This cover image shows a typical vimentin intermediate filament (VIF) network in a mouse embryonic fibroblast (mEF). Intermediate filaments (IFs) are composed of one or more members of a family of related proteins encoded by ~70 different genes that share common features in their protein sequence and structure. With an average diameter of 10 nanometers intermediate filaments together with actin filaments and microtubules, are the major cytoskeletal component in the mammalian cells. IFs were first identified many years ago by electron microscopists , especially those studying the hair and wool keratins intermediate filaments. Currently more than 80 distinct human diseases are known to be associated with abnormalities in IF proteins. As can be seen in the image, IFs distribute throughout the cell extending from the perinuclear regions to the cell periphery. Their role as mechanical integrators of the cell has been speculated upon for years, however, a direct characterization has been lacking. In this current study, we measure the mechanical properties of wild type mEFs and VIF knockout mEFs, using optical tweezer active microrheology and magnetic tweezers. For this study we have collaborated with Saleemulla Mahammad and Robert Goldman from Northwestern University. We report that the cytoplasm of living cells behaves like a weak elastic gel instead of a viscous fluid. Furthermore, we find that VIF are crucial for cytoplasmic mechanics and dynamics; their presence doubles the stiffness of cytoplasm and stabilizes cellular organelle localization.
This cover image provides an overview of a typical extended and intricate network of vimentin intermediate filaments in cells. This image provides a great opportunity to convey the importance of intermediate filaments in various cellular functions including cell signaling, cellular mechanics and cell motility. Furthermore, a good picture is worth a 1000 words and we hope our colorful image will trigger curiosity about intermediate filaments and their role in various aspects of cell biology. In addition, we hope to attract more researchers to join the intermediate filament research field. We consider ourselves scientists, not artists. However, scientists usually share some things in common with artists: We have to be creative while investigating a phenomenon/function and we sometimes need intuition to guide our research. Naturally, we are always trying to create an appealing representation of our work and to express the message in a more effective, easily understandable way. More about our research work can be found on our lab websites of the Weitz lab at Harvard University and the Goldman lab at Northwestern University. This work was supported by funding from NIH (P01GM096971). The vimentin intermediate filament network is shown in green and the nucleus is blue.
— Written by Ming Guo, Harvard University