Fig. 3.

Intermediate activity enhances fluctuations in stable actomyosin. a, b Fluorescent F-actin kymograph across a single nematic domain of a 2D network in the presence of 0.25% methylcellulose (MC) (T, a), and 0.25% MC + SkMM (S, b). White scale bar is 5 μm. c 2D F-actin network in the presence of 0.25% MC with alignment vector field (green), scaled by the local nematic order parameter, overlaid. Lower panel shows a schematic of the local alignment vector (n_i), local coordinate system defined by the axes parallel $\left({\widehat{\mathbf{e}}}_{\parallel }\right)$ and perpendicular $\left({\widehat{\mathbf{e}}}_{\perp }\right)$ to the local alignment vector, and local alignment vector fluctuations $\left(\delta {\mathbf{n}}_i\equiv {\mathbf{n}}_i-⟨{\mathbf{n}}_i⟩\right)$ used to calculate fluctuation autocorrelations. Scale bar is 10 μm. d Equal time spatial density-density (S_ρρ, top) and director-director (S_nn, bottom) fluctuation autocorrelations as a function of the perpendicular wave vector (k_⊥). The spatial autocorrelations are shown for thermal (orange, 0.25% MC, N = 16) and stable (blue, SkMM, N = 6) experimental conditions within the F-actin network. All experiments contain the same concentration of F-actin (2.32 μM) with 0.25% MC. The dashed black lines follow the predicted autocorrelation decay by active nematic liquid crystal theory. Insets show corresponding results for S_ρρ and S_nn from agent-based simulation. Each curve is an average over 3 simulations. Mean length of simulated filaments is 4.3 μm