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Cellular membrane remodeling by fronts and waves of actin polymerization
During macropinocytosis, cells remodel their morphologies for the
uptake of extracellular matter. This endocytotic mechanism relies on
the collapse and closure of precursory structures, which are
propagating actin-based, ring-shaped vertical undulations at the
dorsal (top) cell membrane, a.k.a. circular dorsal ruffles (CDRs). As
such, CDRs are essential to a range of vital and pathogenic processes
alike. Here we show, based on both experimental data and theoretical
analysis, that CDRs are propagating fronts of actin polymerization in
a bistable system. The theory relies on a novel mass-conserving
reaction–diffusion model, which associates the expansion and
contraction of waves to distinct counter-propagating front solutions.
Moreover, the model predicts that under a change in parameters (for
example, biochemical conditions) CDRs may be pinned and fluctuate near
the cell boundary or exhibit complex spiral wave dynamics due to a
wave instability. We observe both phenomena also in our experiments
indicating the conditions for which macropinocytosis is suppressed.
E. Bernitt, H.-G. Dobereiner, N. S. Gov, and A. Yochelis, Fronts and waves of actin polymerization in a bistability-based mechanism of circular dorsal ruffles. Nat. Commun. 8, 15863 (2017).