FIGURE 1:

An assembling endocytic actin patch exerts strong squeezing forces at its base of an initial invagination. (A) Example of distribution of orthogonal forces in an (r, z)-section of a nascent invagination adapted from simulation results in Figure 5A of Nickaeen et al. (2019). (B) Time dependence of squeezing force acting on the 2 nm wide portion at the base of the nascent tubule in (A), from a simulation described in Figure 5A of Nickaeen et al. (2019). The force of 320 pN applied to a 2 nm-wide band with the radius of 30 nm amounts to additional pressure of ≈ 8.5 atm. (C) Cartoon of a head–neck (flasklike) shape with radii r_neck and R_head; since turgor pressure P is isotropic, f_resist for this shape diminishes to . (D) Graph of f_resist (t) normalized to [dots, A(t) is the cross-action area at the base, see the text] is well approximated by function {1 + exp[(t – t₀)/τ]}^–1 (solid curve) with the fitted timing (t₀) and duration (τ) of the resistance decrease caused by shape change.