Biology subjects

Le Bivic, A.

Publications and source records attributed to Le Bivic, A..

11 recordsLinked to original sources

bioRxiv2026

A non-invasive approach for understanding localized force generation in 3D tissues

The development, maintenance and repair of epithelial tissues critically rely on adhesion complexes that ensure structural integrity while enabling dynamic remodeling. Such tissue remodeling underpins both physiological morphogenesis and pathological transformation. Central to these processes are mechanical forces, which tightly couple cytoskeletal organization to adhesion dynamics. Despite extensive investigations in two-dimensional (2D) systems, how these interactions are orchestrated within polarized three-dimensional (3D) epithelia remains largely unresolved. Here, we introduce a new, non-invasive strategy to probe localized force generation within 3D epithelial tissues. We engineered elastic polyacrylamide (PAAm) microbeads with cell-mimetic size and mechanical properties, enabling their seamless integration. In contrast to conventional bead injection approaches, these PAAm microbeads were spontaneously engulfed by the tissue, thereby establishing an intrinsic interface through which bead deformation can be directly correlated with local cytoskeletal architecture and adhesion organization, as visualized through high-resolution imaging combined with quantitative 3D computational reconstruction. Using this approach, we demonstrated that localized mechanical perturbations trigger pronounced cytoskeletal remodelling while preserving global tissue polarity. We further identified the extracellular matrix composition as key determinant of bead-tissue interactions, with collagen-I coating promoting robust adhesion and efficient incorporation. At the bead-cell interface, cells assembled tension-bearing focal adhesions and organized actin stress fibers, revealing the emergence of active cortical stress. Strikingly, quantitative analysis of bead deformation revealed a previously unrecognized mechanical duality: spatially segregated regions of pulling and pushing forces coexisted at the microscale, directly correlated with local cytoskeleton dynamics. This finding challenges the prevailing view of homogenous force application and instead supports a model in which cells deploy highly coordinated and spatially patterned force-generating strategies. Altogether, this integrative and non-invasive strategy offers a comprehensive pipeline for dissecting the dynamic interplay between cellular processes and tissue mechanics during morphogenesis in 3D model systems.

cell biology↗

bioRxiv2025

Fast calcium-dependent reorientation of motile cilia basal bodies in the simple metazoan, Trichoplax.

Ciliary-based animal locomotion relies on the spatially coordinated beating of motile cilia to displace the body in liquid environments or across solid surfaces. The orientation of ciliary beating largely depends on the rotational polarity of the basal body, which in most animals is fixed and controlled by cues linked to the main body axes. The small marine animal Trichoplax exploits the beating of motile cilia in its lower epithelium to crawl on substrates. However, Trichoplax lacks defined body axes and exhibits rapid changes in body shape and direction of movement, thus raising the question of what controls the orientation and reorientation of ciliary beating. We show here that the basal bodies of the cilia in the lower epithelium of Trichoplax are oriented along the direction of the animal movements, and that they change their orientation throughout the lower epithelium in a few seconds time when the animal modifies its shape or changes direction following external mechanical stimuli. We also show that Ca2+ is required for fast basal body reorientation. Such rapid ciliary basal body reorientation has never been observed in metazoans before. Thus, our results identify a previously undescribed mechanism underlying directional motility in a metazoan and shed light on its subcellular determinants, bridging the scale between intra-cellular ciliary machinery and animal movement.

cell biology↗

bioRxiv2023

Hyperaccumulation of Vanadium in animals: two sponges compete with urochordates

Vanadium (V) is the second most abundant transition metal in the oceans. Nevertheless, its concentration in organisms is generally low despite its involvement in various physiological or enzymatic functions. Because exposure to high concentrations was shown to be harmful for various organisms including animals, the unexpected very high concentrations found in urochordates and annelids yielded additional studies to decipher their biological meaning. Here we report cases of V hyperaccumulators in a distinct animal phylum (Porifera): the two homoscleromorph sponge species Oscarella lobularis and Oscarella tuberculata (up to 30 mg/g dw). These high concentrations overpass those reported previously in urochordates and annelids and are not found in the 5 other sponge species studied here. In both Oscarella species, vanadium is mainly accumulated in the 100 m surface tissues, and in particular in mesohylar cells, as vanadyl (+4) before being partly reduced to V (+3) in the deeper tissues. Genomic surveys failed to find any previously described gene implicated in vanadium metabolism, suggesting that V hyperaccumulation emerged convergently in this lineage. This feature may be of interest for developing bioremediation strategies in marine ecosystems or bioinspired processes to recycle this critical metal. SynopsisThis study reports extremely high concentrations of vanadium in two sponges. This unusual bioaccumulation of reduced V (+3) in mesohylar cells relies on unknown molecular mechanisms.

ecology↗

bioRxiv2023

CRB3 and ARP2/3 regulate cell biomechanical properties to set epithelial monolayers for collective movement

Several cellular processes during morphogenesis, tissue healing or cancer progression involve epithelial to mesenchymal plasticity that leads to collective motion (plasticity?). Even though a rich variety of EMP programs exist, a major hallmark unifying them is the initial breaking of symmetry that modifies the epithelial phenotype and axis of polarity. During this process, the actin cytoskeleton and cellular junctions are extensively remodelled correlating with the build-up of mechanical forces. As the collective migration proceeds, mechanical forces generated by the actin cytoskeleton align with the direction of migration ensuring an organized and efficient collective cell behaviour, but how forces are regulated during the breaking of symmetry at the onset of EMP remains an unaddressed question. It is known that the polarity complex CRB3/PALS1/PATJ, and in particular, CRB3 regulates the organization of the actin cytoskeleton associated to the apical domain thus pointing at a potential role of CRB3 in controlling mechanical forces. Whether and how CRB3 influences epithelial biomechanics during the epithelial-mesenchymal plasticity remains, however, largely unexplored. Here, we systematically combine mechanical and molecular analyses to show that CRB3 regulates the biomechanical properties of collective epithelial cells during the initial breaking of symmetry of the EMP. CRB3 interacts with ARP2/3 and controls the remodelling of actin throughout the monolayer via the modulation of the Rho-/Rac-GTPase balance. Taken together, our results identified CRB3, a polarity protein, as a regulator of epithelial monolayer mechanics during EMP.

cell biology↗

bioRxiv2022

The compact genome of the sponge Oopsacas minuta (Hexactinellida) is lacking key metazoan core genes

BackgroundBilaterian animals today represent 99% of animal biodiversity. Elucidating how bilaterian hallmarks emerged is a central question of animal evo-devo and evolutionary genomics. Studies of non-bilaterian genomes have suggested that the ancestral animal already possessed a diversified developmental toolkit, including some pathways required for bilaterian body plans. Comparing genomes within the early branching metazoan Porifera phylum is key to identify which changes and innovations contributed to the successful transition towards bilaterians. ResultsHere, we report the first whole genome comprehensive analysis of a glass sponge, Oopsacas minuta, a member of the Hexactinellida. Studying this class of sponge is evolutionary relevant because it differs from the three other Porifera classes in terms of development, tissue organization, ecology and physiology. Although O. minuta does not exhibit drastic body simplifications, its genome is among the smallest animal genomes sequenced so far, surprisingly lacking several metazoan core genes (including Wnt and several key transcription factors). Our study also provided the complete genome of the symbiotic organism dominating the associated microbial community: a new Thaumarchaeota species. ConclusionsThe genome of the glass sponge O. minuta differs from all other available sponge genomes by its compactness and smaller number of predicted proteins. The unexpected losses of numerous genes considered as ancestral and pivotal for metazoan morphogenetic processes most likely reflect the peculiar syncytial organization in this group. Our work further documents the importance of convergence during animal evolution, with multiple emergences of sponge skeleton, electrical signaling and multiciliated cells.

evolutionary biology↗

bioRxiv2021

Evolution of mechanisms controlling epithelial morphogenesis across animals: new insights from dissociation - reaggregation experiments in the sponge Oscarella lobularis.

BackgroundThe ancestral presence of epithelia in Metazoa is no longer debated. Even though Porifera seem to be the best candidates to be the sister group to all other Metazoa, hardly anything is known about the proteins involved in the composition of cell-cell junctions or about the mechanisms that regulate epithelial morphogenetic processes in this phylum. ResultsTo get insights into the early evolution of epithelial morphogenesis, we focused on morphogenic characteristics of the homoscleromorph sponge Oscarella lobularis. Homoscleromorpha are a sponge class with a typical basement membrane and adherens-like junctions unknown in other sponge classes. We took advantage of the dynamic context provided by cell dissociation-reaggregation experiments to explore morphogenetic processes in epithelial cells in an early lineage by combining fluorescent and electronic microscopy observations and RNA sequencing approaches at key time-points of the dissociation and reaggregation processes. ConclusionsOur results show that part of the molecular toolkit involved in the loss and restoration of epithelial features such as cell-cell and cell-matrix adhesion is conserved between Homoscleromorpha and Bilateria, suggesting their common role in the last common ancestor of animals. In addition, Sponge-specific genes are differently expressed during the dissociation and reaggregation processes, calling for future functional characterization of these genes.

evolutionary biology↗

bioRxiv2020

Super-resolution imaging uncovers the nanoscopic segregation of polarity proteins in epithelia

Epithelial tissues acquire their integrity and function through the apico-basal polarization of their constituent cells. Proteins of the PAR and Crumbs complexes are pivotal to epithelial polarization, but the mechanistic understanding of polarization is challenging to reach, largely because numerous potential interactions between these proteins and others have been found, without clear hierarchy in importance. We identify the regionalized and segregated organization of members of the PAR and Crumbs complexes at epithelial apical junctions by imaging endogenous proteins using STED microscopy on Caco-2 cells, human and murine intestinal samples. Proteins organize in submicrometric clusters, with PAR3 overlapping with the tight junction (TJ) while PALS1-PATJ and aPKC-PAR6{beta} form segregated clusters that are apical of the TJ and present in an alternated pattern related to actin organization. CRB3A is also apical of the TJ and weakly overlaps with other polarity proteins. This organization at the nanoscale level significantly simplifies our view on how polarity proteins could cooperate to drive and maintain cell polarity.

cell biology↗

bioRxiv2020

The buds of Oscarella lobularis (Porifera): a new convenient model for sponge cell and developmental biology

The comparative study of the four non-bilaterian phyla (Cnidaria, Placozoa, Ctenophora, Porifera) should provide insights into the origin of bilaterian traits. Except for Cnidaria, present knowledge on the cell biology and development of these animals is so far limited. Non-bilaterian models are needed to get further into cell architecture and molecular mechanisms. Given the developmental, histological, ecological and genomic differences between the four sponge classes, we develop a new sponge model: the buds of the Oscarella lobularis (class Homoscleromorpha). This experimental model supplements the two other most famous sponge models Amphimedon queenslandica and Ephydatia muelleri, both belonging to the class Demospongiae. Budding is a natural and spontaneous asexual reproduction mean, but budding can be triggered in vitro ensuring availability of biological material all year long. We provide a full description of buds, from their formation to their development into juveniles. Their transparency enables fluorescent and live imaging, and their abundance allows for experimental replicates. Moreover, regeneration and cell reaggregation capabilities provide interesting experimental morphogenetic contexts. The numerous techniques now mastered on these buds make it a new suitable sponge model. Summary statementStudying sponge biology is needed to understand the evolution of metazoans. We developed a new model suitable for experimental biology that allows to study morphogenetic processes with modern tools.

zoology↗

bioRxiv2019

CRB2 controls primary ciliogenesis in association with PAR6α, HOOK2 and RAB8A

Ciliogenesis is an essential process in animal development and physiology and when affected, the origin of severe pathologies called ciliopathies. CRB2 has been recently implicated when mutated in several pathologies such as retina degeneration and a ciliopathy-like syndrome. Here, we have investigated the role of CRB2 in primary ciliogenesis and showed that CRB2 depletion blocks the formation of the ciliary vesicle after activation of the mother centriole, indicating a defect in either transport or anchoring of the ciliary vesicle. CRB2 is accumulated in intracellular vesicles in the vicinity of the centrosome and we showed here that CRB2 forms a complex made of HOOK2 and PAR6, two proteins important for primary ciliogenesis or centrosome integrity. In addition, CRB2 interacts with RAB8A which over-expression rescued CRB2 knockdown. All together, these findings indicate that CRB2 regulates a membrane transport step essential for the formation of the ciliary vesicle.

cell biology↗

bioRxiv2019

Nectins rather than E-cadherin anchor the actin belts at cell-cell junctions of epithelia

Cell-cell junctions support the mechanical integrity of epithelia by enabling adhesion and tension transmission between neighboring cells. The prevailing mechanistic dogma is that E-cadherin supports and transmits mechanical tension between cells through actin belts in a region named the zonula adherens. Using super-resolution microscopy on human intestinal biopsies and Caco-2 cells, we show that the zonula adherens consists of E-cadherin and nectin belts that are separated by about 150 nm along the apico-basal direction, the nectin belt being in the immediate vicinity of the actin belt. The segregation of nectins and E-cadherin increases as the tissue matures. Our data redefine the structure of the zonula adherens and show that nectins, rather than E-cadherin, are the major connectors of actin belts in epithelia.

cell biology↗

bioRxiv2017

NEW GENOMIC DATA AND ANALYSES CHALLENGE THE TRADITIONAL VISION OF ANIMAL EPITHELIUM EVOLUTION

The emergence of epithelia was the foundation of metazoan expansion. To investigate the early evolution of animal epithelia, we sequenced the genome and transcriptomes of two new sponge species to characterize epithelial markers such as the E-cadherin complex and the polarity complexes for all classes (Calcarea, Demospongiae, Hexactinellida, Homoscleromorpha) of sponges (phylum Porifera) and compare them with their homologs in Placozoa and in Ctenophora. We found that Placozoa and most sponges possess orthologs of all essential genes encoding proteins characteristic of bilaterian epithelial cells, as well as their conserved interaction domains. In stark contrast, we found that ctenophores lack several major polarity complex components such as the Crumbs complex and Scribble. Furthermore, the E-cadherin ctenophore ortholog exhibits a divergent cytoplasmic domain making it unlikely to interact with its canonical cytoplasmic partners. These unexpected findings challenge the current evolutionary paradigm on the emergence of epithelia.\n\nSIGNIFICANT STATEMENTEpithelial tissues are a hallmark of metazoans deeply linked to the evolution of the complex morphogenesis processes characterizing their development. However, studies on the epithelial features of non-bilaterians are still sparse and it remains unclear whether the last common metazoan ancestor possessed a fully functional epithelial toolkit or if it was acquired later during metazoan evolution. In this work, we demonstrate that if sponges have a well conserved and functionally predicted epithelial toolkit, Ctenophores have either divergent adhesion complexes or lack essential polarity complexes. Altogether, our results raise a doubt on the homology of protein complexes and structures involved in cell polarity and adhesive type junctions between Ctenophora and Bilateria epithelia.

evolutionary biology↗