Gong, Reynolds et al. use cryo-electron microscopy and cryo-electron tomography to uncover how the actin cross-linking factor fascin uses structural flexibility to assemble helical actin filaments into symmetry-mismatched hexagonal bundles.

The actin cytoskeleton is crucial for cell and organelle motility. Here, the authors show that actin acts upstream of the mitochondrial fusion machinery to bridge two fusing mitochondria.

Stabilization of a branch structure would intuitively suggest a direct connection between trunk and bough, but in actin filament networks, cortactin clamps the branching Arp2/3 complex to the daughter filament. This has fundamental consequences for mechanistic understanding of actin branch turnover and cortactin biology.

Despite the constant renewal of their components, cellular actin networks maintain their overall appearance, through a subtle balance of filament assembly and disassembly. This balance is key to the remodelling of cellular architecture. We discuss the significance of in vitro reconstitutions in deciphering the complexity of actin regulation.

The intestinal epithelium serves as a barrier that facilitates interaction between intrinsic and environmental factors. Aging is accompanied by the gradual deterioration of this barrier. We postulate that barrier dysfunction results from defects in epithelial membrane trafficking that exacerbate age-related metabolic imbalances. Herein, we integrate barrier integrity, protein homeostasis, membrane trafficking and intracellular lipid sensing into an age-determining mechanism.

Moore et al. show the role of actin assemblies in regulating the balanced distribution of a healthy mitochondrial network between daughter cells in mitosis.

Stress fibres form a fully integrated meshwork with the submembranous contractile actin cortex that generates and propagates traction forces across the entire cell.

Cancer cells have now been shown to lack rigidity-sensing due to alteration in cytoskeletal sensor proteins, but can be reversed from a transformed to a rigidity-dependent growth state by the sensor proteins, resulting in restoration of contractility and adhesion.