Axonemal dyneins power the beating of motile cilia and flagella. These massive multimeric motor complexes are assembled in the cytoplasm, and subsequently trafficked to cilia and incorporated into the axonemal superstructure. Numerous cytoplasmic factors are required for the dynein assembly process, and, in mammals, defects lead to primary ciliary dyskinesia, which results in infertility, bronchial problems and failure to set up the left-right body axis correctly. Liquid-liquid phase separation (LLPS) has been proposed to underlie the formation of numerous membrane-less intracellular assemblies or condensates. In multiciliated cells, cytoplasmic assembly of axonemal dyneins also occurs in condensates that exhibit liquid-like properties, including fusion, fission and rapid exchange of components both within condensates and with bulk cytoplasm. However, a recent extensive meta-analysis suggests that the general methods used to define LLPS systems in vivo may not readily distinguish LLPS from other mechanisms. Here, I consider the time and length scales of axonemal dynein heavy chain synthesis, and the possibility that during translation of dynein heavy chain mRNAs, polysomes are crosslinked via partially assembled proteins. I propose that axonemal dynein factory formation in the cytoplasm may be a direct consequence of the sheer scale and complexity of the assembly process itself.

中文翻译：

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用于轴丝动力蛋白组装的细胞质工厂。


轴丝动力蛋白为活动纤毛和鞭毛的跳动提供动力。这些大量的多聚体运动复合物在细胞质中组装，随后被运输到纤毛并并入轴丝上层结构中。动力蛋白组装过程需要许多细胞质因子，在哺乳动物中，缺陷会导致原发性纤毛运动障碍，从而导致不孕、支气管问题和无法正确建立左右身体轴。液-液相分离（LLPS）被认为是许多无膜细胞内组装体或凝聚物形成的基础。在多纤毛细胞中，轴丝动力蛋白的细胞质组装也发生在表现出液体样特性的凝聚物中，包括融合、裂变和凝聚物内以及与大量细胞质的成分的快速交换。然而，最近的一项广泛的荟萃分析表明，用于定义体内 LLPS 系统的通用方法可能无法轻易将 LLPS 与其他机制区分开来。在这里，我考虑了轴丝动力蛋白重链合成的时间和长度尺度，以及动力蛋白重链 mRNA 翻译过程中，多核糖体通过部分组装的蛋白质交联的可能性。我认为细胞质中轴丝动力蛋白工厂的形成可能是组装过程本身的规模和复杂性的直接结果。