Mutations in Outer Dynein Arm Heavy Chain DNAH9 Cause Motile Cilia Defects and Situs Inversus

Abstract

Motile cilia move body fluids and gametes and the beating of cilia lining the airway epithelial surfaces ensures that they are kept clear and protected from inhaled pathogens and consequent respiratory infections. Dynein motor proteins provide mechanical force for cilia beating. Dynein mutations are a common cause of primary ciliary dyskinesia (PCD), an inherited condition characterized by deficient mucociliary clearance and chronic respiratory disease coupled with laterality disturbances and subfertility. Using next-generation sequencing, we detected mutations in the ciliary outer dynein arm (ODA) heavy chain gene DNAH9 in individuals from PCD clinics with situs inversus and in one case male infertility. DNAH9 and its partner heavy chain DNAH5 localize to type 2 ODAs of the distal cilium and in DNAH9-mutated nasal respiratory epithelial cilia we found a loss of DNAH9/DNAH5-containing type 2 ODAs that was restricted to the distal cilia region. This confers a reduced beating frequency with a subtle beating pattern defect affecting the motility of the distal cilia portion. 3D electron tomography ultrastructural studies confirmed regional loss of ODAs from the distal cilium, manifesting as either loss of whole ODA or partial loss of ODA volume. Paramecium DNAH9 knockdown confirms an evolutionarily conserved function for DNAH9 in cilia motility and ODA stability. We find that DNAH9 is widely expressed in the airways, despite DNAH9 mutations appearing to confer symptoms restricted to the upper respiratory tract. In summary, DNAH9 mutations reduce cilia function but some respiratory mucociliary clearance potential may be retained, widening the PCD disease spectrum.

A DNAH17 missense variant causes flagella destabilization and asthenozoospermia

“…Besides, DNAH9 was also found localized through the sperm flagella except the distal tip (Fliegauf et al, 2005), which is similar to DNAH17 localization in sperm flagella. Biallelic mutations in DNAH9 cause PCD with a frequent loss of ODAs at the distal, but not the proximal, regions of cilia (Fassad et al, 2018;Loges et al, 2018), and the patient carrying two homozygous missense mutations in DNAH9 presented with oligoasthenoteratozoospermia (Fassad et al, 2018), yet the underlying ultrastructural anomalies and pathogenic mechanism remain unknown. Biallelic mutations in DNAH11 in patients are known to cause PCD without obvious defects in the ciliary ultrastructure; however, the sperm motility, flagellar ultrastructure, and fertility status of these patients were not mentioned (Bartoloni et al, 2002;Knowles et al, 2012;Lucas et al, 2012;Pifferi et al, 2010;Schwabe et al, 2008), with the exception of one man, who had one child without the use of medical assistance (Schwabe et al, 2008).…”

“…Heavy chains, also known as dynein axonemal heavy chains (DNAHs), comprise 13 members (5)(6)(7)(8)(9)(10)(11)(12)14,and 17) in humans (Pazour et al, 2006). Disruptions in DNAHs, such as DNAH5 (Hornef et al, 2006;Olbrich et al, 2002), DNAH6 (Li et al, 2016), DNAH9 (Fassad et al, 2018;Loges et al, 2018), and DNAH11 (Bartoloni et al, 2002;Knowles et al, 2012;Lucas et al, 2012;Schwabe et al, 2008), are known to cause, or are associated with, primary ciliary dyskinesia (PCD), a genetically heterogeneous disorder that is characterized by chronic airway diseases, left-right laterality disturbances, and male infertility (Leigh et al, 2009). So far, mutations in only DNAH1 or DNAH9 have been described in patients with asthenozoospermia.…”

Clinical and genetic spectrum in 33 Egyptian families with suspected primary ciliary dyskinesia

“…It has high allelic and locus heterogeneity with mutations in over 40 genes known, so far, to lead to PCD (Table S1). [3][4][5] These genes encode proteins that are either essential for the multiciliogenesis pathway or are structural and assembly proteins (cytoplasmic dynein assembly factors) of the motor machinery of the ciliary axoneme. 6 In the current study, we have used targeted NGS for the genetic investigation of PCD in a cohort of Egyptian families where PCD is highly clinically suspected.…”

Rare Human Diseases: Model Organisms in Deciphering the Molecular Basis of Primary Ciliary Dyskinesia

“…For example, cilia in individuals with PCD caused by the mutation in CCDC39 or CCDC40 (that results in various ciliary defects, see Section 5.2) or DNAH5 (encoding ODA γ dynein heavy chain, Section 5.3.1) were immotile, while the mutation in DNAH9 encoding β dynein heavy chain of ODAs present in the distal part of cilia caused only a slightly reduced bending of the distal part of cilia (see Section 5.3.1). Moreover, neonatal distress, otitis media, or bronchiectasis were not reported in patients with DNAH9 mutation (although the group of PCD patients in this study was small) [33], while such symptoms were very frequent in individuals with mutations in CCDC39, CCDC40, or DNAH5, see Supplementary Materials [34,35].…”

“…Cilia of the respiratory epithelial cells from patients with mutations in DNAH5 are either immotile or exhibit residual twitching movement [85,86]. In contrast, mutations in DNAH11 only reduce the cilia beating amplitude and increase beating frequency [87][88][89], while mutations in DNAH9 do not alter the beating frequency but only slightly reduce the bending of the distal part of cilia [33,84]. The TEM examination of the respiratory epithelial cells revealed that ODAs are missing along the entire cilia length in patients with DNAH5 mutations [35,85,86], but only in the distal part of cilia, if DNAH9 is mutated [33,84] (the distal and proximal parts of cilia are defined based on the absence or presence of the cross-section of the microvilli).…”