Fig. 4: Actin bracket formation establishes elastoplastic transition with a tunable critical duration.

a Time-lapse images of Lifeact-mCherry before indentation and at t = 0 min, t = 10 min, and t = 30 min. F-actin accumulated at fold (arrows). Seven experiments were repeated independently. Scale bars, 15 µm. b Three-dimensional constructed images of SPY650-actin at t = 0 min and t = 30 min. Dotted lines indicate epithelial contours. F-actin accumulated around apical and lateral boundaries (arrows). Kymographs of Lifeact-mCherry intensity along the epithelium contour (c) and apicobasal axis (d) over time. Intensity at each pixel was normalized to the initial intensity and averaged across samples (N = 3). e Time variation of the maximum and average Lifeact-mCherry intensity around fold. f Bending plastic ratio, ψ, under drug treatment for F-actin dynamics inhibition. For τ = 5 min, the condition included treatment with cytochalasin D (p = 0.0683) and Jasplakinolide (p = 1.95e − 4). For τ = 30 min, the condition included treatment with cytochalasin D (p = 1.77e − 4), Latrunculin A (p = 8.94e − 7), CK-666 (p = 0.0225), and Jasplakinolide (p = 0.894). g Lifeact-mCherry intensity around the apex under drug treatment conditions targeting F-actin polymerization inhibition, EGFR inhibition, and mechanosensitive channel inhibition, as well as under a condition of low-curvature folding. For τ = 5 min, the conditions included indentation only (p = 0.00524), treatment with cytochalasin D (p = 0.387) and Jasplakinolide (p = 0.00264). For τ = 30 min, the conditions included indentation only (p = 5.42e − 5), treatment with cytochalasin D (p = 0.364), Latrunculin A (p = 0.223), CK666 (p = 0.105), Jasplakinolide (p = 0.00334), PD153035 (p = 0.343), LY294002 (p = 0.485), Ipatasertib (p = 0.451), PD0325901 (p = 0.00110), GsMTx4 (p = 0.203), BAPTA-AM (p = 0.0631), Pico145 (p = 0.00866), Pyr3 (p = 0.301), SAR7334 (p = 0.925), and low-curvature folding (p = 0.0190). Values were normalized to those before indentation. h Bending plastic ratio, ψ, as a function of duration time, τ, under conditions of actin polymerization inhibition or enhancement. Dotted lines show fitted sigmoid functions. i Mechanical indentation device combined with a local pharmacological intervention. Two glass pipettes were used for indentation and release of inhibitors, respectively. j Time-lapse images of Lifeact-mCherry during hold, at t = 30 min, and 5 min after pipette retraction. k Bending plastic ratio, ψ, under conditions of local cytochalasin D release at the fold (p = 0.00944) and at the region away from the fold (p = 0.113) for τ = 30 min. l Lifeact-mCherry intensity around the apex for τ = 30 min, under conditions of local cytochalasin D release at the fold (p = 9.90e − 4) and the region away from the fold (p = 0.171). Box plots in (f, g, k, l): center, median; bounds, 25th and 75th percentiles; whiskers, min and max; *P < 0.05, **P < 0.01, ***P < 0.001 (two-sided Welch’s t-test). N indicates a biologically independent sample. EGFR epidermal growth factor receptor. Source data are provided as a Source Data file.