El Khouri Elma, Thomas Lucie, Jeanson Ludovic, Bequignon Emilie, Vallette Benoit, Duquesnoy Philippe, Montantin Guy, Copin Bruno, Dastot-Le Moal Florence, Blanchon Sylvain, Papon Jean François, Lorès Patrick, Yuan Li, Collot Nathalie, Tissier Sylvie, Faucon Catherine, Gacon Gérard, Patrat Catherine, Wolf Jean Philippe, Dulioust Emmanuel, Crestani Bruno, Escudier Estelle, Coste André, Legendre Marie, Touré Aminata, Amselem Serge
INSERM U1016, Institut Cochin, Paris 75014, France; Centre National de la Recherche Scientifique UMR8104, Paris 75014, France; Faculté de Médecine, Université Paris Descartes, Sorbonne Paris Cité, Paris 75014, France.
INSERM UMR S933, Université Pierre et Marie Curie (Paris 6), Paris 75012, France.
Am J Hum Genet. 2016 Aug 4;99(2):489-500. doi: 10.1016/j.ajhg.2016.06.022.
Primary ciliary dyskinesia (PCD) is an autosomal-recessive disease due to functional or ultra-structural defects of motile cilia. Affected individuals display recurrent respiratory-tract infections; most males are infertile as a result of sperm flagellar dysfunction. The great majority of the PCD-associated genes identified so far encode either components of dynein arms (DAs), which are multiprotein-ATPase complexes essential for ciliary motility, or proteins involved in DA assembly. To identify the molecular basis of a PCD phenotype characterized by central complex (CC) defects but normal DA structure, a phenotype found in ∼15% of cases, we performed whole-exome sequencing in a male individual with PCD and unexplained CC defects. This analysis, combined with whole-genome SNP genotyping, identified a homozygous mutation in DNAJB13 (c.833T>G), a gene encoding a HSP40 co-chaperone whose ortholog in the flagellated alga Chlamydomonas localizes to the radial spokes. In vitro studies showed that this missense substitution (p.Met278Arg), which involves a highly conserved residue of several HSP40 family members, leads to protein instability and triggers proteasomal degradation, a result confirmed by the absence of endogenous DNAJB13 in cilia and sperm from this individual. Subsequent DNAJB13 analyses identified another homozygous mutation in a second family; the study of DNAJB13 transcripts obtained from airway cells showed that this mutation (c.68+1G>C) results in a splicing defect consistent with a loss-of-function mutation. Overall, this study, which establishes mutations in DNAJB13 as a cause of PCD, unveils the key role played by DNAJB13 in the proper formation and function of ciliary and flagellar axonemes in humans.
原发性纤毛运动障碍（PCD）是一种常染色体隐性疾病，由运动性纤毛的功能或超微结构缺陷引起。患者表现为反复呼吸道感染；多数男性因精子鞭毛功能障碍而不育。目前已鉴定出的绝大多数与PCD相关的基因，要么编码动力蛋白臂（DAs）的组成部分（DAs是纤毛运动所必需的多蛋白ATP酶复合物），要么编码参与DA组装的蛋白质。为了确定一种以中央复合体（CC）缺陷但DA结构正常为特征的PCD表型的分子基础（这种表型在约15%的病例中出现），我们对一名患有PCD且伴有不明原因CC缺陷的男性个体进行了全外显子组测序。该分析结合全基因组SNP基因分型，在DNAJB13基因中鉴定出一个纯合突变（c.833T>G），该基因编码一种HSP40共伴侣蛋白，其在鞭毛藻衣藻中的直系同源物定位于辐条。体外研究表明，这种错义替代（p.Met278Arg）涉及几个HSP40家族成员的一个高度保守残基，导致蛋白质不稳定并触发蛋白酶体降解，该个体的纤毛和精子中缺乏内源性DNAJB13证实了这一结果。随后对DNAJB13的分析在另一个家系中鉴定出另一个纯合突变；对从气道细胞获得的DNAJB13转录本的研究表明，该突变（c.68+1G>C）导致剪接缺陷，与功能丧失突变一致。总体而言，这项将DNAJB13中的突变确定为PCD病因的研究，揭示了DNAJB13在人类纤毛和鞭毛轴丝的正常形成和功能中所起的关键作用。
