Defects in the cytoplasmic assembly of axonemal dynein arms cause morphological abnormalities and dysmotility in sperm cells leading to male infertility

Abstract

Axonemal protein complexes, such as outer (ODA) and inner (IDA) dynein arms, are responsible for the generation and regulation of flagellar and ciliary beating. Studies in various ciliated model organisms have shown that axonemal dynein arms are first assembled in the cell cytoplasm and then delivered into axonemes during ciliogenesis. In humans, mutations in genes encoding for factors involved in this process cause structural and functional defects of motile cilia in various organs such as the airways and result in the hereditary disorder primary ciliary dyskinesia (PCD). Despite extensive knowledge about the cytoplasmic assembly of axonemal dynein arms in respiratory cilia, this process is still poorly understood in sperm flagella. To better define its clinical relevance on sperm structure and function, and thus male fertility, further investigations are required. Here we report the fertility status in different axonemal dynein preassembly mutant males (DNAAF2/ KTU, DNAAF4/ DYX1C1, DNAAF6/ PIH1D3, DNAAF7/ZMYND10, CFAP300/C11orf70 and LRRC6). Besides andrological examinations, we functionally and structurally analyzed sperm flagella of affected individuals by high-speed video- and transmission electron microscopy as well as systematically compared the composition of dynein arms in sperm flagella and respiratory cilia by immunofluorescence microscopy. Furthermore, we analyzed the flagellar length in dynein preassembly mutant sperm. We found that the process of axonemal dynein preassembly is also critical in sperm, by identifying defects of ODAs and IDAs in dysmotile sperm of these individuals. Interestingly, these mutant sperm consistently show a complete loss of ODAs, while some respiratory cilia from the same individual can retain ODAs in the proximal ciliary compartment. This agrees with reports of solely one distinct ODA type in sperm, compared to two different ODA types in proximal and distal respiratory ciliary axonemes. Consistent with observations in model organisms, we also determined a significant reduction of sperm flagellar length in these individuals. These findings are relevant to subsequent studies on the function and composition of sperm flagella in PCD patients and non-syndromic infertile males. Our study contributes to a better understanding of the fertility status in PCD-affected males and should help guide genetic and andrological counselling for affected males and their families.

Diagnostics and Management of Male Infertility in Primary Ciliary Dyskinesia

“…A candidate compensating gene for RSPH4A in the testis is RSPH6A, which is predominantly expressed in the testis [33]. Previous studies and expression data suggest that dynein arm preassembly genes are required for sperm motility and, therefore, mutations in these genes can be expected to cause male infertility (Figure 2, [34]), although differences in assembly mechanisms exist. A lack of dynein arm preassembly factor TTC12 PCD genes can be divided into different categories: multiciliogenesis, dynein arm preassembly, ODA/IDA, RS/CP, and genes associated with nexin links and microtubular organization.…”

Properties of Non-Aminoglycoside Compounds Used to Stimulate Translational Readthrough of PTC Mutations in Primary Ciliary Dyskinesia

“…Clinical symptoms occur from birth (neonatal respiratory distress) and mainly cause recurrent and chronic upper and lower airway infections, which lead to progressive deterioration of pulmonary function if not treated [ 2 ]. Disruption of the left–right asymmetry of inner organs (situs inversus) occurs in approximately half of PCD patients, and both male and female fertility can be affected depending on the causal PCD gene [ 6 , 7 ]. A PCD diagnosis is challenging and requires several specialized tests [ 8 ].…”

Identification of Two Novel DNAAF2 Variants in Two Consanguineous Families with Primary Ciliary Dyskinesia

“…Sperm flagellar length is significantly reduced in DNAAF2-mutant males. 25 However, female infertility and scoliosis has not been investigated in patients with DNAAF2 variant due to fallopian tubes and ependymal cells involved. Both Our patients both exhibited chronic sinusitis, bronchiectasis, reduced nNO production rate and female infertility, and one patient also presented with situs inversus and scoliosis.…”