In our research, we explore the non-equilibrium dynamics of vesicle shape remodeling driven by internal active filaments. We investigate how vesicle volume, filament anisotropy, mobility, and concentration collectively determine the formation and continuous reorganization of complex vesicle morphologies.
On the cover of the December 2 issue of Biophysical Journal, we illustrate how an initially spherical vesicle (upper left) containing inactive filaments transforms into intricate structures when the vesicle volume is reduced and the filaments become active. The peripheral simulation snapshots show vesicles adopting distinct morphologies at different parameter combinations. These structures consist of tubular, sheet-like, and spherical components that dynamically interconvert in a non-equilibrium fashion while maintaining nearly constant proportions of each element. Examples include sheet-tubes, branched tubes, pearled tubes, and compartmentalized vesicles, which continuously remodel their shapes at rates determined by filament mobility and concentration.
Our simulations reveal that less-mobile filaments promote faster restructuring of composite vesicles, leading to highly dynamic morphologies. Conversely, when filaments become shorter or more flexible and lose their anisotropy, these complex, branched and sheet-tubular vesicles collapse into stable cup-like shapes, similar to equilibrium vesicles without active elements. The circular layout of the cover highlights this relationship: peripheral simulation snapshots represent non-equilibrium vesicle dynamics, while the central schematic cell evokes cytoskeleton-driven protrusions such as filopodia and lamellipodia, connecting our findings to cellular membrane remodeling.
— Arash Karaei Shiraz and Amir H. Bahrami