TY - JOUR T1 - Quantitative 4D analyses of epithelial folding during Drosophila gastrulation. JF - Development Y1 - 2014 A1 - Khan, Zia A1 - Wang, Yu-Chiun A1 - Wieschaus, Eric F A1 - Kaschube, Matthias KW - Animals KW - Body Patterning KW - Cell Shape KW - Cell Tracking KW - Drosophila melanogaster KW - Epithelial Cells KW - Epithelium KW - Gastrulation KW - Image Processing, Computer-Assisted KW - software AB -

Understanding the cellular and mechanical processes that underlie the shape changes of individual cells and their collective behaviors in a tissue during dynamic and complex morphogenetic events is currently one of the major frontiers in developmental biology. The advent of high-speed time-lapse microscopy and its use in monitoring the cellular events in fluorescently labeled developing organisms demonstrate tremendous promise in establishing detailed descriptions of these events and could potentially provide a foundation for subsequent hypothesis-driven research strategies. However, obtaining quantitative measurements of dynamic shapes and behaviors of cells and tissues in a rapidly developing metazoan embryo using time-lapse 3D microscopy remains technically challenging, with the main hurdle being the shortage of robust imaging processing and analysis tools. We have developed EDGE4D, a software tool for segmenting and tracking membrane-labeled cells using multi-photon microscopy data. Our results demonstrate that EDGE4D enables quantification of the dynamics of cell shape changes, cell interfaces and neighbor relations at single-cell resolution during a complex epithelial folding event in the early Drosophila embryo. We expect this tool to be broadly useful for the analysis of epithelial cell geometries and movements in a wide variety of developmental contexts.

VL - 141 CP - 14 M3 - 10.1242/dev.107730 ER - TY - JOUR T1 - Distinct Rap1 activity states control the extent of epithelial invagination via α-catenin. JF - Dev Cell Y1 - 2013 A1 - Wang, Yu-Chiun A1 - Khan, Zia A1 - Wieschaus, Eric F KW - Actins KW - alpha Catenin KW - Animals KW - Cell Adhesion KW - Cell Adhesion Molecules KW - Cell Membrane KW - Cell Shape KW - Drosophila KW - Drosophila Proteins KW - Embryo, Nonmammalian KW - Enzyme Activation KW - Epithelial Cells KW - Genes, Insect KW - Green Fluorescent Proteins KW - GTP Phosphohydrolases KW - GTPase-Activating Proteins KW - Intercellular Junctions KW - RNA Interference KW - Time factors KW - Time-Lapse Imaging AB -

Localized cell shape change initiates epithelial folding, while neighboring cell invagination determines the final depth of an epithelial fold. The mechanism that controls the extent of invagination remains unknown. During Drosophila gastrulation, a higher number of cells undergo invagination to form the deep posterior dorsal fold, whereas far fewer cells become incorporated into the initially very similar anterior dorsal fold. We find that a decrease in α-catenin activity causes the anterior fold to invaginate as extensively as the posterior fold. In contrast, constitutive activation of the small GTPase Rap1 restricts invagination of both dorsal folds in an α-catenin-dependent manner. Rap1 activity appears spatially modulated by Rapgap1, whose expression levels are high in the cells that flank the posterior fold but low in the anterior fold. We propose a model whereby distinct activity states of Rap1 modulate α-catenin-dependent coupling between junctions and actin to control the extent of epithelial invagination.

VL - 25 CP - 3 M3 - 10.1016/j.devcel.2013.04.002 ER - TY - JOUR T1 - Differential positioning of adherens junctions is associated with initiation of epithelial folding. JF - Nature Y1 - 2012 A1 - Wang, Yu-Chiun A1 - Khan, Zia A1 - Kaschube, Matthias A1 - Wieschaus, Eric F KW - Adherens Junctions KW - Animals KW - Cell Polarity KW - Cell Shape KW - Choristoma KW - Drosophila melanogaster KW - Drosophila Proteins KW - Epithelial Cells KW - Epithelium KW - Gastrula KW - Gastrulation KW - Glycogen Synthase Kinase 3 KW - Intracellular Signaling Peptides and Proteins KW - Protein-Serine-Threonine Kinases AB -

During tissue morphogenesis, simple epithelial sheets undergo folding to form complex structures. The prevailing model underlying epithelial folding involves cell shape changes driven by myosin-dependent apical constriction. Here we describe an alternative mechanism that requires differential positioning of adherens junctions controlled by modulation of epithelial apical-basal polarity. Using live embryo imaging, we show that before the initiation of dorsal transverse folds during Drosophila gastrulation, adherens junctions shift basally in the initiating cells, but maintain their original subapical positioning in the neighbouring cells. Junctional positioning in the dorsal epithelium depends on the polarity proteins Bazooka and Par-1. In particular, the basal shift that occurs in the initiating cells is associated with a progressive decrease in Par-1 levels. We show that uniform reduction of the activity of Bazooka or Par-1 results in uniform apical or lateral positioning of junctions and in each case dorsal fold initiation is abolished. In addition, an increase in the Bazooka/Par-1 ratio causes formation of ectopic dorsal folds. The basal shift of junctions not only alters the apical shape of the initiating cells, but also forces the lateral membrane of the adjacent cells to bend towards the initiating cells, thereby facilitating tissue deformation. Our data thus establish a direct link between modification of epithelial polarity and initiation of epithelial folding.

VL - 484 CP - 7394 M3 - 10.1038/nature10938 ER -