Cytoskeleton assembly and remodeling during bleb’s life cycle. (A) Branched actin network in lamellipodia with an embedded filopodial bundle. Cytoskeletal network is sparser around the filopodial root. (B) Transitional filopodial stage that precedes the initiation of blebbing. Branched network is suppressed and juxtafilopodial gaps are more prominent. (C) Nascent bleb formed at the filopodial base lacks detectable cytoskeletal filaments. (D) Expanding bleb contains actin filaments invading through the neck from the cell body. Some filaments are also nucleated at the bleb margins. (E) Fully expanded bleb at the stationary/slow retraction phase. Actin filaments form a relatively isotropic network within the bleb. (F) A bleb at the beginning of fast retraction contains cortically enriched cytoskeleton integrated with the sparser internal network. (G) A crumpled bleb during advanced retraction. Membrane folds can be produced by radially oriented pulling force from end-on anchored actin filaments, whereas overall shrinkage could result from contractile activity of tangentially oriented cortical filaments.