Active intracellular mechanics - a key to cellular function and organization

Mechanobiology has demonstrated that precise control over mechanical properties at the whole-cell level is crucial for many biological functions. However, comparatively little attention has been paid to intracellular mechanical properties. Only recently have experimental tools become available to adequately measure the viscoelasticity and mechanical activity of the cytosol, revealing that the active, non-equilibrium nature of the intracellular environment must be carefully considered. To explore the interplay between active forces and viscoelastic properties, it is helpful to consider our current understanding of intracellular active mechanics. In this Review, we aim not only to provide an intuitive and quantitative introduction to the relevant physical concepts, but also to offer an overview of the proteins that establish intracellular active mechanics, highlighting their spatial and temporal variation with a particular focus on the role of mechanical activity, in the form of forces used for enhancing both directed and random transport. Although we are only beginning to uncover the importance of intracellular active mechanics for cellular mechanisms, it is becoming increasingly clear that these properties must be precisely regulated to ensure proper cellular function.