Hereditary Mucin Deficiency Caused by Biallelic Loss of Function of MUC5B.

Rationale: Mucin homeostasis is fundamental to airway health. Upregulation of airway mucus glycoprotein MUC5B is observed in diverse common lung diseases and represents a potential therapeutic target. In mice, Muc5b is required for mucociliary clearance and for controlling inflammation after microbial exposure. The consequences of its loss in humans are unclear. Objectives: The goal of this study was to identify and characterize a family with congenital absence of MUC5B protein. Methods: We performed whole-genome sequencing in an adult proband with unexplained bronchiectasis, impaired pulmonary function, and repeated Staphylococcus aureus infection. Deep phenotyping over a 12-year period included assessments of pulmonary radioaerosol mucociliary clearance. Genotyping with reverse phenotyping was organized for eight family members. Extensive experiments, including immunofluorescence staining and mass spectrometry for mucins, were performed across accessible sample types. Measurements and Main Results: The proband, and her symptomatic sibling who also had extensive sinus disease with nasal polyps, were homozygous for a novel splicing variant in the MUC5B gene (NM_002458.2: c.1938 + 1G>A). MUC5B was absent from saliva, sputum, and nasal samples. Mucociliary clearance was impaired in the proband, and large numbers of apoptotic macrophages were present in sputum. Three siblings heterozygous for the familial MUC5B variant were asymptomatic but had a shared pattern of mild lung function impairments. Conclusions: Congenital absence of MUC5B defines a new category of genetic respiratory disease. The human phenotype is highly concordant with that of the Muc5b-/- murine model. Further study of individuals with decreased MUC5B production could provide unique mechanistic insights into airway mucus biology.

Mutations in TP73 cause impaired mucociliary clearance and lissencephaly.

TP73 belongs to the TP53 family of transcription factors and has therefore been well studied in cancer research. Studies in mice, however, have revealed non-oncogenic activities related to multiciliogenesis. Utilizing whole-exome sequencing analysis in a cohort of individuals with a mucociliary clearance disorder and cortical malformation, we identified homozygous loss-of-function variants in TP73 in seven individuals from five unrelated families. All affected individuals exhibit a chronic airway disease as well as a brain malformation consistent with lissencephaly. We performed high-speed video microscopy, immunofluorescence analyses, and transmission electron microscopy in respiratory epithelial cells after spheroid or air liquid interface culture to analyze ciliary function, ciliary length, and number of multiciliated cells (MCCs). The respiratory epithelial cells studied display reduced ciliary length and basal bodies mislocalized within the cytoplasm. The number of MCCs is severely reduced, consistent with a reduced number of cells expressing the transcription factors crucial for multiciliogenesis (FOXJ1, RFX2). Our data demonstrate that autosomal-recessive deleterious variants in the TP53 family member TP73 cause a mucociliary clearance disorder due to a defect in MCC differentiation.

Planar cell polarity induces local microtubule bundling for coordinated ciliary beating.

Multiciliated cells (MCCs) in tracheas generate mucociliary clearance through coordinated ciliary beating. Apical microtubules (MTs) play a crucial role in this process by organizing the planar cell polarity (PCP)-dependent orientation of ciliary basal bodies (BBs), for which the underlying molecular basis remains elusive. Herein, we found that the deficiency of Daple, a dishevelled-associating protein, in tracheal MCCs impaired the planar polarized apical MTs without affecting the core PCP proteins, causing significant defects in the BB orientation at the cell level but not the tissue level. Using live-cell imaging and ultra-high voltage electron microscope tomography, we found that the apical MTs accumulated and were stabilized by side-by-side association with one side of the apical junctional complex, to which Daple was localized. In vitro binding and single-molecule imaging revealed that Daple directly bound to, bundled, and stabilized MTs through its dimerization. These features convey a PCP-related molecular basis for the polarization of apical MTs, which coordinate ciliary beating in tracheal MCCs.

Compartment-specific transcriptomics of ozone-exposed murine lungs reveals sex- and cell type-associated perturbations relevant to mucoinflammatory lung diseases.

Ozone is known to cause lung injury, and resident cells of the respiratory tract (i.e., epithelial cells and macrophages) respond to inhaled ozone in a variety of ways that affect their survival, morphology, and functioning. However, a complete understanding of the sex-associated and the cell type-specific gene expression changes in response to ozone exposure is still limited. Through transcriptome profiling, we aimed to analyze gene expression alterations and associated enrichment of biological pathways in three distinct cell type-enriched compartments of ozone-exposed murine lungs. We subchronically exposed adult male and female mice to 0.8 ppm ozone or filtered air. RNA-Seq was performed on airway epithelium-enriched airways, parenchyma, and purified airspace macrophages. Differential gene expression and biological pathway analyses were performed and supported by cellular and immunohistochemical analyses. While a majority of differentially expressed genes (DEGs) in ozone-exposed versus air-exposed groups were common between both sexes, sex-specific DEGs were also identified in all of the three tissue compartments. As compared with ozone-exposed males, ozone-exposed females had significant alterations in gene expression in three compartments. Pathways relevant to cell division and DNA repair were enriched in the ozone-exposed airways, indicating ozone-induced airway injury and repair, which was further supported by immunohistochemical analyses. In addition to cell division and DNA repair pathways, inflammatory pathways were also enriched within the parenchyma, supporting contribution by both epithelial and immune cells. Further, immune response and cytokine-cytokine receptor interactions were enriched in macrophages, indicating ozone-induced macrophage activation. Finally, our analyses also revealed the overall upregulation of mucoinflammation- and mucous cell metaplasia-associated pathways following ozone exposure.

SPEF2- and HYDIN-Mutant Cilia Lack the Central Pair-associated Protein SPEF2, Aiding Primary Ciliary Dyskinesia Diagnostics.

Primary ciliary dyskinesia (PCD) is a genetically heterogeneous chronic destructive airway disease. PCD is traditionally diagnosed by nasal nitric oxide measurement, analysis of ciliary beating, transmission electron microscopy (TEM), and/or genetic testing. In most genetic PCD variants, laterality defects can occur. However, it is difficult to establish a diagnosis in individuals with PCD and central pair (CP) defects, and alternative strategies are required because of very subtle ciliary beating abnormalities, a normal ciliary ultrastructure, and normal situs composition. Mutations in HYDIN are known to cause CP defects, but the genetic analysis of HYDIN variants is confounded by the pseudogene HYDIN2, which is almost identical in terms of intron/exon structure. We have previously shown that several types of PCD can be diagnosed via immunofluorescence (IF) microscopy analyses. Here, using IF microscopy, we demonstrated that in individuals with PCD and CP defects, the CP-associated protein SPEF2 is absent in HYDIN-mutant cells, revealing its dependence on functional HYDIN. Next, we performed IF analyses of SPEF2 in respiratory cells from 189 individuals with suspected PCD and situs solitus. Forty-one of the 189 individuals had undetectable SPEF2 and were subjected to a genetic analysis, which revealed one novel loss-of-function mutation in SPEF2 and three reported and 13 novel HYDIN mutations in 15 individuals. The remaining 25 individuals are good candidates for new, as-yet uncharacterized PCD variants that affect the CP apparatus. SPEF2 mutations have been associated with male infertility but have not previously been identified to cause PCD. We identified a mutation of SPEF2 that is causative for PCD with a CP defect. We conclude that SPEF2 IF analyses can facilitate the detection of CP defects and evaluation of the pathogenicity of HYDIN variants, thus aiding the molecular diagnosis of CP defects.

Immunopathology of Airway Surface Liquid Dehydration Disease.

The primary purpose of pulmonary ventilation is to supply oxygen (O2) for sustained aerobic respiration in multicellular organisms. However, a plethora of abiotic insults and airborne pathogens present in the environment are occasionally introduced into the airspaces during inhalation, which could be detrimental to the structural integrity and functioning of the respiratory system. Multiple layers of host defense act in concert to eliminate unwanted constituents from the airspaces. In particular, the mucociliary escalator provides an effective mechanism for the continuous removal of inhaled insults including pathogens. Defects in the functioning of the mucociliary escalator compromise the mucociliary clearance (MCC) of inhaled pathogens, which favors microbial lung infection. Defective MCC is often associated with airway mucoobstruction, increased occurrence of respiratory infections, and progressive decrease in lung function in mucoobstructive lung diseases including cystic fibrosis (CF). In this disease, a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene results in dehydration of the airway surface liquid (ASL) layer. Several mice models of Cftr mutation have been developed; however, none of these models recapitulate human CF-like mucoobstructive lung disease. As an alternative, the Scnn1b transgenic (Scnn1b-Tg+) mouse model overexpressing a transgene encoding sodium channel nonvoltage-gated 1, beta subunit (Scnn1b) in airway club cells is available. The Scnn1b-Tg+ mouse model exhibits airway surface liquid (ASL) dehydration, impaired MCC, increased mucus production, and early spontaneous pulmonary bacterial infections. High morbidity and mortality among mucoobstructive disease patients, high economic and health burden, and lack of scientific understanding of the progression of mucoobstruction warrants in-depth investigation of the cause of mucoobstruction in mucoobstructive disease models. In this review, we will summarize published literature on the Scnn1b-Tg+ mouse and analyze various unanswered questions on the initiation and progression of mucobstruction and bacterial infections.

Mice with a Deletion of Rsph1 Exhibit a Low Level of Mucociliary Clearance and Develop a Primary Ciliary Dyskinesia Phenotype.

Primary ciliary dyskinesia (PCD) is a genetically and phenotypically heterogeneous disease caused by mutations in over 40 different genes. Individuals with PCD caused by mutations in RSPH1 (radial spoke head 1 homolog) have been reported to have a milder phenotype than other individuals with PCD, as evidenced by a lower incidence of neonatal respiratory distress, higher nasal nitric oxide concentrations, and better lung function. To better understand genotype-phenotype relationships in PCD, we have characterized a mutant mouse model with a deletion of Rsph1. Approximately 50% of cilia from Rsph1-/- cells appeared normal by transmission EM, whereas the remaining cilia revealed a range of defects, primarily transpositions or a missing central pair. Ciliary beat frequency in Rsph1-/- cells was significantly lower than in control cells (20.2 ± 0.8 vs. 25.0 ± 0.9 Hz), and the cilia exhibited an aberrant rotational waveform. Young Rsph1-/- animals demonstrated a low rate of mucociliary clearance in the nasopharynx that was reduced to zero by about 1 month of age. Rsph1-/- animals accumulated mucus in the nasal cavity but had a lower bacterial burden than animals with a deletion of dynein axonemal intermediate chain 1 (Dnaic1-/-). Thus, Rsph1-/- mice display a PCD phenotype similar to but less severe than that observed in Dnaic1-/- mice, similar to what has been observed in humans. The results suggest that some individuals with PCD may not have a complete loss of mucociliary clearance and further suggest that early diagnosis and intervention may be important to maintain this low amount of clearance.

Muc5b overexpression causes mucociliary dysfunction and enhances lung fibrosis in mice.

The gain-of-function MUC5B promoter variant rs35705950 is the dominant risk factor for developing idiopathic pulmonary fibrosis (IPF). Here we show in humans that MUC5B, a mucin thought to be restricted to conducting airways, is co-expressed with surfactant protein C (SFTPC) in type 2 alveolar epithelia and in epithelial cells lining honeycomb cysts, indicating that cell types involved in lung fibrosis in distal airspace express MUC5B. In mice, we demonstrate that Muc5b concentration in bronchoalveolar epithelia is related to impaired mucociliary clearance (MCC) and to the extent and persistence of bleomycin-induced lung fibrosis. We also establish the ability of the mucolytic agent P-2119 to restore MCC and to suppress bleomycin-induced lung fibrosis in the setting of Muc5b overexpression. Our findings suggest that mucociliary dysfunction might play a causative role in bleomycin-induced pulmonary fibrosis in mice overexpressing Muc5b, and that MUC5B in distal airspaces is a potential therapeutic target in humans with IPF.

Biallelic Mutations in LRRC56, Encoding a Protein Associated with Intraflagellar Transport, Cause Mucociliary Clearance and Laterality Defects.

Primary defects in motile cilia result in dysfunction of the apparatus responsible for generating fluid flows. Defects in these mechanisms underlie disorders characterized by poor mucus clearance, resulting in susceptibility to chronic recurrent respiratory infections, often associated with infertility; laterality defects occur in about 50% of such individuals. Here we report biallelic variants in LRRC56 (known as oda8 in Chlamydomonas) identified in three unrelated families. The phenotype comprises laterality defects and chronic pulmonary infections. High-speed video microscopy of cultured epithelial cells from an affected individual showed severely dyskinetic cilia but no obvious ultra-structural abnormalities on routine transmission electron microscopy (TEM). Further investigation revealed that LRRC56 interacts with the intraflagellar transport (IFT) protein IFT88. The link with IFT was interrogated in Trypanosoma brucei. In this protist, LRRC56 is recruited to the cilium during axoneme construction, where it co-localizes with IFT trains and is required for the addition of dynein arms to the distal end of the flagellum. In T. brucei carrying LRRC56-null mutations, or a variant resulting in the p.Leu259Pro substitution corresponding to the p.Leu140Pro variant seen in one of the affected families, we observed abnormal ciliary beat patterns and an absence of outer dynein arms restricted to the distal portion of the axoneme. Together, our findings confirm that deleterious variants in LRRC56 result in a human disease and suggest that this protein has a likely role in dynein transport during cilia assembly that is evolutionarily important for cilia motility.

Cigarette smoke promotes HIV infection of primary bronchial epithelium and additively suppresses CFTR function.

Recurrent lung infections are a common cause of morbidity and mortality in people living with HIV and this is exacerbated in smokers even when administered combination antiretroviral therapy (cART). The incidence of pneumonia is increased with smoking and treatment interruption and is directly dependent on viral load in patients when adjusted for CD4 counts. CFTR dysfunction plays an important role in aberrant airway innate immunity as it is pivotal in regulating mucociliary clearance (MCC) rates and other antibacterial mechanisms of the airway. In our earlier work, we have demonstrated that bronchial epithelium expresses canonical HIV receptors CD4, CCR5 and CXCR4 and can be infected with HIV. HIV Tat suppresses CFTR mRNA and function via TGF-ß signaling. In the present study, we demonstrate that cigarette smoke (CS) potentiates HIV infection of bronchial epithelial cells by upregulating CD4 and CCR5 expression. HIV and CS individually and additively suppress CFTR biogenesis and function, possibly explaining the increased incidence of lung infections in HIV patients and its exacerbation in HIV smokers.

Pathophysiology and Genetics of Bronchiectasis Unrelated to Cystic Fibrosis.

Bronchiectasis is characterized by deregulated inflammatory response and recurrent bacterial infection resulting in progressive lung damage and an irreversible dilatation of bronchi and bronchioles. Generally accepted model of the development of bronchiectasis is the "vicious cycle hypothesis" that proposes compromising of the mucociliary clearance by an initial event, which leads to the infection of the respiratory tract followed by further impairment of mucociliary function, bacterial proliferation, and more inflammation. Bronchiectasis is a very common symptom in patients with cystic fibrosis (CF), while bronchiectasis unrelated to CF is heterogeneous pathology of unknown cause with a large number of potential contributory factors and poorly understood pathogenesis. It is presumed that bronchiectasis unrelated to CF is a multifactorial condition predisposed by genetic factors. Different molecules have been implicated in the onset and development of idiopathic bronchiectasis, as well as modulation of the disease severity and response to therapy. Most of these molecules are involved in the processes that contribute to the homeostasis of the lung tissue, especially mucociliary clearance, protease-antiprotease balance, and immunomodulation. Evaluation of the studies performed towards investigation of the role these molecules play in bronchiectasis identifies genetic variants that may be of potential importance for clinical management of the disease, and also of interest for future research efforts. This review focuses on the molecules with major roles in lung homeostasis and their involvement in bronchiectasis unrelated to CF.

Seeing cilia: imaging modalities for ciliary motion and clinical connections.

The respiratory tract is lined with multiciliated epithelial cells that function to move mucus and trapped particles via the mucociliary transport apparatus. Genetic and acquired ciliopathies result in diminished mucociliary clearance, contributing to disease pathogenesis. Recent innovations in imaging technology have advanced our understanding of ciliary motion in health and disease states. Application of imaging modalities including transmission electron microscopy, high-speed video microscopy, and micron-optical coherence tomography could improve diagnostics and be applied for precision medicine. In this review, we provide an overview of ciliary motion, imaging modalities, and ciliopathic diseases of the respiratory system including primary ciliary dyskinesia, cystic fibrosis, chronic obstructive pulmonary disease, and idiopathic pulmonary fibrosis.

Clinical care for primary ciliary dyskinesia: current challenges and future directions.

Primary ciliary dyskinesia (PCD) is a rare genetic disease that affects the motility of cilia, leading to impaired mucociliary clearance. It is estimated that the vast majority of patients with PCD have not been diagnosed as such, providing a major obstacle to delivering appropriate care. Challenges in diagnosing PCD include lack of disease-specific symptoms and absence of a single, "gold standard", diagnostic test. Management of patients is currently not based on high-level evidence because research findings are mostly derived from small observational studies with limited follow-up period. In this review, we provide a critical overview of the available literature on clinical care for PCD patients, including recent advances. We identify barriers to PCD research and make suggestions for overcoming challenges.

What we can learn from a tadpole about ciliopathies and airway diseases: Using systems biology in Xenopus to study cilia and mucociliary epithelia.

Over the past years, the Xenopus embryo has emerged as an incredibly useful model organism for studying the formation and function of cilia and ciliated epithelia in vivo. This has led to a variety of findings elucidating the molecular mechanisms of ciliated cell specification, basal body biogenesis, cilia assembly, and ciliary motility. These findings also revealed the deep functional conservation of signaling, transcriptional, post-transcriptional, and protein networks employed in the formation and function of vertebrate ciliated cells. Therefore, Xenopus research can contribute crucial insights not only into developmental and cell biology, but also into the molecular mechanisms underlying cilia related diseases (ciliopathies) as well as diseases affecting the ciliated epithelium of the respiratory tract in humans (e.g., chronic lung diseases). Additionally, systems biology approaches including transcriptomics, genomics, and proteomics have been rapidly adapted for use in Xenopus, and broaden the applications for current and future translational biomedical research. This review aims to present the advantages of using Xenopus for cilia research, highlight some of the evolutionarily conserved key concepts and mechanisms of ciliated cell biology that were elucidated using the Xenopus model, and describe the potential for Xenopus research to address unresolved questions regarding the molecular mechanisms of ciliopathies and airway diseases.

Contribution of mucus concentration and secreted mucins Muc5ac and Muc5b to the pathogenesis of muco-obstructive lung disease.

Airway diseases, including cigarette smoke-induced chronic bronchitis, cystic fibrosis, and primary ciliary dyskinesia are associated with decreased mucociliary clearance (MCC). However, it is not known whether a simple reduction in MCC or concentration-dependent mucus adhesion to airway surfaces dominates disease pathogenesis or whether decreasing the concentration of secreted mucins may be therapeutic. To address these questions, Scnn1b-Tg mice, which exhibit airway mucus dehydration/adhesion, were compared and crossed with Muc5b- and Muc5ac-deficient mice. Absence of Muc5b caused a 90% reduction in MCC, whereas Scnn1b-Tg mice exhibited an ∼50% reduction. However, the degree of MCC reduction did not correlate with bronchitic airway pathology, which was observed only in Scnn1b-Tg mice. Ablation of Muc5b significantly reduced the extent of mucus plugging in Scnn1b-Tg mice. However, complete absence of Muc5b in Scnn1b-Tg mice was associated with increased airway inflammation, suggesting that Muc5b is required to maintain immune homeostasis. Loss of Muc5ac had few phenotypic consequences in Scnn1b-Tg mice. These data suggest that: (i) mucus hyperconcentration dominates over MCC reduction alone to produce bronchitic airway pathology; (ii) Muc5b is the dominant contributor to the Scnn1b-Tg phenotype; and (iii) therapies that limit mucin secretion may reduce plugging, but complete Muc5b removal from airway surfaces may be detrimental.

[Zivert-Kartagener's syndrome encountered in the practical work of an otorhionolaryngologist, pulmonologist, obstetrician, and gynecologist]. / Sindrom Ziverta­Kartagenera v praktike LOR-vracha, pul'monologa i akushera-ginekologa.

The objective of the present work was to analyze the current concept of the genetically predetermined condition Zivert-Kartagener's syndrome with special reference to the pathogenetic mechanisms underlying the development of this condition, its clinical picture and methods of treatment. The authors' original observations of the patients presenting with Zivert-Kartagener's syndrome are reported.

Idiopathic Pulmonary Fibrosis: A Genetic Disease That Involves Mucociliary Dysfunction of the Peripheral Airways.

Idiopathic pulmonary fibrosis (IPF) is an incurable complex genetic disorder that is associated with sequence changes in 7 genes (MUC5B, TERT, TERC, RTEL1, PARN, SFTPC, and SFTPA2) and with variants in at least 11 novel loci. We have previously found that 1) a common gain-of-function promoter variant in MUC5B rs35705950 is the strongest risk factor (genetic and otherwise), accounting for 30-35% of the risk of developing IPF, a disease that was previously considered idiopathic; 2) the MUC5B promoter variant can potentially be used to identify individuals with preclinical pulmonary fibrosis and is predictive of radiologic progression of preclinical pulmonary fibrosis; and 3) MUC5B may be involved in the pathogenesis of pulmonary fibrosis with MUC5B message and protein expressed in bronchiolo-alveolar epithelia of IPF and the characteristic IPF honeycomb cysts. Based on these considerations, we hypothesize that excessive production of MUC5B either enhances injury due to reduced mucociliary clearance or impedes repair consequent to disruption of normal regenerative mechanisms in the distal lung. In aggregate, these novel considerations should have broad impact, resulting in specific etiologic targets, early detection of disease, and novel biologic pathways for use in the design of future intervention, prevention, and mechanistic studies of IPF.

Mitochondrial iron chelation ameliorates cigarette smoke-induced bronchitis and emphysema in mice.

Chronic obstructive pulmonary disease (COPD) is linked to both cigarette smoking and genetic determinants. We have previously identified iron-responsive element-binding protein 2 (IRP2) as an important COPD susceptibility gene and have shown that IRP2 protein is increased in the lungs of individuals with COPD. Here we demonstrate that mice deficient in Irp2 were protected from cigarette smoke (CS)-induced experimental COPD. By integrating RNA immunoprecipitation followed by sequencing (RIP-seq), RNA sequencing (RNA-seq), and gene expression and functional enrichment clustering analysis, we identified Irp2 as a regulator of mitochondrial function in the lungs of mice. Irp2 increased mitochondrial iron loading and levels of cytochrome c oxidase (COX), which led to mitochondrial dysfunction and subsequent experimental COPD. Frataxin-deficient mice, which had higher mitochondrial iron loading, showed impaired airway mucociliary clearance (MCC) and higher pulmonary inflammation at baseline, whereas mice deficient in the synthesis of cytochrome c oxidase, which have reduced COX, were protected from CS-induced pulmonary inflammation and impairment of MCC. Mice treated with a mitochondrial iron chelator or mice fed a low-iron diet were protected from CS-induced COPD. Mitochondrial iron chelation also alleviated CS-induced impairment of MCC, CS-induced pulmonary inflammation and CS-associated lung injury in mice with established COPD, suggesting a critical functional role and potential therapeutic intervention for the mitochondrial-iron axis in COPD.

Iron acquisition in the cystic fibrosis lung and potential for novel therapeutic strategies.

Iron acquisition is vital to microbial survival and is implicated in the virulence of many of the pathogens that reside in the cystic fibrosis (CF) lung. The multifaceted nature of iron acquisition by both bacterial and fungal pathogens encompasses a range of conserved and species-specific mechanisms, including secretion of iron-binding siderophores, utilization of siderophores from other species, release of iron from host iron-binding proteins and haemoproteins, and ferrous iron uptake. Pathogens adapt and deploy specific systems depending on iron availability, bioavailability of the iron pool, stage of infection and presence of competing pathogens. Understanding the dynamics of pathogen iron acquisition has the potential to unveil new avenues for therapeutic intervention to treat both acute and chronic CF infections. Here, we examine the range of strategies utilized by the primary CF pathogens to acquire iron and discuss the different approaches to targeting iron acquisition systems as an antimicrobial strategy.

Cyclin O (Ccno) functions during deuterosome-mediated centriole amplification of multiciliated cells.

Mucociliary clearance and fluid transport along epithelial surfaces are carried out by multiciliated cells (MCCs). Recently, human mutations in Cyclin O (CCNO) were linked to severe airway disease. Here, we show that Ccno expression is restricted to MCCs and the genetic deletion of Ccno in mouse leads to reduced numbers of multiple motile cilia and characteristic phenotypes of MCC dysfunction including severe hydrocephalus and mucociliary clearance deficits. Reduced cilia numbers are caused by compromised generation of centrioles at deuterosomes, which serve as major amplification platform for centrioles in MCCs. Ccno-deficient MCCs fail to sufficiently generate deuterosomes, and only reduced numbers of fully functional centrioles that undergo maturation to ciliary basal bodies are formed. Collectively, this study implicates CCNO as first known regulator of deuterosome formation and function for the amplification of centrioles in MCCs.