Crystal structure of the stalk region of axonemal inner-arm dynein-d reveals unique features in the coiled-coil and microtubule-binding domain

Functional and structural significance of the inner-arm-dynein subspecies d in ciliary motility

Motile cilia play various important physiological roles in eukaryotic organisms including cell motility and fertility. Inside motile cilia, large motor-protein complexes called "ciliary dyneins" coordinate their activities and drive ciliary motility. The ciliary dyneins include the outer-arm dyneins, the double-headed inner-arm dynein (IDA f/I1), and several single-headed inner-arm dyneins (IDAs a, b, c, d, e, and g). Among these single-headed IDAs, one of the ciliary dyneins, IDA d, is of particular interest because of its unique properties and subunit composition. In addition, defects in this subspecies have recently been associated with several types of ciliopathies in humans, such as primary ciliary dyskinesia and multiple morphologic abnormalities of the flagellum. In this mini-review, we discuss the composition, structure, and motor properties of IDA d, which have been studied in the model organism Chlamydomonas reinhardtii, and further discuss the relationship between IDA d and human ciliopathies. In addition, we provide future perspectives and discuss remaining questions regarding this intriguing dynein subspecies.

AXDND1 is required to balance spermatogonial commitment and for sperm tail formation in mice and humans

Dynein complexes are large, multi-unit assemblies involved in many biological processes via their critical roles in protein transport and axoneme motility. Using next-generation sequencing of infertile men presenting with low or no sperm in their ejaculates, we identified damaging variants in the dynein-related gene AXDND1. We thus hypothesised that AXDND1 is a critical regulator of male fertility. To test this hypothesis, we produced a knockout mouse model. Axdnd1-/- males were sterile at all ages but presented with an evolving testis phenotype wherein they could undergo one round of histologically replete spermatogenesis followed by a rapid depletion of the seminiferous epithelium. Marker experiments identified a role for AXDND1 in maintaining the balance between differentiation-committed and self-renewing spermatogonial populations, resulting in disproportionate production of differentiating cells in the absence of AXDND1 and increased sperm production during initial spermatogenic waves. Moreover, long-term spermatogonial maintenance in the Axdnd1 knockout was compromised, ultimately leading to catastrophic germ cell loss, destruction of blood-testis barrier integrity and immune cell infiltration. In addition, sperm produced during the first wave of spermatogenesis were immotile due to abnormal axoneme structure, including the presence of ectopic vesicles and abnormalities in outer dense fibres and microtubule doublet structures. Sperm output was additionally compromised by a severe spermiation defect and abnormal sperm individualisation. Collectively these data identify AXDND1 as an atypical dynein complex-related protein with a role in protein/vesicle transport of relevance to spermatogonial function and sperm tail formation in mice and humans. This study underscores the importance of studying the consequences of gene loss-of-function on both the establishment and maintenance of male fertility.

Identification of high-risk non-synonymous SNPs (nsSNPs) in DNAH1 and DNAH17 genes associated with male infertility: a bioinformatics analysis

Male infertility is a significant reproductive issue affecting a considerable number of couples worldwide. While there are various causes of male infertility, genetic factors play a crucial role in its development. We focused on identifying and analyzing the high-risk nsSNPs in DNAH1 and DNAH17 genes, which encode proteins involved in sperm motility. A total of 20 nsSNPs for DNAH1 and 10 nsSNPs for DNAH17 were analyzed using various bioinformatics tools including SIFT, PolyPhen-2, CADD, PhD-SNPg, VEST-4, and MutPred2. As a result, V1287G, L2071R, R2356W, R3169C, R3229C, E3284K, R4096L, R4133C, and A4174T in DNAH1 gene and C1803Y, C1829Y, R1903C, and L3595P in DNAH17 gene were identified as high-risk nsSNPs. These nsSNPs were predicted to decrease protein stability, and almost all were found in highly conserved amino acid positions. Additionally, 4 nsSNPs were observed to alter post-translational modification status. Furthermore, the interaction network analysis revealed that DNAH1 and DNAH17 interact with DNAH2, DNAH3, DNAH5, DNAH7, DNAH8, DNAI2, DNAL1, CFAP70, DNAI3, DNAI4, ODAD1, and DNAI7, demonstrating the importance of DNAH1 and DNAH17 proteins in the overall functioning of the sperm motility machinery. Taken together, these findings revealed the detrimental effects of identified high-risk nsSNPs on protein structure and function and highlighted their potential relevance to male infertility. Further studies are warranted to validate these findings and to elucidate the underlying mechanisms.

AXDND1 is required to balance spermatogonial commitment and for sperm tail formation in mice and humans

Dynein complexes are large, multi-unit assemblies involved in many biological processes including male fertility via their critical roles in protein transport and axoneme motility. Previously we identified a pathogenic variant in the dynein gene AXDND1 in an infertile man. Subsequently we identified an additional four potentially compound heterozygous variants of unknown significance in AXDND1 in two additional infertile men. We thus tested the role of AXDND1 in mammalian male fertility by generating a knockout mouse model. Axdnd1-/- males were sterile at all ages but could undergo one round of histologically complete spermatogenesis. Subsequently, a progressive imbalance of spermatogonial commitment to spermatogenesis over self-renewal occurred, ultimately leading to catastrophic germ cell loss, loss of blood-testis barrier patency and immune cell infiltration. Sperm produced during the first wave of spermatogenesis were immotile due to abnormal axoneme structure, including the presence of ectopic vesicles and abnormalities in outer dense fibres and microtubule doublet structures. Sperm output was additionally compromised by a severe spermiation defect and abnormal sperm individualisation. Collectively, our data highlight the essential roles of AXDND1 as a regulator of spermatogonial commitment to spermatogenesis and during the processes of spermiogenesis where it is essential for sperm tail development, release and motility.