High-resolution mapping of intracellular fluctuations using carbon nanotubes

Fakhri, Nikta; Wessel, Alok D.; Willms, Charlotte; Pasquali, Matteo; Klopfenstein, Dieter R.; MacKintosh, F. C.; Schmidt, Christoph F.

doi:10.1126/science.1250170

Cited by 208 publications

(293 citation statements)

References 42 publications

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“…Taken together, these cellular proteins form an elastic network with contractility induced by nonequilibrium motor stresses [16,18]. The motors generate forces that propagate through the network, changing the viscoelastic properties, structure, and fluctuations in living systems [16,17,[19][20][21][22][23][24][25][26][27][28][29][30].…”

Section: Resultsmentioning

confidence: 99%

Inherently unstable networks collapse to a critical point

et al. 2015

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Nonequilibrium systems that are driven or drive themselves towards a critical point have been studied for almost three decades. Here we present a minimalist example of such a system, motivated by experiments on collapsing active elastic networks. Our model of an unstable elastic network exhibits a collapse towards a critical point from any macroscopically connected initial configuration. Taking into account steric interactions within the network, the model qualitatively and quantitatively reproduces results of the experiments on collapsing active gels.

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Section: Resultsmentioning

confidence: 99%

Inherently unstable networks collapse to a critical point

et al. 2015

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“…Although this is a simple model for the dynamics of motor-generated forces, the corresponding power spectrum SðωÞ is Lorentzian. Such a Lorentzian spectrum captures the essential features observed in experiments [7][8][9][10] of becoming white-noise-like, SðωÞ ∼ const, for low frequencies, while following a power-law SðωÞ ∝ ω −2 , for high frequencies. It is convenient to expand the deflections of the probe filament r ⊥ ðs; tÞ ¼ L P q a q ðtÞy q ðsÞ into a sum of orthogonal eigenmodes y q ðsÞ with eigenvector q of the beam equation γ∂r ⊥ =∂t ¼ −κ∂ 4 r ⊥ =∂s 4 with free boundary conditions at the ends [24].…”

mentioning

confidence: 99%

“…Living cells are a prime example of active matter, typically driven out of thermodynamic equilibrium by molecular force generators [1][2][3][4][5]. In cytoskeletal networks, myosin motors are the dominant actors driving nonequilibrium dynamics [6][7][8][9][10][11][12][13], which can be captured in simplified reconstituted systems [14][15][16][17][18][19][20]. Myosin motors generate mechanical force by coupling the hydrolysis of adenosine triphosphate to conformational changes in a mechanochemical cycle [6].…”

mentioning

confidence: 99%

“…However, it remains unclear how broken detailed balance propagates from molecular-scale dynamics to large-scale collective dynamics in cytoskeletal networks. An elegant way of noninvasively investigating the dynamics of active biological networks across a range of length scales is to track embedded probe filaments such as microtubules [15] or single-walled carbon nanotubes [9]. A careful analysis of the shape fluctuations of such a probe filament can reveal the active nature of its environment including potential violations of detailed balance, but a theory for the stochastic dynamics of these systems is still lacking.…”

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confidence: 99%

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Broken Detailed Balance of Filament Dynamics in Active Networks

et al. 2016

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Myosin motor proteins drive vigorous steady-state fluctuations in the actin cytoskeleton of cells. Endogenous embedded semiflexible filaments such as microtubules, or added filaments such as singlewalled carbon nanotubes are used as novel tools to noninvasively track equilibrium and nonequilibrium fluctuations in such biopolymer networks. Here, we analytically calculate shape fluctuations of semiflexible probe filaments in a viscoelastic environment, driven out of equilibrium by motor activity. Transverse bending fluctuations of the probe filaments can be decomposed into dynamic normal modes. We find that these modes no longer evolve independently under nonequilibrium driving. This effective mode coupling results in nonzero circulatory currents in a conformational phase space, reflecting a violation of detailed balance. We present predictions for the characteristic frequencies associated with these currents and investigate how the temporal signatures of motor activity determine mode correlations, which we find to be consistent with recent experiments on microtubules embedded in cytoskeletal networks.

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“…Consequently, the intracellular dynamics of eukaryotic cells has an analog in all cells. For instance, Fakkhri et al 33 report scaling exponents between 1/4 and 1.0 for the intracellular relationship between the mean squared displacement trajectories (MSD) of tagged carbon nanotubules and the lag time t of transport, i.e., MSD / t 1/4-1/1 .…”

Section: The Metabolic Theory Of Ecologymentioning

confidence: 99%

Kleiber's Law: How theFire of Lifeignited debate, fueled theory, and neglected plants as model organisms

Niklas¹,

Kutschera

2015

Plant Signaling & Behavior

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Size is a key feature of any organism since it influences the rate at which resources are consumed and thus affects metabolic rates. In the 1930s, size-dependent relationships were codified as "allometry" and it was shown that most of these could be quantified using the slopes of log-log plots of any 2 variables of interest. During the decades that followed, physiologists explored how animal respiration rates varied as a function of body size across taxa. The expectation was that rates would scale as the 2/3 power of body size as a reflection of the Euclidean relationship between surface area and volume. However, the work of Max Kleiber (1893Kleiber ( -1976 and others revealed that animal respiration rates apparently scale more closely as the 3/4 power of body size. This phenomenology, which is called "Kleiber's Law," has been described for a broad range of organisms, including some algae and plants. It has also been severely criticized on theoretical and empirical grounds. Here, we review the history of the analysis of metabolism, which originated with the works of Antoine L. Lavoisier (1743-1794) and Julius Sachs (1832-1897), and culminated in Kleiber's book The Fire of Life (1961; 2. ed. 1975). We then evaluate some of the criticisms that have been leveled against Kleiber's Law and some examples of the theories that have tried to explain it. We revive the speculation that intracellular exo-and endocytotic processes are resource delivery-systems, analogous to the supercellular systems in multicellular organisms. Finally, we present data that cast doubt on the existence of a single scaling relationship between growth and body size in plants.

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High-resolution mapping of intracellular fluctuations using carbon nanotubes

Cited by 208 publications

References 42 publications

Inherently unstable networks collapse to a critical point

Inherently unstable networks collapse to a critical point

Broken Detailed Balance of Filament Dynamics in Active Networks

Kleiber's Law: How theFire of Lifeignited debate, fueled theory, and neglected plants as model organisms

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