated cardiomyopathy and heart failure. This study sought to investigate the role of the Exchange Protein directly Activated by cAMP (EPAC) in Dox-induced cardiotoxicity and the potential cardioprotective effects of EPAC inhibition. We show that Dox induces DNA damage and cardiomyocyte cell death with apoptotic features. Dox also led to an increase in both cAMP concentration and EPAC1 activity. The pharmacological inhibition of EPAC1 (with CE3F4) but not EPAC2 alleviated the whole Dox-induced pattern of alterations. When administered in vivo, Dox-treated WT mice developed a dilated cardiomyopathy which was totally prevented in EPAC1 KO mice. Moreover, EPAC1 inhibition potentiated Dox-induced cell death in several human cancer cell lines. Thus, EPAC1 inhibition appears as a potential therapeutic strategy to limit Dox-induced cardiomyopathy without interfering with its antitumoral activity.

pathology↗