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Liu Q, Zhang Q, Pierce EA. Photoreceptor sensory cilia and inherited retinal degeneration. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 664:223-32. [PMID: 20238021 DOI: 10.1007/978-1-4419-1399-9_26] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
The outer segments of photoreceptor cells are specialized sensory cilia, and share many features with other primary and sensory cilia. Like other cilia, photoreceptor sensory cilium (PSC) comprises a membrane domain of outer segment and its cytoskeleton. We have recently identified the protein components of mouse PSCs, and found that the list of PSC proteins, called the PSC proteome, contains many novel cilia proteins. Studies have shown that many of the identified retinal degeneration disease genes encode proteins which are part of the PSC. Furthermore, mutations in genes encoding proteins expressed both in photoreceptors and other cilia result in systemic diseases, such as Usher syndrome, Bardet-Biedl syndrome (BBS), and Senior-Loken syndrome that involve retinal degeneration along with other disorders consequent to cilia dysfunction such as deafness and polycystic kidney disease. Based on these findings, we hypothesize that genes that encode proteins required for formation of PSCs are good candidate retinal degeneration disease genes. This chapter will summarize our studies on identifying novel PSC proteins from the PSC proteome. As an example of these studies, we demonstrated that tetratricopeptide the repeat domain 21B (TTC21B) protein is a novel PSC protein and is required for normal cilia formation in primary and photoreceptor sensory cilia.
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Affiliation(s)
- Qin Liu
- University of Pennsylvania School of Medicine, Philadelphia, PA, USA.
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253
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Beales PL. Obesity in Single Gene Disorders. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2010; 94:125-57. [DOI: 10.1016/b978-0-12-375003-7.00005-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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254
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Seeley ES, Nachury MV. Constructing and deconstructing roles for the primary cilium in tissue architecture and cancer. Methods Cell Biol 2009; 94:299-313. [PMID: 20362097 DOI: 10.1016/s0091-679x(08)94015-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Primary cilia are exquisitely designed sensory machines that have evolved at least three distinct sensory modalities to monitor the extracellular environment. The presence and activation of growth factor, morphogen, and hormone receptors within the confines of the ciliary membrane, the intrinsic physical relationship between the ciliary axoneme and the centriole, and the preferential assembly of primary cilia on the apical surfaces of tissue epithelia highlight the importance of this organelle in the establishment and maintenance of tissue architecture and homeostasis. Accordingly, recent studies begin to suggest roles for these organelles in oncogenesis and tumor suppression. Here, we review the sensory properties of primary cilia, assess the "history" of the primary cilium in cancer, and draw upon recent findings in a discussion of how the primary cilium may influence tissue architecture and neoplasia.
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Affiliation(s)
- E Scott Seeley
- Department of Pathology, Stanford University, Stanford, California 94305, USA
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255
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Duldulao NA, Lee S, Sun Z. Cilia localization is essential for in vivo functions of the Joubert syndrome protein Arl13b/Scorpion. Development 2009; 136:4033-42. [PMID: 19906870 DOI: 10.1242/dev.036350] [Citation(s) in RCA: 109] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
arl13b was initially cloned as the novel cystic kidney gene scorpion (sco) in zebrafish and was shown to be required for cilia formation in the kidney duct. In mouse, a null mutant of Arl13b shows abnormal ultrastructure of the cilium and defective sonic hedgehog (Shh) signaling. Importantly, a recent study linked mutations in ARL13B to a classical form of Joubert syndrome (JS), an autosomal recessive disorder characterized by a distinctive cerebellar malformation. In this study, we analyzed the zebrafish arl13b (sco) mutant and gene products in detail. We first demonstrate that Arl13b is a protein that is highly enriched in the cilium and is required for cilia formation in multiple organs in zebrafish, and that knockdown of arl13b leads to multiple cilia-associated phenotypes. We additionally show that multiple regions of Arl13b are required for its localization to the cilium. By means of rescuing experiments with a series of deletion and point mutants, we further demonstrate that the ciliary localization is crucial for the in vivo function of Arl13b. Together, these results strongly support the hypothesis that JS-related disease (JSRD) is a ciliopathy, or a disease caused by ciliary defects, and that Arl13b functions mainly through the cilium.
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Affiliation(s)
- Neil A Duldulao
- Department of Genetics, Yale University School of Medicine, 333 Cedar Street, NSB-393, New Haven, CT 06520, USA
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256
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Gli2 trafficking links Hedgehog-dependent activation of Smoothened in the primary cilium to transcriptional activation in the nucleus. Proc Natl Acad Sci U S A 2009; 106:21666-71. [PMID: 19996169 DOI: 10.1073/pnas.0912180106] [Citation(s) in RCA: 244] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Stimulation by the extracellular Hedgehog (Hh) protein signal has been shown to alter ciliary localization of the mammalian Hh receptor components Smoothened (Smo) and Patched (Ptc), and mutations that disrupt the structure and function of the cilium also disrupt Hh-induced changes in gene expression. But how ciliary events affect gene expression in the nucleus is not known, and to address this question we have characterized the cellular trafficking of Gli2, the principal mediator of Hh-dependent transcriptional activation. From a combination of pharmacological and genetic manipulations we find in resting cells that both Gli2 and Smo appear to shuttle in and out of the cilium, with Gli2 but not Smo requiring intact cytoplasmic microtubules for ciliary entry and both requiring the ciliary retrograde motor, cytoplasmic dynein 2, for ciliary exit. We also find that changes in ciliary and nuclear trafficking of Gli2 are triggered by the Hh-dependent accumulation of activated Smo in the cilium, resulting in a shift from primarily cytoplasmic localization to accumulation at the distal tip of the cilium and within the nucleus. Gli2 thus functions as a dynamic monitor of Smo activity in the cilium and thereby links Hh pathway activation in the cilium to transcriptional activation in the nucleus.
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257
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Line up and listen: Planar cell polarity regulation in the mammalian inner ear. Semin Cell Dev Biol 2009; 20:978-85. [PMID: 19508855 DOI: 10.1016/j.semcdb.2009.02.007] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2008] [Accepted: 02/13/2009] [Indexed: 11/21/2022]
Abstract
The inner ear sensory organs possess extraordinary structural features necessary to conduct mechanosensory transduction for hearing and balance. Their structural beauty has fascinated scientists since the dawn of modern science and ensured a rigorous pursuit of the understanding of mechanotransduction. Sensory cells of the inner ear display unique structural features that underlie their mechanosensitivity and resolution, and represent perhaps the most distinctive form of a type of cellular polarity, known as planar cell polarity (PCP). Until recently, however, it was not known how the precise PCP of the inner ear sensory organs was achieved during development. Here, we review the PCP of the inner ear and recent advances in the quest for an understanding of its formation.
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258
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Shu X, Zeng Z, Gautier P, Lennon A, Gakovic M, Patton EE, Wright AF. Zebrafish Rpgr is required for normal retinal development and plays a role in dynein-based retrograde transport processes. Hum Mol Genet 2009; 19:657-70. [DOI: 10.1093/hmg/ddp533] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
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259
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Cardenas-Rodriguez M, Badano JL. Ciliary biology: Understanding the cellular and genetic basis of human ciliopathies. AMERICAN JOURNAL OF MEDICAL GENETICS PART C-SEMINARS IN MEDICAL GENETICS 2009; 151C:263-80. [PMID: 19876935 DOI: 10.1002/ajmg.c.30227] [Citation(s) in RCA: 117] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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260
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Abstract
Abnormalities in the central nervous system and renal function are seen together in a variety of congenital syndromes. This Review examines the clinical presentation and the genetic basis of several such syndromes. The X-linked oculocerebrorenal syndrome of Lowe is characterized by developmental delay, blindness, renal tubular dysfunction, and progressive renal failure. This syndrome results from mutations in the OCRL gene, which encodes a phosphatase involved in endosomal trafficking. Mutations in OCRL also occur in Dent disease, which has a milder disease phenotype than Lowe syndrome. Patients with Joubert syndrome have cerebellar ataxia, pigmentary retinopathy, and nephronophthisis. Joubert syndrome is a genetically heterogeneous condition associated with mutations in at least five genes that encode ciliary proteins. Bardet-Biedl syndrome is a clinically variable condition associated with learning disabilities, progressive visual loss, obesity, polydactyly, hypogonadism, and cystic and fibrotic renal changes that can lead to renal failure. Most of the 12 genes mutated in Bardet-Biedl syndrome are also involved in ciliary function, as are the genes implicated in other 'ciliopathies' with similar phenotypes, including Meckel syndrome.
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Affiliation(s)
- Scott J Schurman
- Department of Pediatrics, SUNY Upstate Medical University, Syracuse, NY 13210, USA
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261
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Huang P, Schier AF. Dampened Hedgehog signaling but normal Wnt signaling in zebrafish without cilia. Development 2009; 136:3089-98. [PMID: 19700616 DOI: 10.1242/dev.041343] [Citation(s) in RCA: 158] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Cilia have been implicated in Hedgehog (Hh) and Wnt signaling in mouse but not in Drosophila. To determine whether the role of cilia is conserved in zebrafish, we generated maternal-zygotic (MZ) oval (ovl; ift88) mutants that lack all cilia. MZovl mutants display normal canonical and non-canonical Wnt signaling but show defects in Hh signaling. As in mouse, zebrafish cilia are required to mediate the activities of Hh, Ptc, Smo and PKA. However, in contrast to mouse Ift88 mutants, which show a dramatic reduction in Hh signaling, zebrafish MZovl mutants display dampened, but expanded, Hh pathway activity. This activity is largely due to gli1, the expression of which is fully dependent on Hh signaling in mouse but not in zebrafish. These results reveal a conserved requirement for cilia in transducing the activity of upstream regulators of Hh signaling but distinct phenotypic effects due to differential regulation and differing roles of transcriptional mediators.
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Affiliation(s)
- Peng Huang
- Department of Molecular and Cellular Biology, Center for Brain Science, Harvard Stem Cell Institute, Broad Institute, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA.
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262
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Maisonneuve C, Guilleret I, Vick P, Weber T, Andre P, Beyer T, Blum M, Constam DB. Bicaudal C, a novel regulator of Dvl signaling abutting RNA-processing bodies, controls cilia orientation and leftward flow. Development 2009; 136:3019-30. [PMID: 19666828 DOI: 10.1242/dev.038174] [Citation(s) in RCA: 98] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Polycystic diseases and left-right (LR) axis malformations are frequently linked to cilia defects. Renal cysts also arise in mice and frogs lacking Bicaudal C (BicC), a conserved RNA-binding protein containing K-homology (KH) domains and a sterile alpha motif (SAM). However, a role for BicC in cilia function has not been demonstrated. Here, we report that targeted inactivation of BicC randomizes left-right (LR) asymmetry by disrupting the planar alignment of motile cilia required for cilia-driven fluid flow. Furthermore, depending on its SAM domain, BicC can uncouple Dvl2 signaling from the canonical Wnt pathway, which has been implicated in antagonizing planar cell polarity (PCP). The SAM domain concentrates BicC in cytoplasmic structures harboring RNA-processing bodies (P-bodies) and Dvl2. These results suggest a model whereby BicC links the orientation of cilia with PCP, possibly by regulating RNA silencing in P-bodies.
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263
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Planar cell polarity and cilia. Semin Cell Dev Biol 2009; 20:998-1005. [PMID: 19815086 DOI: 10.1016/j.semcdb.2009.09.016] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2009] [Revised: 09/24/2009] [Accepted: 09/25/2009] [Indexed: 11/22/2022]
Abstract
In the last few years, evidence has come to light suggesting that planar cell polarity signaling in vertebrates may be controlled and modulated by primary cilia, subcellular organelles that emerge from the plasma membrane of most cell types. This characteristic distinguishes vertebrate planar cell polarity signaling from that in insects. We review here some of the experimental evidence contributing to this finding. These observations have begun to suggest molecular and cellular mechanisms of the so-called ciliopathies, important human diseases characterized by defective ciliary functions.
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264
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Berbari NF, O'Connor AK, Haycraft CJ, Yoder BK. The primary cilium as a complex signaling center. Curr Biol 2009; 19:R526-35. [PMID: 19602418 DOI: 10.1016/j.cub.2009.05.025] [Citation(s) in RCA: 470] [Impact Index Per Article: 31.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Respect for the primary cilium has undergone a remarkable renaissance over the past decade, and it is now thought to be an essential regulator of numerous signaling pathways. The primary cilium's functions range from the movement of cells and fluid, to sensory inputs involved with olfaction and photoreception. Disruption of cilia function is involved in multiple human syndromes collectively called 'ciliopathies'. The cilium's activities are mediated by targeting of receptors, channels, and their downstream effector proteins to the ciliary or basal body compartment. These combined properties of the cilium make it a critical organelle facilitating the interactions between the cell and its environment. Here, we review many of the recent advances contributing to the ascendancy of the primary cilium and how the extraordinary complexity of this organelle inevitably assures many more exciting future discoveries.
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Affiliation(s)
- Nicolas F Berbari
- Department of Cell Biology, University of Alabama at Birmingham, School of Medicine, Birmingham, AL 35294, USA
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265
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Chen M, Philipp M, Wang J, Premont RT, Garrison TR, Caron MG, Lefkowitz RJ, Chen W. G Protein-coupled receptor kinases phosphorylate LRP6 in the Wnt pathway. J Biol Chem 2009; 284:35040-8. [PMID: 19801552 PMCID: PMC2787365 DOI: 10.1074/jbc.m109.047456] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Wnt ligands conduct their functions in canonical Wnt signaling by binding to two receptors, the single transmembrane low density lipoprotein receptor-related proteins 5 and 6 (LRP5/6) and seven transmembrane (7TM) Frizzled receptors. Subsequently, phosphorylation of serine/threonine residues within five repeating signature PPPSP motifs on LRP6 is responsible for LRP6 activation. GSK3β, a cytosolic kinase for phosphorylation of a downstream effector β-catenin, was proposed to participate in such LRP6 phosphorylation. Here, we report a new class of membrane-associated kinases for LRP6 phosphorylation. We found that G protein-coupled receptor kinases 5 and 6 (GRK5/6), traditionally known to phosphorylate and desensitize 7TM G protein-coupled receptors, directly phosphorylate the PPPSP motifs on single transmembrane LRP6 and regulate Wnt/LRP6 signaling. GRK5/6-induced LRP6 activation is inhibited by the LRP6 antagonist Dickkopf. Depletion of GRK5 markedly reduces Wnt3A-stimulated LRP6 phosphorylation in cells. In zebrafish, functional knock-down of GRK5 results in reduced Wnt signaling, analogous to LRP6 knock-down, as assessed by decreased abundance of β-catenin and lowered expression of the Wnt target genes cdx4, vent, and axin2. Expression of GRK5 rescues the diminished β-catenin and axin2 response caused by GRK5 depletion. Thus, our findings identify GRK5/6 as novel kinases for the single transmembrane receptor LRP6 during Wnt signaling.
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Affiliation(s)
- Minyong Chen
- Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA
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266
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Itoh K, Jenny A, Mlodzik M, Sokol SY. Centrosomal localization of Diversin and its relevance to Wnt signaling. J Cell Sci 2009; 122:3791-8. [PMID: 19789178 DOI: 10.1242/jcs.057067] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Wnt pathways regulate many developmental processes, including cell-fate specification, cell polarity, and cell movements during morphogenesis. The subcellular distribution of pathway mediators in specific cellular compartments might be crucial for the selection of pathway targets and signaling specificity. We find that the ankyrin-repeat protein Diversin, which functions in different Wnt signaling branches, localizes to the centrosome in Xenopus ectoderm and mammalian cells. Upon stimulation with Wnt ligands, the centrosomal distribution of Diversin is transformed into punctate cortical localization. Also, Diversin was recruited by Frizzled receptors to non-homogeneous Dishevelled-containing cortical patches. Importantly, Diversin deletion constructs, which did not localize to the centrosome, failed to efficiently antagonize Wnt signaling. Furthermore, a C-terminal construct that interfered with Diversin localization inhibited Diversin-mediated beta-catenin degradation. These observations suggest that the centrosomal localization of Diversin is crucial for its function in Wnt signaling.
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Affiliation(s)
- Keiji Itoh
- Department of Developmental and Regenerative Biology, Mount Sinai School of Medicine, New York, NY 10029, USA
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267
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Abstract
Over the last 5 years, disorders of nonmotile cilia have come of age and their study has contributed immeasurably to our understanding of cell biology and human genetics. This review summarizes the main features of the ciliopathies, their underlying genetics, and the functions of the proteins involved. We describe some of the key findings in the field, including new animal models, the role of ciliopathy proteins in signaling pathways and development, and the unusual genetics of these diseases. We also discuss the therapeutic potential for these diseases and finally, discuss important future work that will extend our understanding of this fascinating organelle and its associated pathologies.
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268
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Lunt SC, Haynes T, Perkins BD. Zebrafish ift57, ift88, and ift172 intraflagellar transport mutants disrupt cilia but do not affect hedgehog signaling. Dev Dyn 2009; 238:1744-59. [PMID: 19517571 DOI: 10.1002/dvdy.21999] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cilia formation requires intraflagellar transport (IFT) proteins. Recent studies indicate that mammalian Hedgehog (Hh) signaling requires cilia. It is unclear, however, if the requirement for cilia and IFT proteins in Hh signaling represents a general rule for all vertebrates. Here we examine zebrafish ift57, ift88, and ift172 mutants and morphants for defects in Hh signaling. Although ift57 and ift88 mutants and morphants contained residual maternal protein, the cilia were disrupted. In contrast to previous genetic studies in mouse, mutations in zebrafish IFT genes did not affect the expression of Hh target genes in the neural tube and forebrain and had no quantitative effect on Hh target gene expression. Zebrafish IFT mutants also exhibited no dramatic changes in the craniofacial skeleton, somite formation, or motor neuron patterning. Thus, our data indicate the requirement for cilia in the Hh signal transduction pathway may not represent a universal mechanism in vertebrates.
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Affiliation(s)
- Shannon C Lunt
- Department of Biology, Texas A&M University, College Station, Texas 77843, USA
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269
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Abstract
The association between renal dysplasia and minor malformations of the external ear is weak. However, there is a remarkable list of syndromes that link the kidney to the inner ear. To organize these seemingly disparate syndromes, we cluster representative examples into three groups: (a) syndromes that share pathways regulating development; (b) syndromes involving dysfunction of the primary cilium, which normally provides critical information to epithelial cells about the fluid in which they are bathed; (c) syndromes arising from dysfunction of specialized proteins that transport ions and drugs in and out of the extracellular fluid or provide structural support.
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Affiliation(s)
- Elena Torban
- Departments of Medicine, Faculty of Medicine, McGill University, Montreal, Quebec, Canada
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270
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Stottmann RW, Tran PV, Turbe-Doan A, Beier DR. Ttc21b is required to restrict sonic hedgehog activity in the developing mouse forebrain. Dev Biol 2009; 335:166-78. [PMID: 19732765 DOI: 10.1016/j.ydbio.2009.08.023] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2009] [Revised: 08/24/2009] [Accepted: 08/24/2009] [Indexed: 10/20/2022]
Abstract
Organizing centers in the developing brain provide an assortment of instructive patterning cues, including Sonic hedgehog (Shh). Here we characterize the forebrain phenotype caused by loss of Ttc21b, a gene we identified in an ENU mutagenesis screen as a novel ciliary gene required for retrograde intraflagellar transport. The Ttc21b mutant has defects in limb, eye and, most dramatically, brain development. We show that Shh signaling is elevated in the rostral portion of the mutant embryo, including in a domain in or near the zona limitans intrathalamica. We demonstrate here that ciliary defects seen in the Ttc21b mutant extend to the embryonic brain, adding forebrain development to the spectrum of tissues affected by defects in ciliary physiology. We show that development of the Ttc21b brain phenotype is modified by lowering levels of the Shh ligand, supporting our hypothesis that the abnormal patterning is a consequence of elevated Shh signaling. Finally, we evaluate Wnt signaling but do not find evidence that this plays a role in causing the perturbed neurodevelopmental phenotype we describe.
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Affiliation(s)
- R W Stottmann
- Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA
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271
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Ocbina PJR, Tuson M, Anderson KV. Primary cilia are not required for normal canonical Wnt signaling in the mouse embryo. PLoS One 2009; 4:e6839. [PMID: 19718259 PMCID: PMC2729396 DOI: 10.1371/journal.pone.0006839] [Citation(s) in RCA: 113] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2009] [Accepted: 07/29/2009] [Indexed: 01/08/2023] Open
Abstract
Background Sonic hedgehog (Shh) signaling in the mouse requires the microtubule-based organelle, the primary cilium. The primary cilium is assembled and maintained through the process of intraflagellar transport (IFT) and the response to Shh is blocked in mouse mutants that lack proteins required for IFT. Although the phenotypes of mouse IFT mutants do not overlap with phenotypes of known Wnt pathway mutants, recent studies report data suggesting that the primary cilium modulates responses to Wnt signals. Methodology/Principal Findings We therefore carried out a systematic analysis of canonical Wnt signaling in mutant embryos and cells that lack primary cilia because of loss of the anterograde IFT kinesin-II motor (Kif3a) or IFT complex B proteins (Ift172 or Ift88). We also analyzed mutant embryos with abnormal primary cilia due to defects in retrograde IFT (Dync2h1). The mouse IFT mutants express the canonical Wnt target Axin2 and activate a transgenic canonical Wnt reporter, BAT-gal, in the normal spatial pattern and to the same quantitative level as wild type littermates. Similarly, mouse embryonic fibroblasts (MEFs) derived from IFT mutants respond normally to added Wnt3a. The switch from canonical to non-canonical Wnt also appears normal in IFT mutant MEFs, as both wild-type and mutant cells do not activate the canonical Wnt reporter in the presence of both Wnt3a and Wnt5a. Conclusions We conclude that loss of primary cilia or defects in retrograde IFT do not affect the response of the midgestation embryo or embryo-derived fibroblasts to Wnt ligands.
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Affiliation(s)
- Polloneal Jymmiel R. Ocbina
- Developmental Biology Program, Sloan-Kettering Institute, New York, New York, United States of America
- Neuroscience Program, Weill Cornell Graduate School of Medical Sciences, Cornell University, New York, New York, United States of America
| | - Miquel Tuson
- Developmental Biology Program, Sloan-Kettering Institute, New York, New York, United States of America
| | - Kathryn V. Anderson
- Developmental Biology Program, Sloan-Kettering Institute, New York, New York, United States of America
- * E-mail:
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272
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Primary cilia can both mediate and suppress Hedgehog pathway-dependent tumorigenesis. Nat Med 2009; 15:1055-61. [PMID: 19701205 DOI: 10.1038/nm.2011] [Citation(s) in RCA: 355] [Impact Index Per Article: 23.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2009] [Accepted: 07/01/2009] [Indexed: 01/06/2023]
Abstract
Primary cilia are present on most mammalian cells and are implicated in transducing Hedgehog (Hh) signals during development; however, the prevalence of cilia on human tumors remains unclear, and the role of cilia in cancer has not been examined. Here we show that human basal cell carcinomas (BCCs) are frequently ciliated, and we test the role of cilia in BCC by conditionally deleting Kif3a (encoding kinesin family member 3A) or Ift88 (encoding intraflagellar transport protein 88), genes required for ciliogenesis, in two Hh pathway-dependent mouse tumor models. Ciliary ablation strongly inhibited BCC-like tumors induced by an activated form of Smoothened. In contrast, removal of cilia accelerated tumors induced by activated Gli2, a transcriptional effector of Hh signaling. These seemingly paradoxical effects are consistent with a dual role for cilia in mediating both the activation and the repression of the Hh signaling pathway. Our findings demonstrate that cilia function as unique signaling organelles that can either mediate or suppress tumorigenesis depending on the nature of the oncogenic initiating event.
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273
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Han YG, Kim HJ, Dlugosz AA, Ellison DW, Gilbertson RJ, Alvarez-Buylla A. Dual and opposing roles of primary cilia in medulloblastoma development. Nat Med 2009; 15:1062-5. [PMID: 19701203 PMCID: PMC2771737 DOI: 10.1038/nm.2020] [Citation(s) in RCA: 309] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2009] [Accepted: 07/28/2009] [Indexed: 01/04/2023]
Abstract
Recent work has shown that primary cilia are essential for Hh signaling during mammalian development1–9. It is also known that aberrant Hedgehog (Hh) signaling can lead to cancer10, but the role of primary cilia in oncogenesis is not known. Cerebellar granule neuron precursors (GNPs) can give rise to medulloblastomas, the most common malignant brain tumor in children11,12. The primary cilium and Hh signaling are required for GNPs proliferation8,13–16. We asked whether primary cilia in GNPs play a role in medulloblastoma growth in mice. Genetic ablation of primary cilia blocked medulloblastoma growth when this tumor was driven by a constitutively active Smoothened (Smo), an upstream activator of Hh signaling. In contrast, removal of cilia was required for medulloblastoma growth by a constitutively active Gli2, a downstream transcription factor. Thus, primary cilia are required for, or inhibit medulloblastoma formation, depending on the initiating oncogenic event. Remarkably, presence or absence of cilia were associated with specific variants of human medulloblastomas; primary cilia were found in medulloblastomas with activation in HH or WNT signaling, but not in most medulloblastomas in other distinct molecular subgroups. Primary cilia could serve as a diagnostic tool and provide new insights into the mechanism of tumorigenesis.
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Affiliation(s)
- Young-Goo Han
- Department of Neurological Surgery and The Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research University of California-San Francisco (UCSF), California, USA
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274
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Epistasis between RET and BBS mutations modulates enteric innervation and causes syndromic Hirschsprung disease. Proc Natl Acad Sci U S A 2009; 106:13921-6. [PMID: 19666486 DOI: 10.1073/pnas.0901219106] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Hirschsprung disease (HSCR) is a common, multigenic neurocristopathy characterized by incomplete innervation along a variable length of the gut. The pivotal gene in isolated HSCR cases, either sporadic or familial, is RET. HSCR also presents in various syndromes, including Shah-Waardenburg syndrome (WS), Down (DS), and Bardet-Biedl (BBS). Here, we report 3 families with BBS and HSCR with concomitant mutations in BBS genes and regulatory RET elements, whose functionality is tested in physiologically relevant assays. Our data suggest that BBS mutations can potentiate HSCR predisposing RET alleles, which by themselves are insufficient to cause disease. We also demonstrate that these genes interact genetically in vivo to modulate gut innervation, and that this interaction likely occurs through complementary, yet independent, pathways that converge on the same biological process.
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275
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Hsiao YC, Tong ZJ, Westfall JE, Ault JG, Page-McCaw PS, Ferland RJ. Ahi1, whose human ortholog is mutated in Joubert syndrome, is required for Rab8a localization, ciliogenesis and vesicle trafficking. Hum Mol Genet 2009; 18:3926-41. [PMID: 19625297 DOI: 10.1093/hmg/ddp335] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The primary non-motile cilium, a membrane-ensheathed, microtubule-bundled organelle, extends from virtually all cells and is important for development. Normal functioning of the cilium requires proper axoneme assembly, membrane biogenesis and ciliary protein localization, in tight coordination with the intraflagellar transport system and vesicular trafficking. Disruptions at any level can induce severe alterations in cell function, giving rise to a myriad of human genetic diseases known as ciliopathies. Here we show that the Abelson helper integration site 1 (Ahi1) gene, whose human ortholog is mutated in Joubert syndrome, regulates cilium formation via its interaction with Rab8a, a small GTPase critical for polarized membrane trafficking. We find that the Ahi1 protein localizes to a single centriole, the mother centriole, which becomes the basal body of the primary cilium. In order to determine whether Ahi1 functions in ciliogenesis, loss of function analysis of Ahi1 was performed in cell culture models of ciliogenesis. Knockdown of Ahi1 expression by shRNAi in cells or targeted deletion of Ahi1 (Ahi1 knockout mouse) leads to impairments in ciliogenesis. In Ahi1-knockdown cells, Rab8a is destabilized and does not properly localize to the basal body. Since Rab8a is implicated in vesicular trafficking, we next examined this process in Ahi1-knockdown cells. Defects in the trafficking of endocytic vesicles from the plasma membrane to the Golgi and back to the plasma membrane were observed in Ahi1-knockdown cells. Overall, our data indicate that the distribution and functioning of Rab8a is regulated by Ahi1, not only affecting cilium formation, but also vesicle transport.
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Affiliation(s)
- Yi-Chun Hsiao
- Department of Biology, Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, NY 12180, USA
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276
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Abstract
PURPOSE OF REVIEW Polycystic kidney disease (PKD) is the most common genetic cause of chronic renal failure. Mouse models of PKD, especially those with mutations in genes that are orthologous to human disease genes, have provided insights into the pathogenesis of cyst formation and advanced the preclinical testing of new drugs. RECENT FINDINGS PKD is a ciliopathy that arises from abnormalities in the primary cilium, a sensory organelle present on the surface of most cells. The primary cilium is required for the maintenance of planar cell polarity, which regulates tubular diameter. Acute kidney injury stimulates cell proliferation and promotes cyst formation in a mouse model of PKD. Studies of signaling pathways that are perturbed in PKD have identified new potential therapeutic targets. Drugs that have shown beneficial effects in orthologous animal models of PKD include tolvaptan, octreotide, src inhibitors, CFTR inhibitors, pioglitazone, etanercept, and triptolide. SUMMARY Abnormalities in the primary cilium perturb signaling pathways that regulate renal epithelial cell growth and differentiation and lead to the formation of kidney cysts. Acute kidney injury promotes cyst formation and may underlie the variability in disease progression that is observed in affected individuals. Several promising new therapeutic agents that have been validated in orthologous animal models have entered clinical trials in humans.
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277
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Abstract
From the onset of zebrafish development both canonical and noncanonical Wnt signaling play major roles in a diverse array of developmental processes such as patterning, gastrulation, and neuralation making both pathways unarguably prime requests for normal development to occur. In this review, we will focus on their association with cilia and, in particular, how they regulate ciliogenesis and consequently how cilia may regulate them.
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Affiliation(s)
- Chris Jopling
- The Center of Regenerative Medicine in Barcelona, Barcelona, Spain
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278
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Dale RM, Sisson BE, Topczewski J. The emerging role of Wnt/PCP signaling in organ formation. Zebrafish 2009; 6:9-14. [PMID: 19250029 DOI: 10.1089/zeb.2008.0563] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Over the last two decades zebrafish has been an excellent model organism to study vertebrate development. Mutant analysis combined with gene knockdown and other manipulations revealed an essential role of Wnt signaling, independent of beta-catenin, during development. Especially well characterized is the function of Wnt/planar cell polarity (PCP) signaling in the regulation of gastrulation movements and neurulation, described in other reviews within this special issue. Here, we set out to highlight some of the new and exciting research that is being carried out in zebrafish to elucidate the role that Wnt/PCP signaling plays in the formation of specific organs, including the lateral line, craniofacial development, and regeneration. We also summarized the emerging connection of the Wnt/PCP pathway with primary cilia function, an essential organelle in several organ activities.
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Affiliation(s)
- Rodney M Dale
- Department of Pediatrics, Northwestern University Feinberg School of Medicine, Children's Memorial Research Center, Chicago, Illinois 60614, USA
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279
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Abstract
The Wnt family of secreted ligands act through many receptors to stimulate distinct intracellular signalling pathways in embryonic development, in adults and in disease processes. Binding of Wnt to the Frizzled family of receptors and to low density lipoprotein receptor-related protein 5 (LRP5) or LRP6 co-receptors stimulates the intracellular Wnt-beta-catenin signalling pathway, which regulates beta-cateninstability and context-dependent transcription. This signalling pathway controls many processes, such as cell fate determination, cell proliferation and self-renewal of stem and progenitor cells. Intriguingly, the transmembrane receptor Tyr kinases Ror2 and Ryk, as well as Frizzledreceptors that act independently of LRP5 or LRP6, function as receptors for Wnt and activate beta-catenin-independent pathways. This leads to changes in cell movement and polarity and to the antagonism of the beta-catenin pathway.
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Affiliation(s)
- Stephane Angers
- Leslie Dan Faculty of Pharmacy and the Department of Biochemistry, University of Toronto, Ontario, M5S 3M2, Canada.
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280
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May-Simera HL, Ross A, Rix S, Forge A, Beales PL, Jagger DJ. Patterns of expression of Bardet-Biedl syndrome proteins in the mammalian cochlea suggest noncentrosomal functions. J Comp Neurol 2009; 514:174-88. [PMID: 19396898 DOI: 10.1002/cne.22001] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Bardet-Biedl syndrome is a heterogeneous disorder causing a spectrum of symptoms, including visual impairment, kidney disease, and hearing impairment. Evidence suggests that BBS gene mutations cause defective ciliogenesis and/or cilium dysfunction. Cochlear development is affected by BBS gene deletion, and adult Bbs6(-/-) and Bbs4(-/-) mice are hearing impaired. This study addresses BBS protein expression in the rodent cochlea, to gain a better understanding of its function in vivo. As predicted by in vitro studies, Bbs6 immunofluorescence was localized to the basal bodies of supporting cells and sensory hair cells prior to the onset of hearing. In adult tissue, Bbs6 expression persisted in afferent neurons, including within the dendrites that innervate hair cells, implicating Bbs6 in a sensory neuronal function. Bbs2, which interacts with Bbs6, was also localized to hair cell basal bodies and stereociliary bundles. Additionally, Bbs2 was expressed in supporting cells at their intercellular boundaries, in a spatiotemporal pattern mirroring the development of the microtubule network. Bbs4 localized to cilia and developing cytoplasmic microtubule arrays. Pcm-1, a microtubular protein that interacts with Bbs4 in vitro, showed a comparable expression. Depolymerization of microtubules in slice preparations of the living cochlea resulted in Bbs4 and Pcm-1 mislocalization. Pcm-1 was also mislocalized in Bbs4(-/-) mice. This suggests that Bbs4/Pcm-1 interactions may be important in microtubule-dependent cytoplasmic trafficking in vivo. In summary, our findings indicate that BBS proteins adopt a range of cellular distributions in vivo, not restricted to the centrosome or cilium, and so broaden the possible underlying pathomechanisms of the disease.
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Affiliation(s)
- Helen L May-Simera
- Institute of Child Health, University College London, London WC1N1EH, United Kingdom
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281
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Wnt9b signaling regulates planar cell polarity and kidney tubule morphogenesis. Nat Genet 2009; 41:793-9. [PMID: 19543268 PMCID: PMC2761080 DOI: 10.1038/ng.400] [Citation(s) in RCA: 268] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2008] [Accepted: 04/29/2009] [Indexed: 01/14/2023]
Abstract
Although many vertebrate organs, such as kidneys, lungs and liver, are composed of epithelial tubules, little is known of the mechanisms that establish the length or diameter of these tubules. In the kidney, defects in the establishment and/or maintenance of tubule diameter are associated with one of the most common inherited human disorders, polycystic kidney disease. Here, we show that attenuation of Wnt9b signaling during kidney morphogenesis affects the planar cell polarity of the epithelium and leads to tubules with significantly increased diameter. Although previous studies showed that polarized cell divisions maintain the diameter of postnatal kidney tubules, we find cell divisions are randomly oriented during embryonic development. Our data suggest that diameter is established during early morphogenetic stages by convergent extension processes and maintained by polarized cell divisions. Wnt9b, signaling through the non-canonical Rho/Jnk branch of the Wnt pathway, is necessary for both of these processes.
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282
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Lancaster MA, Gleeson JG. The primary cilium as a cellular signaling center: lessons from disease. Curr Opin Genet Dev 2009; 19:220-9. [PMID: 19477114 DOI: 10.1016/j.gde.2009.04.008] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2009] [Revised: 04/16/2009] [Accepted: 04/20/2009] [Indexed: 01/18/2023]
Abstract
Genetic diseases known as ciliopathies have recently entered the limelight, placing new importance on a previously mysterious organelle: the primary cilium. Mutations affecting the primary cilium in both humans and animal models can lead to a plethora of distinct phenotypes including retinal degeneration, kidney cysts, and brain malformations. New findings are quickly lending insight into the functions of this cellular extension that seems to be especially important in modulation of subcellular signaling cascades at various stages of development and adult homeostasis.
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Affiliation(s)
- Madeline A Lancaster
- Biomedical Sciences Program, Department of Neurosciences, University of California, San Diego, United States
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283
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Aanstad P, Santos N, Corbit KC, Scherz PJ, Trinh LA, Salvenmoser W, Huisken J, Reiter JF, Stainier DYR. The extracellular domain of Smoothened regulates ciliary localization and is required for high-level Hh signaling. Curr Biol 2009; 19:1034-9. [PMID: 19464178 DOI: 10.1016/j.cub.2009.04.053] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2008] [Revised: 04/10/2009] [Accepted: 04/14/2009] [Indexed: 01/01/2023]
Abstract
Members of the Hedgehog (Hh) family of secreted proteins function as morphogens to pattern developing tissues and control cell proliferation. The seven-transmembrane domain (7TM) protein Smoothened (Smo) is essential for the activation of all levels of Hh signaling. However, the mechanisms by which Smo differentially activates low- or high-level Hh signaling are not known. Here we show that a newly identified mutation in the extracellular domain (ECD) of zebrafish Smo attenuates Smo signaling. The Smo agonist purmorphamine induces the stabilization, ciliary translocation, and high-level signaling of wild-type Smo. In contrast, purmorphamine induces the stabilization but not the ciliary translocation or high-level signaling of the Smo ECD mutant protein. Surprisingly, a truncated form of Smo that lacks the cysteine-rich domain of the ECD localizes to the cilium but is unable to activate high-level Hh signaling. We also present evidence that cilia may be required for Hh signaling in early zebrafish embryos. These data indicate that the ECD, previously thought to be dispensable for vertebrate Smo function, both regulates Smo ciliary localization and is essential for high-level Hh signaling.
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Affiliation(s)
- Pia Aanstad
- Department of Biochemistry & Biophysics, Programs in Developmental Biology, Genetics, and Human Genetics, Cardiovascular Research Institute, Diabetes Center, University of California, San Francisco, CA 94158, USA.
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284
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D'Angelo A, Franco B. The dynamic cilium in human diseases. PATHOGENETICS 2009; 2:3. [PMID: 19439065 PMCID: PMC2694804 DOI: 10.1186/1755-8417-2-3] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/22/2008] [Accepted: 05/13/2009] [Indexed: 01/09/2023]
Abstract
Cilia are specialized organelles protruding from the cell surface of almost all mammalian cells. They consist of a basal body, composed of two centrioles, and a protruding body, named the axoneme. Although the basic structure of all cilia is the same, numerous differences emerge in different cell types, suggesting diverse functions. In recent years many studies have elucidated the function of 9+0 primary cilia. The primary cilium acts as an antenna for the cell, and several important pathways such as Hedgehog, Wnt and planar cell polarity (PCP) are transduced through it. Many studies on animal models have revealed that during embryogenesis the primary cilium has an essential role in defining the correct patterning of the body. Cilia are composed of hundreds of proteins and the impairment or dysfunction of one protein alone can cause complete loss of cilia or the formation of abnormal cilia. Mutations in ciliary proteins cause ciliopathies which can affect many organs at different levels of severity and are characterized by a wide spectrum of phenotypes. Ciliary proteins can be mutated in more than one ciliopathy, suggesting an interaction between proteins. To date, little is known about the role of primary cilia in adult life and it is tempting to speculate about their role in the maintenance of adult organs. The state of the art in primary cilia studies reveals a very intricate role. Analysis of cilia-related pathways and of the different clinical phenotypes of ciliopathies helps to shed light on the function of these sophisticated organelles. The aim of this review is to evaluate the recent advances in cilia function and the molecular mechanisms at the basis of their activity.
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Affiliation(s)
- Anna D'Angelo
- Telethon Institute of Genetics and Medicine (TIGEM), Naples, Italy.
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285
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A common allele in RPGRIP1L is a modifier of retinal degeneration in ciliopathies. Nat Genet 2009; 41:739-45. [PMID: 19430481 PMCID: PMC2783476 DOI: 10.1038/ng.366] [Citation(s) in RCA: 230] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2009] [Accepted: 02/26/2009] [Indexed: 11/08/2022]
Abstract
Despite rapid advances in the identification of genes involved in disease, the predictive power of the genotype remains limited, in part owing to poorly understood effects of second-site modifiers. Here we demonstrate that a polymorphic coding variant of RPGRIP1L (retinitis pigmentosa GTPase regulator-interacting protein-1 like), a ciliary gene mutated in Meckel-Gruber (MKS) and Joubert (JBTS) syndromes, is associated with the development of retinal degeneration in individuals with ciliopathies caused by mutations in other genes. As part of our resequencing efforts of the ciliary proteome, we identified several putative loss-of-function RPGRIP1L mutations, including one common variant, A229T. Multiple genetic lines of evidence showed this allele to be associated with photoreceptor loss in ciliopathies. Moreover, we show that RPGRIP1L interacts biochemically with RPGR, loss of which causes retinal degeneration, and that the Thr229-encoded protein significantly compromises this interaction. Our data represent an example of modification of a discrete phenotype of syndromic disease and highlight the importance of a multifaceted approach for the discovery of modifier alleles of intermediate frequency and effect.
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286
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Jenkins PM, McEwen DP, Martens JR. Olfactory cilia: linking sensory cilia function and human disease. Chem Senses 2009; 34:451-64. [PMID: 19406873 DOI: 10.1093/chemse/bjp020] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The olfactory system gives us an awareness of our immediate environment by allowing us to detect airborne stimuli. The components necessary for detection of these odorants are compartmentalized in the cilia of olfactory sensory neurons. Cilia are microtubule-based organelles, which can be found projecting from the surface of almost any mammalian cell, and are critical for proper olfactory function. Mislocalization of ciliary proteins and/or the loss of cilia cause impaired olfactory function, which is now recognized as a clinical manifestation of a broad class of human diseases, termed ciliopathies. Future work investigating the mechanisms of olfactory cilia function will provide us important new information regarding the pathogenesis of human sensory perception diseases.
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Affiliation(s)
- Paul M Jenkins
- Department of Pharmacology, University of Michigan, 1301 MSRB III, Ann Arbor, MI 48109-5632, USA
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287
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Voronina VA, Takemaru KI, Treuting P, Love D, Grubb BR, Hajjar AM, Adams A, Li FQ, Moon RT. Inactivation of Chibby affects function of motile airway cilia. ACTA ACUST UNITED AC 2009; 185:225-33. [PMID: 19364920 PMCID: PMC2700371 DOI: 10.1083/jcb.200809144] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Chibby (Cby) is a conserved component of the Wnt–β-catenin pathway. Cby physically interacts with β-catenin to repress its activation of transcription. To elucidate the function of Cby in vertebrates, we generated Cby−/− mice and found that after 2–3 d of weight loss, the majority of mice die before or around weaning. All Cby−/− mice develop rhinitis and sinusitis. When challenged with Pseudomonas aeruginosa isolates, Cby−/− mice are unable to clear the bacteria from the nasal cavity. Notably, Cby−/− mice exhibit a complete absence of mucociliary transport caused by a marked paucity of motile cilia in the nasal epithelium. Moreover, ultrastructural experiments reveal impaired basal body docking to the apical surface of multiciliated cells. In support of these phenotypes, endogenous Cby protein is localized at the base of cilia. As the phenotypes of Cby−/− mice bear striking similarities to primary ciliary dyskinesia, Cby−/− mice may prove to be a useful model for this condition.
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Affiliation(s)
- Vera A Voronina
- Department of Pharmacology, Howard Hughes Medical Institute, USA
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288
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Abstract
Cilia are complex structures that have garnered interest because of their roles in vertebrate development and their involvement in human genetic disorders. In contrast to multicellular invertebrates in which cilia are restricted to specific cell types, these organelles are found almost ubiquitously in vertebrate cells, where they serve a diverse set of signaling functions. Here, we highlight properties of vertebrate cilia, with particular emphasis on their relationship with other subcellular structures, and explore the physiological consequences of ciliary dysfunction.
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Affiliation(s)
- Jantje M Gerdes
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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289
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Veland IR, Awan A, Pedersen LB, Yoder BK, Christensen ST. Primary cilia and signaling pathways in mammalian development, health and disease. NEPHRON. PHYSIOLOGY 2009; 111:p39-53. [PMID: 19276629 PMCID: PMC2881330 DOI: 10.1159/000208212] [Citation(s) in RCA: 207] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Although first described as early as 1898 and long considered a vestigial organelle of little functional importance, the primary cilium has become one of the hottest research topics in modern cell biology and physiology. Primary cilia are nonmotile sensory organelles present in a single copy on the surface of most growth-arrested or differentiated mammalian cells, and defects in their assembly or function are tightly coupled to many developmental defects, diseases and disorders. In normal tissues, the primary cilium coordinates a series of signal transduction pathways, including Hedgehog, Wnt, PDGFRalpha and integrin signaling. In the kidney, the primary cilium may function as a mechano-, chemo- and osmosensing unit that probes the extracellular environment and transmits signals to the cell via, e.g., polycystins, which depend on ciliary localization for appropriate function. Indeed, hypomorphic mutations in the mouse ift88 (previously called Tg737) gene, which encodes a ciliogenic intraflagellar transport protein, result in malformation of primary cilia, and in the collecting ducts of kidney tubules this is accompanied by development of autosomal recessive polycystic kidney disease (PKD). While PKD was one of the first diseases to be linked to dysfunctional primary cilia, defects in this organelle have subsequently been associated with many other phenotypes, including cancer, obesity, diabetes as well as a number of developmental defects. Collectively, these disorders of the cilium are now referred to as the ciliopathies. In this review, we provide a brief overview of the structure and function of primary cilia and some of their roles in coordinating signal transduction pathways in mammalian development, health and disease.
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Affiliation(s)
- Iben R Veland
- Department of Biology, Section of Cell and Developmental Biology, University of Copenhagen, Copenhagen, Denmark
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290
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Affiliation(s)
- Masazumi Tada
- Department of Cell and Developmental Biology, University College London, London, United Kingdom
| | - Masatake Kai
- Department of Cell and Developmental Biology, University College London, London, United Kingdom
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291
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Zaghloul NA, Katsanis N. Mechanistic insights into Bardet-Biedl syndrome, a model ciliopathy. J Clin Invest 2009; 119:428-37. [PMID: 19252258 PMCID: PMC2648685 DOI: 10.1172/jci37041] [Citation(s) in RCA: 265] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Bardet-Biedl syndrome (BBS) is a multisystemic disorder typified by developmental and progressive degenerative defects. A combination of genetic, in vitro, and in vivo studies have highlighted ciliary dysfunction as a primary cause of BBS pathology, which has in turn contributed to the improved understanding of the functions of the primary cilium in humans and other vertebrates. Here we discuss the evidence linking the clinical BBS phenotype to ciliary defects, highlight how the genetic and cellular characteristics of BBS overlap with and inform other ciliary disorders, and explore the possible mechanistic underpinnings of ciliary dysfunction.
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Affiliation(s)
- Norann A. Zaghloul
- McKusick-Nathans Institute of Genetic Medicine, Wilmer
Eye Institute, and Department of Molecular Biology and Genetics, Johns
Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Nicholas Katsanis
- McKusick-Nathans Institute of Genetic Medicine, Wilmer
Eye Institute, and Department of Molecular Biology and Genetics, Johns
Hopkins University School of Medicine, Baltimore, Maryland, USA
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292
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FGF signalling during embryo development regulates cilia length in diverse epithelia. Nature 2009; 458:651-4. [PMID: 19242413 PMCID: PMC2688717 DOI: 10.1038/nature07753] [Citation(s) in RCA: 199] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2008] [Accepted: 01/05/2009] [Indexed: 01/28/2023]
Abstract
Cilia are cell surface organelles found on most epithelia in vertebrates. Specialized groups of cilia have critical roles in embryonic development, including left-right axis formation. Recently, cilia have been implicated as recipients of cell-cell signalling. However, little is known about cell-cell signalling pathways that control the length of cilia. Here we provide several lines of evidence showing that fibroblast growth factor (FGF) signalling regulates cilia length and function in diverse epithelia during zebrafish and Xenopus development. Morpholino knockdown of FGF receptor 1 (Fgfr1) in zebrafish cell-autonomously reduces cilia length in Kupffer's vesicle and perturbs directional fluid flow required for left-right patterning of the embryo. Expression of a dominant-negative FGF receptor (DN-Fgfr1), treatment with SU5402 (a pharmacological inhibitor of FGF signalling) or genetic and morpholino reduction of redundant FGF ligands Fgf8 and Fgf24 reproduces this cilia length phenotype. Knockdown of Fgfr1 also results in shorter tethering cilia in the otic vesicle and shorter motile cilia in the pronephric ducts. In Xenopus, expression of a dn-fgfr1 results in shorter monocilia in the gastrocoel roof plate that control left-right patterning and in shorter multicilia in external mucociliary epithelium. Together, these results indicate a fundamental and highly conserved role for FGF signalling in the regulation of cilia length in multiple tissues. Abrogation of Fgfr1 signalling downregulates expression of two ciliogenic transcription factors, foxj1 and rfx2, and of the intraflagellar transport gene ift88 (also known as polaris), indicating that FGF signalling mediates cilia length through an Fgf8/Fgf24-Fgfr1-intraflagellar transport pathway. We propose that a subset of developmental defects and diseases ascribed to FGF signalling are due in part to loss of cilia function.
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293
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Bialas NJ, Inglis PN, Li C, Robinson JF, Parker JDK, Healey MP, Davis EE, Inglis CD, Toivonen T, Cottell DC, Blacque OE, Quarmby LM, Katsanis N, Leroux MR. Functional interactions between the ciliopathy-associated Meckel syndrome 1 (MKS1) protein and two novel MKS1-related (MKSR) proteins. J Cell Sci 2009; 122:611-24. [PMID: 19208769 DOI: 10.1242/jcs.028621] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Meckel syndrome (MKS) is a ciliopathy characterized by encephalocele, cystic renal disease, liver fibrosis and polydactyly. An identifying feature of MKS1, one of six MKS-associated proteins, is the presence of a B9 domain of unknown function. Using phylogenetic analyses, we show that this domain occurs exclusively within a family of three proteins distributed widely in ciliated organisms. Consistent with a ciliary role, all Caenorhabditis elegans B9-domain-containing proteins, MKS-1 and MKS-1-related proteins 1 and 2 (MKSR-1, MKSR-2), localize to transition zones/basal bodies of sensory cilia. Their subcellular localization is largely co-dependent, pointing to a functional relationship between the proteins. This localization is evolutionarily conserved, because the human orthologues also localize to basal bodies, as well as cilia. As reported for MKS1, disrupting human MKSR1 or MKSR2 causes ciliogenesis defects. By contrast, single, double and triple C. elegans mks/mksr mutants do not display overt defects in ciliary structure, intraflagellar transport or chemosensation. However, we find genetic interactions between all double mks/mksr mutant combinations, manifesting as an increased lifespan phenotype, which is due to abnormal insulin-IGF-I signaling. Our findings therefore demonstrate functional interactions between a novel family of proteins associated with basal bodies or cilia, providing new insights into the molecular etiology of a pleiotropic human disorder.
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Affiliation(s)
- Nathan J Bialas
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, BC V5A 1S6, Canada
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294
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Abstract
Most, if not all, cell types and tissues display several aspects of polarization. In addition to the ubiquitous epithelial cell polarity along the apical-basolateral axis, many epithelial tissues and organs are also polarized within the plane of the epithelium. This is generally referred to as planar cell polarity (PCP; or historically, tissue polarity). Genetic screens in Drosophila pioneered the discovery of core PCP factors, and subsequent work in vertebrates has established that the respective pathways are evolutionarily conserved. PCP is not restricted only to epithelial tissues but is also found in mesenchymal cells, where it can regulate cell migration and cell intercalation. Moreover, particularly in vertebrates, the conserved core PCP signaling factors have recently been found to be associated with the orientation or formation of cilia. This review discusses new developments in the molecular understanding of PCP establishment in Drosophila and vertebrates; these developments are integrated with new evidence that links PCP signaling to human disease.
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Affiliation(s)
- Matias Simons
- Mount Sinai School of Medicine, Department of Developmental & Regenerative Biology, New York, NY 10029, USA
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295
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Abstract
Primary cilia are important sites of signal transduction involved in a wide range of developmental and postnatal functions. Proteolytic processing of the transcription factor Gli3, for example, occurs in primary cilia, and defects in intraflagellar transport (IFT), which is crucial for the maintenance of primary cilia, can lead to severe developmental defects and diseases. Here we report an essential role of primary cilia in forebrain development. Uncovered by N-ethyl-N-nitrosourea-mutagenesis, cobblestone is a hypomorphic allele of the IFT gene Ift88, in which Ift88 mRNA and protein levels are reduced by 70-80%. cobblestone mutants are distinguished by subpial heterotopias in the forebrain. Mutants show both severe defects in the formation of dorsomedial telencephalic structures, such as the choroid plexus, cortical hem and hippocampus, and also a relaxation of both dorsal-ventral and rostral-caudal compartmental boundaries. These defects phenocopy many of the abnormalities seen in the Gli3 mutant forebrain, and we show that Gli3 proteolytic processing is reduced, leading to an accumulation of the full-length activator isoform. In addition, we observe an upregulation of canonical Wnt signaling in the neocortex and in the caudal forebrain. Interestingly, the ultrastructure and morphology of ventricular cilia in the cobblestone mutants remains intact. Together, these results indicate a critical role for ciliary function in the developing forebrain.
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296
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Romaker D, Puetz M, Teschner S, Donauer J, Geyer M, Gerke P, Rumberger B, Dworniczak B, Pennekamp P, Buchholz B, Neumann HPH, Kumar R, Gloy J, Eckardt KU, Walz G. Increased expression of secreted frizzled-related protein 4 in polycystic kidneys. J Am Soc Nephrol 2009; 20:48-56. [PMID: 18945944 PMCID: PMC2615724 DOI: 10.1681/asn.2008040345] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2008] [Accepted: 07/24/2008] [Indexed: 11/03/2022] Open
Abstract
Autosomal dominant polycystic kidney disease (ADPKD) is a common hereditary disease associated with progressive renal failure. Although cyst growth and compression of surrounding tissue may account for some loss of renal tissue, the other factors contributing to the progressive renal failure in patients with ADPKD are incompletely understood. Here, we report that secreted frizzled-related protein 4 (sFRP4) is upregulated in human ADPKD and in four different animal models of PKD, suggesting that sFRP4 expression is triggered by a common mechanism that underlies cyst formation. Cyst fluid from ADPKD kidneys activated the sFRP4 promoter and induced production of sFRP4 protein in renal tubular epithelial cell lines. Antagonism of the vasopressin 2 receptor blocked both promoter activity and tubular sFRP4 expression. In addition, sFRP4 selectively influenced members of the canonical Wnt signaling cascade and promoted cystogenesis of the zebrafish pronephros. sFRP4 was detected in the urine of both patients and animals with PKD, suggesting that sFRP4 may be a potential biomarker for monitoring the progression of ADPKD. Taken together, these observations suggest a potential role for SFRP4 in the pathogenesis of ADPKD.
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Affiliation(s)
- Daniel Romaker
- Renal Division, University Hospital Freiburg, Hugstetter Strasse 55, D-79106 Freiburg, Germany
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297
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DiBella LM, Park A, Sun Z. Zebrafish Tsc1 reveals functional interactions between the cilium and the TOR pathway. Hum Mol Genet 2008; 18:595-606. [PMID: 19008302 DOI: 10.1093/hmg/ddn384] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The cell surface organelle called the cilium is essential for preventing kidney cyst formation and for establishing left-right asymmetry of the vertebrate body plan. Recent advances suggest that the cilium functions as a sensory organelle in vertebrate cells for multiple signaling pathways such as the hedgehog and the Wnt pathways. Prompted by kidney cyst formation in tuberous sclerosis complex (TSC) patients and rodent models, we investigated the role of the cilium in the TSC-target of rapamycin (TOR) pathway using zebrafish. TSC1 and TSC2 genes are causal for TSC, and their protein products form a complex in the TOR pathway that integrates environmental signals to regulate cell growth, proliferation and survival. Two TSC1 homologs were identified in zebrafish, which we refer to as tsc1a and tsc1b. Morpholino knockdown of tsc1a led to a ciliary phenotype including kidney cyst formation and left-right asymmetry defects. Tsc1a was observed to localize to the Golgi, but morpholinos against it, nonetheless, acted synthetically with ciliary genes in producing kidney cysts. Consistent with a role of the cilium in the same pathway as Tsc genes, the TOR pathway is aberrantly activated in ciliary mutants, resembling the effect of tsc1a knockdown. Moreover, kidney cyst formation in ciliary mutants was blocked by the Tor inhibitor, rapamycin. Surprisingly, we observed elongation of cilia in tsc1a knockdown animals. Together, these data suggest a signaling network between the cilium and the TOR pathway in that ciliary signals can feed into the TOR pathway and that Tsc1a regulates the length of the cilium itself.
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Affiliation(s)
- Linda M DiBella
- Department of Genetics, Yale University School of Medicine, New Haven, CT 06520, USA
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298
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Lehman JM, Laag E, Michaud EJ, Yoder BK. An essential role for dermal primary cilia in hair follicle morphogenesis. J Invest Dermatol 2008; 129:438-48. [PMID: 18987668 DOI: 10.1038/jid.2008.279] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The primary cilium is a microtubule-based organelle implicated as an essential component of a number of signaling pathways. It is present on cells throughout the mammalian body; however, its functions in most tissues remain largely unknown. Herein we demonstrate that primary cilia are present on cells in murine skin and hair follicles throughout morphogenesis and during hair follicle cycling in postnatal life. Using the Cre-lox system, we disrupted cilia assembly in the ventral dermis and evaluated the effects on hair follicle development. Mice with disrupted dermal cilia have severe hypotrichosis (lack of hair) in affected areas. Histological analyses reveal that most follicles in the mutants arrest at stage 2 of hair development and have small or absent dermal condensates. This phenotype is reminiscent of that seen in the skin of mice lacking Shh or Gli2. In situ hybridization and quantitative RT-PCR analysis indicates that the hedgehog pathway is downregulated in the dermis of the cilia mutant hair follicles. Thus, these data establish cilia as a critical signaling component required for normal hair morphogenesis and suggest that this organelle is needed on cells in the dermis for reception of signals such as sonic hedgehog.
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Affiliation(s)
- Jonathan M Lehman
- Department of Cell Biology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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299
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Farkas LM, Huttner WB. The cell biology of neural stem and progenitor cells and its significance for their proliferation versus differentiation during mammalian brain development. Curr Opin Cell Biol 2008; 20:707-15. [PMID: 18930817 DOI: 10.1016/j.ceb.2008.09.008] [Citation(s) in RCA: 173] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2008] [Accepted: 09/23/2008] [Indexed: 12/24/2022]
Abstract
The switch of neural stem and progenitor cells from proliferation to differentiation during development is a crucial determinant of brain size. This switch is intimately linked to the architecture of the two principal classes of neural stem and progenitor cells, the apical (neuroepithelial, radial glial) and basal (intermediate) progenitors, which in turn is crucial for their symmetric versus asymmetric divisions. Focusing on the developing rodent neocortex, we discuss here recent advances in understanding the cell biology of apical and basal progenitors, place key regulatory molecules into subcellular context, and highlight their roles in the control of proliferation versus differentiation.
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Affiliation(s)
- Lilla M Farkas
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstr. 108, D-01307 Dresden, Germany
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300
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Ferrante MI, Romio L, Castro S, Collins JE, Goulding DA, Stemple DL, Woolf AS, Wilson SW. Convergent extension movements and ciliary function are mediated by ofd1, a zebrafish orthologue of the human oral-facial-digital type 1 syndrome gene. Hum Mol Genet 2008; 18:289-303. [PMID: 18971206 PMCID: PMC2638777 DOI: 10.1093/hmg/ddn356] [Citation(s) in RCA: 106] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In humans, OFD1 is mutated in oral-facial-digital type I syndrome leading to prenatal death in hemizygous males and dysmorphic faces and brain malformations, with polycystic kidneys presenting later in life in heterozygous females. To elucidate the function of Ofd1, we have studied its function during zebrafish embryonic development. In wild-type embryos, ofd1 mRNA is widely expressed and Ofd1-green fluorescent protein (GFP) fusion localizes to the centrosome/basal body. Disrupting Ofd1 using antisense morpholinos (MOs) led to bent body axes, hydrocephalus and oedema. Laterality was randomized in the brain, heart and viscera, likely a consequence of shorter cilia with disrupted axonemes and perturbed intravesicular fluid flow in Kupffer's vesicle. Embryos injected with ofd1 MOs also displayed convergent extension (CE) defects, which were enhanced by loss of Slb/Wnt11 or Tri/Vangl2, two proteins functioning in a non-canonical Wnt/Planar Cell Polarity (PCP) pathway. Pronephric glomerular midline fusion was compromised in vangl2 and ofd1 loss of function embryos and we suggest this anomaly may be a novel CE defect. Thus, Ofd1 is required for ciliary motility and function in zebrafish, supporting data showing that Ofd1 is essential for primary cilia function in mice. In addition, our data show that Ofd1 is important for CE during gastrulation, consistent with data linking primary cilia and non-canonical Wnt/PCP signalling.
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Affiliation(s)
- Maria I Ferrante
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Cambridge CB10 1SA, UK
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