Fig. 6: Forces applied by PLPs facilitate cell spreading.
From: Force-exerting perpendicular lateral protrusions in fibroblastic cell contraction
a (i) Representative images and schematic of forces exerted by twine-bridges. Force vectors are assumed to act along the membrane curvature with origin at paxillin cluster lengths. The force vectors R1 and R2 are calculated by minimizing the objective function, where VEXP represents the experimental displacement profile of the fixed-fixed beam and VFEM is the prediction from the finite element model. (ii) Representative immunostained images for actin localization in twines and PLPs of varying sizes (top panel) and both structures formed simultaneously in the same cell (bottom panel). Force response of twines and PLPs with corresponding images. (iii) Forces in developing PLPs increase beyond 10 µm width (W) shown in the cartoon (n = 25 PLPs). (iv) f-actin stress fibers transition from being along the direction of developing PLPs to along the neighboring fibers in developed PLPs. b Left-panel: f-actin stress fibers, paxillin and pFAK in twines and PLPs show transition from classic focal adhesions in twines to elongated 3D-adhesions in PLPs. Right-panel shows magnified color images regions shown by yellow arrows in left-panel and signifying highlighted regions in the cartoon. c (i) Schematic representation of NFM method to measure contractile forces of single cells attached to multiple fibers. Force vectors originate from paxillin focal adhesion clustering (green) and act along f-actin stress fibers (red and white). (ii) Representative phase images of anisotropically stretched cells on 3, 4, and 5 fibers. iii F-actin stress fiber angle data used in measurement of forces: fiber 1 and 3 (n = 53, n signifying number of stress fibers) and fiber 2 (n = 30) in 3-fiber category, fiber 1 and 4 (n = 80) and fiber 2 and 3 (n = 84) in 4-fiber category, fiber 1 and 5 (n = 72), fiber 2 and 4 (n = 70), and fiber 3 (n = 35) in 5-fiber category. iv NFM based average force calculated for 3 time points separated by 3 min each for each cell (n = 13, 14, and 15 for 3, 4, and 5 fiber categories, respectively). v. Migration rates for each fiber category (n = 15 in each). Scale bar: a (i) 10 µm, (ii) 10 μm, (iv) 10 μm, b 5 μm, c (i) 20 μm, (ii) 50 μm.
