Structure Of Primary Cilia Research Articles

Structure, interaction and nervous connectivity of beta cell primary cilia

Primary cilia are sensory organelles present in many cell types, partaking in various signaling processes. Primary cilia of pancreatic beta cells play pivotal roles in paracrine signaling and their dysfunction is linked to diabetes. Yet, the structural basis for their functions is unclear. We present three-dimensional reconstructions of beta cell primary cilia by electron and expansion microscopy. These cilia are spatially confined within deep ciliary pockets or narrow spaces between cells, lack motility components and display an unstructured axoneme organization. Furthermore, we observe a plethora of beta cell cilia-cilia and cilia-cell interactions with other islet and non-islet cells. Most remarkably, we have identified and characterized axo-ciliary synapses between beta cell cilia and the cholinergic islet innervation. These findings highlight the beta cell cilia’s role in islet connectivity, pointing at their function in integrating islet intrinsic and extrinsic signals and contribute to understanding their significance in health and diabetes.

Primary cilia in Parkinson's disease: summative roles in signaling pathways, genes, defective mitochondrial function, and substantia nigra dopaminergic neurons.

Primary cilia (PC) are microtubules-based, independent antennal-like sensory organelles, that are seen in most vertebrate cells of different types, including astrocytes and neurons. They send signals to cells to control many physiological and cellular processes by detecting changes in the extracellular environment. Parkinson's disease (PD), a neurodegenerative disease that progresses over time, is primarily caused by a gradual degradation of the dopaminergic pathway in the striatum nigra, which results in a large loss of neurons in the substantia nigra compact (SNpc) and a depletion of dopamine (DA). PD samples have abnormalities in the structure and function of PC. The alterations contribute to the cause, development, and recovery of PD via influencing signaling pathways (SHH, Wnt, Notch-1, α-syn, and TGFβ), genes (MYH10 and LRRK2), defective mitochondrial function, and substantia nigra dopaminergic neurons. Thus, restoring the normal structure and physiological function of PC and neurons in the brain are effective treatment for PD. This review summarizes the function of PC in neurodegenerative diseases and explores the pathological mechanisms caused by PC alterations in PD, in order to provide references and ideas for future research.

Excess microtubule and F-actin formation mediates shortening and loss of primary cilia in response to a hyperosmotic milieu.

The primary cilium is a small organelle protruding from the cell surface that receives signals from the extracellular milieu. Although dozens of studies have reported that several genetic factors can impair the structure of primary cilia, evidence for environmental stimuli affecting primary cilia structures is limited. Here, we investigated an extracellular stress that affected primary cilia morphology and its underlying mechanisms. Hyperosmotic shock induced reversible shortening and disassembly of the primary cilia of murine intramedullary collecting duct cells. The shortening of primary cilia caused by hyperosmotic shock followed delocalization of the pericentriolar material (PCM). Excessive microtubule and F-actin formation in the cytoplasm coincided with the hyperosmotic shock-induced changes to primary cilia and the PCM. Treatment with a microtubule-disrupting agent, nocodazole, partially prevented the hyperosmotic shock-induced disassembly of primary cilia and almost completely prevented delocalization of the PCM. An actin polymerization inhibitor, latrunculin A, also partially prevented the hyperosmotic shock-induced shortening and disassembly of primary cilia and almost completely prevented delocalization of the PCM. We demonstrate that hyperosmotic shock induces reversible morphological changes in primary cilia and the PCM in a manner dependent on excessive formation of microtubule and F-actin.

Structure, function, and research progress of primary cilia in reproductive physiology and reproductive diseases.

Primary cilia, serving as the central hub for cellular signal transduction, possess the remarkable ability to translate diverse extracellular signals, both chemical and mechanical, into intracellular responses. Their ubiquitous presence in the reproductive system underscores their pivotal roles in various cellular processes including development, differentiation, and migration. Emerging evidence suggests primary cilia as key players in reproductive physiology and associated pathologies. Notably, primary cilia have been identified in granulosa cells within mouse ovaries and uterine stromal cells, and perturbations in their structure and function have been implicated in a spectrum of reproductive dysfunctions and ciliary-related diseases. Furthermore, disruptions in primary cilia-mediated signal transduction pathways under pathological conditions exacerbate the onset and progression of reproductive disorders. This review provides a comprehensive overview of current research progress on primary cilia and their associated signaling pathways in reproductive physiology and diseases, with the aim of furnishing theoretical groundwork for the prevention and management of primary cilia-related structural and functional abnormalities contributing to reproductive system pathologies.

Primary cilia as a targetable node between biliary injury, senescence and regeneration in liver transplantation

Biliary complications are a major cause of morbidity and mortality in liver transplantation. Up to 25% of patients that develop biliary complications require additional surgical procedures, re-transplantation or die in the absence of a suitable regraft. Here, we investigate the role of the primary cilium, a highly specialised sensory organelle, in biliary injury leading to post-transplant biliary complications. Human biopsies were used to study the structure and function of primary cilia in liver transplant recipients that develop biliary complications (n= 7) in comparison with recipients without biliary complications (n= 12). To study the biological effects of the primary cilia during transplantation, we generated murine models that recapitulate liver procurement and cold storage, and assessed the elimination of the primary cilia in biliary epithelial cells in the K19CreERTKif3afl/fl mouse model. To explore the molecular mechanisms responsible for the observed phenotypes we used invitro models of ischemia, cellular senescence and primary cilia ablation. Finally, we used pharmacological and genetic approaches to target cellular senescence and the primary cilia, both in mouse models and discarded human donor livers. Prolonged ischemic periods before transplantation result in ciliary shortening and cellular senescence, an irreversible cell cycle arrest that blocks regeneration. Our results indicate that primary cilia damage results in biliary injury and a loss of regenerative potential. Senescence negatively impacts primary cilia structure and triggers a negative feedback loop that further impairs regeneration. Finally, we explore how targeted interventions for cellular senescence and/or the stabilisation of the primary cilia improve biliary regeneration following ischemic injury. Primary cilia play an essential role in biliary regeneration and we demonstrate that senolytics and cilia-stabilising treatments provide a potential therapeutic opportunity to reduce the rate of biliary complications and improve clinical outcomes in liver transplantation. Up to 25% of liver transplants result in biliary complications, leading to additional surgery, retransplants, or death. We found that the incidence of biliary complications is increased by damage to the primary cilium, an antenna that protrudes from the cell and is key to regeneration. Here, we show that treatments that preserve the primary cilia during the transplant process provide a potential solution to reduce the rates of biliary complications.

The role of primary cilia in thyroid diseases.

Primary cilia (PC) are non-motile and microtube-based organelles protruding from the surface of almost all thyroid follicle cells. They maintain homeostasis in thyrocytes and loss of PC can result in diverse thyroid diseases. The dysfunction of structure and function of PC are found in many patients with common thyroid diseases. The alterations are associated with the cause, development, and recovery of the diseases and are regulated by PC-mediated signals. Restoring normal PC structure and function in thyrocytes is a promising therapeutic strategy to treat thyroid diseases. This review explores the function of PC in normal thyroid glands. It summarizes the pathology caused by PC alterations in thyroid cancer (TC), autoimmune thyroid diseases (AITD), hypothyroidism, and thyroid nodules (TN) to provide comprehensive references for further study.

Differential alternative splicing analysis links variation in ZRSR2 to a novel type of oral-facial-digital syndrome

PurposeOral-facial-digital (OFD) syndromes are genetically heterogeneous developmental disorders, caused by pathogenic variants in genes involved in primary cilia formation and function. We identified a previously undescribed type of OFD with brain anomalies, ranging from alobar holoprosencephaly to pituitary anomalies, in 6 unrelated families. MethodsExome sequencing of affected probands was supplemented with alternative splicing analysis in patient and control lymphoblastoid and fibroblast cell lines, and primary cilia structure analysis in patient fibroblasts. ResultsIn 1 family with 2 affected males, we identified a germline variant in the last exon of ZRSR2, NM_005089.4:c.1211_1212del NP_005080.1:p.(Gly404GlufsTer23), whereas 7 affected males from 5 unrelated families were hemizygous for the ZRSR2 variant NM_005089.4:c.1207_1208del NP_005080.1:p.(Arg403GlyfsTer24), either occurring de novo or inherited in an X-linked recessive pattern. ZRSR2, located on chromosome Xp22.2, encodes a splicing factor of the minor spliceosome complex, which recognizes minor introns, representing 0.35% of human introns. Patient samples showed significant enrichment of minor intron retention. Among differentially spliced targets are ciliopathy-related genes, such as TMEM107 and CIBAR1. Primary fibroblasts containing the NM_005089.4:c.1207_1208del ZRSR2 variant had abnormally elongated cilia, confirming an association between defective U12-type intron splicing, OFD and abnormal primary cilia formation. ConclusionWe introduce a novel type of OFD associated with elongated cilia and differential splicing of minor intron-containing genes due to germline variation in ZRSR2.

Mapping of neuronal and glial primary cilia contactome and connectome in the human cerebral cortex

Primary cilia act as antenna receivers of environmental signals and enable effective neuronal or glial responses. Disruption of their function is associated with circuit disorders. To understand the signals these cilia receive, we comprehensively mapped cilia's contacts within the human cortical connectome using serial-section EM reconstruction of a 1mm3 cortical volume, spanning the entire cortical thickness. We mapped the "contactome" of cilia emerging from neurons and astrocytes in every cortical layer. Depending on the layer and cell type, cilia make distinct patterns of contact. Primary cilia display cell-type- and layer-specific variations in size, shape, and microtubule axoneme core, which may affect their signaling competencies. Neuronal cilia are intrinsic components of a subset of cortical synapses and thus a part of the connectome. This diversity in the structure, contactome, and connectome of primary cilia endows each neuron or glial cell with a unique barcode of access to the surrounding neural circuitry.

Effects of Sesquiterpene Lactones on Primary Cilia Formation (Ciliogenesis).

Sesquiterpene lactones (SLs), plant-derived metabolites with broad spectra of biological effects, including anti-tumor and anti-inflammatory, hold promise for drug development. Primary cilia, organelles extending from cell surfaces, are crucial for sensing and transducing extracellular signals essential for cell differentiation and proliferation. Their life cycle is linked to the cell cycle, as cilia assemble in non-dividing cells of G0/G1 phases and disassemble before entering mitosis. Abnormalities in both primary cilia (non-motile cilia) and motile cilia structure or function are associated with developmental disorders (ciliopathies), heart disease, and cancer. However, the impact of SLs on primary cilia remains unknown. This study evaluated the effects of selected SLs (grosheimin, costunolide, and three cyclocostunolides) on primary cilia biogenesis and stability in human retinal pigment epithelial (RPE) cells. Confocal fluorescence microscopy was employed to analyze the effects on primary cilia formation (ciliogenesis), primary cilia length, and stability. The effects on cell proliferation were evaluated by flow cytometry. All SLs disrupted primary cilia formation in the early stages of ciliogenesis, irrespective of starvation conditions or cytochalasin-D treatment, with no effect on cilia length or cell cycle progression. Interestingly, grosheimin stabilized and promoted primary cilia formation under cilia homeostasis and elongation treatment conditions. Thus, SLs have potential as novel drugs for ciliopathies and tumor treatment.

Expansion Microscopy of Ciliary Proteins.

Label-retention expansion microscopy (LR-ExM) is a sample preparation technique, which embeds the cells or tissues in a swellable hydrogel and expands the sample so that one can achieve a high resolution with any conventional fluorescence microscopes. Fluorescence loss during polymerization and protein denaturation have been a major limitation of standard expansion microscopy. To minimize fluorescence loss, LR-ExM uses trifunctional anchors, which can survive from polymerization and denaturation, and then introduce fluorophores after expansion. By using LR-ExM, one can study the structure of primary cilia at molecular-scale resolution with a much higher signal-to-noise ratio, compared with previously introduced expansion microscopy methods. In this chapter, we describe a detailed procedure showing how LR-ExM is used to study ciliary proteins.

Primary cilia: Structure, dynamics, and roles in cancer cells and tumor microenvironment.

Despite the initiation of tumor arises from tumorigenic transformation signaling in cancer cells, cancer cell survival, invasion, and metastasis also require a dynamic and reciprocal association with extracellular signaling from tumor microenvironment (TME). Primary cilia are the antenna-like structure that mediate signaling sensation and transduction in different tissues and cells. Recent studies have started to uncover that the heterogeneous ciliation in cancer cells and cells from the TME in tumor growth impels asymmetric paracellular signaling in the TME, indicating the essential functions of primary cilia in homeostasis maintenance of both cancer cells and the TME. In this review, we discussed recent advances in the structure and assembly of primary cilia, and the role of primary cilia in tumor and TME formation, as well as the therapeutic potentials that target ciliary dynamics and signaling from the cells in different tumors and the TME.

IFT74 variants cause skeletal ciliopathy and motile cilia defects in mice and humans.

Motile and non-motile cilia play critical roles in mammalian development and health. These organelles are composed of a 1000 or more unique proteins, but their assembly depends entirely on proteins synthesized in the cell body and transported into the cilium by intraflagellar transport (IFT). In mammals, malfunction of non-motile cilia due to IFT dysfunction results in complex developmental phenotypes that affect most organs. In contrast, disruption of motile cilia function causes subfertility, disruption of the left-right body axis, and recurrent airway infections with progressive lung damage. In this work, we characterize allele specific phenotypes resulting from IFT74 dysfunction in human and mice. We identified two families carrying a deletion encompassing IFT74 exon 2, the first coding exon, resulting in a protein lacking the first 40 amino acids and two individuals carrying biallelic splice site mutations. Homozygous exon 2 deletion cases presented a ciliary chondrodysplasia with narrow thorax and progressive growth retardation along with a mucociliary clearance disorder phenotype with severely shorted cilia. Splice site variants resulted in a lethal skeletal chondrodysplasia phenotype. In mice, removal of the first 40 amino acids likewise results in a motile cilia phenotype but with little effect on primary cilia structure. Mice carrying this allele are born alive but are growth restricted and developed hydrocephaly in the first month of life. In contrast, a strong, likely null, allele of Ift74 in mouse completely blocks ciliary assembly and causes severe heart defects and midgestational lethality. In vitro studies suggest that the first 40 amino acids of IFT74 are dispensable for binding of other IFT subunits but are important for tubulin binding. Higher demands on tubulin transport in motile cilia compared to primary cilia resulting from increased mechanical stress and repair needs could account for the motile cilia phenotype observed in human and mice.

A novel pathogenic variant of CEP164 in an infant with Senior-Loken syndrome.

A novel pathogenic variant of CEP164 in an infant with Senior-Loken syndrome.

Role of lipids in the control of autophagy and primary cilium signaling in neurons.

The brain is, after the adipose tissue, the organ with the greatest amount of lipids and diversity in their composition in the human body. In neurons, lipids are involved in signaling pathways controlling autophagy, a lysosome-dependent catabolic process essential for the maintenance of neuronal homeostasis and the function of the primary cilium, a cellular antenna that acts as a communication hub that transfers extracellular signals into intracellular responses required for neurogenesis and brain development. A crosstalk between primary cilia and autophagy has been established; however, its role in the control of neuronal activity and homeostasis is barely known. In this review, we briefly discuss the current knowledge regarding the role of autophagy and the primary cilium in neurons. Then we review the recent literature about specific lipid subclasses in the regulation of autophagy, in the control of primary cilium structure and its dependent cellular signaling in physiological and pathological conditions, specifically focusing on neurons, an area of research that could have major implications in neurodevelopment, energy homeostasis, and neurodegeneration.

Molecular resolution imaging reveals step-wise reduction of axonemal diameter and ultrastructural architecture of intraflagellar transport proteins.

Primary cilia are microtubule-based organelles essential for mediating mechano-/photo-/chemo-sensations in mammalian cells. Intraflagellar transport (IFT) proteins are crucial components to support ciliary assembly, maintenance, and cellular signaling. The ciliary microtubule doublets of the ‘9 + 0’ arrangement serve as tracks for molecular motor-based transport along cilia. Although the tapering structure of primary cilia has been examined by electron microscopy, the spatial correlation between the IFT pattern and axonemal structure remains elusive due to insufficient light resolution. Here, we integrated single-molecule localization microscopy and sample expansion techniques achieving two-color imaging with effective localization precision of sub-5 nm to explore the axonemal ultrastructure and molecular organization of IFT and IFT-associated proteins in retinal pigment epithelial cilia. Our results revealed the step-wise reduction of ciliary diameter, different from the well-known paradigm showing a gradual change in the width of axonemal bundles. Surprisingly, our data showed that the IFT proteins congested near the end of the microtubule doubles within the ciliary compartment. In addition, we resolved the molecular architecture of IFT complexes, cargo, and motor proteins to characterize their relative localizations. We found that IFT proteins presented distinct distributions, including isolated units, paired configurations, or alternating arrangements in IFT trains. Together, our ultrastructural light nanoscopic imaging enables us to perform morphological analysis of primary cilia, which guides the localization of IFT complexes at segmented sites of cilia, suggesting the asynchronous axonemal growth of microtubule doubles.

Retinal Degeneration Animal Models in Bardet-Biedl Syndrome and Related Ciliopathies.

Retinal degeneration due to photoreceptor ciliary-related proteins dysfunction accounts for more than 25% of all inherited retinal dystrophies. The cilium, being an evolutionarily conserved and ubiquitous organelle implied in many cellular functions, can be investigated by way of many models from invertebrate models to nonhuman primates, all these models have massively contributed to the pathogenesis understanding of human ciliopathies. Taking the Bardet-Biedl syndrome (BBS) as an emblematic example as well as other related syndromic ciliopathies, the contribution of a wide range of models has enabled to characterize the role of the BBS proteins in the archetypical cilium but also at the level of the connecting cilium of the photoreceptors. There are more than 24 BBS genes encoding for proteins that form different complexes such as the BBSome and the chaperone proteins complex. But how they lead to retinal degeneration remains a matter of debate with the possible accumulation of proteins in the inner segment and/or accumulation of unwanted proteins in the outer segment that cannot return in the inner segment machinery. Many BBS proteins (but not the chaperonins for instance) can be modeled in primitive organisms such as Paramecium, Chlamydomonas reinardtii, Trypanosoma brucei, and Caenorhabditis elegans These models have enabled clarifying the role of a subset of BBS proteins in the primary cilium as well as their relations with other modules such as the intraflagellar transport (IFT) module, the nephronophthisis (NPHP) module, or the Meckel-Gruber syndrome (MKS)/Joubert syndrome (JBTS) module mostly involved with the transition zone of the primary cilia. Assessing the role of the primary cilia structure of the connecting cilium of the photoreceptor cells has been very much studied by way of zebrafish modeling (Danio rerio) as well as by a plethora of mouse models. More recently, large animal models have been described for three BBS genes and one nonhuman primate model in rhesus macaque for BBS7 In completion to animal models, human cell models can now be used notably thanks to gene editing and the use of induced pluripotent stem cells (iPSCs). All these models are not only important for pathogenesis understanding but also very useful for studying therapeutic avenues, their pros and cons, especially for gene replacement therapy as well as pharmacological triggers.

Primary Cilia Dysfunction in Neurodevelopmental Disorders beyond Ciliopathies.

Primary cilia are specialized, microtubule-based structures projecting from the surface of most mammalian cells. These organelles are thought to primarily act as signaling hubs and sensors, receiving and integrating extracellular cues. Several important signaling pathways are regulated through the primary cilium including Sonic Hedgehog (Shh) and Wnt signaling. Therefore, it is no surprise that mutated genes encoding defective proteins that affect primary cilia function or structure are responsible for a group of disorders collectively termed ciliopathies. The severe neurologic abnormalities observed in several ciliopathies have prompted examination of primary cilia structure and function in other brain disorders. Recently, neuronal primary cilia defects were observed in monogenic neurodevelopmental disorders that were not traditionally considered ciliopathies. The molecular mechanisms of how these genetic mutations cause primary cilia defects and how these defects contribute to the neurologic manifestations of these disorders remain poorly understood. In this review we will discuss monogenic neurodevelopmental disorders that exhibit cilia deficits and summarize findings from studies exploring the role of primary cilia in the brain to shed light into how these deficits could contribute to neurologic abnormalities.

Bardet–Biedl Syndrome: A Brief Overview on Clinics and Genetics

AbstractBardet–Biedl syndrome is a genetically pleiotropic disorder characterized by high clinical heterogeneity with severe multiorgan impairment. Clinically, it encompasses primary and secondary manifestations, mainly including retinal dystrophy, mental retardation, obesity, polydactyly, hypogonadism in male, and renal abnormalities. At least 21 different genes have been identified, all involved into primary cilium structure or function. To date, genotype–phenotype correlation is still poor.

Primary cilia: The central role in the electromagnetic field induced bone healing.

Primary cilia have emerged as the cellular "antenna" that can receive and transduce extracellular chemical/physical signals, thus playing an important role in regulating cellular activities. Although the electromagnetic field (EMF) is an effective treatment for bone fractures since 1978, however, the detailed mechanisms leading to such positive effects are still unclear. Primary cilia may play a central role in receiving EMF signals, translating physical signals into biochemical information, and initiating various signalingsignaling pathways to transduce signals into the nucleus. In this review, we elucidated the process of bone healing, the structure, and function of primary cilia, as well as the application and mechanism of EMF in treating fracture healing. To comprehensively understand the process of bone healing, we used bioinformatics to analyze the molecular change and associated the results with other studies. Moreover, this review summarizedsummarized some limitations in EMFs-related research and provides an outlook for ongoing studies. In conclusion, this review illustrated the primary cilia and related molecular mechanisms in the EMF-induced bone healing process, and it may shed light on future research.

Techniques for Visualization and Quantification of Primary Cilia in Chondrocytes.

Primary cilia regulate and coordinate a variety of cell signaling pathways important in chondrocyte physiology and cartilage development, health, and disease. Despite this, the chondrocyte primary cilium and its associated role in cartilage biology remains poorly understood. Key to elucidating primary cilia structure and function in chondrocytes is the ability to visualize this unique structure. Here we describe materials and methods for immunofluorescence labeling, microscopy, and measurement of chondrocyte primary cilia.