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Vimentin is a protein that has been linked to a large variety of pathophysiological conditions, including cataracts, Crohn’s disease, rheumatoid arthritis, HIV and cancer. Vimentin has also been shown to regulate a wide spectrum of basic cellular functions. In cells, vimentin assembles into a network of filaments that spans the cytoplasm. It can also be found in smaller, non-filamentous forms that can localise both within cells and within the extracellular microenvironment. The vimentin structure can be altered by subunit exchange, cleavage into different sizes, re-annealing, post-translational modifications and interacting proteins. Together with the observation that different domains of vimentin might have evolved under different selection pressures that defined distinct biological functions for different parts of the protein, the many diverse variants of vimentin might be the cause of its functional diversity. A number of review articles have focussed on the biology and medical aspects of intermediate filament proteins without particular commitment to vimentin, and other reviews have focussed on intermediate filaments in an in vitro context. In contrast, the present review focusses almost exclusively on vimentin, and covers both ex vivo and in vivo data from tissue culture and from living organisms, including a summary of the many phenotypes of vimentin knockout animals. Our aim is to provide a comprehensive overview of the current understanding of the many diverse aspects of vimentin, from biochemical, mechanical, cellular, systems biology and medical perspectives
The rapid development of advanced microscopy techniques over recent decades has significantly increased the quality of imaging and our understanding of subcellular structures, such as the organization of the filaments of the cytoskeleton using fluorescence and electron microscopy. However, these recent improvements in imaging techniques have not been matched by similar development of techniques for computational analysis of the images of filament networks that can now be obtained. Hence, for a wide range of applications, reliable computational analysis of such two-dimensional methods remains challenging. Here, we present a new algorithm for tracing of filament networks. This software can extract many important parameters from grayscale images of filament networks, including the mesh hole size, and filament length and connectivity (also known as Coordination Number). In addition, the method allows sub-networks to be distinguished in two-dimensional images using intensity thresholding. We show that the algorithm can be used to analyze images of cytoskeleton networks obtained using different advanced microscopy methods. We have thus developed a new improved method for computational analysis of two-dimensional images of filamentous networks that has wide applications for existing imaging techniques. The algorithm is available as open-source software.
Metastasizing tumor cells show increased expression of the intermediate filament (IF) protein vimentin, which has been used to diagnose invasive tumors for decades. Recent observations indicate that vimentin is not only a passive marker for carcinoma, but may also induce tumor cell invasion. To clarify how vimentin IFs control cell adhesions and migration, we analyzed the nanoscale (30–50 nm) spatial organization of vimentin IFs and cell-matrix adhesions in metastatic fibroblast cells, using three-color stimulated emission depletion (STED) microscopy. We also studied whether wild-type and phospho-deficient or -mimicking mutants of vimentin changed the size and lifetime of focal adhesions (FAs), cell shape, and cell migration, using live-cell total internal reflection imaging and confocal microscopy. We observed that vimentin exists in fragments of different lengths. Short fragments were mostly the size of a unit-length filament and were mainly localized close to small cell-matrix adhesions. Long vimentin filaments were found in the proximity of large FAs. Vimentin expression in these cells caused a reduction in FAs size and an elongated cell shape, but did not affect FA lifetime, or the speed or directionality of cell migration. Expression of a phospho-mimicking mutant (S71D) of vimentin increased the speed of cell migration. Taken together, our results suggest that in highly migratory, transformed mesenchymal cells, vimentin levels control the cell shape and FA size, but not cell migration, which instead is linked to the phosphorylation status of S71 vimentin. These observations are consistent with the possibility that not only levels, but also the assembly status of vimentin control cell migration.
