Ciliary motility: the components and cytoplasmic preassembly mechanisms of the axonemal dyneins

Chlamydomonas FBB18 is a ubiquitin-like protein essential for the cytoplasmic preassembly of various ciliary dyneins

Motile cilia are organelles found on many eukaryotic cells that play critical roles in development and fertility. Human CFAP298 has been implicated in the transport/assembly of ciliary dyneins, and defects in this protein cause primary ciliary dyskinesia. However, neither the exact function nor the structure of CFAP298 have been elucidated. Here, we took advantage of Chlamydomonas, a ciliated alga, to study the structure and function of FBB18, an ortholog of CFAP298. Multiple ciliary dyneins were greatly reduced in cilia of Chlamydomonas fbb18 mutants. In addition, we found that both the stability of ciliary dynein heavy chains (HCs) and the association between HCs and intermediate/light chains (IC/LCs) are greatly reduced in fbb18 cytoplasm, strongly suggesting that FBB18 functions in the cytoplasmic assembly (the so-called "preassembly") of dynein complexes from HC/IC/LCs. Furthermore, X-ray crystallography revealed that FBB18 forms a bilobed structure with globular domains at both ends of the molecule, connected by an α-helical bundle. Unexpectedly, one globular domain shows high similarity to ubiquitin, a small protein critical for the modification of a variety of protein complexes, and this ubiquitin-like domain is indispensable for the molecular function of FBB18. Our results demonstrate that FBB18, a specialized member of the ubiquitin-like protein family, plays a critical role in dynein preassembly, most likely by mediating diverse interactions between dynein HCs, molecular chaperone(s), and other preassembly factor(s) using the ubiquitin-like domain as well as other regions, and by facilitating the proper folding of dynein HCs.

Effects of different concentrations of N-acetylcysteine on the sperm quality, antioxidant enzyme activity, and antioxidant gene expression of cryopreserved goat semen

During cryopreservation, spermatozoa produce excess reactive oxygen species (ROS), which attack the plasma membrane, disrupt the physiological structure of the sperm, and ultimately decrease semen quality. This study investigated the effects of different N-acetylcysteine (NAC) concentrations on the cryopreservation of semen from Qianbei Ma goats. Semen samples were collected from five bucks with motility rates above 80 %. The treatment groups were diluted 20-fold in extenders containing 3 or 9 mM NAC and cryopreserved in liquid nitrogen, whereas the control group did not include NAC. After thawing, the sperm motility, antioxidant gene expression, enzyme activity, and cell structure were analysed. The NAC-treated groups showed improved post-thaw sperm motility. The 9 mM NAC group presented the highest catalase (CAT) and glutathione peroxidase activities, lowest ROS levels, and fewest apoptotic sperms. Moreover, the 3 mM NAC group presented the highest superoxide dismutase activity and L-cysteine levels and the lowest malondialdehyde levels. Additionally, sperm membrane integrity and mitochondrial membrane potential were significantly higher in the NAC-treated group than that in the control. Further analysis of antioxidant and apoptotic gene expression in the treated sperm revealed that the 9 mM NAC group presented significantly greater CAT and GPX4 expression than the control and 3 mM NAC groups, whereas the apoptotic genes BAX and Caspase3 were elevated in the control group compared to both the NAC groups. In summary, adding NAC to semen extenders enhanced antioxidant gene expression, increased enzyme activity, and improved post-thaw semen quality, with the 9 mM NAC treatment showing the optimal effects.

Mapping the proteome landscape of Indian Zebu (Sahiwal) spermatozoa using high-resolution mass spectrometry and in-silico annotation

Proteomic analysis of sperm cells offers significant insights into proteins' structural, functional, and localization aspects within biological systems. Sahiwal, a native Indian cattle breed, is well known for its disease resistance, calving ease, and resilience to drought. This study addressed the gap in Sahiwal's comprehensive sperm proteome profiling data. The research involved the global in-silico quantitative high-resolution mass spectrometry-based protein profiling of Indian Zebu sperm, identifying 4651 sperm proteins. Beyond mere identification, the study characterized these proteins at a sub-organellar level to facilitate a better understanding of their functional attributes. Gene Ontology analysis of sperm proteins facilitated the segregation of proteins based on their function, localization, and mode of action. The study revealed that despite the limited number of organelles, sperm cells encapsulate a wide array of crucial proteins, compensating for the deficiency of organelles through the presence of multifunctional proteins. Most identified sperm proteins actively participate in spermatogenesis, motility, acrosome reaction, capacitation, and seminal plasma binding, directly or indirectly. Notably, the results not only present the highest number of identified bovine sperm proteins but also hold the potential to pave the way for empirical research on sperm functionality, egg-sperm interaction, sperm-sex sorting biomarkers, sperm quality, and bull fertility.

The Domestication of Wild Boar Could Result in a Relaxed Selection for Maintaining Olfactory Capacity

Domesticated animals are artificially selected to exhibit desirable traits, however not all traits of domesticated animals are the result of deliberate selection. Loss of olfactory capacity in the domesticated pig (Sus scrofa domesticus) is one example. We used whole transcriptome analysis (RNA-Seq) to compare patterns of gene expression in the olfactory mucosa of the pig and two subspecies of wild boar (Sus scrofa), and investigate candidate genes that could be responsible for the loss of olfactory capacity. We identified hundreds of genes with reductions in transcript abundance in pig relative to wild boar as well as differences between the two subspecies of wild boar. These differences were detected mainly in genes involved in the formation and motility of villi, cilia and microtubules, functions associated with olfaction. In addition, differences were found in the abundances of transcripts of genes related to immune defenses, with the highest levels in continental wild boar subspecies. Overall, the loss of olfactory capacity in pigs appears to have been accompanied by reductions in the expression of candidate genes for olfaction. These changes could have resulted from unintentional selection for reduced olfactory capacity, relaxed selection for maintaining olfactory capacity, pleiotropic effects of genes under selection, or other non-selective processes. Our findings could be a cornerstone for future researches on wild boars, pigs, feral populations, and their evolutionary trajectories, aimed to provide tools to better calibrate species management as well as guidelines for breeders.

Dnali1 is required for sperm motility and male fertility in mice

BACKGROUND

The sperm flagellum is an evolutionarily conserved specialized organelle responsible for sperm motility and male fertility. Deleterious mutations in genes involved in the sperm flagellum assembly can often cause sperm motility defects and male infertility. The murine Dnali1 gene encodes a protein that is known to interact with the cytoplasmic dynein heavy chain 1.

RESULTS

A Dnali1-mutated mouse model was generated by inducing a nonsense mutation in the Dnali1 gene. The Dnali1-mutated male mice presented impaired sperm motility and were completely infertile. Although no obviously abnormal sperm morphology was observed in Dnali1-mutated male mice, the ultrastructural structure of sperm flagellum was disrupted, displaying as an asymmetrical distribution of the longitudinal columns (LCs). Notably, infertile Dnali1-mutated male mice were able to obtain offspring via ICSI.

CONCLUSIONS

Our results uncover a role of DNALI1 in sperm motility and male fertility in mice, and demonstrate that ICSI overcomes Dnali1-associated male infertility, thus providing guidance for the diagnosis and genetic counseling of DNALI1-associated human infertility.

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.

Establishment of a repertoire of fertility associated sperm proteins and their differential abundance in buffalo bulls (Bubalus bubalis) with contrasting fertility

Sperm harbours a wide range of proteins regulating their functions and fertility. In the present study, we made an effort to characterize and quantify the proteome of buffalo bull spermatozoa, and to identify fertility associated sperm proteins through comparative proteomics. Using high-throughput mass spectrometry platform, we identified 1305 proteins from buffalo spermatozoa and found that these proteins were mostly enriched in glycolytic process, mitochondrial respiratory chain, tricarboxylic acid cycle, protein folding, spermatogenesis, sperm motility and sperm binding to zona pellucida (p < 7.74E-08) besides metabolic (p = 4.42E-31) and reactive oxygen species (p = 1.81E-30) pathways. Differential proteomic analysis revealed that 844 proteins were commonly expressed in spermatozoa from both the groups while 77 and 52 proteins were exclusively expressed in high- and low-fertile bulls, respectively. In low-fertile bulls, 75 proteins were significantly (p < 0.05) upregulated and 176 proteins were significantly (p < 0.05) downregulated; these proteins were highly enriched in mitochondrial respiratory chain complex I assembly (p = 2.63E-07) and flagellated sperm motility (p = 7.02E-05) processes besides oxidative phosphorylation pathway (p = 6.61E-15). The down regulated proteins in low-fertile bulls were involved in sperm motility, metabolism, sperm-egg recognition and fertilization. These variations in the sperm proteome could be used as potential markers for the selection of buffalo bulls for fertility.

Fixation methods and immunolabeling for cilia proteins in ciliary and extraciliary locations

Primary cilia are complex organelles, usually singularly located on cell surfaces that are now known to be important for signaling and whose defect is implicated in a category of developmental diseases known as ciliopathies. They are composed of a microtubule axoneme and contain a cilia membrane that is unique and distinct from the plasma membrane. Primary cilia also have their own transport system termed the intraflagellar transport (IFT) system that allows for proteins to be trafficked along the microtubule axoneme in either an anterograde or retrograde manner. Proteins that localize to the primary cilium are referred to as ciliary proteins and have been implicated directly or indirectly in ciliogenesis or ciliary function. It is now recognized that cilia proteins can localize to different compartments of cilia, but can also localize to multiple sites outside of cilia (extraciliary sites). This complexity results in a need for a better understanding of ciliary protein fixation and immunolabeling protocols, as different methods are required to visualize different cilia proteins and reveal novel or unique localizations. Here, we detail a variety of fixation methods and their effects on ciliary protein immunolabeling.

Understanding sperm motility mechanisms and the implication of sperm surface molecules in promoting motility

Background

It is estimated that approximately 8–12% of couples globally face problems associated with infertility. A large number of men exhibit suboptimal sperm parameters. Sperm motility is one of the factors that is measured when analysing sperm parameters. The indication of several crucial sperm surface molecules, having the ability to modulate motility, has opened new avenues in understanding the complex processes involved in motility.

Main body of the abstract

There are various mechanisms that regulate and enhance sperm motility. Several surface molecules on sperm cells can also regulate motility, thus showing their possible application as a treatment for infertility caused by impaired motility. Sperm motility is regulated by intracellular and extracellular pH, along with calcium ions (Ca2+) and carbonate ion (HCO3−) concentrations. Moreover, sperm cells have an array of surface proteins which play a critical role in their function and motility. The indication of surface molecules presented new opportunities for understanding sperm motility and the possibility of treating infertility caused by impaired sperm function. Infertility and problems associated with conception can cause underlying stress and mental trauma. Although there are several methods for treating infertility, most are complex, invasive, and expensive.

Conclusion

It is important to understand how surface molecules and proteins on the sperm cell regulate motility. This will enable us to treat anomalies associated with proper sperm function. This review highlights the general mechanisms that regulate sperm motility, and it stresses the importance and relevance of sperm surface molecules in regulating sperm motility.

CCDC40 mutation as a cause of infertility in a Chinese family with primary ciliary dyskinesia

TRIAL DESIGN

Primary ciliary dyskinesia (PCD) is a genetical disease that inherited in an autosomal-recessive way. Its clinical manifestations (such as male infertility) are mainly caused by defects of motion-related cilia that encoded by mutated genes. Although some mutation has been verified, a number of mutations of PCD remain elusive. The main purpose of this study is to identify mutant genes in a Chinese family with PCD, and to verify the safety and effectiveness of intracytoplasmic sperm injection (ICSI) of infertility caused by PCD.

METHODS

Imaging examination was used to exclude pulmonary inflammation and visceral translocation. Semen analysis was used to assess the quality of the proband's sperm. Transmission electron microscopy (TEM) was conducted to assess the ultrastructure of flagella and cilia. Targeted next generation sequencing and Sanger sequencing and qPCR (real-time quantitative polymerase chain reaction detecting system) were applied to identified mutation of Chinese Family suspected of having PCD. Viable sperm were selected by hypo-osmotic swelling test (HOST) for ICSI.

RESULTS

We report 2 novel mutations in CCDC40 gene (c.1259delA and EX17_20 deletion) resulted in immobility of sperm and infertility of the proband. These mutations were confirmed in the proband's sister (heterozygous) and his parents (recessive carrier) by Sanger sequencing and qPCR. All the spermatozoa from the proband were immotile. Ultrastructural defects were found in flagella and cilia of proband and his sister. Viable sperms were selected by HOST for ICSI and fertilized 9 of 21 eggs. Two frozen embryos were transplanted and a healthy 3500 g boy was delivered at 40 + 4 weeks' gestation. And then, we summarized the genes related to PCD and the mutant sites of CCDC40 gene.

CONCLUSION

We reported 2 novel mutants in CCDC40 gene (c.1259delA and EX17_20 deletion), which could be candidates for genetic diagnosis in PCD patients. The combination of targeted next generation sequencing and Sanger sequencing may be a useful tool to diagnose PCD. ICSI is a considerable method in treatment of infertility caused by PCD.

CFAP53 regulates mammalian cilia-type motility patterns through differential localization and recruitment of axonemal dynein components

Motile cilia can beat with distinct patterns, but how motility variations are regulated remain obscure. Here, we have studied the role of the coiled-coil protein CFAP53 in the motility of different cilia-types in the mouse. While node (9+0) cilia of Cfap53 mutants were immotile, tracheal and ependymal (9+2) cilia retained motility, albeit with an altered beat pattern. In node cilia, CFAP53 mainly localized at the base (centriolar satellites), whereas it was also present along the entire axoneme in tracheal cilia. CFAP53 associated tightly with microtubules and interacted with axonemal dyneins and TTC25, a dynein docking complex component. TTC25 and outer dynein arms (ODAs) were lost from node cilia, but were largely maintained in tracheal cilia of Cfap53^-/- mice. Thus, CFAP53 at the base of node cilia facilitates axonemal transport of TTC25 and dyneins, while axonemal CFAP53 in 9+2 cilia stabilizes dynein binding to microtubules. Our study establishes how differential localization and function of CFAP53 contributes to the unique motion patterns of two important mammalian cilia-types.

Motile cilia in various kinds of tissues and cell-types drive fluid flow over epithelia or facilitate cellular locomotion. There are two types of motile cilia. Motile cilia with a 9+2 configuration of microtubules are found on tracheal epithelial cells and brain ependymal cells, and exhibit planar beating with effective and recovery strokes. On the other hand, 9+0 motile cilia are found in the embryonic node, show rotational movement and are involved in establishing left-right asymmetry of visceral organs. However, it is not well understood how these two types of motile cilia exhibit their characteristic motion patterns. We have uncovered distinct roles and subcellular localization of the CFAP53 protein in 9+0 versus the 9+2 motile cilia of the mouse. Our data provide novel insights into the molecular basis of motility differences that characterize these two types of mammalian motile cilia.

The anatomy, movement, and functions of human sperm tail: an evolving mystery

Sperms have attracted attention of many researchers since it was discovered by Antonie van Leeuwenhoek in 1677. Though a small cell, its every part has complex structure and different function to play in carrying life. Sperm tail is most complicated structure with more than 1000 proteins involved in its functioning. With the advent of three-dimensional microscopes, many studies are undergoing to understand exact mechanism of sperm tail movement. Most recent studies have shown that sperms move by spinning rather than swimming. Each subunit of tail, including axonemal, peri-axonemal structures, plays essential roles in sperm motility, capacitation, hyperactivation, fertilization. Furthermore, over 2300 genes are involved in spermatogenesis. A number of genetic mutations have been linked with abnormal sperm flagellar development leading to motility defects and male infertility. It was found that 6% of male infertility cases are related to genetic causes, and 4% of couples undergoing intracytoplasmic sperm injection for male subfertility have chromosomal abnormalities. Hence, an understanding of sperm tail development and genes associated with its normal functioning can help in better diagnosis of male infertility and its management. There is still a lot that needs to be discovered about genes, proteins contributing to normal human sperm tail development, movement, and role in male fertility. Sperm tail has complex anatomy, with surrounding axoneme having 9 + 2 microtubules arrangement along its entire length and peri-axonemal structures that contribute in sperm motility and fertilization. In future sperm tail-associated genes, proteins and subunits can be used as markers of male fertility.

Mutations in PIH proteins MOT48, TWI1 and PF13 define common and unique steps for preassembly of each, different ciliary dynein

Ciliary dyneins are preassembled in the cytoplasm before being transported into cilia, and a family of proteins containing the PIH1 domain, PIH proteins, are involved in the assembly process. However, the functional differences and relationships between members of this family of proteins remain largely unknown. Using Chlamydomonas reinhardtii as a model, we isolated and characterized two novel Chlamydomonas PIH preassembly mutants, mot48-2 and twi1-1. A new allele of mot48 (ida10), mot48-2, shows large defects in ciliary dynein assembly in the axoneme and altered motility. A second mutant, twi1-1, shows comparatively smaller defects in motility and dynein assembly. A double mutant mot48-2; twi1-1 displays greater reduction in motility and in dynein assembly compared to each single mutant. Similarly, a double mutant twi1-1; pf13 also shows a significantly greater defect in motility and dynein assembly than either parent mutant. Thus, MOT48 (IDA10), TWI1 and PF13 may define different steps, and have partially overlapping functions, in a pathway required for ciliary dynein preassembly. Together, our data suggest the three PIH proteins function in preassembly steps that are both common and unique for different ciliary dyneins.

Motile cilia are hair-like organelles that protrude from many eukaryotic cells, and play vital roles in organisms including cell motility, environmental sensing and removal of infectious materials. Motile cilia are driven by gigantic motor protein complexes, called ciliary dyneins, defects in which cause abnormal ciliary motility, ultimately resulting in human diseases collectively called primary ciliary dyskinesia (PCD). Ciliary dyneins are preassembled in the cytoplasm before being transported into cilia, and preassembly requires a family of potential co-chaperones, the PIH proteins. Mutations in the PIH proteins cause defective assembly of ciliary dyneins and can result in PCD. However, despite their importance, the precise functions, and functional relationships, between the PIH proteins are unclear. In this study, using Chlamydomonas reinhardtii, we assessed the functional relationship between three PIH proteins with respect to dynein preassembly and motility. We found that these PIH proteins have complicated and related roles in dynein assembly, possibly with each playing common and unique roles in dynein assembly. Our results provide new information on each conserved PIH protein for dynein assembly and provide a new understanding of PCD caused by PIH mutations.

Mycoplasma hyopneumoniae J elicits an antioxidant response and decreases the expression of ciliary genes in infected swine epithelial cells

Mycoplasma hyopneumoniae is the most costly pathogen for swine production. Although several studies have focused on the host-bacterium association, little is known about the changes in gene expression of swine cells upon infection. To improve our understanding of this interaction, we infected swine epithelial NPTr cells with M. hyopneumoniae strain J to identify differentially expressed mRNAs and miRNAs. The levels of 1,268 genes and 170 miRNAs were significantly modified post-infection. Up-regulated mRNAs were enriched in genes related to redox homeostasis and antioxidant defense, known to be regulated by the transcription factor NRF2 in related species. Down-regulated mRNAs were enriched in genes associated with cytoskeleton and ciliary functions. Bioinformatic analyses suggested a correlation between changes in miRNA and mRNA levels, since we detected down-regulation of miRNAs predicted to target antioxidant genes and up-regulation of miRNAs targeting ciliary and cytoskeleton genes. Interestingly, most down-regulated miRNAs were detected in exosome-like vesicles suggesting that M. hyopneumoniae infection induced a modification of the composition of NPTr-released vesicles. Taken together, our data indicate that M. hyopneumoniae elicits an antioxidant response induced by NRF2 in infected cells. In addition, we propose that ciliostasis caused by this pathogen is partially explained by the down-regulation of ciliary genes.

Vertebrate Dynein-f depends on Wdr78 for axonemal localization and is essential for ciliary beat

Motile cilia and flagella are microtubule-based organelles important for cell locomotion and extracellular liquid flow through beating. Although axonenal dyneins that drive ciliary beat have been extensively studied in unicellular Chlamydomonas, to what extent such knowledge can be applied to vertebrate is poorly known. In Chlamydomonas, Dynein-f controls flagellar waveforms but is dispensable for beating. The flagellar assembly of its heavy chains (HCs) requires its intermediate chain (IC) IC140 but not IC138. Here we show that, unlike its Chlamydomonas counterpart, vertebrate Dynein-f is essential for ciliary beat. We confirmed that Wdr78 is the vertebrate orthologue of IC138. Wdr78 associated with Dynein-f subunits such as Dnah2 (a HC) and Wdr63 (IC140 orthologue). It was expressed as a motile cilium-specific protein in mammalian cells. Depletion of Wdr78 or Dnah2 by RNAi paralyzed mouse ependymal cilia. Zebrafish Wdr78 morphants displayed ciliopathy-related phenotypes, such as curved bodies, hydrocephalus, abnormal otolith, randomized left-right asymmetry, and pronephric cysts, accompanied with paralyzed pronephric cilia. Furthermore, all the HCs and ICs of Dynein-f failed to localize in the Wdr78-depleted mouse ependymal cilia. Therefore, both the functions and subunit dependency of Dynein-f are altered in evolution, probably to comply with ciliary roles in higher organisms.

Transcriptome-Wide Regulation of Key Developmental Pathways in the Mouse Neural Tube by Prenatal Alcohol Exposure

BACKGROUND

Early gestational alcohol exposure is associated with severe craniofacial and CNS dysmorphologies and behavioral abnormalities during adolescence and adulthood. Alcohol exposure during the formation of the neural tube (gestational day [GD] 8 to 10 in mice; equivalent to4th week of human pregnancy) disrupts development of ventral midline brain structures such as the pituitary, septum, and ventricles. This study identifies transcriptomic changes in the rostroventral neural tube (RVNT), the region of the neural tube that gives rise to the midline structures sensitive to alcohol exposure during neurulation.

METHODS

Female C57BL/6J mice were administered 2 doses of alcohol (2.9 g/kg) or vehicle 4 hours apart on GD 9.0. The RVNTs of embryos were collected 6 or 24 hours after the first dose and processed for RNA-seq.

RESULTS

Six hours following GD 9.0 alcohol exposure (GD 9.25), over 2,300 genes in the RVNT were determined to be differentially regulated by alcohol. Enrichment analysis determined that PAE affected pathways related to cell proliferation, p53 signaling, ribosome biogenesis, and immune activation. In addition, over 100 genes involved in primary cilia formation and function and regulation of morphogenic pathways were altered 6 hours after alcohol exposure. The changes to gene expression were largely transient, as only 91 genes identified as differentially regulated by prenatal alcohol at GD 10 (24 hours postexposure). Functionally, the differentially regulated genes at GD 10 were related to organogenesis and cell migration.

CONCLUSIONS

These data give a comprehensive view of the changing landscape of the embryonic transcriptome networks in regions of the neural tube that give rise to brain structures impacted by a neurulation-stage alcohol exposure. Identification of gene networks dysregulated by alcohol will help elucidate the pathogenic mechanisms of alcohol's actions.

Control of assembly of extra-axonemal structures: the paraflagellar rod of trypanosomes

Eukaryotic flagella are complex microtubule-based organelles that, in many organisms, contain extra-axonemal structures, such as the outer dense fibres of mammalian sperm and the paraflagellar rod (PFR) of trypanosomes. Flagellum assembly is a complex process occurring across three main compartments, the cytoplasm, the transition zone and the flagellum itself. The process begins with the translation of protein components followed by their sorting and trafficking into the flagellum, transport to the assembly site and incorporation. Flagella are formed from over 500 proteins and the principles governing assembly of the axonemal components are relatively clear. However, the coordination and location of assembly of extra-axonemal structures are less clear. We have discovered two cytoplasmic proteins in Trypanosoma brucei that are required for PFR formation, PFR assembly factors 1 and 2 (PFR-AF1 and PFR-AF2, respectively). Deletion of either PFR-AF1 or PFR-AF2 dramatically disrupted PFR formation and caused a reduction in the amount of major PFR proteins. The existence of cytoplasmic factors required for PFR formation aligns with the concept that processes facilitating axoneme assembly occur across multiple compartments, and this is likely a common theme for extra-axonemal structure assembly.

Activation and Regulation of Cytoplasmic Dynein

Cytoplasmic dynein is an AAA+ motor that drives the transport of many intracellular cargoes towards the minus end of microtubules (MTs). Previous in vitro studies characterized isolated dynein as an exceptionally weak motor that moves slowly and diffuses on an MT. Recent studies altered this view by demonstrating that dynein remains in an autoinhibited conformation on its own, and processive motility is activated when it forms a ternary complex with dynactin and a cargo adaptor. This complex assembles more efficiently in the presence of Lis1, providing an explanation for why Lis1 is a required cofactor for most cytoplasmic dynein-driven processes in cells. This review describes how dynein motility is activated and regulated by cargo adaptors and accessory proteins.

MIP-T3 Expression Associated with Defects of Ciliogenesis in Airway of COPD Patients

Introduction. Some studies have found that cilia were shorter in COPD smokers than in nonsmokers or healthy smokers. However, the structural abnormalities of cilia and the cause of such abnormalities in COPD patients still remain unknown. Tumor necrosis factor alpha receptor 3 interacting protein 1 (MIP-T3) may play an important role in the progress of ciliary protein transporting.

TTC12 Loss-of-Function Mutations Cause Primary Ciliary Dyskinesia and Unveil Distinct Dynein Assembly Mechanisms in Motile Cilia Versus Flagella

Cilia and flagella are evolutionarily conserved organelles whose motility relies on the outer and inner dynein arm complexes (ODAs and IDAs). Defects in ODAs and IDAs result in primary ciliary dyskinesia (PCD), a disease characterized by recurrent airway infections and male infertility. PCD mutations in assembly factors have been shown to cause a combined ODA-IDA defect, affecting both cilia and flagella. We identified four loss-of-function mutations in TTC12, which encodes a cytoplasmic protein, in four independent families in which affected individuals displayed a peculiar PCD phenotype characterized by the absence of ODAs and IDAs in sperm flagella, contrasting with the absence of only IDAs in respiratory cilia. Analyses of both primary cells from individuals carrying TTC12 mutations and human differentiated airway cells invalidated for TTC12 by a CRISPR-Cas9 approach revealed an IDA defect restricted to a subset of single-headed IDAs that are different in flagella and cilia, whereas TTC12 depletion in the ciliate Paramecium tetraurelia recapitulated the sperm phenotype. Overall, our study, which identifies TTC12 as a gene involved in PCD, unveils distinct dynein assembly mechanisms in human motile cilia versus flagella.

The genetic architecture of morphological abnormalities of the sperm tail

Spermatozoa contain highly specialized structural features reflecting unique functions required for fertilization. Among them, the flagellum is a sperm-specific organelle required to generate the motility, which is essential to reach the egg. The flagellum integrity is, therefore, critical for normal sperm function and flagellum defects consistently lead to male infertility due to reduced or absent sperm motility defined as asthenozoospermia. Multiple morphological abnormalities of the flagella (MMAF), also called short tails, is among the most severe forms of sperm flagellum defects responsible for male infertility and is characterized by the presence in the ejaculate of spermatozoa being short, coiled, absent and of irregular caliber. Recent studies have demonstrated that MMAF is genetically heterogeneous which is consistent with the large number of proteins (over one thousand) localized in the human sperm flagella. In the past 5 years, genomic investigation of the MMAF phenotype allowed the identification of 18 genes whose mutations induce MMAF and infertility. Here we will review information about those genes including their expression pattern, the features of the encoded proteins together with their localization within the different flagellar protein complexes (axonemal or peri-axonemal) and their potential functions. We will categorize the identified MMAF genes following the protein complexes, functions or biological processes they may be associated with, based on the current knowledge in the field.

Quantifying Ciliary Dynamics during Assembly Reveals Stepwise Waveform Maturation in Airway Cells

Motile cilia are essential for clearance of particulates and pathogens from airways. For effective transport, ciliary motor proteins and axonemal structures interact to generate the rhythmic, propulsive bending, but the mechanisms that produce a dynamic waveform remain incompletely understood. Biomechanical measures of human ciliary motion and their relationships to ciliary assembly are needed to illuminate the biophysics of normal ciliary function and to quantify dysfunction in ciliopathies. To these ends, we analyzed ciliary motion by high-speed video microscopy of ciliated cells sampled from human lung airways compared with primary culture cells that undergo ciliogenesis in vitro. Quantitative assessment of waveform parameters showed variations in waveform shape between individual cilia; however, general trends in waveform parameters emerged, associated with progression of cilia length and stage of differentiation. When cilia emerged from cultured cells, beat frequency was initially elevated, then fell and remained stable as cilia lengthened. In contrast, the average bending amplitude and the ability to generate force gradually increased and eventually approached values observed in ex vivo samples. Dynein arm motor proteins DNAH5, DNAH9, DNAH11, and DNAH6 were localized within specific regions of the axoneme in the ex vivo cells; however, distinct stages of in vitro waveform development identified by biomechanical features were associated with the progressive movement of dyneins to the appropriate proximal or distal sections of the cilium. These observations suggest that the stepwise variation in waveform development during ciliogenesis is dependent on cilia length and potentially on outer dynein arm assembly.

ZMYND10 functions in a chaperone relay during axonemal dynein assembly

Molecular chaperones promote the folding and macromolecular assembly of a diverse set of 'client' proteins. How ubiquitous chaperone machineries direct their activities towards specific sets of substrates is unclear. Through the use of mouse genetics, imaging and quantitative proteomics we uncover that ZMYND10 is a novel co-chaperone that confers specificity for the FKBP8-HSP90 chaperone complex towards axonemal dynein clients required for cilia motility. Loss of ZMYND10 perturbs the chaperoning of axonemal dynein heavy chains, triggering broader degradation of dynein motor subunits. We show that pharmacological inhibition of FKBP8 phenocopies dynein motor instability associated with the loss of ZMYND10 in airway cells and that human disease-causing variants of ZMYND10 disrupt its ability to act as an FKBP8-HSP90 co-chaperone. Our study indicates that primary ciliary dyskinesia (PCD), caused by mutations in dynein assembly factors disrupting cytoplasmic pre-assembly of axonemal dynein motors, should be considered a cell-type specific protein-misfolding disease.

Systematic studies of all PIH proteins in zebrafish reveal their distinct roles in axonemal dynein assembly

Construction of motile cilia/flagella requires cytoplasmic preassembly of axonemal dyneins before transport into cilia. Axonemal dyneins have various subtypes, but the roles of each dynein subtype and their assembly processes remain elusive in vertebrates. The PIH protein family, consisting of four members, has been implicated in the assembly of different dynein subtypes, although evidence for this idea is sparse. Here, we established zebrafish mutants of all four PIH-protein genes: pih1d1, pih1d2, ktu, and twister, and analyzed the structures of axonemal dyneins in mutant spermatozoa by cryo-electron tomography. Mutations caused the loss of specific dynein subtypes, which was correlated with abnormal sperm motility. We also found organ-specific compositions of dynein subtypes, which could explain the severe motility defects of mutant Kupffer’s vesicle cilia. Our data demonstrate that all vertebrate PIH proteins are differently required for cilia/flagella motions and the assembly of axonemal dyneins, assigning specific dynein subtypes to each PIH protein.

Many cells have long, thin structures called cilia on their surface, some types of which can beat back and forth. This beating motion has many roles; for example, cilia on the cells that line the lungs help to sweep out debris, and the tails of sperm beat to move them forward.

A structure called the axonemal dynein complex at the core of the cilia generates the beating motion. When the cell makes new cilia, it assembles the complexes in the main body of the cell and then transports them to the right place, like erecting a prefabricated building. Various proteins help to assemble the complexes, of which there are more than eight types. However, the identities of all of these proteins, and their roles in constructing specific axonemal dynein complexes, is not fully known.

Studies in algae have suggested that a family of proteins known as PIH (short for protein interacting with Hsp90) helps to construct axonemal dynein complexes. Zebrafish – which share many of the same protein-encoding genes as humans – produce four PIH family proteins. To investigate the roles that each of these proteins play, Yamaguchi et al. used genetic engineering to create four zebrafish mutants that were each unable to produce a different PIH protein.

A technique called cryo-electron microscopy enabled the axonemal dynein complexes in the tails of the sperm produced by the zebrafish to be visualized. The sperm from each mutant lacked specific axonemal dynein complexes, revealing that each PIH protein assembles different complexes. The sperm also had difficulties moving. Yamaguchi et al. examined this movement to deduce how specific complexes affect the ability of the sperm to beat their tails.

Further work on how PIH proteins interact with the axonemal dynein complexes will help us to understand how cells make cilia, and what happens when this process goes wrong. This could ultimately help us to treat genetic disorders known as ciliopathies, which arise when cilia do not develop normally.

The IDA3 adapter, required for intraflagellar transport of I1 dynein, is regulated by ciliary length

We determined how the ciliary motor I1 dynein is transported. A specialized adapter, IDA3, facilitates I1 dynein attachment to the ciliary transporter called intraflagellar transport (IFT). Loading of IDA3 and I1 dynein on IFT is regulated by ciliary length.

ZMYND10 stabilizes intermediate chain proteins in the cytoplasmic pre-assembly of dynein arms

Zinc finger MYND-type-containing 10 (ZMYND10), a cytoplasmic protein expressed in ciliated cells, causes primary ciliary dyskinesia (PCD) when mutated; however, its function is poorly understood. Therefore, in this study, we examined the roles of ZMYND10 using Zmynd10^–/–mice exhibiting typical PCD phenotypes, including hydrocephalus and laterality defects. In these mutants, morphology, the number of motile cilia, and the 9+2 axoneme structure were normal; however, inner and outer dynein arms (IDA and ODA, respectively) were absent. ZMYND10 interacted with ODA components and proteins, including LRRC6, DYX1C1, and C21ORF59, implicated in the cytoplasmic pre-assembly of DAs, whose levels were significantly reduced in Zmynd10^–/–mice. LRRC6 and DNAI1 were more stable when co-expressed with ZYMND10 than when expressed alone. DNAI2, which did not interact with ZMYND10, was not stabilized by co-expression with ZMYND10 alone, but was stabilized by co-expression with DNAI1 and ZMYND10, suggesting that ZMYND10 stabilized DNAI1, which subsequently stabilized DNAI2. Together, these results demonstrated that ZMYND10 regulated the early stage of DA cytoplasmic pre-assembly by stabilizing DNAI1.

Dynein arm defects are linked to primary ciliary dyskinesia (PCD). ZMYND10 increased the stability of its interacting proteins and specifically regulated intermediate chain protein assembly, revealing tightly regulated mechanisms underlying dynein arm assembly and PCD-related pathogenesis. Increasing protein stability could be useful for developing PCD therapeutics.

Chlamydomonas DYX1C1/PF23 is essential for axonemal assembly and proper morphology of inner dynein arms

Cytoplasmic assembly of ciliary dyneins, a process known as preassembly, requires numerous non-dynein proteins, but the identities and functions of these proteins are not fully elucidated. Here, we show that the classical Chlamydomonas motility mutant pf23 is defective in the Chlamydomonas homolog of DYX1C1. The pf23 mutant has a 494 bp deletion in the DYX1C1 gene and expresses a shorter DYX1C1 protein in the cytoplasm. Structural analyses, using cryo-ET, reveal that pf23 axonemes lack most of the inner dynein arms. Spectral counting confirms that DYX1C1 is essential for the assembly of the majority of ciliary inner dynein arms (IDA) as well as a fraction of the outer dynein arms (ODA). A C-terminal truncation of DYX1C1 shows a reduction in a subset of these ciliary IDAs. Sucrose gradients of cytoplasmic extracts show that preassembled ciliary dyneins are reduced compared to wild-type, which suggests an important role in dynein complex stability. The role of PF23/DYX1C1 remains unknown, but we suggest that DYX1C1 could provide a scaffold for macromolecular assembly.

Most animal cells have antenna-like organelles called “cilia”. These organelles have various important functions both in motility and sensing the environment. Motile cilia are essential for moving cells as well as moving fluids across a surface. The waveform of motile cilia requires large macromolecular motors; these are the ciliary dyneins. These dynein complexes are assembled in the cytoplasm in a pathway called preassembly, and then transported into cilia. Defects in this process cause a heterogeneous human disease called primary ciliary dyskinesia that results, for example, in the disruption of the motility of respiratory tract cilia, sperm and nodal cilia during development. The mechanisms of the preassembly pathway are not fully understood. In this study, we use a mutation in the well-conserved DYX1C1/PF23 gene of the green alga, Chlamydomonas reinhardtii. Loss of a conserved domain (DYX) reveals a failure to assemble most ciliary dyneins. Preassembly of inner arm dyneins is particularly affected. We find that if dynein arms are not assembled, dynein subunits in the cytoplasm are unstable. We suggest that DYX1C1 may play a role as a scaffold for other preassembly factors and the dynein subunits.

Loss of zinc finger MYND-type containing 10 (zmynd10) affects cilia integrity and axonemal localization of dynein arms, resulting in ciliary dysmotility, polycystic kidney and scoliosis in medaka (Oryzias latipes)

Cilia and flagella are hair-like organelles that project from the cell surface and play important roles in motility and sensory perception. Motility defects in cilia and flagella lead to primary ciliary dyskinesia (PCD), a rare human disease. Recently zinc finger MYND-type containing 10 (ZMYND10) was identified in humans as a PCD-associated gene. In this study, we use medaka fish as a model to characterize the precise functions of zmynd10. In medaka, zmynd10 is exclusively expressed in cells with motile cilia. Embryos with zmynd10 Morpholino knockdown exhibited a left-right (LR) defect associated with loss of motility in Kupffer's vesicle (KV) cilia. This immotility was caused by loss of the outer dynein arms, which is a characteristic ultrastructural phenotype in PCD. In addition, KV cilia in zmynd10 knockdown embryos had a swollen and wavy morphology. Together, these results suggest that zmynd10 is a multi-functional protein that has independent roles in axonemal localization of dynein arms and in formation and/or maintenance of cilia. The C-terminal region of zmynd10 has a MYND-type zinc finger domain (zf-MYND) that is important for its function. Our rescue experiment showed that the zmynd10-ΔC truncated protein, which lacks zf-MYND, was still partially functional, suggesting that zmynd10 has another functional domain besides zf-MYND. To analyze the later stages of development, we generated a zmynd10 knockout mutant using transcription activator-like effector nuclease (TALEN) technology. Adult mutants exhibited sperm dysmotility, scoliosis and progressive polycystic kidney.

The secret life of kinases: insights into non-catalytic signalling functions from pseudokinases

Over the past decade, our understanding of the mechanisms by which pseudokinases, which comprise ∼10% of the human and mouse kinomes, mediate signal transduction has advanced rapidly with increasing structural, biochemical, cellular and genetic studies. Pseudokinases are the catalytically defective counterparts of conventional, active protein kinases and have been attributed functions as protein interaction domains acting variously as allosteric modulators of conventional protein kinases and other enzymes, as regulators of protein trafficking or localisation, as hubs to nucleate assembly of signalling complexes, and as transmembrane effectors of such functions. Here, by categorising mammalian pseudokinases based on their known functions, we illustrate the mechanistic diversity among these proteins, which can be viewed as a window into understanding the non-catalytic functions that can be exerted by conventional protein kinases.

Fixation methods can differentially affect ciliary protein immunolabeling

BACKGROUND

Primary cilia are immotile, microtubule-based organelles present on most cells. Defects in primary cilia presence/function result in a category of developmental diseases referred to as ciliopathies. As the cilia field progresses, there is a need to consider both the ciliary and extraciliary roles of cilia proteins. However, traditional fixation methods are not always suitable for examining the full range of localizations of cilia proteins. Here, we tested a variety of fixation methods with commonly used cilia markers to determine the most appropriate fixation method for different cilia proteins.

METHODS

Mouse inner medullary collecting duct and human retinal pigmented epithelial cells were grown to confluence, serum starved, and fixed with one of the following fixation agents: paraformaldehyde-sucrose, paraformaldehyde-PBS, methanol, cytoskeletal buffer followed by methanol, or three variations of cytoskeletal buffer-paraformaldehyde fixation. Each cell type and fixation method combination was probed with the following ciliary markers: acetylated α-tubulin, detyrosinated tubulin, polyglutamylated tubulin, β-tubulin, adenylyl cyclase 3 (AC3), ADP-ribosylation factor-like protein 13b (Arl13b), centrosome and spindle pole associated protein 1 (CSPP1), or intraflagellar transport protein 20 (IFT20). Intraflagellar transport protein 88 (IFT88) and GM130 (Golgi marker) were also used. We assessed actin (via phalloidin) and microtubule integrity, centrioles, cilia, and two extraciliary sites (mitotic figures and Golgi).

RESULTS

For the cilia markers examined, paraformaldehyde fixation preserved cilia immunolabeling of cilia-membrane proteins (AC3 and Arl13b), but failed to reveal cilia immunostaining of axonemal proteins (CSPP1 and IFT20). Methanol revealed cilia labeling for some axonemal proteins, but not others, and this depended on cell type. Generally, any method that first included a wash in cytoskeletal buffer, before fixing, revealed more distinct cilia immunolabeling for axonemal proteins (CSPP1, IFT20, and IFT88), but resulted in the loss of cilia labeling for cilia-membrane proteins (AC3 and Arl13b). All three different post-translational modifications of tubulin antibodies positively immunolabeled cilia in all fixation methods tested. Ultimately, we found that fixing cells in a solution of paraformaldehyde prepared in cytoskeletal buffer allowed for the preservation of cilia immunolabeling for most cilia proteins tested and allowed visualization of two extraciliary sites (mitotic figures and Golgi).

CONCLUSION

Some general patterns were observed to guide in the choice of a fixation agent. Cilia-membrane proteins generally benefit from quick fixation with no prior permeabilization, whereas axonemal proteins tend to benefit from permeabilization and use of cytoskeletal buffer.

X-linked primary ciliary dyskinesia due to mutations in the cytoplasmic axonemal dynein assembly factor PIH1D3

By moving essential body fluids and molecules, motile cilia and flagella govern respiratory mucociliary clearance, laterality determination and the transport of gametes and cerebrospinal fluid. Primary ciliary dyskinesia (PCD) is an autosomal recessive disorder frequently caused by non-assembly of dynein arm motors into cilia and flagella axonemes. Before their import into cilia and flagella, multi-subunit axonemal dynein arms are thought to be stabilized and pre-assembled in the cytoplasm through a DNAAF2-DNAAF4-HSP90 complex akin to the HSP90 co-chaperone R2TP complex. Here, we demonstrate that large genomic deletions as well as point mutations involving PIH1D3 are responsible for an X-linked form of PCD causing disruption of early axonemal dynein assembly. We propose that PIH1D3, a protein that emerges as a new player of the cytoplasmic pre-assembly pathway, is part of a complementary conserved R2TP-like HSP90 co-chaperone complex, the loss of which affects assembly of a subset of inner arm dyneins.

Dynein axonemal heavy chain 8 promotes androgen receptor activity and associates with prostate cancer progression

To gain insight into cellular factors regulating AR action that could promote castration resistant prostate cancer (CRPC), we performed a genome-wide RNAi screen for factors that promote ligand-independent AR transcriptional activity and integrated clinical databases for candidate genes that are positively associated with prostate cancer metastasis and recurrence. From this analysis, we identified Dynein Axonemal Heavy Chain 8 (DNAH8) as an AR regulator that displayed higher mRNA expression in metastatic than in primary tumors, and showed high expression in patients with poor prognosis. Axonemal dyneins function in cellular motility, but the function of DNAH8 in prostate cancer or other cell types has not been reported. DNAH8 is on chromosome 6q21.2, a cancer-associated amplicon, and is primarily expressed in prostate and testis. Its expression is higher in primary tumors compared to normal prostate, and is further increased in metastatic prostate cancers. Patients expressing high levels of DNAH8 have a greater risk of relapse and a poor prognosis after prostatectomy. Depletion of DNAH8 in prostate cancer cells suppressed AR transcriptional activity and proliferation. Androgen treatment increased DNAH8 mRNA expression, and AR bound the DNAH8 promoter sequence indicating DNAH8 is an AR target gene. Thus, DNAH8 is a new regulator of AR associated with metastatic tumors and poor prognosis.

Planar Organization of Multiciliated Ependymal (E1) Cells in the Brain Ventricular Epithelium

Cerebrospinal fluid (CSF) continuously flows through the cerebral ventricles, a process essential for brain homeostasis. Multiciliated ependymal (E1) cells line the walls of the ventricles and contribute importantly to CSF flow through ciliary beating. Key to this function is the rotational and translational planar cell polarity (PCP) of E1 cells. Defects in the PCP of E1 cells can result in abnormal CSF accumulation and hydrocephalus. Here, we integrate recent data on the roles of early CSF flow in the embryonic ventricles, PCP regulators (e.g., Vangl2 and Dishevelled), and cytoskeletal networks in the establishment, refinement, and maintenance of E1 cells' PCP. The planar organization mechanisms of E1 cells could explain how CSF flow contributes to brain function and may help in the diagnosis and prevention of hydrocephalus.

The ciliopathy-associated CPLANE proteins direct basal body recruitment of intraflagellar transport machinery

Cilia use microtubule-based intraflagellar transport (IFT) to organize intercellular signaling. Ciliopathies are a spectrum of human diseases resulting from defects in cilia structure or function. The mechanisms regulating the assembly of ciliary multiprotein complexes and the transport of these complexes to the base of cilia remain largely unknown. Combining proteomics, in vivo imaging and genetic analysis of proteins linked to planar cell polarity (Inturned, Fuzzy and Wdpcp), we identified and characterized a new genetic module, which we term CPLANE (ciliogenesis and planar polarity effector), and an extensive associated protein network. CPLANE proteins physically and functionally interact with the poorly understood ciliopathy-associated protein Jbts17 at basal bodies, where they act to recruit a specific subset of IFT-A proteins. In the absence of CPLANE, defective IFT-A particles enter the axoneme and IFT-B trafficking is severely perturbed. Accordingly, mutation of CPLANE genes elicits specific ciliopathy phenotypes in mouse models and is associated with ciliopathies in human patients.

Analysis of cilia structure and function in zebrafish

Cilia are microtubule-based protrusions on the surface of most eukaryotic cells. They are found in most, if not all, vertebrate organs. Prominent cilia form in sensory structures, the eye, the ear, and the nose, where they are crucial for the detection of environmental stimuli, such as light and odors. Cilia are also involved in developmental processes, including left-right asymmetry formation, limb morphogenesis, and the patterning of neurons in the neural tube. Some cilia, such as those found in nephric ducts, are thought to have mechanosensory roles. Zebrafish proved very useful in genetic analysis and imaging of cilia-related processes, and in the modeling of mechanisms behind human cilia abnormalities, known as ciliopathies. A number of zebrafish defects resemble those seen in human ciliopathies. Forward and reverse genetic strategies generated a wide range of cilia mutants in zebrafish, which can be studied using sophisticated genetic and imaging approaches. In this chapter, we provide a set of protocols to examine cilia morphology, motility, and cilia-related defects in a variety of organs, focusing on the embryo and early postembryonic development.

Genetics and biology of primary ciliary dyskinesia

Ciliopathies are a growing class of disorders caused by abnormal ciliary axonemal structure and function. Our understanding of the complex genetic and functional phenotypes of these conditions has rapidly progressed. Primary ciliary dyskinesia (PCD) remains the sole genetic disorder of motile cilia dysfunction. However, unlike many Mendelian genetic disorders, PCD is not caused by mutations in a single gene or locus, but rather, autosomal recessive mutation in one of many genes that lead to a similar phenotype. The first reported PCD mutations, more than a decade ago, identified genes encoding known structural components of the ciliary axoneme. In recent years, mutations in genes encoding novel cytoplasmic and regulatory proteins have been discovered. These findings have provided new insights into the functions of the motile cilia, and a better understanding of motile cilia disease. Advances in genetic tools will soon allow more precise genetic testing, mandating that clinicians must understand the genetic basis of PCD. Here, we review genetic mutations, their biological impact on cilia structure and function, and the implication of emerging genetic diagnostic tools.

c21orf59/kurly Controls Both Cilia Motility and Polarization

Cilia are microtubule-based projections that function in the movement of extracellular fluid. This requires cilia to be: (1) motile and driven by dynein complexes and (2) correctly polarized on the surface of cells, which requires planar cell polarity (PCP). Few factors that regulate both processes have been discovered. We reveal that C21orf59/Kurly (Kur), a cytoplasmic protein with some enrichment at the base of cilia, is needed for motility; zebrafish mutants exhibit characteristic developmental abnormalities and dynein arm defects. kur was also required for proper cilia polarization in the zebrafish kidney and the larval skin of Xenopus laevis. CRISPR/Cas9 coupled with homologous recombination to disrupt the endogenous kur locus in Xenopus resulted in the asymmetric localization of the PCP protein Prickle2 being lost in mutant multiciliated cells. Kur also makes interactions with other PCP components, including Disheveled. This supports a model wherein Kur plays a dual role in cilia motility and polarization.

Analysis of Axonemal Assembly During Ciliary Regeneration in Chlamydomonas

Chlamydomonas reinhardtii is an outstanding model genetic organism for study of assembly of cilia. Here, methods are described for synchronization of ciliary regeneration in Chlamydomonas to analyze the sequence in which ciliary proteins assemble. In addition, the methods described allow analysis of the mechanisms involved in regulation of ciliary length, the proteins required for ciliary assembly, and the temporal expression of genes encoding ciliary proteins. Ultimately, these methods can contribute to discovery of conserved genes that when defective lead to abnormal ciliary assembly and human disease.

Crescerin uses a TOG domain array to regulate microtubules in the primary cilium

Primary cilia are critical organelles involved in development, sensation, and signaling. Crescerin, a conserved protein family in ciliated and flagellated eukaryotes, uses a TOG domain array with tubulin polymerization activity to regulate cilia microtubules and facilitate proper cilia length, ultrastructure, and function.

Eukaryotic cilia are cell-surface projections critical for sensing the extracellular environment. Defects in cilia structure and function result in a broad range of developmental and sensory disorders. However, mechanisms that regulate the microtubule (MT)-based scaffold forming the cilia core are poorly understood. TOG domain array–containing proteins ch-TOG and CLASP are key regulators of cytoplasmic MTs. Whether TOG array proteins also regulate ciliary MTs is unknown. Here we identify the conserved Crescerin protein family as a cilia-specific, TOG array-containing MT regulator. We present the crystal structure of mammalian Crescerin1 TOG2, revealing a canonical TOG fold with conserved tubulin-binding determinants. Crescerin1's TOG domains possess inherent MT-binding activity and promote MT polymerization in vitro. Using Cas9-triggered homologous recombination in Caenorhabditis elegans, we demonstrate that the worm Crescerin family member CHE-12 requires TOG domain–dependent tubulin-binding activity for sensory cilia development. Thus, Crescerin expands the TOG domain array–based MT regulatory paradigm beyond ch-TOG and CLASP, representing a distinct regulator of cilia structure.

Late steps in cytoplasmic maturation of assembly-competent axonemal outer arm dynein in Chlamydomonas require interaction of ODA5 and ODA10 in a complex

In humans, homologues of Chlamydomonas ciliary docking complex subunit DC2 and assembly factor ODA10 are interacting axonemal proteins needed for outer dynein arm assembly. Surprisingly, Chlamydomonas ODA10 does not interact with DC2, localizes to a proximal axonemal domain, and is needed for cytoplasmic steps in dynein assembly, not for docking.

Axonemal dyneins are multisubunit enzymes that must be preassembled in the cytoplasm, transported into cilia by intraflagellar transport, and bound to specific sites on doublet microtubules, where their activity facilitates microtubule sliding-based motility. Outer dynein arms (ODAs) require assembly factors to assist their preassembly, transport, and attachment to cargo (specific doublet A-tubule sites). In Chlamydomonas, three assembly factors—ODA5, ODA8, and ODA10—show genetic interactions and have been proposed to interact in a complex, but we recently showed that flagellar ODA8 does not copurify with ODA5 or ODA10. Here we show that ODA5 and ODA10 depend on each other for stability and coexist in a complex in both cytoplasmic and flagellar extracts. Immunofluorescence and immuno–electron microscopy reveal that ODA10 in flagella localizes strictly to a proximal region of doublet number 1, which completely lacks ODAs in Chlamydomonas. Studies of the in vitro binding of ODAs to axonemal doublets reveal a role for the ODA5/ODA10 assembly complex in cytoplasmic maturation of ODAs into a form that can bind to doublet microtubules.

The ciliary inner dynein arm, I1 dynein, is assembled in the cytoplasm and transported by IFT before axonemal docking

To determine mechanisms of assembly of ciliary dyneins, we focused on the Chlamydomonas inner dynein arm, I1 dynein, also known as dynein f. I1 dynein assembles in the cytoplasm as a 20S complex similar to the 20S I1 dynein complex isolated from the axoneme. The intermediate chain subunit, IC140 (IDA7), and heavy chains (IDA1, IDA2) are required for 20S I1 dynein preassembly in the cytoplasm. Unlike I1 dynein derived from the axoneme, the cytoplasmic 20S I1 complex will not rebind I1-deficient axonemes in vitro. To test the hypothesis that I1 dynein is transported to the distal tip of the cilia for assembly in the axoneme, we performed cytoplasmic complementation in dikaryons formed between wild-type and I1 dynein mutant cells. Rescue of I1 dynein assembly in mutant cilia occurred first at the distal tip and then proceeded toward the proximal axoneme. Notably, in contrast to other combinations, I1 dynein assembly was significantly delayed in dikaryons formed between ida7 and ida3. Furthermore, rescue of I1 dynein assembly required new protein synthesis in the ida7 × ida3 dikaryons. On the basis of the additional observations, we postulate that IDA3 is required for 20S I1 dynein transport. Cytoplasmic complementation in dikaryons using the conditional kinesin-2 mutant, fla10-1 revealed that transport of I1 dynein is dependent on kinesin-2 activity. Thus, I1 dynein complex assembly depends upon IFT for transport to the ciliary distal tip prior to docking in the axoneme.

Cilia dysfunction in lung disease

A characteristic feature of the human airway epithelium is the presence of ciliated cells bearing motile cilia, specialized cell surface projections containing axonemes composed of microtubules and dynein arms, which provide ATP-driven motility. In the airways, cilia function in concert with airway mucus to mediate the critical function of mucociliary clearance, cleansing the airways of inhaled particles and pathogens. The prototypical disorder of respiratory cilia is primary ciliary dyskinesia, an inherited disorder that leads to impaired mucociliary clearance, to repeated chest infections, and to the progressive destruction of lung architecture. Numerous acquired lung diseases are also marked by abnormalities in both cilia structure and function. In this review we summarize current knowledge regarding airway ciliated cells and cilia, how they function to maintain a healthy epithelium, and how disorders of cilia structure and function contribute to inherited and acquired lung disease.

Pih1d3 is required for cytoplasmic preassembly of axonemal dynein in mouse sperm

Pih1d3 promotes the stability and assembly of axonemal outer and inner dynein arms to allow for cytoplasmic preassembly of dynein complexes in spermatogenic cells.

Axonemal dynein complexes are preassembled in the cytoplasm before their transport to cilia, but the mechanism of this process remains unclear. We now show that mice lacking Pih1d3, a PIH1 domain–containing protein, develop normally but manifest male sterility. Pih1d3^−/− sperm were immotile and fragile, with the axoneme of the flagellum lacking outer dynein arms (ODAs) and inner dynein arms (IDAs) and showing a disturbed 9+2 microtubule organization. Pih1d3 was expressed specifically in spermatogenic cells, with the mRNA being most abundant in pachytene spermatocytes. Pih1d3 localized to the cytoplasm of spermatogenic cells but was not detected in spermatids or mature sperm. The levels of ODA and IDA proteins were reduced in the mutant testis and sperm, and Pih1d3 was found to interact with an intermediate chain of ODA as well as with Hsp70 and Hsp90. Our results suggest that Pih1d3 contributes to cytoplasmic preassembly of dynein complexes in spermatogenic cells by stabilizing and promoting complex formation by ODA and IDA proteins.

Picking up speed: advances in the genetics of primary ciliary dyskinesia

Abnormal ciliary axonemal structure and function are linked to the growing class of genetic disorders collectively known as ciliopathies, and our understanding of the complex genetics and functional phenotypes of these conditions has rapidly expanded. While progress in genetics and biology has uncovered numerous cilia-related syndromes, primary ciliary dyskinesia (PCD) remains the sole genetic disorder of motile cilia dysfunction. The first disease-causing mutation was described just 13 y ago, and since that time, the pace of gene discovery has quickened. These mutations separate into genes that encode axonemal motor proteins, structural and regulatory elements, and cytoplasmic proteins that are involved in assembly and preassembly of ciliary elements. These findings have yielded novel insights into the processes involved in ciliary assembly, structure, and function, which will allow us to better understand the clinical manifestations of PCD. Moreover, advances in techniques for genetic screening and sequencing are improving diagnostic approaches. In this article, we will describe the structure, function, and emerging genetics of respiratory cilia, review the genotype-phenotype relationships of motor ciliopathies, and explore the implications of recent discoveries for diagnostic testing for PCD.

Roles of cilia, fluid flow, and Ca2+ signaling in breaking of left-right symmetry

The emergence of left-right (L-R) asymmetry during embryogenesis is a classic problem in developmental biology. It is only since the 1990s, however, that substantial insight into this problem has been achieved by molecular and genetic approaches. Various genes required for L-R asymmetric morphogenesis in vertebrates have now been identified, and many of these genes are required for the formation and motility of cilia. Breaking of L-R symmetry in the mouse embryo occurs in the ventral node, where two types of cilia are present. Whereas centrally located motile cilia generate a leftward fluid flow, peripherally located immotile cilia sense a flow-dependent signal, which is either chemical or mechanical in nature. Although Ca2+ signaling is implicated in flow sensing, the precise mechanism remains unknown. Here we summarize current knowledge of L-R symmetry breaking in vertebrates (focusing on the mouse), with a special emphasis on the roles of cilia, fluid flow, and Ca2+ signaling.

A complex of BBS1 and NPHP7 is required for cilia motility in zebrafish

Bardet-Biedl syndrome (BBS) and nephronophthisis (NPH) are hereditary autosomal recessive disorders, encoded by two families of diverse genes. BBS and NPH display several overlapping phenotypes including cystic kidney disease, retinitis pigmentosa, liver fibrosis, situs inversus and cerebellar defects. Since most of the BBS and NPH proteins localize to cilia and/or their appendages, BBS and NPH are considered ciliopathies. In this study, we characterized the function of the transcription factor Nphp7 in zebrafish, and addressed the molecular connection between BBS and NPH. The knockdown of zebrafish bbs1 and nphp7.2 caused similar phenotypic changes including convergent extension defects, curvature of the body axis, hydrocephalus, abnormal heart looping and cystic pronephros, all consistent with an altered ciliary function. Immunoprecipitation assays revealed a physical interaction between BBS1 and NPHP7, and the simultaneous knockdown of zbbs1 and znphp7.2 enhanced the cystic pronephros phenotype synergistically, suggesting a genetic interaction between zbbs1 and znphp7.2 in vivo. Deletion of zBbs1 or zNphp7.2 did not compromise cilia formation, but disrupted cilia motility. Although NPHP7 has been shown to act as transcriptional repressor, our studies suggest a crosstalk between BBS1 and NPHP7 in regulating normal function of the cilium.