Biology subjects

Combredet, C.

Publications and source records attributed to Combredet, C..

6 recordsLinked to original sources

bioRxiv2026

Rapid repurposing of microvillar content drives a flagellate-to-amoeboid switch in the closest relative of animals

Animal cells extensively remodel their cytoskeleton during differentiation and can notably switch between two major motility modes: flagellum-based swimming and actin-based crawling. We previously showed that choanoflagellates, the closest living relatives of animals and classically viewed as obligate flagellated swimmers, can retract their collar complex and adopt an amoeboid form within seconds under spatial confinement, independently of regulated gene expression. Here, using live imaging, ultrastructural expansion microscopy, and cryo-electron tomography in Salpingoeca rosetta, we identify rapid, cell-wide cytoskeletal remodeling as the ultrastructural basis of this switch. Unconfined choanoflagellates lack a detectable actin cortex but display an apical flagellum and cortical microtubules, with F-actin being largely restricted to microvilli. Confinement triggers calcium release from intracellular stores, which induces microvillar retraction and absorption of microvillar material into the cell body, including actin, ezrin-radixin-moesin 1, and plasma membrane. Remodeling of the internalized F-actin and repurposing of associated proteins supports de novo actin cortex formation, which is necessary for amoeboid motility. In parallel, cortical microtubules are disassembled, and the reabsorbed microvillar plasma membrane increases the surface area of the cell body, allowing the cell to flatten under confinement. Cryo-electron tomography reveals stepwise actin reorganization from internalized microvillar bundles to a cortical contractile meshwork combining bundles and scattered filaments. This work reveals considerable ultrastructural plasticity in the cytoskeletal architecture of choanoflagellates and supports an ancestral role for microvilli as reservoirs of membrane and cytoskeleton to potentiate cell phenotypic transitions.

evolutionary biology↗

bioRxiv2025

A modified oncolytic measles virus exhibits strong immunotherapeutic potential through RIG-I activation by defective viral genomes

Oncolytic viruses can destroy tumors directly or by activating antitumor immunity, but balancing safety with potent immune stimulation remains challenging. Here, we show that deletion of the measles virus C protein, a key viral antagonist of innate immunity, reprograms the live-attenuated vaccine strain into a RIG-I-driven cancer immunotherapy. The resulting virus, MVdeltaC, accumulates defective viral genomes that activate RIG-I/MAVS signaling and trigger robust type I interferon and pro-inflammatory cytokine responses. MVdeltaC kills tumor cells more rapidly and efficiently than the parental virus and induces hallmarks of immunogenic cell death, including HMGB1 release and dendritic cell maturation. Intratumoral administration in immunocompetent mice bearing syngeneic neuroblastoma induced complete tumor regression in 90% of animals and established long-term antitumor memory. Antitumor responses were dependent on CD8 T and NK cells and were further enhanced by anti-CTLA-4 therapy or CD4 T-cell depletion. Prior measles immunization accelerated tumor clearance, indicating vaccine-boosted responses. MVdeltaC also controlled the growth of human mesothelioma, melanoma, and triple-negative breast cancer xenografts and patient-derived tumors in immunodeficient models. These findings establish MVdeltaC as a clinically ready, broad-spectrum immunotherapeutic that links RIG-I activation through defective viral genome generation to elicit potent and durable antitumor immunity. IMPACT StatementA modified measles virus lacking a viral innate immunity antagonist triggers potent antitumor responses via RIG-I sensing of defective viral genomes, revealing a new strategy for cancer immunotherapy.

immunology↗

bioRxiv2024

A fast and robust gene knockout method for Salpingoeca rosetta clarifies the genetics of choanoflagellate multicellular development

As the closest living relatives of animals, choanoflagellates offer crucial insights into the evolutionary origin of animals. Notably, certain choanoflagellate species engage in facultative multicellular development that resembles the early stages of embryogenesis. In the past few years, Salpingoeca rosetta has emerged as a tractable model for choanoflagellate cell biology and multicellular development, in particular through mutant screens and CRISPR/Cas9-mediated gene knockout (KO). However, existing KO pipelines have variable and sometimes low efficiency, frequently requiring isolation and genotyping of hundreds of clones without guarantee to obtain a KO strain. Here, we present a robust method for gene inactivation in S. rosetta that relies on insertion by CRISPR/Cas9 of a single 1.9 kb cassette encoding both a premature termination sequence and an antibiotic resistance gene. We show that this approach allows robust, fast and efficient isolation of KO clones after antibiotic selection. As a proof of principle, we first knocked out all three genes previously reported to regulate S. rosetta multicellular development in a published mutant screen (rosetteless, couscous and jumble), and confirmed that all three KOs abolished multicellular development. To showcase the potential of this method for de novo characterization of candidate developmental genes, we then inactivated three homologs of genes in the Hippo pathway: hippo, warts and yorkie, which together control cell proliferation and multicellular size in animals. Interestingly, warts KO rosettes were consistently about twice as large as their wild-type counterparts, showing our KO pipeline can reveal novel loss-of-function phenotypes of biological interest. Thus, this method has the potential to accelerate choanoflagellate functional genetics.

evolutionary biology↗

bioRxiv2024

Mixed clonal-aggregative multicellularity entrained by extreme salinity fluctuations in a close relative of animals

Multicellularity evolved multiple times independently during eukaryotic diversification1-4. Two distinct mechanisms underpin multicellularity5: clonality (serial cell division without sister-cell separation) and aggregation (whereby independent cells assemble into a multicellular entity). Clonal and aggregative multicellularity are traditionally considered mutually exclusive1,6-9, with rare exceptions10, and evolutionary hypotheses have addressed why multicellularity might diverge toward one or the other extreme3,4. Both animals and their sister group, the choanoflagellates, are currently only known to acquire multicellularity clonally4,11-13. Here, we show that the choanoflagellate Choanoeca flexa14 forms motile and contractile cell monolayers (or "sheets") through multiple mechanisms: C. flexa sheets can form purely clonally, purely aggregatively, or by a combination of both processes. We characterise the life history of C. flexa in its natural environment - ephemeral splash pools on the island of Curacao - and show that C. flexa undergoes reversible transitions between unicellularity and multicellularity during cycles of evaporation and refilling. Different splash pools house genetically distinct strains of C. flexa, between which aggregation is constrained by kin recognition15-18. We show that clonal-aggregative multicellularity serves as a versatile strategy for the robust re-establishment of multicellularity in this variable and fast-fluctuating environment. Our findings challenge former generalisations about choanoflagellates and expand the option space of choanozoan multicellularity.

evolutionary biology↗

bioRxiv2021

A measles-vectored COVID-19 vaccine induces long-term immunity and protection from SARS-CoV-2 challenge in mice

In light of the expanding SARS-CoV-2 pandemic, developing efficient vaccines that can provide sufficient coverage for the world population is a global health priority. The measles virus (MV)-vectored vaccine is an attractive candidate given the measles vaccines extensive safety history, well-established manufacturing process, and induction of strong, long-lasting immunity. We developed an MV-based SARS-CoV-2 vaccine using either the full-length spike (S) or S2 subunit as the antigen. While the S2 antigen failed to induce neutralizing antibodies, the prefusion-stabilized, full-length S (MV-ATU2-SF-2P-dER) construct proved to be an attractive vaccine candidate, eliciting strong Th1-dominant T-cell and neutralizing antibody responses against the S antigen while minimizing reactivity to the vector itself. Neutralizing antibody titers remained high three months after homologous prime-boost immunization, and infectious virus was undetectable in all animals after challenge with a mouse-adapted SARS-CoV-2 virus.

immunology↗

bioRxiv2020

Proteomic Analysis Uncovers Measles Virus Protein C Interaction with p65/iASPP/p53 Protein Complex

Viruses manipulate central machineries of host cells to their advantage. They prevent host cell antiviral responses to create a favorable environment for their survival and propagation. Measles virus (MV) encodes two non-structural proteins MV-V and MV-C known to counteract the host interferon response and to regulate cell death pathways. Several molecular mechanisms underlining MV-V regulation of innate immunity and cell death pathways have been proposed, whereas MV-C host protein partners are less studied. We suggest that some cellular factors that are controlled by MV-C protein during viral replication could be components of innate immunity and the cell death pathways. To determine which host factors are targeted by MV-C, we captured both direct and indirect host protein partners of MV-C protein. For this, we used a strategy based on recombinant viruses expressing tagged viral proteins followed by affinity purification and a bottom-up mass spectrometry analysis. From the list of host proteins specifically interacting with MV-C protein in different cell lines we selected the host targets that belong to immunity and cell death pathways for further validation. Direct protein partners of MV-C were determined by applying protein complementation assay (PCA) and the bioluminescence resonance energy transfer (BRET) approach. As a result, we found that MV-C protein specifically interacts with p65/iASPP/p53 protein complex that controls both cell death and innate immunity pathways.

microbiology↗