The formation of synapses during neuronal development is essential for establishing neural circuits and a nervous system 1 . Every presynapse builds a core ‘active zone’ structure, where ion channels cluster and synaptic vesicles release their neurotransmitters 2 . Although the composition of active zones is well characterized 2 , 3 , it is unclear how active-zone proteins assemble together and recruit the machinery required for vesicle release during development. Here we find that the core active-zone scaffold proteins SYD-2 (also known as liprin-α) and ELKS-1 undergo phase separation during an early stage of synapse development, and later mature into a solid structure. We directly test the in vivo function of phase separation by using mutant SYD-2 and ELKS-1 proteins that specifically lack this activity. These mutant proteins remain enriched at synapses in Caenorhabditis elegans , but show defects in active-zone assembly and synapse function. The defects are rescued by introducing a phase-separation motif from an unrelated protein. In vitro, we reconstitute the SYD-2 and ELKS-1 liquid-phase scaffold, and find that it is competent to bind and incorporate downstream active-zone components. We find that the fluidity of SYD-2 and ELKS-1 condensates is essential for efficient mixing and incorporation of active-zone components. These data reveal that a developmental liquid phase of scaffold molecules is essential for the assembly of the synaptic active zone, before maturation into a stable final structure. The components of active zones at neuronal synapses are well known, but the processes underlying the assembly of these structures are less so; here, a role for liquid–liquid phase separation of scaffold proteins is identified.

中文翻译：

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突触活动区的组装需要支架分子的相分离

神经元发育过程中突触的形成对于建立神经回路和神经系统 1 至关重要。每个突触前都构建了一个核心“活动区”结构，其中离子通道聚集，突触小泡释放其神经递质 2。尽管活性区的组成已得到很好的表征 2、3，但尚不清楚活性区蛋白质如何组装在一起并募集发育过程中囊泡释放所需的机制。在这里，我们发现核心活性区支架蛋白 SYD-2（也称为 liprin-α）和 ELKS-1 在突触发育的早期阶段经历相分离，然后成熟为固体结构。我们通过使用特别缺乏这种活性的突变体 SYD-2 和 ELKS-1 蛋白直接测试相分离的体内功能。这些突变蛋白在秀丽隐杆线虫的突触中仍然富集，但在活性区组装和突触功能方面表现出缺陷。通过从不相关的蛋白质中引入相分离基序来挽救缺陷。在体外，我们重构了 SYD-2 和 ELKS-1 液相支架，发现它能够结合和整合下游活性区成分。我们发现 SYD-2 和 ELKS-1 冷凝物的流动性对于活性区组分的有效混合和掺入至关重要。这些数据表明，在成熟为稳定的最终结构之前，支架分子的发育液相对于突触活性区的组装至关重要。神经元突触的活动区域的组成部分是众所周知的，但这些结构组装的过程却不太清楚。这里，