Anomalous dynamics of the endoplasmic reticulum network

Large portions of the endoplasmic reticulum (ER) in eukaryotic cells are organized as dynamic networks whose segments are connected by three-way junctions. Here we show that ER junctions move subdiffusively with signatures of fractional Brownian motion and a strong dependence on the cytoskeleton's integrity: The time-averagedmean square displacement scales as < r(2)(tau)>(t) similar to tau(alpha) with alpha approximate to 0.5 in untreated cells and alpha approximate to 0.3when disrupting microtubules, with successive steps being anticorrelated in both cases. We explain our observations by considering ER junctions to move like monomers in (semi) flexible polymer segments immersed in a viscoelastic environment. We also report that ER networks have a nontrivial fractal dimension d(f) approximate to 1.6 on mesoscopic scales and we provide evidence that the organelle's dynamics is governed by fractons.