Mutation of CFAP57, a protein required for the asymmetric targeting of a subset of inner dynein arms in Chlamydomonas, causes primary ciliary dyskinesia

Abstract

Primary ciliary dyskinesia (PCD) is characterized by chronic airway disease, reduced fertility, and randomization of the left/right body axis. It is caused by defects of motile cilia and sperm flagella. We screened a cohort of affected individuals that lack an obvious axonemal defect for pathogenic variants using whole exome capture, next generation sequencing, and bioinformatic analysis assuming an autosomal recessive trait. We identified one subject with an apparently homozygous nonsense variant [(c.1762C>T), p.(Arg588*)] in the uncharacterized CFAP57 gene. Interestingly, the variant results in the skipping of exon 11 (58 amino acids), which may be due to disruption of an exonic splicing enhancer. In normal human nasal epithelial cells, CFAP57 localizes throughout the ciliary axoneme. Nasal cells from the PCD patient express a shorter, mutant version of CFAP57 and the protein is not incorporated into the axoneme. The missing 58 amino acids include portions of WD repeats that may be important for loading onto the intraflagellar transport (IFT) complexes for transport or docking onto the axoneme. A reduced beat frequency and an alteration in ciliary waveform was observed. Knockdown of CFAP57 in human tracheobronchial epithelial cells (hTECs) recapitulates these findings. Phylogenetic analysis showed that CFAP57 is highly conserved in organisms that assemble motile cilia. CFAP57 is allelic with the BOP2/IDA8/ FAP57 gene identified previously in Chlamydomonas reinhardtii. Two independent, insertional fap57 Chlamydomonas mutant strains show reduced swimming velocity and altered a1111111111 a1111111111 a1111111111 a1111111111 a1111111111

Composition and function of ciliary inner‐dynein‐arm subunits studied in Chlamydomonas reinhardtii

“…Also, human DNAH2 gene, a potential orthologue of Chlamydomonas IDA f/I1β HC ( DHC10 ) (Kollmar, 2016) is a candidate gene of one type of the teratozoospermia, multiple morphological abnormalities of the sperm flagella (MMAF) (Li et al, 2019). In addition, defects in human DNAH6 gene, a potential orthologue of Chlamydomonas DHC7 (IDA g) or minor IDA DHC3 (Bustamante‐Marin et al, 2020; Kollmar, 2016), have been reported to cause azoospermia, suggesting the important role of IDA g in spermatogenesis and sperm motility (Gershoni et al, 2017; Y. Li et al, 2016).…”

“…IDA d and e may be partially replaced by minor IDAs DHC11 and DHC4 in the proximal portion of the axonemes (Bui et al, 2012). Also, replacement of IDA g by DHC3 was proposed in Bustamante‐Marin et al, (2020). DMT1 has unique organization of IDAs throughout the axonemes (Bui et al, 2012; Hoops & Witman, 1983).…”

“…In contrast, failure in assembly of multiple IDAs (e.g., the pf23 mutant) results in paralyzed cilia or in defective motility (Huang, Piperno, & Luck, 1979; Yamamoto et al, 2017, 2020). Notably, most of the proteins associated with IDAs, including IDA subunits, are conserved in eukaryotic organisms that bear motile cilia (Wickstead & Gull, 2007), and recent studies revealed unexpected links between IDAs and human diseases (Ben Khelifa et al, 2014; Bustamante‐Marin et al, 2020).…”

Mucociliary Respiratory Epithelium Integrity in Molecular Defense and Susceptibility to Pulmonary Viral Infections

“…Recently, a mutation in the CFAP57 gene has been identified to be associated with PCD. This protein is involved in IDA assembly, and its absence resulted in a reduced beating frequency of cilia with an altered beating pattern [ 153 ].…”

Ciliary Dyneins and Dynein Related Ciliopathies

“…Mutations in ODA docking complex genes usually cause a complete absence of outer dynein arms and static cilia [168]. Mutation in CFAP57, an inner arm assembly component, causes a mild respiratory phenotype, where ciliary movement shows heterogeneous waveforms with reduced frequency, and patients do not show any defect in the ultra-structure of the cilia [173]. PCD patients with only inner dynein arm defects are difficult to diagnose; often, repeat collection of samples for EM and ciliary beat pattern analysis is required [174].…”