751
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Raychowdhury MK, Ramos AJ, Zhang P, McLaughin M, Dai XQ, Chen XZ, Montalbetti N, Del Rocío Cantero M, Ausiello DA, Cantiello HF. Vasopressin receptor-mediated functional signaling pathway in primary cilia of renal epithelial cells. Am J Physiol Renal Physiol 2008; 296:F87-97. [PMID: 18945824 DOI: 10.1152/ajprenal.90509.2008] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The primary cilium of renal epithelial cells is a nonmotile sensory organelle, implicated in mechanosensory transduction signals. Recent studies from our laboratory indicate that renal epithelial primary cilia display abundant channel activity; however, the presence and functional role of specific membrane receptors in this organelle are heretofore unknown. Here, we determined a functional signaling pathway associated with the type 2 vasopressin receptor (V2R) in primary cilia of renal epithelial cells. Besides their normal localization on basolateral membrane, V2R was expressed in primary cilia of LLC-PK(1) renal epithelial cells. The presence of V2R in primary cilia was determined by spontaneous fluorescence of a V2R-gfp chimera and confirmed by immunocytochemical analysis of wild-type LLC-PK(1) cells stained with anti-V2R antibodies and in LLC-PK(1) cells overexpressing the V2R-Flag, with anti-Flag antibody. Ciliary V2R colocalized with adenylyl cyclase (AC) type V/VI in all cell types tested. Functional coupling of the receptors with AC was confirmed by measurement of cAMP production in isolated cilia and by testing AVP-induced cation-selective channel activity either in reconstituted lipid bilayers or subjected to membrane-attached patch clamping. Addition of either 10 microM AVP (trans) or forskolin (cis) in the presence but not the absence of ATP (1 mM, cis) stimulated cation-selective channel activity in ciliary membranes. This channel activity was reduced by addition of the PKA inhibitor PKI. The data provide the first demonstration for the presence of V2R in primary cilia of renal epithelial cells, and a functional cAMP-signaling pathway, which targets ciliary channel function and may help control the sensory function of the primary cilium.
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Affiliation(s)
- Malay K Raychowdhury
- Nephrology Div. and Electrophysiology Core, Massachusetts General Hospital East, 149 13th St., Charlestown, MA 02129, USA
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752
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Stark TA, McKinney AM, Palmer CS, Maisel RH, Truwit CL. Dilation of the subarachnoid spaces surrounding the cranial nerves with petrous apex cephaloceles in Usher syndrome. AJNR Am J Neuroradiol 2008; 30:434-6. [PMID: 18945801 DOI: 10.3174/ajnr.a1283] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Limited studies of brain MR imaging findings in Usher syndrome have reported atrophy with enlarged subarachnoid spaces. However, the specific appearance of the subarachnoid spaces surrounding the cranial nerves has not yet been described. Herein we describe the skull base MR imaging findings in an adult with Usher syndrome. Multiple cranial nerve exits were enlarged to the point of causing cephaloceles with bony remodeling. A combination of uncommon findings in this rare disorder raises the question of an etiologic association.
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Affiliation(s)
- T A Stark
- Department of Radiology, University of Minnesota Medical School & Hennepin County Medical Center, Minneapolis, MN 55415, USA
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753
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Kubo A, Yuba-Kubo A, Tsukita S, Tsukita S, Amagai M. Sentan: a novel specific component of the apical structure of vertebrate motile cilia. Mol Biol Cell 2008; 19:5338-46. [PMID: 18829862 DOI: 10.1091/mbc.e08-07-0691] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Human respiratory and oviductal cilia have specific apical structures characterized by a narrowed distal portion and a ciliary crown. These structures are conserved among vertebrates that have air respiration systems; however, the molecular components of these structures have not been defined, and their functions are unknown. To identify the molecular component(s) of the cilia apical structure, we screened EST libraries to identify gene(s) that are exclusively expressed in ciliated tissues, are transcriptionally up-regulated during in vitro ciliogenesis, and are not expressed in testis (because sperm flagella have no such apical structures). One of the identified gene products, named sentan, was localized to the distal tip region of motile cilia. Using anti-sentan polyclonal antibodies and electron microscopy, sentan was shown to localize exclusively to the bridging structure between the cell membrane and peripheral singlet microtubules, which specifically exists in the narrowed distal portion of cilia. Exogenously expressed sentan showed affinity for the membrane protrusions, and a protein-lipid binding assay revealed that sentan bound to phosphatidylserine. These findings suggest that sentan is the first molecular component of the ciliary tip to bridge the cell membrane and peripheral singlet microtubules, making the distal portion of the cilia narrow and stiff to allow for better airway clearance or ovum transport.
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Affiliation(s)
- Akiharu Kubo
- Department of Dermatology, Keio University School of Medicine, Tokyo 160-8582, Japan.
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754
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Fernandez-Gonzalez A, Kourembanas S, Wyatt TA, Mitsialis SA. Mutation of murine adenylate kinase 7 underlies a primary ciliary dyskinesia phenotype. Am J Respir Cell Mol Biol 2008; 40:305-13. [PMID: 18776131 DOI: 10.1165/rcmb.2008-0102oc] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Primary ciliary dyskinesia (PCD) is a genetically and phenotypically heterogeneous disorder, characterized by progressive development of bronchiectasis, inflammation, and features characteristic of chronic obstructive pulmonary disease. We report here that a murine mutation of the evolutionarily conserved adenylate kinase 7 (Ak7) gene results in animals presenting with pathological signs characteristic of PCD, including ultrastructural ciliary defects and decreased ciliary beat frequency in respiratory epithelium. The mutation is associated with hydrocephalus, abnormal spermatogenesis, mucus accumulation in paranasal passages, and a dramatic respiratory pathology upon allergen challenge. Ak7 appears to be a marker for cilia with (9 + 2) microtubular organization. This is suggested by its tissue specificity of expression and also the stringent conservation of Ak7 ortholog structure only in protozoans and metazoans possessing motile (9 + 2) cilia. Collectively, our results indicate an ancestral and crucial role of Ak7 in maintaining ciliary structure and function, and suggest that mutations of the human ortholog may underlie a subset of genetically uncharacterized PCD cases.
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Affiliation(s)
- Angeles Fernandez-Gonzalez
- Division of Newborn Medicine, Enders 970, 300 Longwood Avenue, Children's Hospital Boston, Boston, MA 02115, USA
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755
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Kim J, Krishnaswami SR, Gleeson JG. CEP290 interacts with the centriolar satellite component PCM-1 and is required for Rab8 localization to the primary cilium. Hum Mol Genet 2008; 17:3796-805. [PMID: 18772192 DOI: 10.1093/hmg/ddn277] [Citation(s) in RCA: 232] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Joubert syndrome (JS) is a developmental brain disorder characterized by cerebellar vermis hypoplasia, abnormal eye movement, ataxia and mental retardation. Mutations in CEP290 mutations are responsible for the cerebello-oculo-renal subtype of JS that includes kidney cysts and retinal degeneration, two phenotypes commonly linked to ciliopathies. CEP290 mutations are also associated with Meckel-Gruber syndrome and Bardet-Biedl syndrome (BBS). Here we demonstrate that CEP290 interacts with a centriolar satellite protein PCM-1, which is implicated in BBS4 function. CEP290 binds to PCM-1 and localizes to centriolar satellites in a PCM-1- and microtubule-dependent manner. The depletion of CEP290 disrupts subcellular distribution and protein complex formation of PCM-1. In accord with PCM-1's role in microtubule organization, CEP290 knockdown causes the disorganization of the cytoplasmic microtubule network. Moreover, we show that both CEP290 and PCM-1 are required for ciliogenesis and are involved in the ciliary targeting of Rab8, a small GTPase shown to collaborate with BBS protein complex to promote ciliogenesis. Our results suggest that PCM-1 is a potential mediator that may link CEP290 with BBS proteins in common molecular pathways.
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Affiliation(s)
- Joon Kim
- Department of Neurosciences, Howard Hughes Medical Institute, University of California, San Diego, La Jolla, CA 92093, USA
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756
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Donnelly E, Williams R, Farnum C. The Primary Cilium of Connective Tissue Cells: Imaging by Multiphoton Microscopy. Anat Rec (Hoboken) 2008; 291:1062-73. [DOI: 10.1002/ar.20665] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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757
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Jiang ST, Chiou YY, Wang E, Lin HK, Lee SP, Lu HY, Wang CKL, Tang MJ, Li H. Targeted disruption of Nphp1 causes male infertility due to defects in the later steps of sperm morphogenesis in mice. Hum Mol Genet 2008; 17:3368-79. [PMID: 18684731 DOI: 10.1093/hmg/ddn231] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Juvenile nephronophthisis type I is the most common genetic disorder causing end-stage renal failure in children and young adults. The defective gene responsible has been identified as NPHP1. Its gene product, nephrocystin-1, is a novel protein of uncertain function that is widely expressed in many tissues and not just confined to the kidney. To gain insight into the physiological function of nephrocystin, Nphp1-targeted mutant mice were generated by homologous recombination. Interestingly, homozygous Nphp1 mutant mice were viable without renal manifestations of nephronophthisis. They appeared normal, but males were infertile with oligoteratozoospermia. Histological analysis of the seminiferous tubules showed that spermatogenesis was blocked at the early stages of spermatid elongation, with degenerating spermatids sloughing off into the lumen. Electron microscopic analysis revealed detachment of early elongating spermatids from Sertoli cells, and a failure of sperm head and tail morphogenesis. However, a few mature spermatozoa were still deposited in the epididymis, though they were frequently dead, immotile, or malformed. These novel findings indicate that nephrocystin is critically required for the differentiation of early elongating spermatids into spermatozoa in mice. The possible roles of nephrocystin in the formation and maintenance of Sertoli-spermatid junctions are still under investigation.
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Affiliation(s)
- Si-Tse Jiang
- Institute of Molecular Biology, Academia Sinica, Taipei 115, Taiwan
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758
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Aftab S, Semenec L, Chu JSC, Chen N. Identification and characterization of novel human tissue-specific RFX transcription factors. BMC Evol Biol 2008; 8:226. [PMID: 18673564 PMCID: PMC2533330 DOI: 10.1186/1471-2148-8-226] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2008] [Accepted: 08/01/2008] [Indexed: 02/06/2023] Open
Abstract
Background Five regulatory factor X (RFX) transcription factors (TFs)–RFX1-5–have been previously characterized in the human genome, which have been demonstrated to be critical for development and are associated with an expanding list of serious human disease conditions including major histocompatibility (MHC) class II deficiency and ciliaophathies. Results In this study, we have identified two additional RFX genes–RFX6 and RFX7–in the current human genome sequences. Both RFX6 and RFX7 are demonstrated to be winged-helix TFs and have well conserved RFX DNA binding domains (DBDs), which are also found in winged-helix TFs RFX1-5. Phylogenetic analysis suggests that the RFX family in the human genome has undergone at least three gene duplications in evolution and the seven human RFX genes can be clearly categorized into three subgroups: (1) RFX1-3, (2) RFX4 and RFX6, and (3) RFX5 and RFX7. Our functional genomics analysis suggests that RFX6 and RFX7 have distinct expression profiles. RFX6 is expressed almost exclusively in the pancreatic islets, while RFX7 has high ubiquitous expression in nearly all tissues examined, particularly in various brain tissues. Conclusion The identification and further characterization of these two novel RFX genes hold promise for gaining critical insight into development and many disease conditions in mammals, potentially leading to identification of disease genes and biomarkers.
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Affiliation(s)
- Syed Aftab
- Department of Molecular Biology and Biochemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada.
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759
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Affiliation(s)
- Rajat Rohatgi
- Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA 94305-5439, USA
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760
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Rougemont AL, Bouron-Dal Soglio D, Désilets V, Jovanovic M, Perreault G, Laurier Oligny L, Fournet JC. Caudal dysgenesis, sirenomelia, and situs inversus totalis: a primitive defect in blastogenesis. Am J Med Genet A 2008; 146A:1470-6. [PMID: 18470923 DOI: 10.1002/ajmg.a.32081] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Caudal dysgenesis (CD) constitutes a heterogeneous spectrum of congenital caudal anomalies, including varying degrees of agenesis of the vertebral column, as well as anorectal and genitourinary anomalies. Sirenomelia, characterized by a fusion of the lower limbs, could represent the most severe end of this spectrum. The two main debated pathogenic hypotheses are an aberrant vascular supply versus a primary axial mesoderm defect. We present the autopsy findings of two fetuses of non-diabetic mothers, with normal karyotype. Both fetuses presented situs inversus associated with a CD, in one case consisting of sirenomelia, establishing a very rare association profile that might be random. This association also suggests the occurrence of a common pathogenic mechanism, in accordance to recent genetic data, such as displayed in the Kif3A murine mutation phenotype. Some cases of sirenomelia and CD could represent developmental field defects of blastogenesis involving the caudal mesoderm, rather than being related to vascular insufficiency.
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761
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Kunitomo H, Iino Y. Caenorhabditis elegans DYF-11, an orthologue of mammalian Traf3ip1/MIP-T3, is required for sensory cilia formation. Genes Cells 2008; 13:13-25. [PMID: 18173744 DOI: 10.1111/j.1365-2443.2007.01147.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Cilia and flagella play critical roles in cell motility, development and sensory perception in animals. Formation and maintenance of cilia require a conserved protein transport system called intraflagellar transport (IFT). Here, we show that Caenorhabditis elegans dyf-11 encodes an evolutionarily conserved protein required for cilium biogenesis. dyf-11 is expressed in most of the ciliated neurons and is regulated by DAF-19, a crucial transcription factor for ciliary genes in C. elegans. dyf-11 mutants exhibit stunted cilia, fluorescent dye-filling defects (Dyf) of sensory neurons, and abnormal chemotaxis (Che). Cell- and stage-specific rescue experiments indicated that DYF-11 is required for formation and maintenance of sensory cilia in cell-autonomous manner. Fluorescent protein-tagged DYF-11 localizes to cilia and moves antero- and retrogradely via IFT. Analysis of DYF-11 movement in bbs mutants further suggested that DYF-11 is likely associated with IFT complex B. Domain analysis using DYF-11 deletion constructs revealed that the coiled-coil region is required for proper localization and ciliogenesis. We further show that Traf3ip1/MIP-T3, the mammalian orthologue of DYF-11, localizes to cilia in the MDCK renal epithelial cells.
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Affiliation(s)
- Hirofumi Kunitomo
- Molecular Genetics Research Laboratory, Graduate School of Science, The University of Tokyo, Tokyo, Japan
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762
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White MC, Quarmby LM. The NIMA-family kinase, Nek1 affects the stability of centrosomes and ciliogenesis. BMC Cell Biol 2008; 9:29. [PMID: 18533026 PMCID: PMC2442590 DOI: 10.1186/1471-2121-9-29] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2007] [Accepted: 06/04/2008] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND Mutations in Nek1 (NIMA-Related Kinase 1) are causal in the murine models of polycystic kidney disease kat and kat2J. The Neks are known as cell cycle kinases, but recent work in protists has revealed that in addition to roles in the regulation of cell cycle progression, some Neks also regulate cilia. In most cells, cilia are disassembled prior to mitosis and are regenerated after cytokinesis. We propose that Neks participate in the coordination of ciliogenesis with cell cycle progression. Mammalian Nek1 is a candidate for this activity because renal cysts form in response to dysfunctional ciliary signalling. RESULTS Here we report that over-expression of full-length mNek1 inhibited ciliogenesis without disrupting centrosomes in the murine renal epithelial cell line IMCD3. In contrast, over-expression of the kinase domain with its associated basic region, but without the acidic domain, caused loss of centrosomes. As expected, these cells also failed to grow cilia. Both defective ciliogenesis in response to too much mNek1 and disassembly of centrosomes in response to expression of the kinase lacking the presumptive regulatory domain was abrogated by kinase-inactivating mutations or by removal of the coiled-coil domain. We observed that kinase-inactive, C-terminal truncations of mNek1 retaining the coiled-coil domain localized to the cilium, and we define a ciliary targeting region within the coiled-coil domain. CONCLUSION Based on our data, we propose that Nek1 plays a role in centrosome integrity, affecting both ciliogenesis and centrosome stability.
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Affiliation(s)
- Mark C White
- Department of Molecular Biology & Biochemistry, Simon Fraser University, Burnaby, Canada.
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763
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Chen CP. Syndromes, Disorders and Maternal Risk Factors Associated with Neural Tube Defects (III). Taiwan J Obstet Gynecol 2008; 47:131-40. [DOI: 10.1016/s1028-4559(08)60070-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
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764
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Laurençon A, Dubruille R, Efimenko E, Grenier G, Bissett R, Cortier E, Rolland V, Swoboda P, Durand B. Identification of novel regulatory factor X (RFX) target genes by comparative genomics in Drosophila species. Genome Biol 2008; 8:R195. [PMID: 17875208 PMCID: PMC2375033 DOI: 10.1186/gb-2007-8-9-r195] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2007] [Revised: 09/14/2007] [Accepted: 09/17/2007] [Indexed: 01/02/2023] Open
Abstract
An RFX-binding site is shown to be conserved in the promoters of a subset of ciliary genes and a subsequent screen for this site in two Drosophila species identified novel RFX target genes that are involved in sensory ciliogenesis. Background Regulatory factor X (RFX) transcription factors play a key role in ciliary assembly in nematode, Drosophila and mouse. Using the tremendous advantages of comparative genomics in closely related species, we identified novel genes regulated by dRFX in Drosophila. Results We first demonstrate that a subset of known ciliary genes in Caenorhabditis elegans and Drosophila are regulated by dRFX and have a conserved RFX binding site (X-box) in their promoters in two highly divergent Drosophila species. We then designed an X-box consensus sequence and carried out a genome wide computer screen to identify novel genes under RFX control. We found 412 genes that share a conserved X-box upstream of the ATG in both species, with 83 genes presenting a more restricted consensus. We analyzed 25 of these 83 genes, 16 of which are indeed RFX target genes. Two of them have never been described as involved in ciliogenesis. In addition, reporter construct expression analysis revealed that three of the identified genes encode proteins specifically localized in ciliated endings of Drosophila sensory neurons. Conclusion Our X-box search strategy led to the identification of novel RFX target genes in Drosophila that are involved in sensory ciliogenesis. We also established a highly valuable Drosophila cilia and basal body dataset. These results demonstrate the accuracy of the X-box screen and will be useful for the identification of candidate genes for human ciliopathies, as several human homologs of RFX target genes are known to be involved in diseases, such as Bardet-Biedl syndrome.
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Affiliation(s)
- Anne Laurençon
- Université de Lyon, Lyon, F-69003, France
- Université Lyon 1, CNRS, UMR5534, Centre de Génétique Moléculaire et Cellulaire, Villeurbanne, F-69622, France
| | - Raphaëlle Dubruille
- Université de Lyon, Lyon, F-69003, France
- Université Lyon 1, CNRS, UMR5534, Centre de Génétique Moléculaire et Cellulaire, Villeurbanne, F-69622, France
- University of Massachusetts Medical School, Department of Neurobiology, Worcester, MA 01605, USA
| | - Evgeni Efimenko
- Karolinska Institute, Department of Biosciences and Nutrition, Södertörn University College, School of Life Sciences, S-14189 Huddinge, Sweden
| | - Guillaume Grenier
- Université de Lyon, Lyon, F-69003, France
- Université Lyon 1, CNRS, UMR5534, Centre de Génétique Moléculaire et Cellulaire, Villeurbanne, F-69622, France
| | - Ryan Bissett
- Université de Lyon, Lyon, F-69003, France
- Université Lyon 1, CNRS, UMR5534, Centre de Génétique Moléculaire et Cellulaire, Villeurbanne, F-69622, France
- University of Glasgow, Glasgow Biomedical Research Centre, Wellcome Centre for Molecular Parasitology and Infection and Immunity, Glasgow G12 8TA, UK
| | - Elisabeth Cortier
- Université de Lyon, Lyon, F-69003, France
- Université Lyon 1, CNRS, UMR5534, Centre de Génétique Moléculaire et Cellulaire, Villeurbanne, F-69622, France
| | - Vivien Rolland
- Université de Lyon, Lyon, F-69003, France
- Université Lyon 1, CNRS, UMR5534, Centre de Génétique Moléculaire et Cellulaire, Villeurbanne, F-69622, France
| | - Peter Swoboda
- Karolinska Institute, Department of Biosciences and Nutrition, Södertörn University College, School of Life Sciences, S-14189 Huddinge, Sweden
| | - Bénédicte Durand
- Université de Lyon, Lyon, F-69003, France
- Université Lyon 1, CNRS, UMR5534, Centre de Génétique Moléculaire et Cellulaire, Villeurbanne, F-69622, France
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765
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Lu CJ, Du H, Wu J, Jansen DA, Jordan KL, Xu N, Sieck GC, Qian Q. Non-random distribution and sensory functions of primary cilia in vascular smooth muscle cells. Kidney Blood Press Res 2008; 31:171-84. [PMID: 18483460 DOI: 10.1159/000132462] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2008] [Accepted: 03/10/2008] [Indexed: 12/16/2022] Open
Abstract
Although primary cilia are increasingly recognized to play sensory roles in several cellular systems, their role in vascular smooth muscle cells (VSMCs) has not been defined. We examined in situ position/orientation of primary cilia and ciliary proteins in VSMCs and tested the hypothesis that primary cilia of VSMCs exert sensory functions. By immunofluorescence and electron microscopic imaging, primary cilia of VSMCs were positioned with their long axis aligned at 58.3 degrees angle in relation to the cross-sectional plane of the artery, projecting into the extracellular matrix (ECM). Polycystin-1, polycystin-2 and alpha 3- and beta1-integrins are present in cilia. In scratch wound experiments, the majority of cilia were repositioned to the cell-wound interface. Such repositioning was largely abolished by a beta1-integrin blocker. Moreover, compared to non-ciliated/deciliated cells, ciliated VSMCs showed more efficient migration in wound repair. Lastly, when directly stimulated with collagen (an ECM component and cognate ligand for alpha 3beta1-integrins) or induced ciliary deflection, VSMCs responded with a rise in [Ca(2+)](i) that is dependent on the presence of cilia. Taken together, primary cilia of VSMCs are preferentially oriented, possess proteins critical for cell-ECM interaction and mechanosensing and respond to ECM protein and mechanical stimulations. These observations suggest a role for primary cilia in mechanochemical sensing in vasculature.
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Affiliation(s)
- C J Lu
- Division of Nephrology and Hypertension, Mayo Clinic College of Medicine and Mayo Graduate School, Rochester, MN 55905, USA
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766
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Rahmouni K, Fath MA, Seo S, Thedens DR, Berry CJ, Weiss R, Nishimura DY, Sheffield VC. Leptin resistance contributes to obesity and hypertension in mouse models of Bardet-Biedl syndrome. J Clin Invest 2008; 118:1458-67. [PMID: 18317593 DOI: 10.1172/jci32357] [Citation(s) in RCA: 167] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2007] [Accepted: 01/16/2008] [Indexed: 12/19/2022] Open
Abstract
Bardet-Biedl syndrome (BBS) is a heterogeneous genetic disorder characterized by many features, including obesity and cardiovascular disease. We previously developed knockout mouse models of 3 BBS genes: BBS2, BBS4, and BBS6. To dissect the mechanisms involved in the metabolic disorders associated with BBS, we assessed the development of obesity in these mouse models and found that BBS-null mice were hyperphagic, had low locomotor activity, and had elevated circulating levels of the hormone leptin. The effect of exogenous leptin on body weight and food intake was attenuated in BBS mice, which suggests that leptin resistance may contribute to hyperleptinemia. In other mouse models of obesity, leptin resistance may be selective rather than systemic; although mice became resistant to leptin's anorectic effects, the ability to increase renal sympathetic nerve activity (SNA) was preserved. Although all 3 of the BBS mouse models were similarly resistant to leptin, the sensitivity of renal SNA to leptin was maintained in Bbs4 -/- and Bbs6 -/- mice, but not in Bbs2 -/- mice. Consequently, Bbs4 -/- and Bbs6 -/- mice had higher baseline renal SNA and arterial pressure and a greater reduction in arterial pressure in response to ganglionic blockade. Furthermore, we found that BBS mice had a decreased hypothalamic expression of proopiomelanocortin, which suggests that BBS genes play an important role in maintaining leptin sensitivity in proopiomelanocortin neurons.
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Affiliation(s)
- Kamal Rahmouni
- Department of Internal Medicine, Center on Functional Genomics of Hypertension, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242, USA.
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767
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Ciliary syndromes and treatment. Pathol Res Pract 2008; 204:77-88. [PMID: 18312782 DOI: 10.1016/j.prp.2007.10.013] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/27/2006] [Revised: 10/26/2007] [Accepted: 10/30/2007] [Indexed: 12/21/2022]
Abstract
Abnormal visceral patterning has been known for centuries. However, it has not been associated with ciliary dysfunction until recently. Overlapping clinical entities including situs inversus, certain infertility disorders, as well as chronic respiratory infections have their roots in abnormal ciliary function. Current research focuses on causative factors and genes involved in signal transduction pathways that define ciliary function and structure, as well as treatment. In this review, attempts are made to outline selected, yet key topics related to ciliary function in health and disease.
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768
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Bae YK, Barr MM. Sensory roles of neuronal cilia: cilia development, morphogenesis, and function in C. elegans. FRONTIERS IN BIOSCIENCE : A JOURNAL AND VIRTUAL LIBRARY 2008; 13:5959-74. [PMID: 18508635 PMCID: PMC3124812 DOI: 10.2741/3129] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
In the free-living nematode Caenorhabditis elegans, cilia are found on the dendritic endings of sensory neurons. C. elegans cilia are classified as 'primary' or 'sensory' according to the '9+0' axonemal ultrastructure (nine doublet outer microtubules with no central microtubule pair) and lack of motility, characteristics of '9+2' cilia. The C. elegans ciliated nervous system allows the animal to perceive environmental stimuli and make appropriate developmental, physiological, and behavioral decisions. In vertebrates, the biological significance of primary cilia had been largely neglected. Recent findings have placed primary/sensory cilia in the center of cellular signaling and developmental processes. Studies using genetic model organisms such as C. elegans identified the link between ciliary dysfunction and human ciliopathies. Future studies in the worm will address important basic questions regarding ciliary development, morphogenesis, specialization, and signaling functions.
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Affiliation(s)
- Young-Kyung Bae
- Laboratory of Genetics, University of Wisconsin-Madison, Madison, Wisconsin 53705, USA
- Department of Genetics and The Waksman Institute of Microbiology, Rutgers University, Piscataway, New Jersey 08854, USA
| | - Maureen M. Barr
- Department of Genetics and The Waksman Institute of Microbiology, Rutgers University, Piscataway, New Jersey 08854, USA
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769
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Kolb RJ, Nauli SM. Ciliary dysfunction in polycystic kidney disease: an emerging model with polarizing potential. FRONTIERS IN BIOSCIENCE : A JOURNAL AND VIRTUAL LIBRARY 2008; 13:4451-66. [PMID: 18508522 DOI: 10.2741/3016] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The majority of different cell types in the human body have a cilium, a thin rod-like structure of uniquely arranged microtubules that are encapsulated by the surface plasma membrane. The cilium originates from a basal body, a mature centriole that has migrated and docked to the cell surface. The non-motile cilia are microtubule-based organelles that are generally considered sensory structures. The purpose of this review is to discuss the practicality of the ciliary hypothesis as a unifying concept for polycystic kidney disease and to review current literature in the field of cilium biology, as it relates to mechanosensation and planar cell polarity. The polycystins and fibrocystin localization at the cilium and other subcellular localizations are discussed, followed by a hypothetical model for the cilium's role in mechanosensing, planar cell polarity, and cystogenesis.
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Affiliation(s)
- Robert J Kolb
- Department of Pediatrics, Medical University of South Carolina, Charleston, SC 29425, USA
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770
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Kiprilov EN, Awan A, Desprat R, Velho M, Clement CA, Byskov AG, Andersen CY, Satir P, Bouhassira EE, Christensen ST, Hirsch RE. Human embryonic stem cells in culture possess primary cilia with hedgehog signaling machinery. ACTA ACUST UNITED AC 2008; 180:897-904. [PMID: 18332216 PMCID: PMC2265400 DOI: 10.1083/jcb.200706028] [Citation(s) in RCA: 118] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Human embryonic stem cells (hESCs) are potential therapeutic tools and models of human development. With a growing interest in primary cilia in signal transduction pathways that are crucial for embryological development and tissue differentiation and interest in mechanisms regulating human hESC differentiation, demonstrating the existence of primary cilia and the localization of signaling components in undifferentiated hESCs establishes a mechanistic basis for the regulation of hESC differentiation. Using electron microscopy (EM), immunofluorescence, and confocal microscopies, we show that primary cilia are present in three undifferentiated hESC lines. EM reveals the characteristic 9 + 0 axoneme. The number and length of cilia increase after serum starvation. Important components of the hedgehog (Hh) pathway, including smoothened, patched 1 (Ptc1), and Gli1 and 2, are present in the cilia. Stimulation of the pathway results in the concerted movement of Ptc1 out of, and smoothened into, the primary cilium as well as up-regulation of GLI1 and PTC1. These findings show that hESCs contain primary cilia associated with working Hh machinery.
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Affiliation(s)
- Enko N Kiprilov
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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771
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Bergmann C, Fliegauf M, Brüchle NO, Frank V, Olbrich H, Kirschner J, Schermer B, Schmedding I, Kispert A, Kränzlin B, Nürnberg G, Becker C, Grimm T, Girschick G, Lynch SA, Kelehan P, Senderek J, Neuhaus TJ, Stallmach T, Zentgraf H, Nürnberg P, Gretz N, Lo C, Lienkamp S, Schäfer T, Walz G, Benzing T, Zerres K, Omran H. Loss of nephrocystin-3 function can cause embryonic lethality, Meckel-Gruber-like syndrome, situs inversus, and renal-hepatic-pancreatic dysplasia. Am J Hum Genet 2008; 82:959-70. [PMID: 18371931 PMCID: PMC2427297 DOI: 10.1016/j.ajhg.2008.02.017] [Citation(s) in RCA: 208] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2007] [Revised: 01/17/2008] [Accepted: 02/22/2008] [Indexed: 10/22/2022] Open
Abstract
Many genetic diseases have been linked to the dysfunction of primary cilia, which occur nearly ubiquitously in the body and act as solitary cellular mechanosensory organelles. The list of clinical manifestations and affected tissues in cilia-related disorders (ciliopathies) such as nephronophthisis is broad and has been attributed to the wide expression pattern of ciliary proteins. However, little is known about the molecular mechanisms leading to this dramatic diversity of phenotypes. We recently reported hypomorphic NPHP3 mutations in children and young adults with isolated nephronophthisis and associated hepatic fibrosis or tapetoretinal degeneration. Here, we chose a combinatorial approach in mice and humans to define the phenotypic spectrum of NPHP3/Nphp3 mutations and the role of the nephrocystin-3 protein. We demonstrate that the pcy mutation generates a hypomorphic Nphp3 allele that is responsible for the cystic kidney disease phenotype, whereas complete loss of Nphp3 function results in situs inversus, congenital heart defects, and embryonic lethality in mice. In humans, we show that NPHP3 mutations can cause a broad clinical spectrum of early embryonic patterning defects comprising situs inversus, polydactyly, central nervous system malformations, structural heart defects, preauricular fistulas, and a wide range of congenital anomalies of the kidney and urinary tract (CAKUT). On the functional level, we show that nephrocystin-3 directly interacts with inversin and can inhibit like inversin canonical Wnt signaling, whereas nephrocystin-3 deficiency leads in Xenopus laevis to typical planar cell polarity defects, suggesting a role in the control of canonical and noncanonical (planar cell polarity) Wnt signaling.
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Affiliation(s)
- Carsten Bergmann
- Department of Human Genetics, RWTH Aachen University, 52074 Aachen, Germany.
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772
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Li C, Inglis PN, Leitch CC, Efimenko E, Zaghloul NA, Mok CA, Davis EE, Bialas NJ, Healey MP, Héon E, Zhen M, Swoboda P, Katsanis N, Leroux MR. An essential role for DYF-11/MIP-T3 in assembling functional intraflagellar transport complexes. PLoS Genet 2008; 4:e1000044. [PMID: 18369462 PMCID: PMC2268012 DOI: 10.1371/journal.pgen.1000044] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2007] [Accepted: 02/28/2008] [Indexed: 11/30/2022] Open
Abstract
MIP-T3 is a human protein found previously to associate with microtubules and the kinesin-interacting neuronal protein DISC1 (Disrupted-in-Schizophrenia 1), but whose cellular function(s) remains unknown. Here we demonstrate that the C. elegans MIP-T3 ortholog DYF-11 is an intraflagellar transport (IFT) protein that plays a critical role in assembling functional kinesin motor-IFT particle complexes. We have cloned a loss of function dyf-11 mutant in which several key components of the IFT machinery, including Kinesin-II, as well as IFT subcomplex A and B proteins, fail to enter ciliary axonemes and/or mislocalize, resulting in compromised ciliary structures and sensory functions, and abnormal lipid accumulation. Analyses in different mutant backgrounds further suggest that DYF-11 functions as a novel component of IFT subcomplex B. Consistent with an evolutionarily conserved cilia-associated role, mammalian MIP-T3 localizes to basal bodies and cilia, and zebrafish mipt3 functions synergistically with the Bardet-Biedl syndrome protein Bbs4 to ensure proper gastrulation, a key cilium- and basal body-dependent developmental process. Our findings therefore implicate MIP-T3 in a previously unknown but critical role in cilium biogenesis and further highlight the emerging role of this organelle in vertebrate development. The transport of protein complexes and associated cargo along microtubule tracks represents an essential eukaryotic process responsible for a multitude of cellular functions, including cell division, vesicle movement to membranes, and trafficking along dendrites, axons, and cilia. The latter organelles are hair-like cellular appendages implicated in cell and fluid motility, sensing and transducing information from their environment, and development. Their biogenesis and maintenance depends on a kinesin- and dynein-mediated motility process termed intraflagellar transport (IFT). In addition to comprising these specialized molecular motors, the IFT machinery consists of large multisubunit complexes whose exact composition and organization has not been fully defined. Here we identify a protein, DYF-11/MIP-T3, that is conserved in all ciliated organisms and is associated with IFT in C. elegans. Disruption of C. elegans DYF-11 results in structurally compromised cilia, likely as a result of IFT motor and subunit misassembly. Animals lacking DYF-11 display chemosensory anomalies, consistent with a role for the protein in cilia-associated sensory processes. In zebrafish, MIP-T3 is essential for gastrulation movements during development, similar to that observed for other ciliary components, including Bardet-Biedl syndrome proteins. In conclusion, we have identified a novel IFT machinery component that is also essential for development in vertebrates.
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Affiliation(s)
- Chunmei Li
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada
| | - Peter N. Inglis
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada
| | - Carmen C. Leitch
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Evgeni Efimenko
- Karolinska Institute, Department of Biosciences and Nutrition, Södertörn University College, School of Life Sciences, Huddinge, Sweden
| | - Norann A. Zaghloul
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Calvin A. Mok
- Samuel Lunenfeld Research Institute, Mount Sinai Hospital and Department of Microbiology and Medical Genetics, University of Toronto, Ontario, Canada
- Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children and University of Toronto, Toronto, Ontario, Canada
| | - Erica E. Davis
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Nathan J. Bialas
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada
| | - Michael P. Healey
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada
| | - Elise Héon
- Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children and University of Toronto, Toronto, Ontario, Canada
| | - Mei Zhen
- Samuel Lunenfeld Research Institute, Mount Sinai Hospital and Department of Microbiology and Medical Genetics, University of Toronto, Ontario, Canada
| | - Peter Swoboda
- Karolinska Institute, Department of Biosciences and Nutrition, Södertörn University College, School of Life Sciences, Huddinge, Sweden
| | - Nicholas Katsanis
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Michel R. Leroux
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada
- * E-mail:
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773
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Ralston KS, Hill KL. The flagellum of Trypanosoma brucei: new tricks from an old dog. Int J Parasitol 2008; 38:869-84. [PMID: 18472102 DOI: 10.1016/j.ijpara.2008.03.003] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2008] [Revised: 03/03/2008] [Accepted: 03/03/2008] [Indexed: 11/30/2022]
Abstract
African trypanosomes, i.e. Trypanosoma brucei and related sub-species, are devastating human and animal pathogens that cause significant human mortality and limit sustained economic development in sub-Saharan Africa. T. brucei is a highly motile protozoan parasite and coordinated motility is central to both disease pathogenesis in the mammalian host and parasite development in the tsetse fly vector. Therefore, understanding unique aspects of the T. brucei flagellum may uncover novel targets for therapeutic intervention in African sleeping sickness. Moreover, studies of conserved features of the T. brucei flagellum are directly relevant to understanding fundamental aspects of flagellum and cilium function in other eukaryotes, making T. brucei an important model system. The T. brucei flagellum contains a canonical 9+2 axoneme, together with additional features that are unique to kinetoplastids and a few closely-related organisms. Until recently, much of our knowledge of the structure and function of the trypanosome flagellum was based on analogy and inference from other organisms. There has been an explosion in functional studies in T. brucei in recent years, revealing conserved as well as novel and unexpected structural and functional features of the flagellum. Most notably, the flagellum has been found to be an essential organelle, with critical roles in parasite motility, morphogenesis, cell division and immune evasion. This review highlights recent discoveries on the T. brucei flagellum.
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Affiliation(s)
- Katherine S Ralston
- Department of Microbiology, Immunology, and Molecular Genetics, University of California, Los Angeles, CA 90095, USA
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774
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Abstract
In the past half century, beginning with electron microscopic studies of 9 + 2 motile and 9 + 0 primary cilia, novel insights have been obtained regarding the structure and function of mammalian cilia. All cilia can now be viewed as sensory cellular antennae that coordinate a large number of cellular signaling pathways, sometimes coupling the signaling to ciliary motility or alternatively to cell division and differentiation. This view has had unanticipated consequences for our understanding of developmental processes and human disease.
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Affiliation(s)
- Peter Satir
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, NY, USA
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775
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Bishop GA, Berbari NF, Lewis J, Mykytyn K. Type III adenylyl cyclase localizes to primary cilia throughout the adult mouse brain. J Comp Neurol 2008; 505:562-71. [PMID: 17924533 DOI: 10.1002/cne.21510] [Citation(s) in RCA: 242] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Solitary primary cilia project from nearly every cell type in the human body. These organelles are considered to have important sensory and signaling functions. Although primary cilia have been detected throughout the mammalian brain, their functions are unknown. The study of primary cilia in the brain is constrained by the scarcity of specific markers for these organelles. We previously demonstrated that type III adenylyl cyclase (ACIII) is a marker for primary cilia on neonatal hippocampal neurons in vivo and in vitro. We further showed that ACIII localizes to cilia on cultured glial cells. Here, we report that ACIII is a marker for primary cilia throughout many regions of the adult mouse brain. Furthermore, we report that ACIII localizes to primary cilia on choroid plexus cells and some astrocytes in the brain, which to our knowledge is the first report of a marker for visualizing cilia on glia in vivo. Overall, our data indicate that ACIII is a prominent marker of primary cilia in the brain and will provide an important tool to facilitate further investigations into the functions of these organelles.
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Affiliation(s)
- Georgia A Bishop
- Department of Neuroscience, College of Medicine, The Ohio State University, Columbus, Ohio 43210, USA
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776
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Williams CL, Winkelbauer ME, Schafer JC, Michaud EJ, Yoder BK. Functional redundancy of the B9 proteins and nephrocystins in Caenorhabditis elegans ciliogenesis. Mol Biol Cell 2008; 19:2154-68. [PMID: 18337471 DOI: 10.1091/mbc.e07-10-1070] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Meckel-Gruber syndrome (MKS), nephronophthisis (NPHP), and Joubert syndrome (JBTS) are a group of heterogeneous cystic kidney disorders with partially overlapping loci. Many of the proteins associated with these diseases interact and localize to cilia and/or basal bodies. One of these proteins is MKS1, which is disrupted in some MKS patients and contains a B9 motif of unknown function that is found in two other mammalian proteins, B9D2 and B9D1. Caenorhabditis elegans also has three B9 proteins: XBX-7 (MKS1), TZA-1 (B9D2), and TZA-2 (B9D1). Herein, we report that the C. elegans B9 proteins form a complex that localizes to the base of cilia. Mutations in the B9 genes do not overtly affect cilia formation unless they are in combination with a mutation in nph-1 or nph-4, the homologues of human genes (NPHP1 and NPHP4, respectively) that are mutated in some NPHP patients. Our data indicate that the B9 proteins function redundantly with the nephrocystins to regulate the formation and/or maintenance of cilia and dendrites in the amphid and phasmid ciliated sensory neurons. Together, these data suggest that the human homologues of the novel B9 genes B9D2 and B9D1 will be strong candidate loci for pathologies in human MKS, NPHP, and JBTS.
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Affiliation(s)
- Corey L Williams
- Department of Cell Biology, University of Alabama at Birmingham Medical Center, Birmingham, AL 35294, USA
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777
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Wei HC, Rollins J, Fabian L, Hayes M, Polevoy G, Bazinet C, Brill JA. Depletion of plasma membrane PtdIns(4,5)P2 reveals essential roles for phosphoinositides in flagellar biogenesis. J Cell Sci 2008; 121:1076-84. [PMID: 18334551 DOI: 10.1242/jcs.024927] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Axonemes are microtubule-based organelles of crucial importance in the structure and function of eukaryotic cilia and flagella. Despite great progress in understanding how axonemes are assembled, the signals that initiate axoneme outgrowth remain unknown. Here, we identified phosphatidylinositol phosphates (phosphoinositides) as key regulators of early stages of axoneme outgrowth in Drosophila melanogaster spermatogenesis. In a study of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] function in developing Drosophila male germ cells, we depleted PtdIns(4,5)P2 by expression of a potent phosphoinositide phosphatase. Phosphatase expression dramatically inhibited sperm tail formation and perturbed microtubule organization in a manner reversible by co-expression of a PtdIns 4-phosphate 5-kinase. Depletion of PtdIns(4,5)P2 caused increased levels of basal body gamma-tubulin and altered the distribution of proteins known to be required for axoneme assembly. Examination of PtdIns(4,5)P2-depleted spermatids by transmission electron microscopy revealed defects in basal body docking to the nuclear envelope, and in axoneme architecture and integrity of the developing flagellar axoneme and axial sheath. Our results provide the first evidence that phosphoinositides act at several steps during flagellar biogenesis, coordinately regulating microtubule and membrane organization. They further suggest that phosphoinositides play evolutionarily conserved roles in flagella and cilia, across phyla and in structurally diverse cell types.
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Affiliation(s)
- Ho-Chun Wei
- Program in Developmental and Stem Cell Biology, The Hospital for Sick Children, Toronto, Ontario M5G 1L7, Canada
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778
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Bardet-Biedl syndrome proteins are required for the localization of G protein-coupled receptors to primary cilia. Proc Natl Acad Sci U S A 2008; 105:4242-6. [PMID: 18334641 DOI: 10.1073/pnas.0711027105] [Citation(s) in RCA: 364] [Impact Index Per Article: 22.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Primary cilia are ubiquitous cellular appendages that provide important yet not well understood sensory and signaling functions. Ciliary dysfunction underlies numerous human genetic disorders. However, the precise defects in cilia function and the basis of disease pathophysiology remain unclear. Here, we report that the proteins disrupted in the human ciliary disorder Bardet-Biedl syndrome (BBS) are required for the localization of G protein-coupled receptors to primary cilia on central neurons. We demonstrate a lack of ciliary localization of somatostatin receptor type 3 (Sstr3) and melanin-concentrating hormone receptor 1 (Mchr1) in neurons from mice lacking the Bbs2 or Bbs4 gene. Because Mchr1 is involved in the regulation of feeding behavior and BBS is associated with hyperphagia-induced obesity, our results suggest that altered signaling caused by mislocalization of ciliary signaling proteins underlies the BBS phenotypes. Our results also provide a potential molecular mechanism to link cilia defects with obesity.
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779
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Jauregui AR, Nguyen KCQ, Hall DH, Barr MM. The Caenorhabditis elegans nephrocystins act as global modifiers of cilium structure. J Cell Biol 2008; 180:973-88. [PMID: 18316409 PMCID: PMC2265406 DOI: 10.1083/jcb.200707090] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2007] [Accepted: 02/07/2008] [Indexed: 12/15/2022] Open
Abstract
Nephronophthisis (NPHP) is the most common genetic cause of end-stage renal disease in children and young adults. In Chlamydomonas reinhardtii, Caenorhabditis elegans, and mammals, the NPHP1 and NPHP4 gene products nephrocystin-1 and nephrocystin-4 localize to basal bodies or ciliary transition zones (TZs), but their function in this location remains unknown. We show here that loss of C. elegans NPHP-1 and NPHP-4 from TZs is tolerated in developing cilia but causes changes in localization of specific ciliary components and a broad range of subtle axonemal ultrastructural defects. In amphid channel cilia, nphp-4 mutations cause B tubule defects that further disrupt intraflagellar transport (IFT). We propose that NPHP-1 and NPHP-4 act globally at the TZ to regulate ciliary access of the IFT machinery, axonemal structural components, and signaling molecules, and that perturbing this balance results in cell type-specific phenotypes.
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Affiliation(s)
- Andrew R Jauregui
- Department of Genetics, Rutgers University, Piscataway, NJ 08854, USA
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780
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Leitch CC, Zaghloul NA, Davis EE, Stoetzel C, Diaz-Font A, Rix S, Alfadhel M, Al-Fadhel M, Lewis RA, Eyaid W, Banin E, Dollfus H, Beales PL, Badano JL, Katsanis N. Hypomorphic mutations in syndromic encephalocele genes are associated with Bardet-Biedl syndrome. Nat Genet 2008; 40:443-8. [PMID: 18327255 DOI: 10.1038/ng.97] [Citation(s) in RCA: 298] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2007] [Accepted: 01/23/2008] [Indexed: 11/09/2022]
Abstract
Meckel-Gruber syndrome (MKS) is a genetically heterogeneous, neonatally lethal malformation and the most common form of syndromic neural tube defect (NTD). To date, several MKS-associated genes have been identified whose protein products affect ciliary function. Here we show that mutations in MKS1, MKS3 and CEP290 (also known as NPHP6) either can cause Bardet-Biedl syndrome (BBS) or may have a potential epistatic effect on mutations in known BBS-associated loci. Five of six families with both MKS1 and BBS mutations manifested seizures, a feature that is not a typical component of either syndrome. Functional studies in zebrafish showed that mks1 is necessary for gastrulation movements and that it interacts genetically with known bbs genes. Similarly, we found two families with missense or splice mutations in MKS3, in one of which the affected individual also bears a homozygous nonsense mutation in CEP290 that is likely to truncate the C terminus of the protein. These data extend the genetic stratification of ciliopathies and suggest that BBS and MKS, although distinct clinically, are allelic forms of the same molecular spectrum.
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Affiliation(s)
- Carmen C Leitch
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, 733. N Broadway, Baltimore, Maryland 21205, USA
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781
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Molecular dissection of ODF2/Cenexin revealed a short stretch of amino acids necessary for targeting to the centrosome and the primary cilium. Eur J Cell Biol 2008; 87:137-46. [DOI: 10.1016/j.ejcb.2007.10.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2007] [Revised: 09/20/2007] [Accepted: 10/19/2007] [Indexed: 11/19/2022] Open
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782
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Phenome connections. Trends Genet 2008; 24:103-6. [DOI: 10.1016/j.tig.2007.12.005] [Citation(s) in RCA: 98] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2007] [Revised: 12/18/2007] [Accepted: 12/18/2007] [Indexed: 11/23/2022]
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783
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Hedgehog signaling and primary cilia are required for the formation of adult neural stem cells. Nat Neurosci 2008; 11:277-84. [PMID: 18297065 DOI: 10.1038/nn2059] [Citation(s) in RCA: 389] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2007] [Accepted: 01/29/2008] [Indexed: 02/04/2023]
Abstract
Neural stem cells that continue to produce neurons are retained in the adult hippocampal dentate gyrus. The mechanisms by which embryonic neural progenitors expand and transform into postnatal neural stem cells, an essential process for the continual production of neurons throughout life, remain unknown. We found that radial astrocytes, the postnatal progenitors in the dentate gyrus, failed to develop after embryonic ablation of ciliary genes or Smoothened (Smo), an essential component for Sonic hedgehog (Shh) signaling. Postnatal dentate neurogenesis failed in these mutant mice, and the dentate gyrus became severely hypotrophic. In contrast, expression of a constitutively active Smo (SmoM2-YFP) resulted in a marked expansion of the dentate gyrus. Double-mutant analyses suggested that both wild-type Smo and SmoM2-YFP function through the primary cilia. We conclude that Shh signaling, acting through the primary cilia, has a critical role in the expansion and establishment of postnatal hippocampal progenitors.
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784
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Abstract
Knocking out primary cilia of adult mouse tissues or a specific subset of cilia from POMC-expressing neurons in the brain initiates uncontrolled eating. This behavior leads to obesity and kidney disease.
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Affiliation(s)
- Peter Satir
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, New York, USA.
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785
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Patel V, Li L, Cobo-Stark P, Shao X, Somlo S, Lin F, Igarashi P. Acute kidney injury and aberrant planar cell polarity induce cyst formation in mice lacking renal cilia. Hum Mol Genet 2008; 17:1578-90. [PMID: 18263895 DOI: 10.1093/hmg/ddn045] [Citation(s) in RCA: 257] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Polycystic kidney disease (PKD) is an inherited disorder that is characterized by the accumulation of cysts in the renal parenchyma and progressive decline in renal function. Recent studies suggest that PKD arises from abnormalities of the primary cilium. We have previously shown that kidney-specific inactivation of the ciliogenic gene Kif3a during embryonic development produces kidney cysts and renal failure. Here, we used tamoxifen-inducible, kidney-specific gene targeting to inactivate Kif3a in the postnatal mouse kidney. Kidney-specific inactivation of Kif3a in newborn mice resulted in the loss of primary cilia and produced kidney cysts primarily in the loops of Henle, whereas inactivation in adult mice did not lead to the rapid development of cysts despite a comparable loss of primary cilia. The age-dependence and locations of the cysts suggested that cyst formation required increased rates of cell proliferation. To test this possibility, we stimulated cell proliferation in the adult kidney by inducing acute kidney injury and tubular regeneration. Acute kidney injury induced cyst formation in adult Kif3a mutant mice. Analysis of pre-cystic tubules in Kif3a mutant mice showed that the loss of cilia did not stimulate cell proliferation but instead resulted in aberrant planar cell polarity as manifested by abnormalities in the orientation of cell division. We conclude that primary cilia are required for the maintenance of planar cell polarity in the mammalian kidney and that acute kidney injury exacerbates cystic disease.
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Affiliation(s)
- Vishal Patel
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
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786
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Frank V, den Hollander AI, Brüchle NO, Zonneveld MN, Nürnberg G, Becker C, Du Bois G, Kendziorra H, Roosing S, Senderek J, Nürnberg P, Cremers FPM, Zerres K, Bergmann C. Mutations of the CEP290 gene encoding a centrosomal protein cause Meckel-Gruber syndrome. Hum Mutat 2008; 29:45-52. [PMID: 17705300 DOI: 10.1002/humu.20614] [Citation(s) in RCA: 101] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Meckel-Gruber syndrome (MKS) is an autosomal recessive, lethal multisystemic disorder characterized by meningooccipital encephalocele, cystic kidney dysplasia, hepatobiliary ductal plate malformation, and postaxial polydactyly. Recently, genes for MKS1 and MKS3 were identified, putting MKS on the list of ciliary disorders (ciliopathies). By positional cloning in a distantly related multiplex family, we mapped a novel locus for MKS to a 3-Mb interval on 12q21. Sequencing of the CEP290 gene located in the minimal critical region showed a homozygous 1-bp deletion supposed to lead to loss of function of the encoded centrosomal protein CEP290/nephrocystin-6. CEP290 is thought to be involved in chromosome segregation and localizes to cilia, centrosomes, and the nucleus. Subsequent analysis of another consanguineous multiplex family revealed homozygous haplotypes and the same frameshift mutation. Our findings add to the increasing body of evidence that ciliopathies can cause a broad spectrum of disease phenotypes, and pleiotropic effects of CEP290 mutations range from single organ involvement with isolated Leber congenital amaurosis to Joubert syndrome and lethal early embryonic multisystemic malformations in Meckel-Gruber syndrome. We compiled clinical and genetic data of all patients with CEP290 mutations described so far. No clear-cut genotype-phenotype correlations were apparent as almost all mutations are nonsense, frameshift, or splice-site changes and scattered throughout the gene irrespective of the patients' phenotypes. Conclusively, other factors than the type and location of CEP290 mutations may underlie phenotypic variability.
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Affiliation(s)
- Valeska Frank
- Department of Human Genetics, RWTH Aachen University, Aachen, Germany
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787
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Berbari NF, Johnson AD, Lewis JS, Askwith CC, Mykytyn K. Identification of ciliary localization sequences within the third intracellular loop of G protein-coupled receptors. Mol Biol Cell 2008; 19:1540-7. [PMID: 18256283 DOI: 10.1091/mbc.e07-09-0942] [Citation(s) in RCA: 262] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Primary cilia are sensory organelles present on most mammalian cells. The functions of cilia are defined by the signaling proteins localized to the ciliary membrane. Certain G protein-coupled receptors (GPCRs), including somatostatin receptor 3 (Sstr3) and serotonin receptor 6 (Htr6), localize to cilia. As Sstr3 and Htr6 are the only somatostatin and serotonin receptor subtypes that localize to cilia, we hypothesized they contain ciliary localization sequences. To test this hypothesis we expressed chimeric receptors containing fragments of Sstr3 and Htr6 in the nonciliary receptors Sstr5 and Htr7, respectively, in ciliated cells. We found the third intracellular loop of Sstr3 or Htr6 is sufficient for ciliary localization. Comparison of these loops revealed a loose consensus sequence. To determine whether this consensus sequence predicts ciliary localization of other GPCRs, we compared it with the third intracellular loop of all human GPCRs. We identified the consensus sequence in melanin-concentrating hormone receptor 1 (Mchr1) and confirmed Mchr1 localizes to primary cilia in vitro and in vivo. Thus, we have identified a putative GPCR ciliary localization sequence and used this sequence to identify a novel ciliary GPCR. As Mchr1 mediates feeding behavior and metabolism, our results implicate ciliary signaling in the regulation of body weight.
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Affiliation(s)
- Nicolas F Berbari
- Department of Pharmacology, Division of Human Genetics, and College of Medicine, The Ohio State University, Columbus, OH 43210, USA
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788
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Lechtreck KF, Delmotte P, Robinson ML, Sanderson MJ, Witman GB. Mutations in Hydin impair ciliary motility in mice. ACTA ACUST UNITED AC 2008; 180:633-43. [PMID: 18250199 PMCID: PMC2234243 DOI: 10.1083/jcb.200710162] [Citation(s) in RCA: 198] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Chlamydomonas reinhardtii hydin is a central pair protein required for flagellar motility, and mice with Hydin defects develop lethal hydrocephalus. To determine if defects in Hydin cause hydrocephalus through a mechanism involving cilia, we compared the morphology, ultrastructure, and activity of cilia in wild-type and hydin mutant mice strains. The length and density of cilia in the brains of mutant animals is normal. The ciliary axoneme is normal with respect to the 9 + 2 microtubules, dynein arms, and radial spokes but one of the two central microtubules lacks a specific projection. The hydin mutant cilia are unable to bend normally, ciliary beat frequency is reduced, and the cilia tend to stall. As a result, these cilia are incapable of generating fluid flow. Similar defects are observed for cilia in trachea. We conclude that hydrocephalus in hydin mutants is caused by a central pair defect impairing ciliary motility and fluid transport in the brain.
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789
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Dickinson S, Carr S, de Zoysa J, Barratt J. Cystic renal disease presenting in pregnancy: a novel presentation of oral-facial-digital syndrome type 1. Clin Kidney J 2008; 1:23-25. [PMID: 30792778 PMCID: PMC6375236 DOI: 10.1093/ndtplus/sfm012] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2007] [Accepted: 10/15/2007] [Indexed: 01/31/2023] Open
Affiliation(s)
- Steven Dickinson
- The John Walls Renal Unit, Leicester General Hospital, Gwendolen Road, Leicester, LE5 4PW, UK
| | - Susan Carr
- The John Walls Renal Unit, Leicester General Hospital, Gwendolen Road, Leicester, LE5 4PW, UK
| | - Janak de Zoysa
- Department of Renal Medicine, Auckland City Hospital, Park Road, Grafton, Auckland, Private Bag 92024, New Zealand
| | - Jonathan Barratt
- The John Walls Renal Unit, Leicester General Hospital, Gwendolen Road, Leicester, LE5 4PW, UK
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790
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Abstract
The recent identification of RPGRIP1L as a Joubert syndrome gene brings the total of known genes to five. Three of these are also associated with the lethal Meckel syndrome, and two with Senior-Løken syndrome; both of these disorders share Joubert syndrome phenotypes, illustrating the genetic complexity of this.
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Affiliation(s)
- P C Harris
- Division of Nephrology and Hypertension, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
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791
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Abstract
Defects in cilia cause a broad spectrum of human diseases known collectively as the ciliopathies. Although all ciliopathies arise from defective cilia, the range of symptoms can vary significantly, and only a small subset of the possible ciliary disease symptoms may be present in any given syndrome. This complexity is puzzling until one realizes that the cilia are themselves exceedingly complex machines that perform multiple functions simultaneously, such that breaking one piece of the machine can leave some functions intact while destroying others. The clinical complexity of the ciliopathies can therefore only be understood in light of the basic cell biology of the cilia themselves, which I will discuss from the viewpoint of cell biological studies in model organisms.
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Affiliation(s)
- Wallace F Marshall
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94143, USA.
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792
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Gurrieri F, Franco B, Toriello H, Neri G. Oral-facial-digital syndromes: review and diagnostic guidelines. Am J Med Genet A 2008; 143A:3314-23. [PMID: 17963220 DOI: 10.1002/ajmg.a.32032] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
The oral-facial-digital syndromes (OFDS) result from the pleiotropic effect of a morphogenetic impairment affecting almost invariably the mouth, face and digits. Other organ systems can be involved, defining specific types of OFDS. To date, 13 types have been distinguished based on characteristic clinical manifestations. An updated list of these types is provided and recent molecular data are discussed.
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Affiliation(s)
- Fiorella Gurrieri
- Istituto di Genetica Medica, Università Cattolica Facoltà di Medicina, Roma, Italy.
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793
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Abstract
With the increase in complexity of morphogenetic signaling cascades over the course of evolution and the emergence of broadly ciliated organisms, the cilium seems to have acquired a role as regulator of paracrine signal transduction. Recently, several lines of evidence have provided a link between basal body and ciliary proteins and Wnt signaling. In this chapter, we will evaluate the evidence linking the basal body and cilium with the regulation of beta-catenin-dependent (canonical) and beta-catenin-independent (noncanonical) signaling processes as well as which role(s) Wnt signaling might play in ciliogenesis. In addition, we will discuss aberrant Wnt signaling could contribute to phenotypes common to most ciliopathies and why these phenotypes might be driven by loss of noncanonical rather than gain of noncanonical Wnt signaling.
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Affiliation(s)
- Jantje M Gerdes
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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794
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Tobin JL, Beales PL. Restoration of renal function in zebrafish models of ciliopathies. Pediatr Nephrol 2008; 23:2095-9. [PMID: 18604564 PMCID: PMC7462901 DOI: 10.1007/s00467-008-0898-7] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/21/2008] [Revised: 04/23/2008] [Accepted: 05/16/2008] [Indexed: 11/28/2022]
Abstract
The ciliopathies are a class of rare human genetic disease whose aetioligies lie in defective primary cilia. Typical ciliopathies include Bardet-Biedl syndrome (BBS), nephronophthisis (NPHP), Jeune, Joubert, oro-facial-digital (OFD1) and Meckel (MKS) syndromes. All ciliopathies have the common denominator of renal disease, often including tubular cysts. In this study, we have modelled a range of ciliopathies in zebrafish and shown in all cases that knocking down these genes causes cystic lesions in the kidney. We have identified two drugs, rapamycin and roscovitine, which ameliorate the renal phenotype, both morphologically and functionally. This is the first study in which zebrafish has been used to identify potential therapeutic modalities for ciliopathic renal disease, and the results pave the way for further investigations in mammalian models.
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Affiliation(s)
- Jonathan L. Tobin
- Molecular Medicine Unit, UCL Institute of Child Health, 30 Guilford Street, London, WC1N 1EH UK
| | - Philip L. Beales
- Molecular Medicine Unit, UCL Institute of Child Health, 30 Guilford Street, London, WC1N 1EH UK
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795
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Yoshimura SI, Haas AK, Barr FA. Analysis of Rab GTPase and GTPase-activating protein function at primary cilia. Methods Enzymol 2008; 439:353-64. [PMID: 18374177 DOI: 10.1016/s0076-6879(07)00426-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Primary cilia are sensory structures on the cell surface whose formation requires tight integration of microtubules and polarized membrane trafficking events. Rabs are GTP-binding proteins of the Ras superfamily that control directed membrane trafficking by regulating membrane-membrane and membrane-cytoskeleton interactions. This chapter describes cell biological and biochemical methods for the analysis of Rab function and Rab GTPase-activating proteins during primary cilia formation.
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796
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Abstract
The cilium is a characteristic organelle of eukaryotes constructed from over 600 proteins. Bacterial flagella are entirely different. 9 + 2 motile cilia evolved before the divergence of the last eukaryotic common ancestor (LECA). This chapter explores, compares, and contrasts two potential pathways of evolution: (1) via invasion of a centriolar-like virus and (2) via autogenous formation from a pre-existing microtubule-organizing center (MTOC). In either case, the intraflagellar transport (IFT) machinery that is nearly universally required for the assembly and maintenance of cilia derived from the evolving intracellular vesicular transport system. The sensory function of cilia evolved first and the ciliary axoneme evolved gradually with ciliary motility, an important selection mechanism, as one of the driving forces.
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Affiliation(s)
- Peter Satir
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, New York, USA
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797
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Kilburn C, Winey M. Basal bodies. Curr Biol 2008. [DOI: 10.1016/j.cub.2007.10.057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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798
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799
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Wheatley DN. Chapter 7 Nanobiology of the Primary Cilium—Paradigm of a Multifunctional Nanomachine Complex. Methods Cell Biol 2008; 90:139-56. [DOI: 10.1016/s0091-679x(08)00807-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
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800
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Abstract
Recent studies have revealed unexpected connections between the mammalian Hedgehog (Hh) signal transduction pathway and the primary cilium, a microtubule-based organelle that protrudes from the surface of most vertebrate cells. Intraflagellar transport proteins, which are required for the construction of cilia, are essential for all responses to mammalian Hh proteins, and proteins required for Hh signal transduction are enriched in primary cilia. The phenotypes of different mouse mutants that affect ciliary proteins suggest that cilia may act as processive machines that organize sequential steps in the Hh signal transduction pathway. Cilia on vertebrate cells are likely to be important in additional developmental signaling pathways and are required for PDGF receptor alpha signaling in cultured fibroblasts. Cilia are not essential for either canonical or noncanonical Wnt signaling, although cell-type-specific modulation of cilia components may link cilia and Wnt signaling in some tissues. Because ciliogenesis in invertebrates is limited to a very small number of specialized cell types, the role of cilia in developmental signaling pathways is likely a uniquely vertebrate phenomenon.
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