FIGURE 3:

Invaginations with “head–neck” shape have higher driving forces than cylindrical invaginations, yielding faster elongation and longer displacements. Dependence of (A) net driving force, f_net = f_drive – f_resist, (B) elongation rates, and (C) displacements on the invagination geometry and μ. The model was solved with the same parameters (with the exception of invagination mobility) for the invagination with head–neck shape (r_neck/R_head = 0.1) and mobility coefficients μ = 0.08 μm/s/pN (solid curves) and 0.04 μm/s/pN (dotted curves) and for the cylindrical invagination with μ = 0.08 μm/s/pN (gray dashed curves) and 0.04 μm/s/pN (black dashed curves). The head–neck invaginations began to move at t_begin = –7 s, and the cylindrical invaginations started to elongate at t_begin = –6.8 s. Vesicle scission, terminating elongation, is thought to occur when polymerized actin reaches its maximum. For the head–neck invaginations, t_scission = –0.8 s for μ = 0.08 μm/s/pN and –0.6 s for μ = 0.04 μm/s/pN, and for the cylindrical invaginations, t_scission = 0 s for μ = 0.04 μm/s/pN and 0.9 s for μ = 0.08 μm/s/pN. The displacements at t_scission were 179 nm (solid curve), 153 nm (dotted curve), 64 nm (gray dashed curve), and 52 nm (black dashed curve).