Blood flow diverts extracellular vesicles from endothelial degradative compartments to promote angiogenesis

Extracellular vesicles released by tumors (tEVs) disseminate via circulatory networks and promote microenvironmental changes in distant organs favoring metastatic seeding. Despite their abundance in the bloodstream, how hemodynamics affect the function of circulating tEVs remains unsolved. We demonstrated that efficient uptake of tEVs occurs in venous endothelial cells that are subjected to hemodynamics. Low flow regimes observed in veins partially reroute internalized tEVs toward non-acidic and non-degradative Rab14-positive endosomes, at the expense of lysosomes, suggesting that endothelial mechanosensing diverts tEVs from degradation. Subsequently, tEVs promote the expression of pro-angiogenic transcription factors in low flow-stimulated endothelial cells and favor vessel sprouting in zebrafish. Altogether, we demonstrate that low flow regimes potentiate the pro-tumoral function of circulating tEVs by promoting their uptake and rerouting their trafficking. We propose that tEVs contribute to pre-metastatic niche formation by exploiting endothelial mechanosensing in specific vascular regions with permissive hemodynamics.

Abstract 697: Extracellular vesicles (EV) - mediators of therapeutic vaccination? In vivo and in vitro characterization of EVs generated after infection of human and murine cells with therapeutic poxviruses

Virus-based therapies show promise in inducing systemic anti-tumor immunity. Over the past years, modified poxviruses were developed to induce a sustained antitumoral immune response. Several studies confirm this hypothesis and report induction of T cell response against the antigen targeted by these vaccines. We previously reported MVA induced T-cell response against HPV oncoviral antigens E6 and E7 in HPV anogenital cancers (NCT03260023) and against private tumor neoantigen in ovarian and head and neck cancer. Despite these promising results the molecular and cellular mechanisms involved in vaccine response remains to be elucidated. In this work, we inquired whether EVs, well known for mediating intercellular communication, play a role in these therapeutic vaccination process. We first asked whether poxviral infection of human primary cells modifies their EV secretion properties. To this end, peripheral blood mononuclear cells (PBMCs) from healthy donors were infected with poxviral vectors, cell culture supernatants were harvested, and different isolation methods were compared for their ability to separate EVs from viral particles: ultracentrifugation, immunocapture, density gradient, velocity gradient, size exclusion chromatography and filtration. EVs size distribution and concentration were determined by nanoparticle tracking analysis (NTA) and the presence of infectious viral particles was titrated by plaque assays. Our data showed that 0.1µm filtration allowed the complete separation of EVs from infectious viral particles. All other methods showed co-isolation of EVs and infectious viral particles. Using this method, we demonstrate that infection of PBMCs with the poxviruses VACV, MVA and PCPV significantly increased the amount of secreted EVs. Next, we investigated the molecular content of EVs isolated from MVA-infected PBMCs by mass spectrometry. We observed differences in the abundance of at least 57 human proteins between EVs from infected and non-infected cells. In addition, several viral proteins, including virus-encoded payloads were detected in EVs from infected cells. We are now confirming those data with flow cytometry to detect virus-encoded payloads like tumor antigens, antigen-presenting molecules, and EV markers such as tetraspanins. The RNA content of EVs from infected and non-infected cells will be compared. Finally, EVs were isolated from murine dendritic cells infected with therapeutic pox vaccines. We are now evaluating the effects of local and systemic application of EVs in murine tumor models.

Citation Format: Lucas Walther, Caroline Tosch, Jules Deforges, Christine Carapito, Magali Rompais, Marie-Christine Claudepierre, Nathalie Silvestre, Kaïdre Bendjama, Eric Quemeneur, Jacky Goetz, Vincent Hyenne, Karola Rittner. Extracellular vesicles (EV) - mediators of therapeutic vaccination? In vivo and in vitro characterization of EVs generated after infection of human and murine cells with therapeutic poxviruses [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 697.

Inhibition of the pseudokinase MLKL alters extracellular vesicle release and reduces tumor growth in glioblastoma

Extracellular vesicles (EVs) are lipid-based nanosized particles that convey biological material from donor to recipient cells. EVs play key roles in glioblastoma progression because glioblastoma stem-like cells (GSCs) release pro-oncogenic, pro-angiogenic, and pro-inflammatory EVs. However, the molecular basis of EV release remains poorly understood. Here, we report the identification of the pseudokinase MLKL, a crucial effector of cell death by necroptosis, as a regulator of the constitutive secretion of EVs in GSCs. We find that genetic, protein, and pharmacological targeting of MLKL alters intracellular trafficking and EV release, and reduces GSC expansion. Nevertheless, this function ascribed to MLKL appears independent of its role during necroptosis. In vivo, pharmacological inhibition of MLKL reduces the tumor burden and the level of plasmatic EVs. This work highlights the necroptosis-independent role of MLKL in vesicle release and suggests that interfering with EVs is a promising therapeutic option to sensitize glioblastoma cells.

•

The pseudokinase MLKL governs extracellular vesicle release in glioblastoma cells

•

Blocking MLKL is deleterious to glioblastoma cell expansion in vitro and in vivo

•

MLKL action in glioblastoma patient cells does not involve necroptosis death

•

MLKL inhibition potentiates TMZ-induced cell death in glioblastoma patient cells

Tumor extracellular vesicles drive metastasis (it's a long way from home)

Among a plethora of functions, extracellular vesicles released by primary tumors spread in the organism and reach distant organs where they can induce the formation of a premetastatic niche. This constitutes a favorable microenvironment for circulating tumor cells which facilitates their seeding and colonization. In this review, we describe the journey of extracellular vesicles (EVs) from the primary tumor to the future metastatic organ, with a focus on the mechanisms used by EVs to target organs with a specific tropism (i.e., organotropism). We then highlight important tumor EV cargos in the context of premetastatic niche formation and summarize their known effects on extracellular matrix remodeling, angiogenesis, vessel permeabilization, resident cell activation, recruitment of foreign cells, and ultimately the formation of a pro-inflammatory and immuno-tolerant microenvironment. Finally, we discuss current experimental limitations and remaining opened questions in light of metastatic diagnosis and potential therapies targeting PMN formation.

The power of imaging to understand extracellular vesicle biology in vivo

Extracellular vesicles (EVs) are nano-sized lipid bilayer vesicles released by virtually every cell type. EVs have diverse biological activities, ranging from roles in development and homeostasis to cancer progression, which has spurred the development of EVs as disease biomarkers and drug nanovehicles. Owing to the small size of EVs, however, most studies have relied on isolation and biochemical analysis of bulk EVs separated from biofluids. Although informative, these approaches do not capture the dynamics of EV release, biodistribution, and other contributions to pathophysiology. Recent advances in live and high-resolution microscopy techniques, combined with innovative EV labeling strategies and reporter systems, provide new tools to study EVs in vivo in their physiological environment and at the single-vesicle level. Here we critically review the latest advances and challenges in EV imaging, and identify urgent, outstanding questions in our quest to unravel EV biology and therapeutic applications.

The NANOTUMOR consortium - Towards the Tumor Cell Atlas

Cancer is a multi-step disease where an initial tumour progresses through critical steps shaping, in most cases, life-threatening secondary foci called metastases. The oncogenic cascade involves genetic, epigenetic, signalling pathways, intracellular trafficking and/or metabolic alterations within cancer cells. In addition, pre-malignant and malignant cells orchestrate complex and dynamic interactions with non-malignant cells and acellular matricial components or secreted factors within the tumour microenvironment that is instrumental in the progression of the disease. As our aptitude to effectively treat cancer mostly depends on our ability to decipher, properly diagnose and impede cancer progression and metastasis formation, full characterisation of molecular complexes and cellular processes at play along the metastasis cascade is crucial. For many years, the scientific community lacked adapted imaging and molecular technologies to accurately dissect, at the highest resolution possible, tumour and stromal cells behaviour within their natural microenvironment. In that context, the NANOTUMOR consortium is a French national multi-disciplinary workforce which aims at a providing a multi-scale characterisation of the oncogenic cascade, from the atomic level to the dynamic organisation of the cell in response to genetic mutations, environmental changes or epigenetic modifications. Ultimately, this program aims at identifying new therapeutic targets using innovative drug design.

Ral GTPases promote breast cancer metastasis by controlling biogenesis and organ targeting of exosomes

Cancer extracellular vesicles (EVs) shuttle at distance and fertilize pre-metastatic niches facilitating subsequent seeding by tumor cells. However, the link between EV secretion mechanisms and their capacity to form pre-metastatic niches remains obscure. Using mouse models, we show that GTPases of the Ral family control, through the phospholipase D1, multi-vesicular bodies homeostasis and tune the biogenesis and secretion of pro-metastatic EVs. Importantly, EVs from RalA or RalB depleted cells have limited organotropic capacities in vivoand are less efficient in promoting metastasis. RalA and RalB reduce the EV levels of the adhesion molecule MCAM/CD146, which favors EV-mediated metastasis by allowing EVs targeting to the lungs. Finally, RalA, RalB, and MCAM/CD146, are factors of poor prognosis in breast cancer patients. Altogether, our study identifies RalGTPases as central molecules linking the mechanisms of EVs secretion and cargo loading to their capacity to disseminate and induce pre-metastatic niches in a CD146-dependent manner.

[Influence of fluid mechanics on metastasis formation]

Metastases are the main cause of cancer-related deaths. The chain of events leading to their development is called "the metastatic cascade". The biological and biochemical aspects of this process have been well studied but the importance of biomechanical parameters only recently became a focus in the field. Studies have shown the biological fluids (blood, lymph and interstitial fluid) to play a key role in the metastatic cascade. These fluids participate in the transport of circulating tumor cells (CTCs) as well as the factors that they secrete, while at the same time influencing the events of the metastatic cascade through the forces that they generate. The hemodynamic properties and topological constraints of the vascular architecture control the formation of metastatic niches and the metastatic potential of tumor cells. In this review, we discuss the importance of these mechanical forces and highlight the novel questions and research avenues that they open.

Live tracking of extracellular vesicles in larval zebrafish

Formerly considered as insignificant cell debris, extracellular vesicles (EVs) have emerged as potent mediators of cell-cell communication, both in proximity and at distance from the producing cell. EVs are transported in body fluids and can be internalized by specific distant cells to ultimately deliver a functional message. Despite their striking importance in many physiological and pathological contexts, the exact mechanisms by which EVs impose local and distant modifications of the microenvironment in vivo remain to be fully understood. We realized that some conceptual gaps are direct consequences of the difficulty to visualize the shuttling and targeting of EVs in real time in vivo. The zebrafish larvae offered attractive features for live tracking of EVs, within circulating fluids. Here, we describe the experimental procedures that we have built for dissecting the dissemination of EVs at high spatio-temporal resolution in vivo.

Fluids and their mechanics in tumour transit: shaping metastasis

Metastasis is a dynamic succession of events involving the dissemination of tumour cells to distant sites within the body, ultimately reducing the survival of patients with cancer. To colonize distant organs and, therefore, systemically disseminate within the organism, cancer cells and associated factors exploit several bodily fluid systems, which provide a natural transportation route. Indeed, the flow mechanics of the blood and lymphatic circulatory systems can be co-opted to improve the efficiency of cancer cell transit from the primary tumour, extravasation and metastatic seeding. Flow rates, vessel size and shear stress can all influence the survival of cancer cells in the circulation and control organotropic seeding patterns. Thus, in addition to using these fluids as a means to travel throughout the body, cancer cells exploit the underlying physical forces within these fluids to successfully seed distant metastases. In this Review, we describe how circulating tumour cells and tumour-associated factors leverage bodily fluids, their underlying forces and imposed stresses during metastasis. As the contribution of bodily fluids and their mechanics raises interesting questions about the biology of the metastatic cascade, an improved understanding of this process might provide a new avenue for targeting cancer cells in transit.

Tenascin-C Orchestrates Glioblastoma Angiogenesis by Modulation of Pro- and Anti-angiogenic Signaling

High expression of the extracellular matrix component tenascin-C in the tumor microenvironment correlates with decreased patient survival. Tenascin-C promotes cancer progression and a disrupted tumor vasculature through an unclear mechanism. Here, we examine the angiomodulatory role of tenascin-C. We find that direct contact of endothelial cells with tenascin-C disrupts actin polymerization, resulting in cytoplasmic retention of the transcriptional coactivator YAP. Tenascin-C also downregulates YAP pro-angiogenic target genes, thus reducing endothelial cell survival, proliferation, and tubulogenesis. Glioblastoma cells exposed to tenascin-C secrete pro-angiogenic factors that promote endothelial cell survival and tubulogenesis. Proteomic analysis of their secretome reveals a signature, including ephrin-B2, that predicts decreased survival of glioma patients. We find that ephrin-B2 is an important pro-angiogenic tenascin-C effector. Thus, we demonstrate dual activities for tenascin-C in glioblastoma angiogenesis and uncover potential targeting and prediction opportunities.

Going live with tumor exosomes and microvesicles

Tumor extracellular vesicles (EVs), including exosomes, emerged as key drivers of the pro-tumorigenic dialog between the tumor mass and its microenvironment by mediating long and short distance communication. In vitro studies defined the capacity of tumor EVs to modify the phenotypes of stromal and tumor cells. These studies are now supported by a growing number of functional in vivo experiments. Remarkably, they allowed the identification of a new role for tumor EVs in priming the pre-metastatic niches (PMN). Several molecules transported in tumor EVs (RNAs and proteins) have recently been found to be essential for tumor progression and metastasis in vivo. In parallel, novel EV labeling and tracking strategies have very recently allowed the first descriptions of tumor EVs in vivo and pave the way for a better understanding of their function in realistic pathophysiological contexts. Here, we review the functional approaches and the recent progress in in vivo imaging of EVs, which have refined our understanding of the role played by tumor EVs. Finally, we emphasize the remaining challenges and open questions related to the biology of tumor EVs.

The Small GTPase Ral orchestrates MVB biogenesis and exosome secretion

Extracellular vesicles are novel mediators of cell-cell communication. They are present in all species and involved in physiological and pathological processes. One class of extracellular vesicles, the exosomes, originate from an endosomal compartment, the MultiVesicular Body (MVB), and are released from the cell upon fusion of the MVB with the plasma membrane. Although different molecular mechanisms have been associated with MVB biogenesis and exosome secretion, how they coordinate remains poorly documented. We recently found that the small GTPase Ral contributes to exosome release in nematodes and mammalian tumor cells. More specifically, we found that C. elegans RAL-1 is required for the biogenesis of MVBs, and later for MVB fusion with the plasma membrane. Here, we discuss our results in relationship with other factors involved in extracellular vesicle production such as the ESCRT complex and Phospholipase 1D. We propose models to explain Ral function in exosome secretion, its conservation in animals, and its possible role in tumor progression.

RAL-1 controls multivesicular body biogenesis and exosome secretion

Exosomes are secreted vesicles arising from the fusion of multivesicular bodies (MVBs) with the plasma membrane. Despite their importance in various processes, the molecular mechanisms controlling their formation and release remain unclear. Using nematodes and mammary tumor cells, we show that Ral GTPases are involved in exosome biogenesis. In Caenorhabditis elegans, RAL-1 localizes at the surface of secretory MVBs. A quantitative electron microscopy analysis of RAL-1-deficient animals revealed that RAL-1 is involved in both MVB formation and their fusion with the plasma membrane. These functions do not involve the exocyst complex, a common Ral guanosine triphosphatase (GTPase) effector. Furthermore, we show that the target membrane SNARE protein SYX-5 colocalizes with a constitutively active form of RAL-1 at the plasma membrane, and MVBs accumulate under the plasma membrane when SYX-5 is absent. In mammals, RalA and RalB are both required for the secretion of exosome-like vesicles in cultured cells. Therefore, Ral GTPases represent new regulators of MVB formation and exosome release.

Non-centrosomal epidermal microtubules act in parallel to LET-502/ROCK to promote C. elegans elongation

C. elegans embryonic elongation is a morphogenetic event driven by actomyosin contractility and muscle-induced tension transmitted through hemidesmosomes. A role for the microtubule cytoskeleton has also been proposed, but its contribution remains poorly characterized. Here, we investigate the organization of the non-centrosomal microtubule arrays present in the epidermis and assess their function in elongation. We show that the microtubule regulators γ-tubulin and NOCA-1 are recruited to hemidesmosomes and adherens junctions early in elongation. Several parallel approaches suggest that microtubule nucleation occurs from these sites. Disrupting the epidermal microtubule array by overexpressing the microtubule-severing protein Spastin or by inhibiting the C. elegans ninein homolog NOCA-1 in the epidermis mildly affected elongation. However, microtubules were essential for elongation when hemidesmosomes or the activity of the Rho kinase LET-502/ROCK were partially compromised. Imaging of junctional components and genetic analyses suggest that epidermal microtubules function together with Rho kinase to promote the transport of E-cadherin to adherens junctions and myotactin to hemidesmosomes. Our results indicate that the role of LET-502 in junctional remodeling is likely to be independent of its established function as a myosin II activator, but requires a microtubule-dependent pathway involving the syntaxin SYX-5. Hence, we propose that non-centrosomal microtubules organized by epidermal junctions contribute to elongation by transporting junction remodeling factors, rather than having a mechanical role.

Summary: During C. elegans embryonic elongation, microtubules nucleate at adjerens junctions and hemidesmosomes, and are important for the transport of junctional proteins.

Making sense of glycosphingolipids in epithelial polarity

A potential role for glycosphingolipids and lipid rafts in apical sorting was initially met with enthusiasm, but genetic analysis has since provided little support for it. A report now establishes that glycosphingolipids mediate apical sorting, and specifically help maintain apicobasal polarity in Caenorhabditis elegans.

Understanding the role of asymmetric cell division in cancer using C. elegans

Asymmetric cell division is an important process to generate cell diversity and maintain tissue homeostasis. Recent evidence suggests that this process may also be crucial to prevent tumor formation. In the past 30 years, the embryo of the nematode Caenorhabditis elegans has proven to be a very powerful model to study the molecular and cellular basis of asymmetric cell division. Understanding this process in Caenorhabditis elegans may thus lead to a better understanding of stem cell function and tumorigenesis in humans.

[Mechanisms of asymmetric cell division: from model organisms to tumorigenesis]

Asymmetric cell division is the process by which a single cell gives rise to two different daughter cells. This process is important to generate cell diversity during the development of multicellular organisms, as well as for stem cell self-renewal in adults. Current knowledge on so-called cancer stem cells suggests that a loss of asymmetry during their division could lead to overproliferation and favour tumorigenesis, highlighting the importance of deciphering the mechanisms governing asymmetric cell division. Two mechanisms can lead to an asymmetric cell division: asymmetry can either be governed by proximity to a given cellular environment (or niche), in which case the mechanism is referred to as extrinsic, or the mother cell polarizes itself without external intervention, in which case the mechanism is referred to as intrinsic. In the last 20 years, our understanding of intrinsic mechanisms leading to asymmetric cell division has progressed, largely after studies carried out in model organisms such as the nematode Caenorhabditis elegans and the fruit fly Drosophila melanogaster. These models allowed the identification of molecular complexes used by nearly all the cells that divide asymmetrically, including human cells. Here we review the main intrinsic mechanisms of asymmetric cell division as described in model organisms and discuss their relevance towards mammalian tumorigenesis.

Differential requirements for STRAD in LKB1-dependent functions in C. elegans

The protein kinase LKB1 is a crucial regulator of cell growth/proliferation and cell polarity and is the causative gene in the cancer-predisposing disease Peutz-Jeghers syndrome (PJS). The activity of LKB1 is greatly enhanced following its association with the Ste20-like adapter protein STRAD. Unlike LKB1 however, mutations in STRAD have not been identified in PJS patients and thus, the key tumour suppressive role(s) of LKB1 might be STRAD independent. Here, we report that Caenorhabditis elegans strd-1/STRAD mutants recapitulate many phenotypes typical of par-4/LKB1 loss of function, showing defects during early embryonic and dauer development. Interestingly, although the growth/proliferation defects in severe par-4 and strd-1 mutant dauers are comparable, strd-1 mutant embryos do not share the polarity defects of par-4 embryos. We demonstrate that most of par-4-dependent regulation of germline stem cell (GSC) quiescence occurs through AMPK, whereby PAR-4 requires STRD-1 to phosphorylate and activate AMPK. Consistent with this, even though AMPK plays a major role in the regulation of cell proliferation, like strd-1 it does not affect embryonic polarity. Instead, we found that the PAR-4-mediated phosphorylation of polarity regulators such as PAR-1 and MEX-5 in the early embryo occurs in the absence of STRD-1. Thus, PAR-4 requires STRD-1 to phosphorylate AMPK to regulate cell growth/proliferation under reduced insulin signalling conditions, whereas PAR-4 can promote phosphorylation of key proteins, including PAR-1 and MEX-5, to specify early embryonic polarity independently of STRD-1. Our results therefore identify a key strd-1/STRAD-independent function of par-4/LKB1 in polarity establishment that is likely to be important for tumour suppression in humans.

C. elegans Brat homologs regulate PAR protein-dependent polarity and asymmetric cell division

The evolutionary conserved PAR proteins control polarization and asymmetric division in many organisms. Recent work in Caenorhabditis elegans demonstrated that nos-3 and fbf-1/2 can suppress par-2(it5ts) lethality, suggesting that they participate in cell polarity by regulating the function of the anterior PAR-3/PAR-6/PKC-3 proteins. In Drosophila embryos, Nanos and Pumilio are homologous to NOS-3 and FBF-1/2 respectively and control cell polarity by forming a complex with the tumor suppressor Brat to inhibit Hunchback mRNA translation. In this study, we investigated the possibility that Brat could control cell polarity and asymmetric cell division in C. elegans. We found that disrupting four of the five C. elegans Brat homologs (Cebrats) individually results in suppression of par-2(it5ts) lethality, indicating that these genes are involved in embryonic polarity. Two of the Cebrats, ncl-1 and nhl-2, partially restore the localization of PAR proteins at the cortex. While mutations in the four Cebrat genes do not severely impair polarity, they display polarity-associated defects. Surprisingly, these defects are absent from nos-3 mutants. Similarly, while nos-3 controls PAR-6 protein levels, this is not the case for any of the Cebrats. Our results, together with results from Drosophila, indicate that Brat family members function in generating cellular asymmetries and suggest that, in contrast to Drosophila embryos, the C. elegans homologs of Brat and Nanos could participate in embryonic polarity via distinct mechanisms.

Vezatin, a ubiquitous protein of adherens cell-cell junctions, is exclusively expressed in germ cells in mouse testis

In the male reproductive organs of mammals, the formation of spermatozoa takes place during two successive phases: differentiation (in the testis) and maturation (in the epididymis). The first phase, spermiogenesis, relies on a unique adherens junction, the apical ectoplasmic specialization linking the epithelial Sertoli cells to immature differentiating spermatids. Vezatin is a transmembrane protein associated with adherens junctions and the actin cytoskeleton in most epithelial cells. We report here the expression profile of vezatin during spermatogenesis. Vezatin is exclusively expressed in haploid germ cells. Immunocytochemical and ultrastructural analyses showed that vezatin intimately coincides, temporally and spatially, with acrosome formation. While vezatin is a transmembrane protein associated with adherens junctions in many epithelial cells, it is not seen at the ectoplasmic specializations, neither at the basal nor at the apical sites, in the seminiferous epithelium. In particular, vezatin does not colocalize with espin and myosin VIIa, two molecular markers of the ectoplasmic specialization. In differentiating spermatids, ultrastructural data indicate that vezatin localizes in the acrosome. In epididymal sperm, vezatin localizes also to the outer acrosomal membrane. Considering its developmental and molecular characteristics, vezatin may be involved in the assembly/stability of this spermatic membrane.

Conditional knock-out reveals that zygotic vezatin-null mouse embryos die at implantation

Vezatin, a protein associated to adherens junctions in epithelial cells, is already expressed in mouse oocytes and during pre-implantation development. Using a floxed strategy to generate a vezatin-null allele, we show that the lack of zygotic vezatin is embryonic lethal, indicating that vezatin is an essential gene. Homozygous null embryos are able to elicit a decidual response but as early as day 6.0 post-coitum mutant implantation sites are devoid of embryonic structures. Mutant blastocysts are morphologically normal, but only half of them are able to hatch upon in vitro culture and the blastocyst outgrowths formed after 3.5 days in culture exhibit severe abnormalities, in particular disrupted intercellular adhesion and clear signs of cellular degeneration. Notably, the junctional proteins E-cadherin and beta-catenin are delocalized and not observed at the plasma membrane anymore. These in vitro observations reinforce the idea that homozygous vezatin-null mutants die at the time of implantation because of a defect in intercellular adhesion. Together these results indicate that the absence of zygotic vezatin is deleterious for the implantation process, most likely because cadherin-dependent intercellular adhesion is impaired in late blastocysts when the maternal vezatin is lost.

Vezatin, a protein associated to adherens junctions, is required for mouse blastocyst morphogenesis

Cell-cell interactions play a major role during preimplantation development of the mouse embryo. The formation of adherens junctions is a major feature of compaction, the first morphogenetic event that takes place at the 8-cell stage. Then, during the following two cell cycles, tight junctions form, and the outer layer of cells differentiate into a functional epithelium, leading to the formation of the blastocoel cavity. Until now, E-cadherin was the only transmembrane molecule localized in adherens junctions and required for early development. Vezatin is a transmembrane protein of adherens junctions, interacting with the E-cadherin-catenins complex. Here, we show that vezatin is expressed very early during mouse preimplantation development. It co-localizes with E-cadherin throughout development, being found all around the cell cortex before compaction and basolaterally in adherens junctions thereafter. In addition, vezatin is also detected in nuclei during most of the cell cycle. Finally, using a morpholino-oligonucleotide approach to inhibit vezatin function during preimplantation development, we observed that inhibition of vezatin synthesis leads to a cell cycle arrest with limited cell-cell interactions. This phenotype can be rescued when mRNAs coding for vezatin missing the 5'UTR are co-injected with the anti-vezatin morpholino-oligonucleotide. Cells derived from blastomeres injected with morpholino-oligonucleotide had a reduced amount of vezatin concomitantly with a decrease in the quantity of E-cadherin and beta-catenin localized in the areas of intercellular contact. Shift in E-cadherin cortical distribution was correlated with a strong decrease in E-cadherin mRNA and protein contents. Altogether, these observations demonstrate that vezatin is required for morphogenesis of the preimplantation mouse embryo.