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Key Points The organization of neuronal circuits involves a number of processes that require cell–cell recognition and contacts. Cadherins are a family of cell–cell adhesion molecules comprising more than 100 members in vertebrates, which are grouped into subfamilies including classic cadherins, Flamingo/CELSRs and protocadherins, and are thought to have roles in various steps of neuronal cell interactions. N-cadherin and other vertebrate classic cadherins are essential not only for early morphogenesis of neural tissues but also for correct axon migration towards target areas, and for the extension of neuronal dendrites. Drosophila melanogaster N-cadherin ( D N-cadherin) has been shown to be crucial for the formation of axonal connections with target neurons in both the visual and olfactory systems, and also for confining dendritic arborizations to specific glomeruli in these systems. The activity of D N-cadherin during the axon targeting seems to be controlled by cytoplasmic proteins including leukocyte antigen-related-receptor protein tyrosine phosphatase (LAR). Flamingo, a seven-pass transmembrane cadherin, is required for the correct targeting of retinal axons in visual circuits in D. melanogaster . A vertebrate homologue of Flamingo, CELSR2, regulates dendritic arbor patterning in the cerebellum, and another homologue, CELSR3, is important for axon tract formation. Some protocadherins, which show a large diversification due to a unique gene organization, seem to be involved in synapse formation and neuronal survival. However, the biological roles of this subfamily remain largely unknown. In conclusion, members of the cadherin superfamily control axon–target recognition and connections, as well as other types of neuronal interactions in a subfamily-specific manner. The cadherin superfamily has roles in the development and organization of complex neuronal circuits. Takeichi explores the evidence from invertebrate and vertebrate studies for the involvement in these processes of different cadherin subfamilies, including classic cadherins, Flamingo/CELSRs and the protocadherins. Neural development and the organization of complex neuronal circuits involve a number of processes that require cell–cell interaction. During these processes, axons choose specific partners for synapse formation and dendrites elaborate arborizations by interacting with other dendrites. The cadherin superfamily is a group of cell surface receptors that is comprised of more than 100 members. The molecular structures and diversity within this family suggest that these molecules regulate the contacts or signalling between neurons in a variety of ways. In this review I discuss the roles of three subfamilies — classic cadherins, Flamingo/CELSRs and protocadherins — in the regulation of neuronal recognition and connectivity.

Epithelial–mesenchymal transition (EMT) encompasses dynamic changes in cellular organization from epithelial to mesenchymal phenotypes, which leads to functional changes in cell migration and invasion. EMT occurs in a diverse range of physiological and pathological conditions and is driven by a conserved set of inducing signals, transcriptional regulators and downstream effectors. With over 5,700 publications indexed by Web of Science in 2019 alone, research on EMT is expanding rapidly. This growing interest warrants the need for a consensus among researchers when referring to and undertaking research on EMT. This Consensus Statement, mediated by ‘the EMT International Association’ (TEMTIA), is the outcome of a 2-year-long discussion among EMT researchers and aims to both clarify the nomenclature and provide definitions and guidelines for EMT research in future publications. We trust that these guidelines will help to reduce misunderstanding and misinterpretation of research data generated in various experimental models and to promote cross-disciplinary collaboration to identify and address key open questions in this research field. While recognizing the importance of maintaining diversity in experimental approaches and conceptual frameworks, we emphasize that lasting contributions of EMT research to increasing our understanding of developmental processes and combatting cancer and other diseases depend on the adoption of a unified terminology to describe EMT.In this Consensus Statement, the authors (on behalf of the EMT International Association) propose guidelines to define epithelial–mesenchymal transition, its phenotypic plasticity and the associated multiple intermediate epithelial–mesenchymal cell states. Clarification of nomenclature and definitions will help reduce misinterpretation of research data generated in different experimental model systems and promote cross-disciplinary collaboration.

The cadherin-catenin complex is the major machinery for cell-cell adhesion in many animal species. This complex in general associates with actin fibers at its cytoplasmic side, organizing the adherens junction (AJ). In epithelial cells, the AJ encircles the cells near their apical surface and forms the \"zonula adherens\" or \"adhesion belt.\" The mechanism as to how the cadherin-catenin complex and F-actin cooperate to generate these junctional structures, however, remains unknown. Here, we show that EPLIN (epithelial protein lost in neoplasm; also known as Lima-1), an actin-binding protein, couples with α-catenin and, in turn, links the cadherin-catenin complex to F-actin. Without EPLIN, this linkage was unable to form. When EPLIN had been depleted in epithelial cells, the adhesion belt was disorganized and converted into zipper-like junctions in which actin fibers were radially arranged. However, nonjunctional actin fibers were not particularly affected by EPLIN depletion. As EPLIN is known to have the ability to suppress actin depolymerization, our results suggest that EPLIN functions to link the cadherin-catenin complex to F-actin and simultaneously stabilizes this population of actin fibers, resulting in the establishment of the adhesion belt.

Key Points Epithelial morphogenesis is regulated by the modulation of intercellular junctions, which are known as adherens junctions (AJs). AJs comprise cadherin receptors and associated proteins, including actomyosin filaments. The interactions between cadherins and actomyosin are mediated by α-catenin and vinculin (VCL) through complex mechanisms. The control of AJ-associated actomyosin by small GTPases is important for maintaining and remodelling the AJ. RHO-associated protein kinase (ROCK), an effector of RHO GTPases, induces the contraction of AJ-linked actomyosin networks, which leads to various forms of epithelial remodelling. AJs are also modulated by other mechanisms, including cadherin turnover, sliding of the junctions and transcriptional control of junction regulators. Epithelial cells display dynamic behaviours, such as rearrangement, movement and shape changes. Evidence suggests that the remodelling of cell junctions, especially adherens junctions (AJs), has major roles in controlling these behaviours. It is also clear that RHO GTPases and their effectors regulate actin polymerization and actomyosin contraction at AJs during epithelial reshaping. Epithelial cells display dynamic behaviours, such as rearrangement, movement and shape changes, particularly during embryonic development and in equivalent processes in adults. Accumulating evidence suggests that the remodelling of cell junctions, especially adherens junctions (AJs), has major roles in controlling these behaviours. AJs comprise cadherin adhesion receptors and cytoplasmic proteins that associate with them, including catenins and actin filaments, and exhibit various forms, such as linear or punctate. Remodelling of AJs induces epithelial reshaping in various ways, including by planar-polarized apical constriction that is driven by the contraction of AJ-associated actomyosin and that occurs during neural plate bending and germband extension. RHO GTPases and their effectors regulate actin polymerization and actomyosin contraction at AJs during the epithelial reshaping processes.

Major microtubules in epithelial cells are not anchored to the centrosome, in contrast to the centrosomal radiation of microtubules in other cell types. It remains to be discovered how these epithelial microtubules are generated and stabilized at noncentrosomal sites. Here, we found that Nezha [also known as calmodulin-regulated spectrin-associated protein 3 (CAMSAP3)] and its related protein, CAMSAP2, cooperate in organization of noncentrosomal microtubules. These two CAMSAP molecules coclustered at the minus ends of noncentrosomal microtubules and thereby stabilized them. Depletion of CAMSAPs caused a marked reduction of microtubules with polymerizing plus ends, concomitantly inducing the growth of microtubules from the centrosome. In CAMSAP-depleted cells, early endosomes and the Golgi apparatus exhibited irregular distributions. These effects of CAMSAP depletion were maximized when both CAMSAPs were removed. These findings suggest that CAMSAP2 and -3 work together to maintain noncentrosomal microtubules, suppressing the microtubule-organizing ability of the centrosome, and that the network of CAMSAP-anchored microtubules is important for proper organelle assembly.

Willin and Par3 synergistically recruit aPKC to cell junctions, thus promoting aPKC-mediated phosphorylation of ROCK. This event inhibits ROCK junctional localization and apical constriction to maintain epithelial cell morphology. Apical-domain constriction is important for regulating epithelial morphogenesis. Epithelial cells are connected by apical junctional complexes (AJCs) that are lined with circumferential actomyosin cables. The contractility of these cables is regulated by Rho-associated kinases (ROCKs). Here, we report that Willin (a FERM-domain protein) and Par3 (a polarity-regulating protein) cooperatively regulate ROCK-dependent apical constriction. We found that Willin recruits aPKC and Par6 to the AJCs, independently of Par3. Simultaneous depletion of Willin and Par3 completely removed aPKC and Par6 from the AJCs and induced apical constriction. Induced constriction was through upregulation of the level of AJC-associated ROCKs, which was due to loss of aPKC. Our results indicate that aPKC phosphorylates ROCK and suppresses its junctional localization, thereby allowing cells to retain normally shaped apical domains. Thus, we have uncovered a Willin/Par3–aPKC–ROCK pathway that controls epithelial apical morphology.

The molecular mechanisms that guide each neuron to become polarized, forming a single axon and multiple dendrites, remain unknown. Here we show that CAMSAP3 (calmodulin-regulated spectrin-associated protein 3), a protein that regulates the minusend dynamics of microtubules, plays a key role in maintaining neuronal polarity. In mouse hippocampal neurons, CAMSAP3 was enriched in axons. Although axonal microtubules were generally acetylated, CAMSAP3 was preferentially localized along a less-acetylated fraction of the microtubules. CAMSAP3-mutated neurons often exhibited supernumerary axons, along with an increased number of neurites having nocodazole-resistant/acetylated microtubules compared with wild-type neurons. Analysis using cell lines showed that CAMSAP3 depletion promoted tubulin acetylation, and conversely, mild overexpression of CAMSAP3 inhibited it, suggesting that CAMSAP3 works to retain nonacetylated microtubules. In contrast, CAMSAP2, a protein related to CAMSAP3, was detected along all neurites, and its loss did not affect neuronal polarity, nor did it cause increased tubulin acetylation. Depletion of α-tubulin acetyltransferase-1 (αTAT1), the key enzyme for tubulin acetylation, abolished CAMSAP3 loss-dependent multiple-axon formation. These observations suggest that CAMSAP3 sustains a nonacetylated pool of microtubules in axons, interfering with the action of αTAT1, and this process is important to maintain neuronal polarity.

Stable cell–cell adhesion is essential for maintaining tissue integrity, but cells are also able to relocate, implying the existence of mechanisms for coordinating cell adhesion and movement. Here, we show that, in some transformed lines, cadherin adhesion molecules exhibit a flow-like movement in a basal–apical direction at the cell junction and that this flow is associated with reorganizing actin filaments. Such flow also occurs in normal epithelial sheets, but solely at the junctions formed by moving cells. We propose that cadherin flow may provide a mechanism for facilitating the sliding of the two contacting cell membranes in morphogenetically active cell sheets.

Polarized epithelial cells exhibit a characteristic array of microtubules that are oriented along the apicobasal axis of the cells. The minus-ends of these microtubules face apically, and the plus-ends face toward the basal side. The mechanisms underlying this epithelialspecific microtubule assembly remain unresolved, however. Here, using mouse intestinal cells and human Caco-2 cells, we show that the microtubule minus-end binding protein CAMSAP3 (calmodulin-regulated–spectrin-associated protein 3) plays a pivotal role in orienting the apical-to-basal polarity of microtubules in epithelial cells. In these cells, CAMSAP3 accumulated at the apical cortices, and tethered the longitudinal microtubules to these sites. Camsap3 mutation or depletion resulted in a random orientation of these microtubules; concomitantly, the stereotypic positioning of the nucleus and Golgi apparatus was perturbed. In contrast, the integrity of the plasma membrane was hardly affected, although its structural stability was decreased. Further analysis revealed that the CC1 domain of CAMSAP3 is crucial for its apical localization, and that forced mislocalization of CAMSAP3 disturbs the epithelial architecture. These findings demonstrate that apically localized CAMSAP3 determines the proper orientation of microtubules, and in turn that of organelles, in mature mammalian epithelial cells.

The chirality of tissues and organs is essential for their proper function and development. Tissue-level chirality derives from the chirality of individual cells that comprise the tissue, and cellular chirality is considered to emerge through the organization of chiral molecules within the cell. However, the principle of how molecular chirality leads to cellular chirality remains unresolved. To address this fundamental question, we experimentally studied the chiral behaviors of isolated epithelial cells derived from a carcinoma line and developed a theoretical understanding of how their behaviors arise from molecular-level chirality. We first found that the nucleus undergoes clockwise rotation, accompanied by robust cytoplasmic circulation in the same direction. During the rotation, actin and Myosin IIA assemble into the stress fibers with a vortex-like chiral orientation at the ventral side of the cell periphery, concurrently forming a concentric pattern at the dorsal side. Further analysis revealed that the intracellular rotation is driven by the concentric actomyosin filaments located dorsally, not by the ventral vortex-like chiral stress fibers. To elucidate how these concentric actomyosin filaments induce chiral rotation, we analyzed a theoretical model developed based on the theory of active chiral fluid. This model demonstrated that the observed cell-scale unidirectional rotation is driven by the molecular-scale chirality of actomyosin filaments even in the absence of cell-scale chiral orientational order. Our study thus provides novel mechanistic insights into how the molecular chirality is organized into the cellular chirality, representing an important step toward understanding left–right symmetry breaking in tissues and organs.