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

Isabella Aprea,Johanna Raidt,Judit Horvath,Tabea Nöthe-Menchen,Sabine Kliesch,Inga Marlena Höben,Heike Olbrich,Claudia Krallmann,Frank Tüttelmann,Luisa Biebach,Thomas Kaiser,Petra Pennekamp,Maria Schubert,Niki Tomas Loges,Heymut Omran,Susan K Dutcher

doi:10.1371/journal.pgen.1009306

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.

Highlights

According to the World Health Organization (WHO), infertility is defined as the inability to conceive a child naturally after at least one year of frequent, unprotected sexual intercourse
Patients may present with reduced number or complete absence of sperm in the ejaculate, as well as functional and/or morphological sperm defects compromising sperm motility
Further studies in Chlamydomonas PF13-mutant strain revealed that mutations in DNAAF2 block assembly of the ODA heavy chains while ODA intermediated chains accumulate in the cytoplasm. These findings indicate that DNAAF2 functions as a chaperone and is involved in early steps of dynein assembly [23]

Summary

Introduction

According to the World Health Organization (WHO), infertility is defined as the inability to conceive a child naturally after at least one year of frequent, unprotected sexual intercourse. Male infertility represents a highly heterogeneous pathological condition that affects approximately 7% of the male population [5] comprising various causes. At least 2000 genes are involved in spermatogenesis and complex sperm and histological testicular phenotypes are observed in infertile men [6]. Among these quantitative and qualitative spermatogenic defects, other disturbances contribute to male infertility, such as ductal obstruction or dysfunction, and hypothalamic-pituitary axis dysfunction [7]. The cause and pathomechanism underlying male infertility remain unsolved in approximately 40% of cases [3]. One factor that contributes to idiopathic cases of male infertility is asthenozoospermia (reduced sperm motility) due to defective sperm flagellar function. Combinations with abnormal sperm morphology (asthenoteratozoospermia) and reduced numbers of sperm in the ejaculate (oligoasthenoteratozoospermia) are frequently observed [3]

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