Abstract
Epithelial morphogenesis generates the shape of tissues, organs and embryos and is fundamental for their proper function. It is a dynamic process that occurs at multiple spatial scales from macromolecular dynamics, to cell deformations, mitosis and apoptosis, to coordinated cell rearrangements that lead to global changes of tissue shape. Using time lapse imaging, it is possible to observe these events at a system level. However, to investigate morphogenetic events it is necessary to develop computational tools to extract quantitative information from the time lapse data. Toward this goal, we developed an image-based computational pipeline to preprocess, segment and track epithelial cells in 4D confocal microscopy data. The computational pipeline we developed, for the first time, detects the adherens junctions of epithelial cells in 3D, without the need to first detect cell nuclei. We accentuate and detect cell outlines in a series of steps, symbolically describe the cells and their connectivity, and employ this information to track the cells. We validated the performance of the pipeline for its ability to detect vertices and cell-cell contacts, track cells, and identify mitosis and apoptosis in surface epithelia of Drosophila imaginal discs. We demonstrate the utility of the pipeline to extract key quantitative features of cell behavior with which to elucidate the dynamics and biomechanical control of epithelial tissue morphogenesis. We have made our methods and data available as an open-source multiplatform software tool called TTT (http://github.com/morganrcu/TTT)
Highlights
Epithelial cells form cohesive sheets of cells that play diverse structural and functional roles in multicellular organisms such as the covering of internal and external surfaces, compartmentalization of the body into discrete organs, and the regulation of surface and trans-epithelial transport
Epithelial tissues are remodeled by mechanical forces applied at the Adherens Junctions (AJs)
The AJs form a belt-like structure below the apical surface that functions to both mechanically
Summary
Epithelial cells form cohesive sheets of cells that play diverse structural and functional roles in multicellular organisms such as the covering of internal and external surfaces, compartmentalization of the body into discrete organs, and the regulation of surface and trans-epithelial transport. A range of cellular behaviors drives these epithelial tissue shape changes, including cell shape change, rearrangements of cell-cell contacts, migration, proliferation, and programmed cell death. These behaviors, in turn, depend on intracellular molecular dynamics that allow cells to generate and transmit mechanical forces to one another, while maintaining epithelial cohesion [1, 2]. This dual requirement is fulfilled by the adherens junction (AJ), a specialized protein complex that links epithelial cells together. The intracellular domain of E-cad associates with the force-generating actomyosin cytoskeleton and functions as a site for the transmission of mechanical forces that can remodel cell-cell contacts and cell shape by influencing the dynamics of the AJs themselves [3]
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