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Nat Commun. 2013;4:2224. doi: 10.1038/ncomms3224.

Neurofilament sidearms modulate parallel and crossed-filament orientations inducing nematic to isotropic and re-entrant birefringent hydrogels.

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  • 1Chemistry and Biochemistry Department, University of California, Santa Barbara, California 93106, USA.


Neurofilaments are intermediate filaments assembled from the subunits neurofilament-low, neurofilament-medium and neurofilament-high. In axons, parallel neurofilaments form a nematic liquid-crystal hydrogel with network structure arising from interactions between the neurofilaments' C-terminal sidearms. Here we report, using small-angle X-ray-scattering, polarized-microscopy and rheometry, that with decreasing ionic strength, neurofilament-low-high, neurofilament-low-medium and neurofilament-low-medium-high hydrogels transition from the nematic hydrogel to an isotropic hydrogel (with random, crossed-filament orientation) and to an unexpected new re-entrant liquid-crystal hydrogel with parallel filaments--the bluish-opaque hydrogel--with notable mechanical and water retention properties reminiscent of crosslinked hydrogels. Significantly, the isotropic gel phase stability is sidearm-dependent: neurofilament-low-high hydrogels exhibit a wide ionic strength range, neurofilament-low-medium hydrogels a narrow ionic strength range, whereas neurofilament-low hydrogels lack the isotropic gel phase. This suggests a dominant regulatory role for neurofilament-high sidearms in filament reorientation plasticity, facilitating organelle transport in axons. Neurofilament-inspired biomimetic hydrogels should therefore exhibit remarkable structure-dependent moduli and slow and fast water-release properties.

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