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.

中文翻译：

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肌动蛋白聚合的前沿和波动是基于圆形双背褶皱的双稳态机制。

在巨胞饮过程中，细胞会重塑其形态以吸收细胞外物质。这种胞吞机制依赖于前体结构的折叠和闭合，这些前体结构是在背（顶部）细胞膜（又称圆形背褶）（CDR）上传播基于肌动蛋白的环形垂直起伏。这样，CDR对于一系列重要的和致病的过程都是必不可少的。在此，基于实验数据和理论分析，我们表明CDR是双稳态系统中肌动蛋白聚合的传播前沿。该理论依赖于新颖的质量守恒反应扩散模型，该模型将波的扩展和收缩与独特的反向传播的前沿解相关联。此外，该模型还可以预测在参数变化的情况下（例如，生化条件）CDR可能会被钉扎并在细胞边界附近波动，或者由于波的不稳定性而表现出复杂的螺旋波动力学。我们还在实验中观察到了两种现象，这表明巨胞饮作用被抑制的条件。