Stress fibers are generated by two distinct actin assembly mechanisms in motile cells

Although stress fibers play an important role in the adhesion, migration and morphogenesis of eukaryotic cells, the mechanism by which these and other contractile actin structures are produced is unknown. By analyzing the stress fiber assembly pathway using live cell microscopy, we discovered that these structures are produced by two different mechanisms. The backstressed fiber attached to the substrate by the adhesive spot at one end is assembled by actin polymerization driven by formin (mDia 1 / DRF 1) at the adhesion spot. In contrast, lateral annealing of Arp 2/3 nucleating actin bundles on myosin bundles and sheets produces lateral arcs that are not directly fixed to the substrate. It is worth noting that the stress fibers on the dorsal side and the transverse arc can be converted to the ventral stress fibers fixed at the ends of adhesions. Based on these data, we propose a general model for constructing and maintaining the structure of intracellular contractile actin.

The structure of the stress fiber differs between mobile cells and non-motor cells. Stress fibers in motor and non-motor cells are similar since they all contain actin filaments cross-linked by α-actinin and myosin II, but the spatial orientation of individual actin filaments in stress fibers is not limited to sports and sports There is a difference. Stress fibers in the ventral region of the cell migration cell show the overall displacement of the orientation of the individual actin filaments along the longitudinal axis of the stress fiber so that the positive end of the filament always faces mainly to the focal point . Stress fibers in the ventral region of non-motor cells show periodic polarity similar to sarcomeric tissue

Mesenchymal cell migration is characterized by the polarization distribution of actin filaments with a network of short actin filaments at the leading edge and the actin filament polymer is placed behind the different types of actin at the leading edge. Stress Fibers Importantly, different actin filaments are characteristically associated with distinct adhesive structures and adhesion and actin filaments are coordinately regulated during cell migration. It has been known for a long time that these macromolecular structures are closely related in cells, but it is unknown how they are coordinated. The real-time image data shows that focal adhesion acts as a site for actin polymerization and leads to the production of bound actin bundles (stress fibers) of actin filaments.