A key event at the onset of development is the activation of a contractile actomyosin cortex during the oocyte-to-embryo transition. We here report on the discovery that in C. elegans oocytes, actomyosin cortex activation is supported by the emergence of thousands of short-lived protein condensates rich in F-actin, N-WASP, and ARP2/3 that form an active micro-emulsion. A phase portrait analysis of the dynamics of individual cortical condensates reveals that condensates initially grow, and then switch to disassembly before dissolving completely. We find that in contrast to condensate growth via diffusion, the growth dynamics of cortical condensates are chemically driven. Remarkably, the associated chemical reactions obey mass action kinetics despite governing both composition and size. We suggest that the resultant condensate dynamic instability suppresses coarsening of the active micro-emulsion, ensures reaction kinetics that are independent of condensate size, and prevents runaway F-actin nucleation during the formation of the first cortical actin meshwork.

中文翻译：

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凝聚动态不稳定性协调卵母细胞肌动球蛋白皮层激活

发育开始时的一个关键事件是在卵母细胞到胚胎的过渡过程中激活收缩性肌动球蛋白皮层。我们在这里报告了在秀丽隐杆线虫中的发现在卵母细胞中，肌动球蛋白皮层的激活得到了数千种富含 F-肌动蛋白、N-WASP 和 ARP2/3 的短寿命蛋白质缩合物的支持，这些蛋白质缩合物形成了活性微乳液。对单个皮质凝聚物动力学的相图分析表明，凝聚物最初会生长，然后在完全溶解之前切换到分解。我们发现，与通过扩散的凝聚物生长相反，皮质凝聚物的生长动力学是化学驱动的。值得注意的是，尽管控制成分和尺寸，但相关的化学反应服从质量作用动力学。我们建议由此产生的冷凝液动态不稳定性抑制了活性微乳液的粗化，确保了与冷凝液尺寸无关的反应动力学，