Overview of structure and function of mammalian cilia

Roles for microtubules in the proliferative and differentiated cells of stratified epithelia

While microtubule dynamics and organization have been extensively studied invitro, both biochemically and in cultured cells, recent work has begun to extend this into tissues ex vivo and organisms in vivo. Advances in genetic tools and imaging technology have allowed studies on the dynamics, function, and organization of microtubules in the stratified epithelia of the epidermis. Here, we discuss recent work that highlights the varied roles that microtubules play in supporting epidermal function. These findings demonstrate that studying microtubules in tissues has revealed not only novel aspects of epidermal biology but also new principles of microtubule regulation.

Potential Roles of O-GlcNAcylation in Primary Cilia- Mediated Energy Metabolism

The primary cilium, an antenna-like structure on most eukaryotic cells, functions in transducing extracellular signals into intracellular responses via the receptors and ion channels distributed along it membrane. Dysfunction of this organelle causes an array of human diseases, known as ciliopathies, that often feature obesity and diabetes; this indicates the primary cilia's active role in energy metabolism, which it controls mainly through hypothalamic neurons, preadipocytes, and pancreatic β-cells. The nutrient sensor, O-GlcNAc, is widely involved in the regulation of energy homeostasis. Not only does O-GlcNAc regulate ciliary length, but it also modifies many components of cilia-mediated metabolic signaling pathways. Therefore, it is likely that O-GlcNAcylation (OGN) plays an important role in regulating energy homeostasis in primary cilia. Abnormal OGN, as seen in cases of obesity and diabetes, may play an important role in primary cilia dysfunction mediated by these pathologies.

Morpholino-Mediated Knockdown of Ciliary Genes in Euplotes vannus, a Novel Marine Ciliated Model Organism

Cilia are highly conserved organelles present in almost all types of eukaryotic cells, and defects in cilia structure and/or function are related to many human genetic disorders. Single-celled ciliated protists, which possess diverse types of cilia, are remarkable model organisms for studying cilia structures and functions. Euplotes vannus is a representative ciliate with many intriguing features; for example, it possesses extensively fragmented somatic genomes and a high frequency of + 1 programmed ribosomal frameshifting. However, the molecular mechanisms underlying these remarkable traits remain largely unknown, mainly due to the lack of efficient genetic manipulation tools. Here, we describe the first application of a morpholino-based strategy to knockdown gene expression in E. vannus. Through interfering with the function of two ciliary genes, ZMYND10 and C21ORF59, we showed that these two genes are essential for the ciliary motility and proliferation of E. vannus cells. Strikingly, both ZMYND10- and C21ORF59-knockdown cells developed shorter cilia in the ventral cirri, a special type of ciliary tuft, suggesting a novel role for these genes in the regulation of cilia length. Our data provide a new method to explore gene function in E. vannus, which may help us to understand the functions of evolutionarily conserved cilia-related genes as well as other biological processes in this intriguing model.

Metachronal Actuation of Microscale Magnetic Artificial Cilia

Biological cells often interact with the environment through carpets of microscopic hair-like cilia. These elastic structures are known to beat in a synchronized wavy fashion called metachronal motion to produce fluid transport. Metachronal motion emerges due to a phase difference between beating cycles of neighboring cilia and appears as traveling waves propagating along the ciliary carpet. We demonstrate submerged in water microscale magnetic cilia that are externally actuated to beat in a metachronal fashion. Two approaches are used to induce coordinated phase differences among the beating cilia. In the first case, we fabricate cilia with an imposed gradient of geometrical properties that are subject to a rotating uniform magnetic field. In the second scenario, a ciliary array is composed of identical cilia that experience a magnetic field that varies spatiotemporally. We demonstrate that magnetic cilia can achieve symplectic, antiplectic, and leoplectic metachrony.

Novel dynein axonemal assembly factor 1 mutations identified using whole‑exome sequencing in patients with primary ciliary dyskinesia

Primary ciliary dyskinesia (PCD) is a rare, genetically heterogeneous disorder caused by dysfunction of the cilia and flagella; however, causative genetic defects have not been detected in all patients with PCD. Seven Chinese Han patients with Kartagener syndrome were enrolled onto the present study. Transmission electron microscopy (TEM) was performed to evaluate the cilial defects and whole‑exome sequencing was used to analyze relevant genetic variations in all patients. In two of the seven patients with PCD, four novel dynein axonemal assembly factor 1 (DNAAF1) mutations were identified (NM_178452.6:c.3G>A, c.124+1G>C, c.509delG and c.943A>T) in three alleles. Both of these patients had long‑standing infertility. Their chest computed tomography results showed bronchiectasis, lung infections and situs inversus, and paranasal computed tomography revealed sinusitis. Semen analysis of the male patient showed poor sperm motility. TEM showed defects in the inner and outer dynein arms in both patients. The DNAAF1 sequences of family members were then analyzed. Bioinformatics analysis indicated that these mutations may be the cause of the cilial defects in these two probands. Thus, the present study identified novel PCD‑causing mutations in DNAAF1 in two patients with PCD. These genetic variations were predicted to alter DNAAF1 amino acid residues and lead to loss of function, thereby inhibiting cilia‑mediated motility. Accordingly, the two probands had PCD symptoms, and one of them died due to PCD‑associated complications.

Structural insights into the architecture and assembly of eukaryotic flagella

Cilia and flagella are slender projections found on most eukaryotic cells including unicellular organisms such as Chlamydomonas, Trypanosoma and Tetrahymena, where they serve motility and signaling functions. The cilium is a large molecular machine consisting of hundreds of different proteins that are trafficked into the organelle to organize a repetitive microtubule-based axoneme. Several recent studies took advantage of improved cryo-EM methodology to unravel the high-resolution structures of ciliary complexes. These include the recently reported purification and structure determination of axonemal doublet microtubules from the green algae Chlamydomonas reinhardtii, which allows for the modeling of more than 30 associated protein factors to provide deep molecular insight into the architecture and repetitive nature of doublet microtubules. In addition, we will review several recent contributions that dissect the structure and function of ciliary trafficking complexes that ferry structural and signaling components between the cell body and the cilium organelle.

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

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

A very early diagnosis of Alstrӧm syndrome by next generation sequencing

Background

Alström syndrome is a rare recessively inherited disorder caused by variants in the ALMS1 gene. It is characterized by multiple organ dysfunction, including cone-rod retinal dystrophy, dilated cardiomyopathy, hearing loss, obesity, insulin resistance, hyperinsulinemia, type 2 diabetes mellitus and systemic fibrosis. Heterogeneity and age-dependent development of clinical manifestations make it difficult to obtain a clear diagnosis, especially in pediatric patients.

Case presentation

Here we report the case of a girl with Alström syndrome. Genetic examination was proposed at age 22 months when suspected macular degeneration was the only major finding. Next generation sequencing of a panel of genes linked to eye-related pathologies revealed two compound heterozygous variants in the ALMS1 gene. Frameshift variants c.1196_1202del, p.(Thr399Lysfs*11), rs761292021 and c.11310_11313del, (p.Glu3771Trpfs*18), rs747272625 were detected in exons 5 and 16, respectively. Both variants cause frameshifts and generation of a premature stop-codon that probably leads to mRNA nonsense-mediated decay. Validation and segregation of ALMS1 variants were confirmed by Sanger sequencing.

Conclusions

Genetic testing makes it possible, even in childhood, to increase the number of correct diagnoses of patients who have ambiguous phenotypes caused by rare genetic variants. The development of high-throughput sequencing technologies offers an exceptionally valuable screening tool for clear genetic diagnoses and ensures early multidisciplinary management and treatment of the emerging symptoms.

The primary cilium and lipophagy translate mechanical forces to direct metabolic adaptation of kidney epithelial cells

Organs and cells must adapt to shear stress induced by biological fluids, but how fluid flow contributes to the execution of specific cell programs is poorly understood. Here we show that shear stress favours mitochondrial biogenesis and metabolic reprogramming to ensure energy production and cellular adaptation in kidney epithelial cells. Shear stress stimulates lipophagy, contributing to the production of fatty acids that provide mitochondrial substrates to generate ATP through β-oxidation. This flow-induced process is dependent on the primary cilia located on the apical side of epithelial cells. The interplay between fluid flow and lipid metabolism was confirmed in vivo using a unilateral ureteral obstruction mouse model. Finally, primary cilium-dependent lipophagy and mitochondrial biogenesis are required to support energy-consuming cellular processes such as glucose reabsorption, gluconeogenesis and cytoskeletal remodelling. Our findings demonstrate how primary cilia and autophagy are involved in the translation of mechanical forces into metabolic adaptation.

The Enigmatic Role of Lipids in Cilia Signaling

Primary cilia are specialized cellular structures that project from the surface of most cell types in metazoans and mediate transduction of major signaling pathways. The ciliary membrane is contiguous with the plasma membrane, yet it exhibits distinct protein and lipid composition, which is essential for ciliary function. Diffusion barriers at the base of a cilium are responsible for establishing unique molecular composition of this organelle. Although considerable progress has been made in identifying mechanisms of ciliary protein trafficking in and out of cilia, it remains largely unknown how the distinct lipid identity of the ciliary membrane is achieved. In this mini review, I summarize recent developments in characterizing lipid composition and organization of the ciliary membrane and discuss the emerging roles of lipids in modulating activity of ciliary signaling components including ion channels and G protein-coupled receptors.

Cellular and developmental basis of orofacial clefts

During craniofacial development, defective growth and fusion of the upper lip and/or palate can cause orofacial clefts (OFCs), which are among the most common structural birth defects in humans. The developmental basis of OFCs includes morphogenesis of the upper lip, primary palate, secondary palate, and other orofacial structures, each consisting of diverse cell types originating from all three germ layers: the ectoderm, mesoderm, and endoderm. Cranial neural crest cells and orofacial epithelial cells are two major cell types that interact with various cell lineages and play key roles in orofacial development. The cellular basis of OFCs involves defective execution in any one or several of the following processes: neural crest induction, epithelial-mesenchymal transition, migration, proliferation, differentiation, apoptosis, primary cilia formation and its signaling transduction, epithelial seam formation and disappearance, periderm formation and peeling, convergence and extrusion of palatal epithelial seam cells, cell adhesion, cytoskeleton dynamics, and extracellular matrix function. The latest cellular and developmental findings may provide a basis for better understanding of the underlying genetic, epigenetic, environmental, and molecular mechanisms of OFCs.

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.

Electron cryotomography of intact motile cilia defines the basal body to axoneme transition

Greenan et al. use electron cryotomography on intact motile cilia to elucidate how basal bodies template the formation of motile axonemes.

Cells use motile cilia to generate force in the extracellular space. The structure of a cilium can be classified into three subdomains: the intracellular basal body (BB) that templates cilium formation, the extracellular axoneme that generates force, and the transition zone (TZ) that bridges them. While the BB is composed of triplet microtubules (TMTs), the axoneme is composed of doublet microtubules (DMTs), meaning the cilium must convert between different microtubule geometries. Here, we performed electron cryotomography to define this conversion, and our reconstructions reveal identifying structural features of the BB, TZ, and axoneme. Each region is distinct in terms of microtubule number and geometry, microtubule inner proteins, and microtubule linkers. TMT to DMT conversion occurs within the BB, and microtubule geometry changes to axonemal by the end of the TZ, followed by the addition of axoneme-specific components essential for cilium motility. Our results provide the highest-resolution images of the motile cilium to date and reveal how BBs template axonemes.

Microtubule-associated proteins and emerging links to primary cilium structure, assembly, maintenance, and disassembly

The primary cilium is a microtubule-based structure that protrudes from the cell surface in diverse eukaryotic organisms. It functions as a key signaling center that decodes a variety of mechanical and chemical stimuli and plays fundamental roles in development and homeostasis. Accordingly, structural and functional defects of the primary cilium have profound effects on the physiology of multiple organ systems including kidney, retina, and central nervous system. At the core of the primary cilium is the microtubule-based axoneme, which supports the cilium shape and acts as the scaffold for bidirectional transport of cargoes into and out of cilium. Advances in imaging, proteomics, and structural biology have revealed new insights into the ultrastructural organization and composition of the primary cilium, the mechanisms that underlie its biogenesis and functions, and the pathologies that result from their deregulation termed ciliopathies. In this viewpoint, we first discuss the recent studies that identified the three-dimensional native architecture of the ciliary axoneme and revealed that it is considerably different from the well-known '9 + 0' paradigm. Moving forward, we explore emerging themes in the assembly and maintenance of the axoneme, with a focus on how microtubule-associated proteins regulate its structure, length, and stability. This far more complex picture of the primary cilium structure and composition, as well as the recent technological advances, open up new avenues for future research.

Genetic interaction between central pair apparatus genes CFAP221, CFAP54, and SPEF2 in mouse models of primary ciliary dyskinesia

Primary ciliary dyskinesia (PCD) is a genetically heterogeneous syndrome that results from defects in motile cilia. The ciliary axoneme has a 9 + 2 microtubule structure consisting of nine peripheral doublets surrounding a central pair apparatus (CPA), which plays a critical role in regulating proper ciliary function. We have previously shown that mouse models with mutations in CPA genes CFAP221, CFAP54, and SPEF2 have a PCD phenotype with defects in ciliary motility. In this study, we investigated potential genetic interaction between these CPA genes by generating each combination of double heterozygous and double homozygous mutants. No detectable cilia-related phenotypes were observed in double heterozygotes, but all three double homozygous mutant lines exhibit early mortality and typically develop severe PCD-associated phenotypes of hydrocephalus, mucociliary clearance defects in the upper airway, and abnormal spermatogenesis. Double homozygous cilia are generally intact and display a normal morphology and distribution. Spermiogenesis is aborted in double homozygotes, with an absence of mature flagella on elongating spermatids and epididymal sperm. These findings identify genetic interactions between CPA genes and genetic mechanisms regulating the CPA and motile cilia function.

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.

A comprehensive analysis of Rab GTPases reveals a role for Rab34 in serum starvation-induced primary ciliogenesis

Primary cilia are sensors of chemical and mechanical signals in the extracellular environment. The formation of primary cilia (i.e. ciliogenesis) requires dynamic membrane trafficking events, and several Rab small GTPases, key regulators of membrane trafficking, have recently been reported to participate in ciliogenesis. However, the precise mechanisms of Rab-mediated membrane trafficking during ciliogenesis remain largely unknown. In the present study, we used a collection of siRNAs against 62 human Rabs to perform a comprehensive knockdown screening for Rabs that regulate serum starvation-induced ciliogenesis in human telomerase reverse transcriptase retinal pigment epithelium 1 (hTERT-RPE1) cells and succeeded in identifying Rab34 as an essential Rab. Knockout (KO) of Rab34, but not of Rabs previously reported to regulate ciliogenesis (e.g. Rab8 and Rab10) in hTERT-RPE1 cells, drastically impaired serum starvation-induced ciliogenesis. Rab34 was also required for serum starvation-induced ciliogenesis in NIH/3T3 cells and MCF10A cells but not for ciliogenesis in Madin-Darby canine kidney (MDCK)-II cysts. We then attempted to identify a specific region(s) of Rab34 that is essential for ciliogenesis by performing deletion and mutation analyses of Rab34. Unexpectedly, instead of a specific sequence in the switch II region, which is generally important for recognizing effector proteins (e.g. Rab interacting lysosomal protein [RILP]), a unique long N-terminal region of Rab34 before the conserved GTPase domain was found to be essential. These findings suggest that Rab34 is an atypical Rab that regulates serum starvation-induced ciliogenesis through its unique N-terminal region.

Physiological and Pathophysiological Aspects of Primary Cilia-A Literature Review with View on Functional and Structural Relationships in Cartilage

Cilia are cellular organelles that project from the cell. They occur in nearly all non-hematopoietic tissues and have different functions in different tissues. In mesenchymal tissues primary cilia play a crucial role in the adequate morphogenesis during embryological development. In mature articular cartilage, primary cilia fulfil chemo- and mechanosensitive functions to adapt the cellular mechanisms on extracellular changes and thus, maintain tissue homeostasis and morphometry. Ciliary abnormalities in osteoarthritic cartilage could represent pathophysiological relationships between ciliary dysfunction and tissue deformation. Nevertheless, the molecular and pathophysiological relationships of ‘Primary Cilia’ (PC) in the context of osteoarthritis is not yet fully understood. The present review focuses on the current knowledge about PC and provide a short but not exhaustive overview of their role in cartilage.

The transcriptional signature associated with human motile cilia

Cilia are complex microtubule-based organelles essential to a range of processes associated with embryogenesis and tissue homeostasis. Mutations in components of these organelles or those involved in their assembly may result in a diverse set of diseases collectively known as ciliopathies. Accordingly, many cilia-associated proteins have been described, while those distinguishing cilia subtypes are poorly defined. Here we set out to define genes associated with motile cilia in humans based on their transcriptional signature. To define the signature, we performed network deconvolution of transcriptomics data derived from tissues possessing motile ciliated cell populations. For each tissue, genes coexpressed with the motile cilia-associated transcriptional factor, FOXJ1, were identified. The consensus across tissues provided a transcriptional signature of 248 genes. To validate these, we examined the literature, databases (CilDB, CentrosomeDB, CiliaCarta and SysCilia), single cell RNA-Seq data, and the localisation of mRNA and proteins in motile ciliated cells. In the case of six poorly characterised signature genes, we performed new localisation experiments on ARMC3, EFCAB6, FAM183A, MYCBPAP, RIBC2 and VWA3A. In summary, we report a set of motile cilia-associated genes that helps shape our understanding of these complex cellular organelles.

Intracellular Cl- Regulation of Ciliary Beating in Ciliated Human Nasal Epithelial Cells: Frequency and Distance of Ciliary Beating Observed by High-Speed Video Microscopy

Small inhaled particles, which are entrapped by the mucous layer that is maintained by mucous secretion via mucin exocytosis and fluid secretion, are removed from the nasal cavity by beating cilia. The functional activities of beating cilia are assessed by their frequency and the amplitude. Nasal ciliary beating is controlled by intracellular ions (Ca²⁺, H⁺ and Cl^-), and is enhanced by a decreased concentration of intracellular Cl^- ([Cl^-]_i) in ciliated human nasal epithelial cells (cHNECs) in primary culture, which increases the ciliary beat amplitude. A novel method to measure both ciliary beat frequency (CBF) and ciliary beat distance (CBD, an index of ciliary beat amplitude) in cHNECs has been developed using high-speed video microscopy, which revealed that a decrease in [Cl^-]_i increased CBD, but not CBF, and an increase in [Cl^-]_i decreased both CBD and CBF. Thus, [Cl^-]_i inhibits ciliary beating in cHNECs, suggesting that axonemal structures controlling CBD and CBF may have Cl^- sensors and be regulated by [Cl^-]_i. These observations indicate that the activation of Cl^- secretion stimulates ciliary beating (increased CBD) mediated via a decrease in [Cl^-]_i in cHNECs. Thus, [Cl^-]_i is critical for controlling ciliary beating in cHNECs. This review introduces the concept of Cl^- regulation of ciliary beating in cHNECs.

Dynein assembly factor with WD repeat domains 1 (DAW1) is required for the function of motile cilia in the planarian Schmidtea mediterranea

Motile cilia propel directed cell movements and sweep fluids across the surface of tissues. Orthologs of Dynein Assembly Factor with WD Repeat Domains 1 (DAW1) support normal ciliary beating by enhancing delivery of dynein complexes to axonemal microtubules. DAW1 mutations in vertebrates result in multiple developmental abnormalities and early or prenatal lethality, complicating functional assessment of DAW1 in adult structures. Planarian flatworms maintain cellular homeostasis and regenerate through differentiation of adult pluripotent stem cells, and systemic RNA-interference (RNAi) can be induced to analyze gene function at any point after birth. A single ortholog of DAW1 was identified in the genome of the planarian Schmidtea mediterranea (Smed-daw1). Smed-DAW1 is composed of eight WD repeats, which are 55% identical to the founding member of this protein family (Chlamydomonas reinhardtii ODA16) and 58% identical to human DAW1. Smed-daw1 is expressed in the planarian epidermis, protonephridial excretory system, and testes, all of which contain cells functionally dependent on motile cilia. Smed-daw1 RNAi resulted in locomotion defects and edema, which are phenotypes characteristic of multiciliated epidermis and protonephridial dysfunction, respectively. Changes in abundance or length of motile cilia were not observed at the onset of phenotypic manifestations upon Smed-daw1 RNAi, corroborating with studies showing that DAW-1 loss of function leads to aberrant movement of motile cilia in other organisms, rather than loss of cilia per se. However, extended RNAi treatments did result in shorter epidermal cilia and decreased abundance of ciliated protonephridia, suggesting that Smed-daw1 is required for homeostatic maintenance of these structures in flatworms.

Influence of silica particles on mucociliary structure and MUC5B expression in airways of C57BL/6 mice

Purpose: Impaired mucociliary clearance is an initial characteristic of recurrent cough, respiratory infection and chronic respiratory diseases. It has been demonstrated that prolonged inhalation of respirable silica particles results in a variety of pulmonary diseases, but whether the mucociliary system is involved in this process is unclear. This study aims to evaluate the effects of silica particles on mucociliary structure and MUC5B production in respiratory tract.Materials and Methods: C57BL/6 mice were administered with 2.5 mg silica particles through a single intratracheal instillation. The changes of mucociliary structure and MUC5B expression in trachea was evaluated by HE and AB-PAS staining, transmission electron microscopy and immunohistochemistry on days 1, 7, 28 and 84 post-exposure.Results: The mucociliary structure of airway epithelium was obviously impaired by silica particles, showing disordered, shortened or partially lost cilia on the surface, increased mucus in mucous layer and submucosal glands from day 7 to day 84. A variety of ultrastructural abnormalities were discovered in silica-exposed airway cilia, including absence of central pair microtubules, disorganized microtubules and clusters of axoneme on day 1 and 7. The numbers of ciliary axonemes and basal bodies in ciliated epithelial cells were significantly decreased, whereas the proportion of abnormal axonemes was gradually increased with exposure to silica particles (P < 0.05). In addition, silica particles significantly decreased MUC5B expression on the surface of airway epithelium on day 28 and 84, but obviously increased its production in submucosal glands from day 1 to day 84 (P < 0.01).Conclusions: Silica particles could lead to ultrastructural defects in airway cilia, mucus hypersecretion and altered MUC5B expression in trachea, indicating that impaired mucociliary structure and altered MUC5B production might participate in the development of silica-related respiratory diseases.

Ciliary Genes in Renal Cystic Diseases

Cilia are microtubule-based organelles, protruding from the apical cell surface and anchoring to the cytoskeleton. Primary (nonmotile) cilia of the kidney act as mechanosensors of nephron cells, responding to fluid movements by triggering signal transduction. The impaired functioning of primary cilia leads to formation of cysts which in turn contribute to development of diverse renal diseases, including kidney ciliopathies and renal cancer. Here, we review current knowledge on the role of ciliary genes in kidney ciliopathies and renal cell carcinoma (RCC). Special focus is given on the impact of mutations and altered expression of ciliary genes (e.g., encoding polycystins, nephrocystins, Bardet-Biedl syndrome (BBS) proteins, ALS1, Oral-facial-digital syndrome 1 (OFD1) and others) in polycystic kidney disease and nephronophthisis, as well as rare genetic disorders, including syndromes of Joubert, Meckel-Gruber, Bardet-Biedl, Senior-Loken, Alström, Orofaciodigital syndrome type I and cranioectodermal dysplasia. We also show that RCC and classic kidney ciliopathies share commonly disturbed genes affecting cilia function, including VHL (von Hippel-Lindau tumor suppressor), PKD1 (polycystin 1, transient receptor potential channel interacting) and PKD2 (polycystin 2, transient receptor potential cation channel). Finally, we discuss the significance of ciliary genes as diagnostic and prognostic markers, as well as therapeutic targets in ciliopathies and cancer.

Clinical Implications of Primary Cilia in Skin Cancer

The primary cilium is a cell surface organelle that is an important component of cellular biology. While it was once believed to be a vestigial structure without biologic function, it is now known to have essential roles in critical cellular signaling pathways such as Hedgehog (HH) and Wnt. The HH and Wnt pathways are involved in pathogenesis of basal cell carcinoma and melanoma, respectively, and this knowledge is now beginning to inform therapeutic and diagnostic options for patients. The purpose of this review is to familiarize clinicians with primary cilia biology and how this complex cellular organelle has started to translate into clinical care.

A reduction of primary cilia but not hedgehog signaling disrupts morphogenesis in testicular organoids

Most mammalian cells possess a single, non-motile primary cilium that plays an important role in mediating cellular signaling pathways, such as Hedgehog (Hh) signaling. Primary cilia are present on testicular somatic cells and demonstrate a temporal expression during development; however, their role in testicular morphogenesis is not well characterized. To investigate the role of primary cilia and Hh signaling in Sertoli cells on morphogenesis, we inhibited assembly of primary cilia through CRISPR Cas9-mediated gene editing of ODF2, a structural component of primary cilia and siRNA-mediated gene silencing of IFT88, a functional component of the intraflagellar transport system. Knockdown of ODF2 and IFT88 resulted in a 50% reduction in the number of cells with primary cilia and significant shortening of the remaining cilia. The expression of GLI1, a downstream target of Hh signaling, was significantly reduced when IFT88 but not ODF2, was downregulated. When morphogenesis was examined using tubule formation in vitro and a novel testicular organoid system, loss of cilia after knockdown of both targets affected cellular assembly and organization. While the Hh pathway was found to be active during morphogenesis in vitro, addition of the Hh antagonist cyclopamine did not affect morphogenesis in either in vitro system. These results indicate that primary cilia are important for morphogenesis in vitro but Hh signaling is not the cilia-mediated pathway responsible for orchestrating morphogenic organization.

Current perspectives on the role of biomechanical loading and genetics in development of disc degeneration and low back pain; a narrative review

Degenerative changes in the disc have long been of interest; they are thought to be strongly associated with low back pain and caused by inappropriate loading or through injury. However, independent of the magnitude of occupational spinal loading, twin studies find that the heritability of lumbar disc degeneration is 34-74%. This finding has led to intensive searches for susceptibility genes; some genes associated with disc degeneration have been identified, though all with small effects on the degenerative process. The complex nature of degenerative changes suggests that many different genes are involved, and that interactions with environmental factors are influential in progression of degeneration. Low back pain itself also appears heritable (30-46%). The most important clinical question though, is not how discs degenerate but is disc degeneration related to low back pain. Imaging studies find many people with degenerate discs or even with discs showing pathological features such as herniations, are asymptomatic. However results are obscured by the lack of consistent definitions of the phenotypes of disc degeneration and of low back pain. Epidemiological studies could help disentangle these complex relationships, but they will only be successful once consistent classifications and phenotypes of both disc degeneration and low back pain are developed.

SIRT2 Affects Primary Cilia Formation by Regulating mTOR Signaling in Retinal Pigmented Epithelial Cells

SIRT2, a member of the Class III HDAC family, participates in diverse cellular processes and regulates several pathological conditions. Although a few reports show that SIRT2 regulates the cell cycle, the causes and outcomes of SIRT2-dependent cell proliferation remain unclear. Here, we examined the effects of SIRT2 suppression in human RPE1 cells using siRNA targeting SIRT2, and AK-1, a SIRT2-specific inhibitor. The number of primary cilia in SIRT2-suppressed cells increased under serum-present conditions. Suppressing SIRT2 induced cell cycle arrest at G0/G1 phase by inactivating mammalian target of rapamycin (mTOR) signaling, possibly through mTORC1. Treatment with torin 1, an inhibitor of mTORC1/mTORC2, yielded results similar to those observed after SIRT2 suppression. However, SIRT2 suppression did not affect primary cilia formation or mTOR signaling following serum starvation. This suggests that SIRT2 acts as a critical sensor that links growth factor-dependent signal transduction and primary cilia formation by regulating the cell cycle.

The primary cilia in diabetic kidney disease: A tubulocentric view?

Diabetic kidney disease is growing exponentially. This review aims to discuss alternate therapeutic approaches beyond the glomerulocentric view and to consider a novel tubulocentric approach with focus on the primary cilia. Renin-angiotensin-aldosterone system blockade to decrease glomerular capillary pressure and prevent albuminuria has been the mainstay of treatment for diabetic and non-diabetic proteinuric kidney disease. Landmark clinical trials have also shown cardiorenal benefit with sodium-glucose linked co-transporter 2 inhibitors and glucagon-like peptide 1 receptor analogues in patients with type 2 diabetes. Effective renoprotective drugs seem to have a common mechanistic mode of reducing glomerular hyperfiltration/hypertension. In the tubules, primary cilia act as "antennae" to detect mechanosensory changes such as glomerular hyperfiltration and trgger intracellular signalling pathways. They are also implicated in obesity and metabolic disorders linked to diabetes. To conclude, primary cilia of the kidney tubules offer a novel therapeutic target and may complement the current glomerulocentric approaches.

Schizophrenia-related microdeletion causes defective ciliary motility and brain ventricle enlargement via microRNA-dependent mechanisms in mice

Progressive ventricular enlargement, a key feature of several neurologic and psychiatric diseases, is mediated by unknown mechanisms. Here, using murine models of 22q11-deletion syndrome (22q11DS), which is associated with schizophrenia in humans, we found progressive enlargement of lateral and third ventricles and deceleration of ciliary beating on ependymal cells lining the ventricular walls. The cilia-beating deficit observed in brain slices and in vivo is caused by elevated levels of dopamine receptors (Drd1), which are expressed in motile cilia. Haploinsufficiency of the microRNA-processing gene Dgcr8 results in Drd1 elevation, which is brought about by a reduction in Drd1-targeting microRNAs miR-382-3p and miR-674-3p. Replenishing either microRNA in 22q11DS mice normalizes ciliary beating and ventricular size. Knocking down the microRNAs or deleting their seed sites on Drd1 mimicked the cilia-beating and ventricular deficits. These results suggest that the Dgcr8-miR-382-3p/miR-674-3p-Drd1 mechanism contributes to deceleration of ciliary motility and age-dependent ventricular enlargement in 22q11DS.

Osteocyte-Mediated Translation of Mechanical Stimuli to Cellular Signaling and Its Role in Bone and Non-bone-Related Clinical Complications

PURPOSE OF REVIEW

Osteocytes comprise > 95% of the cellular component in bone tissue and produce a wide range of cytokines and cellular signaling molecules in response to mechanical stimuli. In this review, we aimed to summarize the molecular mechanisms involved in the osteocyte-mediated translation of mechanical stimuli to cellular signaling, and discuss their role in skeletal (bone) diseases and extra-skeletal (non-bone) clinical complications.

RECENT FINDINGS

Two decades before, osteocytes were assumed as a dormant cells buried in bone matrix. In recent years, emerging evidences have shown that osteocytes are pivotal not only for bone homeostasis but also for vital organ functions such as muscle, kidney, and heart. Osteocyte mechanotransduction regulates osteoblast and osteoclast function and maintains bone homeostasis. Mechanical stimuli modulate the release of osteocyte-derived cytokines, signaling molecules, and extracellular cellular vesicles that regulate not only the surrounding bone cell function and bone homeostasis but also the distant organ function in a paracrine and endocrine fashion. Mechanical loading and unloading modulate the osteocytic release of NO, PGE₂, and ATPs that regulates multiple cellular signaling such as Wnt/β-catenin, RANKL/OPG, BMPs, PTH, IGF1, VEGF, sclerostin, and others. Therefore, the in-depth study of the molecular mechanism of osteocyte mechanotransduction could unravel therapeutic targets for various bone and non-bone-related clinical complications such as osteoporosis, sarcopenia, and cancer metastasis to bone.

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

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

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

The inner junction complex of the cilia is an interaction hub that involves tubulin post-translational modifications

Microtubules are cytoskeletal structures involved in stability, transport and organization in the cell. The building blocks, the α- and β-tubulin heterodimers, form protofilaments that associate laterally into the hollow microtubule. Microtubule also exists as highly stable doublet microtubules in the cilia where stability is needed for ciliary beating and function. The doublet microtubule maintains its stability through interactions at its inner and outer junctions where its A- and B-tubules meet. Here, using cryo-electron microscopy, bioinformatics and mass spectrometry of the doublets of Chlamydomonas reinhardtii and Tetrahymena thermophila, we identified two new inner junction proteins, FAP276 and FAP106, and an inner junction-associated protein, FAP126, thus presenting the complete answer to the inner junction identity and localization. Our structural study of the doublets shows that the inner junction serves as an interaction hub that involves tubulin post-translational modifications. These interactions contribute to the stability of the doublet and hence, normal ciliary motility.

Transport of Ciliary Membrane Proteins

Cilia and flagella are highly conserved organelles in eukaryotic cells that drive cell movement and act as cell antennae that receive and transmit signals. In addition to receiving and transducing external signals that activate signal cascades, cilia also secrete ciliary ectosomes that send signals to recipient cells, and thereby mediate cell–cell communication. Abnormal ciliary function leads to various ciliopathies, and the precise transport and localization of ciliary membrane proteins are essential for cilium function. This review summarizes current knowledge about the transport processes of ciliary membrane proteins after their synthesis at the endoplasmic reticulum: modification and sorting in the Golgi apparatus, transport through vesicles to the ciliary base, entrance into cilia through the diffusion barrier, and turnover by ectosome secretion. The molecular mechanisms and regulation involved in each step are also discussed. Transport of ciliary membrane proteins is a complex, precise cellular process coordinated among multiple organelles. By systematically analyzing the existing research, we identify topics that should be further investigated to promote progress in this field of research.

Intraflagellar transport 20: New target for the treatment of ciliopathies

Cilia are ubiquitous in mammalian cells. The formation and assembly of cilia depend on the normal functioning of the ciliary transport system. In recent years, various proteins involved in the intracellular transport of the cilium have attracted attention, as many diseases are caused by disorders in cilia formation. Intraflagellar transport 20 (IFT20) is a subunit of IFT complex B, which contains approximately 20 protein particles. Studies have shown that defects in IFT20 are associated with numerous system -related diseases, such as those of the urinary system, cardiovascular system, skeletal system, nervous system, immune system, reproductive system, and respiratory system. This review summarizes current research on IFT20.We describe studies related to the role of IFT20 in cilia formation and discuss new targets for treating diseases associated with ciliary dysplasia.

Cilia oscillations

Cilia, or eukaryotic flagella, are microscopic active filaments expressed on the surface of many eukaryotic cells, from single-celled protozoa to mammalian epithelial surfaces. Cilia are characterized by a highly conserved and intricate internal structure in which molecular motors exert forces on microtubule doublets causing cilia oscillations. The spatial and temporal regulations of this molecular machinery are not well understood. Several theories suggest that geometric feedback control from cilium deformations to molecular activity is needed. Here, we implement a recent sliding control model, where the unbinding of molecular motors is dictated by the sliding motion between microtubule doublets. We investigate the waveforms exhibited by the model cilium, as well as the associated molecular motor dynamics, for hinged and clamped boundary conditions. Hinged filaments exhibit base-to-tip oscillations while clamped filaments exhibit both base-to-tip and tip-to-base oscillations. We report the change in oscillation frequencies and amplitudes as a function of motor activity and sperm number, and we discuss the validity of these results in the context of experimental observations of cilia behaviour. This article is part of the Theo Murphy meeting issue 'Unity and diversity of cilia in locomotion and transport'.

Rare Human Diseases: Model Organisms in Deciphering the Molecular Basis of Primary Ciliary Dyskinesia

Primary ciliary dyskinesia (PCD) is a recessive heterogeneous disorder of motile cilia, affecting one per 15,000-30,000 individuals; however, the frequency of this disorder is likely underestimated. Even though more than 40 genes are currently associated with PCD, in the case of approximately 30% of patients, the genetic cause of the manifested PCD symptoms remains unknown. Because motile cilia are highly evolutionarily conserved organelles at both the proteomic and ultrastructural levels, analyses in the unicellular and multicellular model organisms can help not only to identify new proteins essential for cilia motility (and thus identify new putative PCD-causative genes), but also to elucidate the function of the proteins encoded by known PCD-causative genes. Consequently, studies involving model organisms can help us to understand the molecular mechanism(s) behind the phenotypic changes observed in the motile cilia of PCD affected patients. Here, we summarize the current state of the art in the genetics and biology of PCD and emphasize the impact of the studies conducted using model organisms on existing knowledge.

Mutations in TTC29, Encoding an Evolutionarily Conserved Axonemal Protein, Result in Asthenozoospermia and Male Infertility

In humans, structural or functional defects of the sperm flagellum induce asthenozoospermia, which accounts for the main sperm defect encountered in infertile men. Herein we focused on morphological abnormalities of the sperm flagellum (MMAF), a phenotype also termed "short tails," which constitutes one of the most severe sperm morphological defects resulting in asthenozoospermia. In previous work based on whole-exome sequencing of a cohort of 167 MMAF-affected individuals, we identified bi-allelic loss-of-function mutations in more than 30% of the tested subjects. In this study, we further analyzed this cohort and identified five individuals with homozygous truncating variants in TTC29, a gene preferentially and highly expressed in the testis, and encoding a tetratricopeptide repeat-containing protein related to the intraflagellar transport (IFT). One individual carried a frameshift variant, another one carried a homozygous stop-gain variant, and three carried the same splicing variant affecting a consensus donor site. The deleterious effect of this last variant was confirmed on the corresponding transcript and protein product. In addition, we produced and analyzed TTC29 loss-of-function models in the flagellated protist T. brucei and in M. musculus. Both models confirmed the importance of TTC29 for flagellar beating. We showed that in T. brucei the TPR structural motifs, highly conserved between the studied orthologs, are critical for TTC29 axonemal localization and flagellar beating. Overall our work demonstrates that TTC29 is a conserved axonemal protein required for flagellar structure and beating and that TTC29 mutations are a cause of male sterility due to MMAF.

Cellular signalling by primary cilia in development, organ function and disease

Primary cilia project in a single copy from the surface of most vertebrate cell types; they detect and transmit extracellular cues to regulate diverse cellular processes during development and to maintain tissue homeostasis. The sensory capacity of primary cilia relies on the coordinated trafficking and temporal localization of specific receptors and associated signal transduction modules in the cilium. The canonical Hedgehog (HH) pathway, for example, is a bona fide ciliary signalling system that regulates cell fate and self-renewal in development and tissue homeostasis. Specific receptors and associated signal transduction proteins can also localize to primary cilia in a cell type-dependent manner; available evidence suggests that the ciliary constellation of these proteins can temporally change to allow the cell to adapt to specific developmental and homeostatic cues. Consistent with important roles for primary cilia in signalling, mutations that lead to their dysfunction underlie a pleiotropic group of diseases and syndromic disorders termed ciliopathies, which affect many different tissues and organs of the body. In this Review, we highlight central mechanisms by which primary cilia coordinate HH, G protein-coupled receptor, WNT, receptor tyrosine kinase and transforming growth factor-β (TGFβ)/bone morphogenetic protein (BMP) signalling and illustrate how defects in the balanced output of ciliary signalling events are coupled to developmental disorders and disease progression.

Polarity in Ciliate Models: From Cilia to Cell Architecture

Tetrahymena and Paramecium are highly differentiated unicellular organisms with elaborated cortical patterns showing a regular arrangement of hundreds to thousands of basal bodies in longitudinal rows that extend from the anterior to the posterior region of the cell. Thus both ciliates exhibit a permanent antero–posterior axis and left–right asymmetry. This cell polarity is reflected in the direction of the structures nucleated around each basal body such as the ciliary rootlets. Studies in these ciliates showed that basal bodies assemble two types of cilia, the cortical cilia and the cilia of the oral apparatus, a complex structure specialized in food capture. These two cilia types display structural differences at their tip domain. Basal bodies possessing distinct compositions creating specialized landmarks are also present. Cilia might be expected to express and transmit polarities throughout signaling pathways given their recognized role in signal transduction. This review will focus on how local polarities in basal bodies/cilia are regulated and transmitted through cell division in order to maintain the global polarity and shape of these cells and locally constrain the interpretation of signals by different cilia. We will also discuss ciliates as excellent biological models to study development and morphogenetic mechanisms and their relationship with cilia diversity and function in metazoans.

Screening prognosis-related genes in glioblastoma by microarray analysis

This study was aimed to explore the prognosis-related biomarkers in glioblastoma and guide the therapy. The gene expression profile of glioblastoma samples with different prognosis outcomes was downloaded from National Center of Biotechnology Information Gene Expression Omnibus. The differently expressed genes (DEGs) among different samples were identified through pairwise comparison via Limma package of R. The DEGs were clustered using the Mfuzz package of R. The clusters with gene expression increasing or decreasing with the prognosis were selected, and functional enrichment of the selected genes was analyzed via the Database for Annotation, Visualization and Integrated Discovery. A protein-protein interaction (PPI) network of the selected genes was constructed through the Search Tool for Retrieval of Interacting Proteins and visualized by Cytoscape. The Cancer Genome Atlas database and IVY-GAP database were used to verify the DEGs. We analyzed the correlation between subtypes and the DEGs. Totally, 2649 DEGs were identified and divided into 10 clusters. Expression value of the genes in clusters 2 and 9 kept increasing and decreasing, respectively, with the improved prognosis. The DEGs of cluster 2/9 were enriched in 23/24 Gene Ontology terms and 6/4 Kyoto Encyclopedia of Genes and Genomes pathways. Annotation of transcription factor binding sites of DEGs revealed that most genes were regulated by transcription factors. In the PPI network, CACNA1D, GNAO1, STAT3 and ERBB3 had 11, 11, 11 and 10 node degree, respectively. Bioinformatics methods could help to identify significant genes and pathways in glioblastoma. CACNA1D, GNAO1, STAT3 and ERBB3 might serve as the prognostic biomarkers in glioblastoma.

Cell Type-Specific Expression of Testis Elevated Genes Based on Transcriptomics and Antibody-Based Proteomics

One of the most complex organs in the human body is the testis, where spermatogenesis takes place. This physiological process involves thousands of genes and proteins that are activated and repressed, making testis the organ with the highest number of tissue-specific genes. However, the function of a large proportion of the corresponding proteins remains unknown and testis harbors many missing proteins (MPs), defined as products of protein-coding genes that lack experimental mass spectrometry evidence. Here, an integrated omics approach was used for exploring the cell type-specific protein expression of genes with an elevated expression in testis. By combining genome-wide transcriptomics analysis with immunohistochemistry, more than 500 proteins with distinct testicular protein expression patterns were identified, and these were selected for in-depth characterization of their in situ expression in eight different testicular cell types. The cell type-specific protein expression patterns allowed us to identify six distinct clusters of expression at different stages of spermatogenesis. The analysis highlighted numerous poorly characterized proteins in each of these clusters whose expression overlapped with that of known proteins involved in spermatogenesis, including 85 proteins with an unknown function and 60 proteins that previously have been classified as MPs. Furthermore, we were able to characterize the in situ distribution of several proteins that previously lacked spatial information and cell type-specific expression within the testis. The testis elevated expression levels both at the RNA and protein levels suggest that these proteins are related to testis-specific functions. In summary, the study demonstrates the power of combining genome-wide transcriptomics analysis with antibody-based protein profiling to explore the cell type-specific expression of both well-known proteins and MPs. The analyzed proteins constitute important targets for further testis-specific research in male reproductive disorders.

A Journey through the Cytoskeleton with Protein Kinase CK2

Substrate pleiotropicity, a very acidic phosphorylation consensus sequence, and an apparent uncontrolled activity, are the main features of CK2, a Ser/Thr protein kinase that is required for a plethora of cell functions. Not surprisingly, CK2 appears to affect cytoskeletal structures and correlated functions such as cell shape, mechanical integrity, cell movement and division. This review outlines our current knowledge of how CK2 regulates cytoskeletal structures, and discusses involved pathways and molecular mechanisms.

Stabilization of primary cilia reduces abortive cell cycle re-entry to protect injured adult CNS neurons from apoptosis

Abortive cell cycle (ACC) re-entry of apoptotic neurons is a recently characterized phenomenon that occurs after central nervous system (CNS) injury or over the course of CNS disease. Consequently, inhibiting cell cycle progression is neuroprotective in numerous CNS pathology models. Primary cilia are ubiquitous, centriole-based cellular organelles that prevent cell cycling, but their ability to modulate abortive cell cycle has not been described. Here, we show that neuronal cilia are ablated in-vitro and in-vivo following injury by hypoxia or optic nerve transection (ONT), respectively. Furthermore, forced cilia resorption sensitized neurons to these injuries and enhanced cell death. In contrast, pharmacological inhibition or shRNA knockdown of the proteins that disassemble the cilia increased neuron survival and decreased the phosphorylation of retinoblastoma (Rb), a master switch for cell cycle re-entry. Our findings show that the stabilization of neuronal primary cilia inhibits, at least transiently, apoptotic cell cycling, which has implications for future therapeutic strategies that halt or slow the progression of neurodegenerative diseases and acute CNS injuries.

Self-organization of self-clearing beating patterns in an array of locally interacting ciliated cells formulated as an adaptive Boolean network

The observed spatiotemporal ciliary beat patterns leading to proper mucociliary clearance on multiciliated epithelia are suspected to be the result of self-organizing processes on various levels. Here, we present a simplified pluricellular epithelium model, which intends to make the self-organization of ciliary beating patterns as well as of the associated fluid transport across the airway epithelium plausible. The model is based on a two-dimensional array of locally interacting oscillating ciliated cells. Ciliated cells are represented by Boolean actuators, and abstracted hydrodynamic mucociliary interactions are formulated in terms of logical update rules (Boolean functions). In the course of a simulation, initial random conformations of an array of actuators self-organize toward metachronally coordinated states exhibiting efficient transport of mucus. Within the framework of Boolean networks ciliated cells represent the nodes of the network and as the mucus establishes the local interactions among nodes, its distribution (together with the formulated local interactions) determines the topology of the network. Consequently, we propose to consider the dynamics on multiciliated epithelia in the context of adaptive (Boolean) networks. Furthermore, we would like to present insights gained from conducted comprehensive parameter studies. In particular, the dynamical response of the network with respect to variations of the boundary conditions, updating schemes (representing intercellular signaling mechanisms) and the proportion of ciliated cells is presented.

How signals of calcium ions initiate the beats of cilia and flagella

Cilia and flagella are cell organelles serving basic roles in cellular motility. Ciliary movement is performed by a sweeping-like repeated bending motion, which gives rise to a self-propagating "ciliary beat". The hallmark structure in cilia is the axoneme, a stable architecture of microtubule doublets. The motion of axoneme is powered by the axonemal dynein motor family powered by ATP hydrolysis. It is still unclear how the organized beat of cilium and flagella emerges from the combined action of hundreds of dynein molecules. It has been hypothesized that such coordination is mediated by mechanical stress due to transverse, radial or sliding deformations. The beating asymmetry is crucial for airway ciliary function and it requires tubulin glutamination a unique posttranslational modification of C-termini of constituent microtubules that is highly abundant in cilia and flagella. The exact role of tubulin glutamination in ciliary or flagellar function is still unclear. In this paper we analyze the role of calcium (Ca²⁺) ions based on the experimental evidence that the flagellar asymmetry can be increased due to the entry of extracellular Ca²⁺ through, for example, the nimodipine-sensitive pathway located in the flagella. We propose a new scenario based on the polyelectrolyte properties of cellular microtubules (MTs) such that dynamic influx of Ca²⁺ ions provides the initiation and synchronization of dynein sliding along microtubules. We also point out the possible interplay between tubulin polyglutaminated C-termini and localized pulses of Ca²⁺ ions along microtubules.

Mutation profile of BBS genes in patients with Bardet-Biedl syndrome: an Italian study

BACKGROUND

Bardet-Biedl syndrome (BBS) is a rare inherited multisystemic disorder with autosomal recessive or complex digenic triallelic inheritance. There is currently no treatment for BBS, but some morbidities can be managed. Accurate molecular diagnosis is often crucial for the definition of appropriate patient management and for the development of a potential personalized therapy.

METHODS

We developed a next-generation-sequencing (NGS) protocol for the screening of the 18 most frequently mutated genes to define the genotype and clarify the mutation spectrum of a cohort of 20 BBS Italian patients.

RESULTS

We defined the causative variants in 60% of patients; four of those are novel. 33% of patients also harboured variants in additional gene/s, suggesting possible oligogenic inheritance. To explore the function of different genes, we looked for correlations between genotype and phenotype in our cohort. Hypogonadism was more frequently detected in patients with variants in BBSome proteins, while renal abnormalities in patients with variations in BBSome chaperonin genes.

CONCLUSIONS

NGS is a powerful tool that can help understanding BBS patients' phenotype through the identification of mutations that could explain differences in phenotype severity and could provide insights for the development of targeted therapy. Furthermore, our results support the existence of additional BBS loci yet to be identified.