Graded actin filament polarity is the organization of oriented actomyosin II filament bundles required for fibroblast polarization.

摘要

Actomyosin II filament assemblies in cells are required for shaping the cell body and forming the cell rear during morphological polarization and triggering of migration. However, precise steps in myosin II-based mechanisms are unknown in this event; one reason is due to lack of information on the organization of the actin filament substrate for myosin II. Whilst muscle sarcomeric-like contraction drives cell tension in stationary nonmuscle cells, alternative nonsarcomeric modes of myosin II force-generation power forwards movement of the cell body in already migrating cells. Which one contributes to initial cell shape change has not previously been experimentally sought in any polarizing cell. Sarcomeric and nonsarcomeric-based force require completely different types of organization and filament polarity in the actin substrate for myosin II, and these can only currently be distinguished by labour-intensive submicron analysis and electron microscopy. For the first time in any polarizing cell using such analysis we have identified that oriented actomyosin II filament bundles, required for fibroblast polarization, are nonsarcomeric and are organized with graded filament polarity. As this actin organization is similar to the organization in already migrating fibroblasts, we conclude that graded filament polarity is a pivotal myosin II substrate coordinating initial cell shape change and triggering of migration.