Varying crosslinking motifs drive the mesoscale mechanics of actin-microtubule composites

Abstract

The cytoskeleton dynamically tunes its mechanical properties by altering the interactions between semiflexible actin filaments, rigid microtubules, and crosslinking proteins. Here, we use optical tweezers microrheology and confocal microscopy to characterize how varying crosslinking motifs impact the microscopic and mesoscale mechanics and mobility of actin-microtubule composites. We show that, upon subtle changes in the crosslinking pattern, composites separate into two distinct classes of force responseprimarily elastic versus more viscous behavior. For example, a composite in which actin and microtubules are crosslinked to each other is markedly more elastic than one in which both filaments are crosslinked but cannot link together. Notably, this distinction only emerges at mesoscopic scales in response to nonlinear forcing, whereas varying crosslinking motifs have little impact on the microscale mechanics and steadystate mobility of composites. Our unexpected scale-dependent results not only inform the physics underlying key cytoskeleton processes and structures, but, more generally, provide valuable perspective to materials engineering endeavors focused on polymer composites.

Topology-dependent anomalous dynamics of ring and linear DNA are sensitive to cytoskeleton crosslinking

“…1 and Methods, the ring and linear DNA used in our experiments have identical contour lengths of L ≅ 38 m (115 kbp) and topology-dependent mean end-to-end coil lengths of R0,R ≅ 1.6 m and R0,L ≅ 2.6 m. The cytoskeleton networks both have a mesh size of ≅ 0.81 m, and in the crosslinked network every filament crossing or entanglement can be assumed to be crosslinked. The longest relaxation times for entangled and crosslinked networks have been reported to be ~3.3 s and ~4.1 s, (16) similar to our measurement timescale for single-molecule tracking.…”

“…The role that crosslinking plays in the viscoelastic properties of in vitro actin and microtubule networks has been widely studied (10,11,14). More recently, the interactions between actin and microtubules and their role in cell mechanics has begun to be explored (15)(16)(17)(18)(19). However, far less understood is the dynamics -both centerof-mass and conformational -of biopolymers like DNA existing within these composite cytoskeletal networks (19).…”

Interactions Within and Between Cytoskeletal Filaments

“…However, here, the precise interaction mechanism remains unknown. The structure, stiffness, particle transport properties and bundling of these composite networks can be further tuned by adding crosslinkers [123][124][125][126][127]. Motor proteins can switch to another filament at the intersection of actin filaments and microtubules, and…”

“…Passive microrheology by Pelletier 2009 [119] Active microrheology by Ricketts 2018 [120] Active microrheology by Ricketts 2019 [125] Bulk rheology by Lin 2011 [123] Fluorescence microscopy by Lopez 2014 [124], by Henty-Ridilla 2016 [121], by Colin, Singaravelu 2018 [122] Fluorescence microscopy by Farhadi 2020 [126] Passive microrheology by Anderson 2021 [127] Bulk rheology with vimentin IFs by Janmey 1998 [129], by Piechocka 2011 [136] Binding plectin [211], and microtubule-actin cross-linking factor [217,219]. Our direct interaction measurements with a buffer supplemented with an additional protein might reveal how these proteins interact with microtubules and vimentin IFs.…”