TY - JOUR T1 - Nano-twines to twine-bridges: Role of force exerting perpendicular lateral protrusions in fibroblastic cell contraction JF - bioRxiv DO - 10.1101/711507 SP - 711507 AU - Abinash Padhi AU - Karanpreet Singh AU - Janusz Franco-Barraza AU - Daniel J. Marston AU - Klaus M. Hahn AU - Edna Cukierman AU - Rakesh K. Kapania AU - Amrinder S. Nain Y1 - 2019/01/01 UR - http://biorxiv.org/content/early/2019/09/13/711507.abstract N2 - Aligned fibrous matrices cause cells to have elongated shapes and anisotropic migration. Current research points to the maintenance of elongated cell shape due to reduced formation and activity of lateral protrusions. Here, we identify a new role of lateral protrusions that can originate from anywhere along the length of elongated cells and can apply contractile forces. Using aligned fiber networks that also serve as force sensors, we quantitate the role of lateral nano-projections (twines) that mature into broad perpendicular lateral protrusions (PLPs) through the formation of twine-bridges, thus allowing anisotropic cells to spread laterally. Using quantitative microscopy at the high spatiotemporal resolution, we show that twines of varying lengths can originate from stratification of cyclic actin waves traversing along the entire length of the cell, and not just at the leading edge. Primary twines can swing freely in 3D and engage with neighboring fibers in interaction times of seconds. Once engaged, the actin lamellum grows along the length of primary twine and re-stratifies to form a secondary twine. Engagement of secondary twine with the neighboring fiber leads to the formation of a suspended primary-secondary twine-bridge; a critical step in providing a conduit for actin to advance along and populate (mature) the twine-bridge. Using force vectors that originate from adhesion sites and directed along f-actin stress fibers, we quantitate the forces exerted by PLPs and find that the majority of force exerting PLPs are oriented perpendicular to the parent cell body. Our data highlights that cell spreading onto multiple fibers occurs through the engagement of PLPs with neighboring fibers and not necessarily from the leading edge. As cells spread on multiple fibers, they achieve higher contractility resulting in lower migration rates. Our identification of force exertion by PLPs that cause the fibers to bend inwards identifies desmoplastic expansion of the native extracellular matrix at single-cell resolution, thus providing new intervention opportunities in pathological biology. ER -