Ciliopathies are inherited disorders caused by defects in motile and non-motile (primary) cilia. Ciliopathy syndromes and associated gene variants are often highly pleiotropic and represent exemplars for interrogating genotype-phenotype correlations. Towards understanding disease mechanisms in the context of ciliopathy mutations, we have employed a leading model organism for cilia and ciliopathy research, Caenorhabditis elegans, together with gene editing, to characterise two missense variants (P74S, G155S) in B9D2/mksr-2 associated with Joubert Syndrome (JBTS). B9D2 functions within the Meckel syndrome (MKS) module at the ciliary base transition zone (TZ) compartment, and regulates the cilium's molecular composition and sensory/signaling functions. Quantitative assays of cilium/TZ structure and function, together with knock-in reporters, confirm both variant alleles are pathogenic in worms. G155S causes a more severe overall phenotype and disrupts endogenous MKSR-2 organisation at the TZ. Recapitulation of the patient biallelic genotype shows that compound heterozygous worms phenocopy worms homozygous for P74S. The P74S and G155S alleles also reveal evidence of a very close functional association between the B9D2-associated B9 complex and TMEM216/MKS-2. Together, these data establish C. elegans as a paradigm for interpreting JBTS mutations, and provide further insight into MKS module organisation.

中文翻译：

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解释秀丽隐杆线虫中 Joubert 综合征错义变异的致病性。

纤毛病是由运动和非运动（初级）纤毛缺陷引起的遗传性疾病。纤毛病综合征和相关基因变异通常是高度多效性的，并且代表了询问基因型 - 表型相关性的范例。为了了解纤毛病突变背景下的疾病机制，我们采用了一种用于纤毛和纤毛病研究的领先模式生物——秀丽隐杆线虫，连同基因编辑，来表征 B9D2/ mksr-2中的两个错义变体（P74S、G155S）与 Joubert 综合征 (JBTS) 相关。B9D2 在纤毛基过渡区 (TZ) 隔室的 Meckel 综合征 (MKS) 模块中发挥作用，并调节纤毛的分子组成和感觉/信号功能。纤毛/TZ 结构和功能的定量分析以及敲入报告基因证实了这两种变异等位基因在蠕虫中都是致病的。G155S 导致更严重的整体表型并破坏 TZ 的内源性 MKSR-2 组织。对患者双等位基因型的概括表明，复合杂合蠕虫表型蠕虫是 P74S 纯合子。P74S 和 G155S 等位基因也揭示了 B9D2 相关 B9 复合物和 TMEM216/MKS-2 之间非常密切的功能关联的证据。这些数据一起建立了C. elegans作为解释 JBTS 突变的范例，并提供对 MKS 模块组织的进一步了解。