Fig. 3: Discreet steps in the formation of force exerting perpendicular lateral protrusions (PLPs).

a (a) Cartoons showing the process of forming force-exerting perpendicular lateral protrusions (PLPs). Cells attached to fibers form filamentous twines that engage with neighboring fiber (i). Subsequently, actin lamellum grows along the base of twine from cell body (ii) followed by formation of secondary twines (iii). Engagement of secondary twine with neighboring fiber leads to formation of a suspended twine-bridge (iv) that facilitates advancement of the lamellum that generates a suspended interfiber lamellum (v). Over time (~minutes), the interfiber lamellum broadens and applies contractile forces causing neighboring fiber to contract inwards, thus creating force exerting PLPs (vii). (b) Phase images in green and red (dashed) boxes depict two sample cases of PLPs in steps (i–vi). (c) Phase images of whole-cell forming PLP. Black dashed lines indicate undeflected position of neighboring fiber. Orange arrow indicates cell migration direction. b Sample images of twine-bridges of varying sizes and shapes and arrows point toward the neighboring fiber. Time in seconds. Scale bar: a (b) 5 μm, (c) 20 μm, b 5 μm.