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The cells of many embryonic tissues actively narrow in one dimension (convergence) and lengthen in the perpendicular dimension (extension). Convergence and extension are ubiquitous and important tissue movements in metazoan morphogenesis. In vertebrates, the dorsal axial and paraxial mesodermal tissues, the notochordal and somitic mesoderm, converge and(More)
We describe mesendoderm morphogenesis during gastrulation in the frog Xenopus laevis and investigate the mechanics of these movements with tissue explants. When a dorsal marginal zone explant is plated onto fibronectin, the mesendoderm moves away from the dorsal axial tissues as an intact sheet. Mesendodermal cells within these explants display monopolar(More)
Although it is rarely considered so in modern developmental biology, morphogenesis is fundamentally a biomechanical process, and this is especially true of one of the first major morphogenic transformations in development, gastrulation. Cells bring about changes in embryonic form by generating patterned forces and by differentiating the tissue mechanical(More)
We have characterized the cell movements and prospective cell identities as neural folds fuse during neural tube formation in Xenopus laevis. A newly developed whole-mount, two-color fluorescent RNA in situ hybridization method, visualized with confocal microscopy, shows that the dorsal neural tube gene xpax3 and the neural-crest-specific gene xslug are(More)
The forces that drive sea urchin primary invagination remain mysterious. To solve this mystery we have developed a set of finite element simulations that test five hypothesized mechanisms. Our models show that each of these mechanisms can generate an invagination; however, the mechanical properties of an epithelial sheet required for proper invagination are(More)
The noncanonical wnt/planar cell polarity (PCP) pathway [1] regulates the mediolaterally (planarly) polarized cell protrusive activity and intercalation that drives the convergent extension movements of vertebrate gastrulation [2], yet the underlying mechanism is unknown. We report that perturbing expression of Xenopus PCP genes, Strabismus (Xstbm),(More)
BACKGROUND Integrin recognition of fibronectin is required for normal gastrulation including the mediolateral cell intercalation behaviors that drive convergent extension and the elongation of the frog dorsal axis; however, the cellular and molecular mechanisms involved are unclear. RESULTS We report that depletion of fibronectin with antisense(More)
We have characterized excisional wounds in the animal cap of early embryos of the frog Xenopus laevis and found that these wounds close accompanied by three distinct processes: (1) the assembly of an actin purse-string in the epithelial cells at the wound margin, (2) contraction and ingression of exposed deep cells, and (3) protrusive activity of epithelial(More)
Computer simulations showed that the elastic modulus of the cell layer relative to the elastic modulus of the extracellular layers predicted the effectiveness of different force-generating mechanisms for sea urchin primary invagination [L. A. Davidson, M. A. R. Koehl, R. Keller, and G. F. Oster (1995) Development 121, 2005-2018]. Here, we measured the(More)
Cells with motile cilia cover the skin of Xenopus tadpoles in a characteristic spacing pattern. This pattern arises during early development when cells within the inner layer of ectoderm are selected out by Notch to form ciliated cell precursors (CCPs) that then radially intercalate into the outer epithelial cell layer to form ciliated cells. When Notch is(More)