Imaging the Cytoskeleton of Migratory Cells
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Cell migration is a complex and important process by which cells move along a surface or within a three-dimensional matrix. The mechanics of motility involve cytoskeletal rearrangement, membrane dynamics, and cell-substrate interactions. This investigation focuses on the morphologies, internal structures, and in vitro behavior of five migratory cell types using an array of microscopic techniques. Killifish keratocytes, HeLa cells, mouse bone-derived stem cells, mouse fibroblasts, and MDCK cells represent a diverse sampling of vertebrates and tissue sources; these cells were studied with brightfield, phase/contrast, fluorescence, and both scanning and transmission electron microscopy. Keratocytes were plated on glass coverslips for phase/contrast time-lapse microscopy in order to create movies of migration. These cells, as well as HeLa cells, were also fixed with formaldehyde, extracted, and stained with a fluorophore that binds to actin in order to view the actin cytoskeleton. Keratocytes, HeLa cells, stem cells, and mouse fibroblasts were plated and fixed for scanning electron microscopy in order to examine external morphology and surface details. In one of these SEM experiments, the HeLa cells were extracted with detergent prior to fixation to remove the plasma membrane. Flat-embedded, thin-sectioned MDCK cells were imaged under transmission electron microscopy to reveal internal details at high magnifications. The resulting images show both continuities and variability between the different cell types in this study. The results also highlight the importance of cellular imaging; both the process and the findings are applicable to cell motility research of all kinds, from in vitro studies to in vivo medical experiments. Ultimately, viewing the cytoskeleton and the larger structures it shapes helps elicit a conceptual understanding of cell migration.