Calaxin is required for cilia-driven determination of vertebrate laterality

Calaxin is a key factor for calcium-dependent waveform control in zebrafish sperm

Calcium is critical for regulating the waveform of motile cilia and flagella. Calaxin is currently the only known molecule involved in the calcium-dependent regulation in ascidians. We have recently shown that Calaxin stabilizes outer arm dynein (OAD), and the knockout of Calaxin results in primary ciliary dyskinesia phenotypes in vertebrates. However, from the knockout experiments, it was not clear which functions depend on calcium and how Calaxin regulates the waveform. To address this question, here, we generated transgenic zebrafish expressing a mutant E130A-Calaxin deficient in calcium binding. E130A-Calaxin restored the OAD reduction of calaxin -/- sperm and the abnormal movement of calaxin -/- left-right organizer cilia, showing that Calaxin's stabilization of OADs is calcium-independent. In contrast, our quantitative analysis of E130A-Calaxin sperms showed that the calcium-induced asymmetric beating was not restored, linking Calaxin's calcium-binding ability with an asymmetric flagellar beating for the first time. Our data show that Calaxin is a calcium-dependent regulator of the ciliary beating and a calcium-independent OAD stabilizer.

Deletion of Pax1 scoliosis-associated regulatory elements leads to a female-biased tail abnormality

Adolescent idiopathic scoliosis (AIS), a sideways curvature of the spine, is sexually dimorphic, with increased incidence in females. A genome-wide association study identified a female-specific AIS susceptibility locus near the PAX1 gene. Here, we use mouse enhancer assays, three mouse enhancer knockouts, and subsequent phenotypic analyses to characterize this region. Using mouse enhancer assays, we characterize a sequence, PEC7, which overlaps the AIS-associated variant, and find it to be active in the tail tip and intervertebral disc. Removal of PEC7 or Xe1, a known sclerotome enhancer nearby, or deletion of both sequences lead to a kinky tail phenotype only in the Xe1 and combined (Xe1+PEC7) knockouts, with only the latter showing a female sex dimorphic phenotype. Extensive phenotypic characterization of these mouse lines implicates several differentially expressed genes and estrogen signaling in the sex dimorphic bias. In summary, our work functionally characterizes an AIS-associated locus and dissects the mechanism for its sexual dimorphism.

Dopamine receptor D2 regulates genes involved in germ cell movement and sperm motility in rat testes†

The function of dopamine receptor D2 (D2R) is well associated with sperm motility; however, the physiological role of D2R present on testicular cells remains elusive. The aim of the present study is to delineate the function of testicular D2R. Serum dopamine levels were found to decrease with age, whereas testicular D2R expression increased. In rat testicular sections, D2R immunolabeling was observed in interstitial cells, spermatogonia, spermatocytes and mature elongated spermatids, whereas tyrosine hydroxylase immunolabeling was selectively detected in Leydig cells. In vitro seminiferous tubule culture following bromocriptine (D2R agonist) treatment resulted in decreased cAMP levels. Microarray identified 1077 differentially expressed genes (511 up-regulated, 566 down-regulated). The majority of differentially expressed genes were present in post-meiotic cells including early and late spermatids, and sperm. Gene ontology elucidated processes related to extra-cellular matrix to be enriched and was supported by differential expression of various collagens and laminins, thereby indicating a role of dopamine in extra-cellular matrix integrity and transport of spermatids across the seminiferous epithelium. Gene ontology and enrichment map also highlighted cell/sperm motility to be significantly enriched. Therefore, genes involved in sperm motility functions were further validated by RT-qPCR. Seven genes (Akap4, Ccnyl1, Iqcf1, Klc3, Prss55, Tbc1d21, Tl18) were significantly up-regulated, whereas four genes (Dnah1, Dnah5, Clxn, Fsip2) were significantly down-regulated by bromocriptine treatment. The bromocriptine-stimulated reduction in seminiferous tubule cyclic AMP and associated changes in spermatid gene expression suggests that dopamine regulates both spermatogenesis and spermiogenesis within the seminiferous epithelium, and spermatozoa motility following spermiation, as essential processes for fertility.

Changes in the Dentate Gyrus Gene Expression Profile Induced by Levetiracetam Treatment in Rats with Mesial Temporal Lobe Epilepsy

Temporal lobe epilepsy (TLE) is one of the most common forms of focal epilepsy. Levetiracetam (LEV) is an antiepileptic drug whose mechanism of action at the genetic level has not been fully described. Therefore, the aim of the present work was to evaluate the relevant gene expression changes in the dentate gyrus (DG) of LEV-treated rats with pilocarpine-induced TLE. Whole-transcriptome microarrays were used to obtain the differential genetic profiles of control (CTRL), epileptic (EPI), and EPI rats treated for one week with LEV (EPI + LEV). Quantitative RT-qPCR was used to evaluate the RNA levels of the genes of interest. According to the results of the EPI vs. CTRL analysis, 685 genes were differentially expressed, 355 of which were underexpressed and 330 of which were overexpressed. According to the analysis of the EPI + LEV vs. EPI groups, 675 genes were differentially expressed, 477 of which were downregulated and 198 of which were upregulated. A total of 94 genes whose expression was altered by epilepsy and modified by LEV were identified. The RT-qPCR confirmed that LEV treatment reversed the increased expression of Hgf mRNA and decreased the expression of the Efcab1, Adam8, Slc24a1, and Serpinb1a genes in the DG. These results indicate that LEV could be involved in nonclassical mechanisms involved in Ca2+ homeostasis and the regulation of the mTOR pathway through Efcab1, Hgf, SLC24a1, Adam8, and Serpinb1a, contributing to reduced hyperexcitability in TLE patients.

On the role of calcium diffusion and its rapid buffering in intraflagellar signaling

We have considered the realistic mechanism of rapid Ca2+ (calcium ion) buffering within the wave of calcium ions progressing along the flagellar axoneme. This buffering is an essential part of the Ca2+ signaling pathway aimed at controlling the bending dynamics of flagella. It is primarily achieved by the mobile region of calmodulin molecules and by stationary calaxin, as well as by the part of calmodulin bound to calcium/calmodulin-dependent kinase II and kinase C. We derived and elaborated a model of Ca2+ diffusion within a signaling wave in the presence of these molecules which rapidly buffer Ca2+. This approach has led to a single nonlinear transport equation for the Ca2+ wave that contains the effects brought about by both as necessary buffers for signaling. The presence of mobile buffer calmodulin gives rise to a transport equation that is not strictly diffusive but also exhibits a sink-like effect. We solved straightforwardly the final transport equation in an analytical framework and obtained the implied function of calcium concentration. The effective diffusion coefficient depends on local Ca2+ concentration. It is plausible that these buffers' presence can impact Ca2+ wave speed and shape, which are essential for decoding Ca2+ signaling in flagella. We present the solution of the transport equation for a few specified cases with physiologically reasonable sets of parameters involved.

Genome-Wide Association Studies for Albuminuria of Nondiabetic Taiwanese Population

INTRODUCTION

Chronic kidney disease, which is defined by a reduced estimated glomerular filtration rate and albuminuria, imposes a large health burden worldwide. Ethnicity-specific associations are frequently observed in genome-wide association studies (GWAS). This study conducts a GWAS of albuminuria in the nondiabetic population of Taiwan.

METHODS

Nondiabetic individuals aged 30-70 years without a history of cancer were enrolled from the Taiwan Biobank. A total of 6,768 subjects were subjected to a spot urine examination. After quality control using PLINK and imputation using SHAPEIT and IMPUTE2, a total of 3,638,350 single-nucleotide polymorphisms (SNPs) remained for testing. SNPs with a minor allele frequency of less than 0.1% were excluded. Linear regression was used to determine the relationship between SNPs and log urine albumin-to-creatinine ratio.

RESULTS

Six suggestive loci are identified in or near the FCRL3 (p = 2.56 × 10-6), TMEM161 (p = 4.43 × 10-6), EFCAB1 (p = 2.03 × 10-6), ELMOD1 (p = 2.97 × 10-6), RYR3 (p = 1.34 × 10-6), and PIEZO2 (p = 2.19 × 10-7). Genetic variants in the FCRL3 gene that encode a secretory IgA receptor are found to be associated with IgA nephropathy, which can manifest as proteinuria. The PIEZO2 gene encodes a sensor for mechanical forces in mesangial cells and renin-producing cells. Five SNPs with a p-value between 5 × 10-6 and 5 × 10-5 are also identified in five genes that may have a biological role in the development of albuminuria.

CONCLUSION

Five new loci and one known suggestive locus for albuminuria are identified in the nondiabetic Taiwanese population.

Calaxin stabilizes the docking of outer arm dyneins onto ciliary doublet microtubule in vertebrates

Outer arm dynein (OAD) is the main force generator of ciliary beating. Although OAD loss is the most frequent cause of human primary ciliary dyskinesia, the docking mechanism of OAD onto the ciliary doublet microtubule (DMT) remains elusive in vertebrates. Here, we analyzed the functions of Calaxin/Efcab1 and Armc4, the two of five components of vertebrate OAD-DC (docking complex), using zebrafish spermatozoa and cryo-electron tomography. Mutation of armc4 caused complete loss of OAD, whereas mutation of calaxin caused only partial loss of OAD. Detailed structural analysis revealed that calaxin-/- OADs are tethered to DMT through DC components other than Calaxin, and that recombinant Calaxin can autonomously rescue the deficient DC structure and the OAD instability. Our data demonstrate the discrete roles of Calaxin and Armc4 in the OAD-DMT interaction, suggesting the stabilizing process of OAD docking onto DMT in vertebrates.

Deletion of Pax1 scoliosis-associated regulatory elements leads to a female-biased tail abnormality

Adolescent idiopathic scoliosis (AIS), a sideways curvature of the spine, is sexually dimorphic, with increased incidence in females. A GWAS identified a female-specific AIS susceptibility locus near the PAX1 gene. Here, we used mouse enhancer assays, three mouse enhancer knockouts and subsequent phenotypic analyses to characterize this region. Using mouse enhancer assays, we characterized a sequence, PEC7, that overlaps the AIS-associated variant, and found it to be active in the tail tip and intervertebral disc. Removal of PEC7 or Xe1, a known sclerotome enhancer nearby, and deletion of both sequences led to a kinky phenotype only in the Xe1 and combined (Xe1+PEC7) knockouts, with only the latter showing a female sex dimorphic phenotype. Extensive phenotypic characterization of these mouse lines implicated several differentially expressed genes and estrogen signaling in the sex dimorphic bias. In summary, our work functionally characterizes an AIS-associated locus and dissects the mechanism for its sexual dimorphism.

Calaxin is required for asymmetric bend initiation and propagation in sperm flagella

Regulation of waveform asymmetry in flagella is critical for changes in direction when sperm are swimming, as seen during the chemotaxis of sperm towards eggs. Ca2+ is an important regulator of asymmetry in flagellar waveforms. A calcium sensor protein, calaxin, is associated with the outer arm dynein and plays a key role in the regulation of flagellar motility in a Ca2+-dependent manner. However, the underlying mechanism of regulating asymmetric waves by means of Ca2+ and calaxin remains unclear. To clarify the calaxin-dependent mechanism for generating Ca2+-dependent asymmetric flagellar waveforms, we analyzed the initial step of flagellar bend formation and propagation in the sperm of the ascidian Ciona intestinalis. Our experiment used demembranated sperm cells, which were then reactivated by UV flash photolysis of caged ATP under both high and low Ca2+ concentrations. Here, we show that initial bends in the flagella are formed at the base of the sperm and propagate towards the tip during waveform generation. However, the direction of the initial bend differed between asymmetric and symmetric waves. When a calaxin inhibitor (repaglinide) was applied, it resulted in the failure of asymmetric wave formation and propagation. This was because repaglinide had no effect on initial bend formation, but it significantly inhibited the generation of the subsequent bend in the reverse direction. Switching of dynein sliding activity by mechanical feedback is crucial for flagellar oscillation. Our results suggest that the Ca2+/calaxin mechanism plays an important role in the switching of dynein activity from microtubule sliding in the principal bend into the suppressed sliding in the reverse bend, thereby allowing the sperm to successfully change direction.

Understanding laterality disorders and the left-right organizer: Insights from zebrafish

Vital internal organs display a left-right (LR) asymmetric arrangement that is established during embryonic development. Disruption of this LR asymmetry-or laterality-can result in congenital organ malformations. Situs inversus totalis (SIT) is a complete concordant reversal of internal organs that results in a low occurrence of clinical consequences. Situs ambiguous, which gives rise to Heterotaxy syndrome (HTX), is characterized by discordant development and arrangement of organs that is associated with a wide range of birth defects. The leading cause of health problems in HTX patients is a congenital heart malformation. Mutations identified in patients with laterality disorders implicate motile cilia in establishing LR asymmetry. However, the cellular and molecular mechanisms underlying SIT and HTX are not fully understood. In several vertebrates, including mouse, frog and zebrafish, motile cilia located in a "left-right organizer" (LRO) trigger conserved signaling pathways that guide asymmetric organ development. Perturbation of LRO formation and/or function in animal models recapitulates organ malformations observed in SIT and HTX patients. This provides an opportunity to use these models to investigate the embryological origins of laterality disorders. The zebrafish embryo has emerged as an important model for investigating the earliest steps of LRO development. Here, we discuss clinical characteristics of human laterality disorders, and highlight experimental results from zebrafish that provide insights into LRO biology and advance our understanding of human laterality disorders.

Consensus nomenclature for dyneins and associated assembly factors

Dyneins are highly complex, multicomponent, microtubule-based molecular motors. These enzymes are responsible for numerous motile behaviors in cytoplasm, mediate retrograde intraflagellar transport (IFT), and power ciliary and flagellar motility. Variants in multiple genes encoding dyneins, outer dynein arm (ODA) docking complex subunits, and cytoplasmic factors involved in axonemal dynein preassembly (DNAAFs) are associated with human ciliopathies and are of clinical interest. Therefore, clear communication within this field is particularly important. Standardizing gene nomenclature, and basing it on orthology where possible, facilitates discussion and genetic comparison across species. Here, we discuss how the human gene nomenclature for dyneins, ODA docking complex subunits, and DNAAFs has been updated to be more functionally informative and consistent with that of the unicellular green alga Chlamydomonas reinhardtii, a key model organism for studying dyneins and ciliary function. We also detail additional nomenclature updates for vertebrate-specific genes that encode dynein chains and other proteins involved in dynein complex assembly.

Common Genetic Variants Contribute to Risk of Transposition of the Great Arteries

RATIONALE

Dextro-transposition of the great arteries (D-TGA) is a severe congenital heart defect which affects approximately 1 in 4,000 live births. While there are several reports of D-TGA patients with rare variants in individual genes, the majority of D-TGA cases remain genetically elusive. Familial recurrence patterns and the observation that most cases with D-TGA are sporadic suggest a polygenic inheritance for the disorder, yet this remains unexplored.

OBJECTIVE

We sought to study the role of common single nucleotide polymorphisms (SNPs) in risk for D-TGA.

METHODS AND RESULTS

We conducted a genome-wide association study in an international set of 1,237 patients with D-TGA and identified a genome-wide significant susceptibility locus on chromosome 3p14.3, which was subsequently replicated in an independent case-control set (rs56219800, meta-analysis P=8.6x10-10, OR=0.69 per C allele). SNP-based heritability analysis showed that 25% of variance in susceptibility to D-TGA may be explained by common variants. A genome-wide polygenic risk score derived from the discovery set was significantly associated to D-TGA in the replication set (P=4x10-5). The genome-wide significant locus (3p14.3) co-localizes with a putative regulatory element that interacts with the promoter of WNT5A, which encodes the Wnt Family Member 5A protein known for its role in cardiac development in mice. We show that this element drives reporter gene activity in the developing heart of mice and zebrafish and is bound by the developmental transcription factor TBX20. We further demonstrate that TBX20 attenuates Wnt5a expression levels in the developing mouse heart.

CONCLUSIONS

This work provides support for a polygenic architecture in D-TGA and identifies a susceptibility locus on chromosome 3p14.3 near WNT5A. Genomic and functional data support a causal role of WNT5A at the locus.

Low-level EFCAB1 promoted progress by upregulated DNMT3B and could be as a potential biomarker in lung adenocarcinoma

BACKGROUND

Lung adenocarcinoma (LUAD) incidence is on the rise. We found that EFCAB1 (EF-Hand Calcium Binding Domain 1) was significantly downregulated in LUAD tissues, but the mechanism of EFCAB1 is unknown.

METHODS

One hundred and two LUAD samples and corresponding NT samples were prospectively collected from patients at the First Affiliated Hospital of Wenzhou Medical University, Wenzhou, China, from August 2018 to August 2021.EFCAB1 expression was estimated in LUAD cells and tissues by qPCR. In-vitro cytology assays were used to detect the role of EFCAB1 in LUAD cells.

RESULTS

EFCAB1 expression level of LUAD was significantly lower than it's adjacent cancer tissues and that of LUAD with big tumor size (>2 cm) was significantly lower than that of small tumor size (≤2 cm) group. It shown that expression levels of EFCAB1 from A549, HCC827, PC9 were lowly expressed. The cell migration, invasion, colony formation, proliferation ability of EFCAB1 OE A549, PC9 were lower than that of EFCAB1 OE A549, PC9 NC group, while the apoptotic cells percentage of the EFCAB1 OE A549, PC9 group were significantly increased. We found that DNMT1 mRNA expression level of PC9 was higher than that of BEAS-2B, while these of A549, HCC827 decreased. Compared with BEAS-2B, DNMT3A mRNA expression level of PC9 increased. DNMT3B mRNA expression level of PC9, HCC827 were higher than these of BEAS-2B.

CONCLUSION

The EFCAB1 mRNA in LUAD patients and cell lines were downregulated; EFCAB1 overexpression inhibited cell proliferation, migration, invasion, while promoted apoptosis. EFCAB1 was expected to become a biomarker of LUAD.

De novo identification of mammalian ciliary motility proteins using cryo-EM

Dynein-decorated doublet microtubules (DMTs) are critical components of the oscillatory molecular machine of cilia, the axoneme, and have luminal surfaces patterned periodically by microtubule inner proteins (MIPs). Here we present an atomic model of the 48-nm repeat of a mammalian DMT, derived from a cryoelectron microscopy (cryo-EM) map of the complex isolated from bovine respiratory cilia. The structure uncovers principles of doublet microtubule organization and features specific to vertebrate cilia, including previously unknown MIPs, a luminal bundle of tektin filaments, and a pentameric dynein-docking complex. We identify a mechanism for bridging 48- to 24-nm periodicity across the microtubule wall and show that loss of the proteins involved causes defective ciliary motility and laterality abnormalities in zebrafish and mice. Our structure identifies candidate genes for diagnosis of ciliopathies and provides a framework to understand their functions in driving ciliary motility.

Co-expression analysis identifies neuro-inflammation as a driver of sensory neuron aging in Aplysia californica

Aging of the nervous system is typified by depressed metabolism, compromised proteostasis, and increased inflammation that results in cognitive impairment. Differential expression analysis is a popular technique for exploring the molecular underpinnings of neural aging, but technical drawbacks of the methodology often obscure larger expression patterns. Co-expression analysis offers a robust alternative that allows for identification of networks of genes and their putative central regulators. In an effort to expand upon previous work exploring neural aging in the marine model Aplysia californica, we used weighted gene correlation network analysis to identify co-expression networks in a targeted set of aging sensory neurons in these animals. We identified twelve modules, six of which were strongly positively or negatively associated with aging. Kyoto Encyclopedia of Genes analysis and investigation of central module transcripts identified signatures of metabolic impairment, increased reactive oxygen species, compromised proteostasis, disrupted signaling, and increased inflammation. Although modules with immune character were identified, there was no correlation between genes in Aplysia that increased in expression with aging and the orthologous genes in oyster displaying long-term increases in expression after a virus-like challenge. This suggests anti-viral response is not a driver of Aplysia sensory neuron aging.

Ultrastructural evidence for an unusual mode of ciliogenesis in mouse multiciliated epithelia

Multiciliogenesis is a cascading process for generating hundreds of motile cilia in single cells. In vertebrates, this process has been investigated in the ependyma of brain ventricles and the ciliated epithelia of the airway and oviduct. Although the early steps to amplify centrioles have been characterized in molecular detail, subsequent steps to establish multicilia have been relatively overlooked. Here, we focused on unusual cilia-related structures previously observed in wild-type mouse ependyma using transmission electron microscopy and analyzed their ultrastructural features and the frequency of their occurrence. In the ependyma, $\sim$5% of cilia existed as bundles; while the majority of the bundles were paired, bundles of more than three cilia were also found. Furthermore, apical protrusions harboring multiple sets of axonemes were occasionally observed (0-2 per section), suggesting an unusual mode of ciliogenesis. In trachea and oviduct epithelia, ciliary bundles were absent, but protrusions containing multiple axonemes were observed. At the base of such protrusions, certain axonemes were completely enwrapped by membranes, whereas others remained incompletely enwrapped. These data suggested that the late steps of multiciliogenesis might include a unique process underlying the development of cilia, which is distinct from the ciliogenesis of primary cilia.

Centrosomes and cilia: always at the center of the action

Centrosomes are the main microtubule-organizing centers in animal cells, indispensable for cell division and the building of a wide range of cilia, which include sensory and motile cilia. We are now inviting submissions related to the fascinating field of centrosomes, cilia and all of the processes that they are involved in with the aim of highlighting this work in a Special Collection.

Motile cilia genetics and cell biology: big results from little mice

Our understanding of motile cilia and their role in disease has increased tremendously over the last two decades, with critical information and insight coming from the analysis of mouse models. Motile cilia form on specific epithelial cell types and typically beat in a coordinated, whip-like manner to facilitate the flow and clearance of fluids along the cell surface. Defects in formation and function of motile cilia result in primary ciliary dyskinesia (PCD), a genetically heterogeneous disorder with a well-characterized phenotype but no effective treatment. A number of model systems, ranging from unicellular eukaryotes to mammals, have provided information about the genetics, biochemistry, and structure of motile cilia. However, with remarkable resources available for genetic manipulation and developmental, pathological, and physiological analysis of phenotype, the mouse has risen to the forefront of understanding mammalian motile cilia and modeling PCD. This is evidenced by a large number of relevant mouse lines and an extensive body of genetic and phenotypic data. More recently, application of innovative cell biological techniques to these models has enabled substantial advancement in elucidating the molecular and cellular mechanisms underlying the biogenesis and function of mammalian motile cilia. In this article, we will review genetic and cell biological studies of motile cilia in mouse models and their contributions to our understanding of motile cilia and PCD pathogenesis.

Dissecting the signaling pathways involved in the function of sperm flagellum

The mammalian flagellum is a specific type of motile cilium required for sperm motility and male fertility. Effective flagellar movement is dependent on axonemal function, which in turn relies on proper ion homeostasis within the flagellar compartment. This ion homeostasis is maintained by the concerted function of ion channels and transporters that initiate signal transduction pathways resulting in motility changes. Advances in electrophysiology and super-resolution microscopy have helped to identify and characterize new regulatory modalities of the mammalian flagellum. Here, we discuss what is currently known about the regulation of flagellar ion channels and transporters that maintain sodium, potassium, calcium, and proton homeostasis. Identification of new regulatory elements and their specific roles in sperm motility is imperative for improving diagnostics of male infertility.

Testis-enriched kinesin KIF9 is important for progressive motility in mouse spermatozoa

Kinesin is a molecular motor that moves along microtubules. Kinesin family member 9 (KIF9) is evolutionarily conserved and expressed strongly in mouse testis. In the unicellular flagellate Chlamydomonas, KLP1 (ortholog of KIF9) is localized to the central pair microtubules of the axoneme and regulates flagellar motility. In contrast, the function of KIF9 remains unclear in mammals. Here, we mutated KIF9 in mice using the CRISPR/Cas9 system. Kif9 mutated mice exhibit impaired sperm motility and subfertility. Further analysis reveals that the flagella lacking KIF9 showed an asymmetric waveform pattern, which leads to a circular motion of spermatozoa. In spermatozoa that lack the central pair protein HYDIN, KIF9 was not detected by immunofluorescence and immunoblot analysis. These results suggest that KIF9 is associated with the central pair microtubules and regulates flagellar motility in mice.

Nexin-Dynein regulatory complex component DRC7 but not FBXL13 is required for sperm flagellum formation and male fertility in mice

Flagella and cilia are evolutionarily conserved cellular organelles. Abnormal formation or motility of these organelles in humans causes several syndromic diseases termed ciliopathies. The central component of flagella and cilia is the axoneme that is composed of the ‘9+2’ microtubule arrangement, dynein arms, radial spokes, and the Nexin-Dynein Regulatory Complex (N-DRC). The N-DRC is localized between doublet microtubules and has been extensively studied in the unicellular flagellate Chlamydomonas. Recently, it has been reported that TCTE1 (DRC5), a component of the N-DRC, is essential for proper sperm motility and male fertility in mice. Further, TCTE1 has been shown to interact with FBXL13 (DRC6) and DRC7; however, functional roles of FBXL13 and DRC7 in mammals have not been elucidated. Here we show that Fbxl13 and Drc7 expression are testes-enriched in mice. Although Fbxl13 knockout (KO) mice did not show any obvious phenotypes, Drc7 KO male mice were infertile due to their short immotile spermatozoa. In Drc7 KO spermatids, the axoneme is disorganized and the ‘9+2’ microtubule arrangement was difficult to detect. Further, other N-DRC components fail to incorporate into the flagellum without DRC7. These results indicate that Drc7, but not Fbxl13, is essential for the correct assembly of the N-DRC and flagella.

In recent years, almost one in six couples face infertility, and nearly 50% of cases are attributed to male factors. It has been shown that approximately 15% of male infertility is caused by genetic factors. The conditions of male infertility mainly include spermatozoa with abnormal morphology (teratozoospermia), reduced sperm motility (asthenozoospermia), and no or low sperm count (azoospermia). Multiple morphological abnormalities of the sperm flagella (MMAF) are characterized as asthenoteratozoospermia, which is a condition with abnormal sperm tail morphology, including absent, coiled, bent, or short tails. Sperm tails are formed during spermiogenesis; however, the mechanism that govern tail formation remains unclear. Here we mutated Fbxl13 and Drc7, two genes with strong expression in mouse testis and which have been shown to be important for flagellum formation and regulation in other systems. Deletion of Drc7 leads to aberrant tail formation in mouse spermatozoa that phenocopies patients with MMAF, while deletion of Fbxl13 has no observable effect on sperm function. Our results identified DRC7 as an important factor for sperm flagellum formation.