Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Vertebrates have a unique 3D body shape in which correct tissue and organ shape and alignment are essential for function. For example, vision requires the lens to be centred in the eye cup which must in turn be correctly positioned in the head(1). Tissue morphogenesis depends on force generation, force transmission through the tissue, and response of tissues and extracellular matrix to force(2,3). Although a century ago D'Arcy Thompson postulated that terrestrial animal body shapes are conditioned by gravity(4), there has been no animal model directly demonstrating how the aforementioned mechano-morphogenetic processes are coordinated to generate a body shape that withstands gravity. Here we report a unique medaka fish (Oryzias latipes) mutant, hirame (hir), which is sensitive to deformation by gravity. hir embryos display a markedly flattened body caused by mutation of YAP, a nuclear executor of Hippo signalling that regulates organ size. We show that actomyosin-mediated tissue tension is reduced in hir embryos, leading to tissue flattening and tissue misalignment, both of which contribute to body flattening. By analysing YAP function in 3D spheroids of human cells, we identify the Rho GTPase activating protein ARHGAP18 as an effector of YAP in controlling tissue tension. Together, these findings reveal a previously unrecognised function of YAP in regulating tissue shape and alignment required for proper 3D body shape. Understanding this morphogenetic function of YAP could facilitate the use of embryonic stem cells to generate complex organs requiring correct alignment of multiple tissues.

DOI： 10.1038/nature14215

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CELL PRESS  

3D amoeboid cell migration is central to many developmental and disease-related processes such as cancer metastasis. Here, we identify a unique prototypic amoeboid cell migration mode in early zebrafish embryos, termed stable-bleb migration. Stable-bleb cells display an invariant polarized balloon-like shape with exceptional migration speed and persistence. Progenitor cells can be reversibly transformed into stable-bleb cells irrespective of their primary fate and motile characteristics by increasing myosin II activity through biochemical or mechanical stimuli. Using a combination of theory and experiments, we show that, in stable-bleb cells, cortical contractility fluctuations trigger a stochastic switch into amoeboid motility, and a positive feedback between cortical flows and gradients in contractility maintains stable-bleb cell polarization. We further show that rearward cortical flows drive stable-bleb cell migration in various adhesive and non-adhesive environments, unraveling a highly versatile amoeboid migration phenotype.

DOI： 10.1016/j.cell.2015.01.008

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Language：English   Publisher：WILEY-BLACKWELL  

In the last several decades, developmental biology has clarified the molecular mechanisms of embryogenesis and organogenesis. In particular, it has demonstrated that the tool-kit genes essential for regulating developmental processes are not only highly conserved among species, but are also used as systems at various times and places in an organism to control distinct developmental events. Therefore, mutations in many of these tool-kit genes may cause congenital diseases involving morphological abnormalities. This link between genes and abnormal morphological phenotypes underscores the importance of understanding how cells behave and contribute to morphogenesis as a result of gene function. Recent improvements in live imaging and in quantitative analyses of cellular dynamics will advance our understanding of the cellular pathogenesis of congenital diseases associated with aberrant morphologies. In these studies, it is critical to select an appropriate model organism for the particular phenomenon of interest.

DOI： 10.1111/cga.12039

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Language：English   Publisher：WILEY-BLACKWELL  

The stable transgenesis of genes encoding functional or spatially localized proteins, fused to fluorescent proteins such as green fluorescent protein (GFP) or red fluorescent protein (RFP), is an extremely important research tool in cell and developmental biology. Transgenic organisms constructed with fluorescent labels for cell membranes, subcellular organelles, and functional proteins have been used to investigate cell cycles, lineages, shapes, and polarity, in live animals and in cells or tissues derived from these animals. Genes of interest have been integrated and maintained in generations of transgenic animals, which have become a valuable resource for the cell and developmental biology communities. Although the use of Xenopus laevis as a transgenic model organism has been hampered by its relatively long reproduction time (compared to Drosophila melanogaster and Caenorhabditis elegans), its large embryonic cells and the ease of manipulation in early embryos have made it a historically valuable preparation that continues to have tremendous research potential. Here, we report on the Xenopus laevis transgenic lines our lab has generated and discuss their potential use in biological imaging.

DOI： 10.1111/dgd.12042

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Language：English   Publisher：CELL PRESS  

DOI： 10.1016/j.devcel.2013.03.007

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：COMPANY OF BIOLOGISTS LTD  

In developing vertebrates, the neural tube forms from a sheet of neural ectoderm by complex cell movements and morphogenesis. Convergent extension movements and the apical constriction along with apical-basal elongation of cells in the neural ectoderm are thought to be essential for the neural tube closure (NTC) process. In addition, it is known that non-neural ectoderm also plays a crucial role in this process, as the neural tube fails to close in the absence of this tissue in chick and axolotl. However, the cellular and molecular mechanisms by which it functions in NTC are as yet unclear. We demonstrate here that the non-neural superficial epithelium moves in the direction of tensile forces applied along the dorsal-ventral axis during NTC. We found that this force is partly attributable to the deep layer of non-neural ectoderm cells, which moved collectively towards the dorsal midline along with the superficial layer. Moreover, inhibition of this movement by deleting integrin. 1 function resulted in incomplete NTC. Furthermore, we demonstrated that other proposed mechanisms, such as oriented cell division, cell rearrangement and cell-shape changes have no or only minor roles in the non-neural movement. This study is the first to demonstrate dorsally oriented deep-cell migration in non-neural ectoderm, and suggests that a global reorganization of embryo tissues is involved in NTC.

DOI： 10.1242/dev.073239

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Language：English   Publisher：WILEY-BLACKWELL  

During early development of the central nervous system, the neuroepithelial cells undergo dynamic changes in shape, cumulative action of which cause the neural plate to bend mediolaterally to form the neural tube. The apicobasal elongation changes the cuboidal cells into columnar ones, whereas apical constriction minimizes the cell apices, causing them to adopt wedge-like shapes. To achieve the morphological changes required for the formation of a hollow structure, these cellular changes must be controlled in time and space. To date, it is widely accepted that spatial and temporal changes of the cytoskeletal organization are fundamental to epithelial cell shape changes, and that noncetrosomal microtubules assembled along apicobasal axis and actin filaments and non-muscle myosin II at the apical side are central machineries of cell elongation and apical constriction, respectively. Hence, especially in the last decade, intracellular mechanisms regulating these cytoskeletons have been extensively investigated at the molecular level. As a result, several actin-binding proteins, Rho/ROCK pathway, and cellcell adhesion molecules have been proven to be the central regulators of apical constriction, while the regulatory mechanisms of cell elongation remain obscure. In this review, we first describe the distribution and role of cytoskeleton in cell shape changes during neural tube closure, and then summarize the current knowledge about the intracellular proteins that directly modulate the cytoskeletal organization and thus the neural tube closure.

DOI： 10.1111/j.1440-169X.2012.01346.x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：COMPANY OF BIOLOGISTS LTD  

Neural tube formation is one of the most dynamic morphogenetic processes of vertebrate development. However, the molecules regulating its initiation are mostly unknown. Here, we demonstrated that nectin-2, an immunoglobulin-like cell adhesion molecule, is involved in the neurulation of Xenopus embryos in cooperation with N-cadherin. First, we found that, at the beginning of neurulation, nectin-2 was strongly expressed in the superficial cells of neuroepithelium. The knockdown of nectin-2 impaired neural fold formation by attenuating F-actin accumulation and apical constriction, a cell-shape change that is required for neural tube folding. Conversely, the overexpression of nectin-2 in non-neural ectoderm induced ectopic apical constrictions with accumulated F-actin. However, experiments with domain-deleted nectin-2 revealed that the intracellular afadin-binding motif, which links nectin-2 and F-actin, was not required for the generation of the ectopic apical constriction. Furthermore, we found that nectin-2 physically interacts with N-cadherin through extracellular domains, and they cooperatively enhanced apical constriction by driving the accumulation of F-actin at the apical cell surface. Interestingly, the accumulation of N-cadherin at the apical surface of neuroepithelium was dependent on the presence of nectin-2, but that of nectin-2 was not affected by depletion of N-cadherin. We propose a novel mechanism of neural tube morphogenesis regulated by the two types of cell adhesion molecules.

DOI： 10.1242/dev.043190

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