Key publications
Barker AR, McIntosh KV, Dawe HR (2016). Centrosome positioning in non-dividing cells.
Protoplasma,
253(4), 1007-1021.
Abstract:
Centrosome positioning in non-dividing cells.
Centrioles and centrosomes are found in almost all eukaryotic cells, where they are important for organising the microtubule cytoskeleton in both dividing and non-dividing cells. The spatial location of centrioles and centrosomes is tightly controlled and, in non-dividing cells, plays an important part in cell migration, ciliogenesis and immune cell functions. Here, we examine some of the ways that centrosomes are connected to other organelles and how this impacts on cilium formation, cell migration and immune cell function in metazoan cells.
Abstract.
Author URL.
Pratt MB, Titlow JS, Davis I, Barker AR, Dawe HR, Raff JW, Roque H (2016). Drosophila sensory cilia lacking MKS proteins exhibit striking defects in development but only subtle defects in adults.
J Cell Sci,
129(20), 3732-3743.
Abstract:
Drosophila sensory cilia lacking MKS proteins exhibit striking defects in development but only subtle defects in adults.
Cilia are conserved organelles that have important motility, sensory and signalling roles. The transition zone (TZ) at the base of the cilium is crucial for cilia function, and defects in several TZ proteins are associated with human congenital ciliopathies such as nephronophthisis (NPHP) and Meckel-Gruber syndrome (MKS). In several species, MKS and NPHP proteins form separate complexes that cooperate with Cep290 to assemble the TZ, but flies seem to lack core components of the NPHP module. We show that MKS proteins in flies are spatially separated from Cep290 at the TZ, and that flies mutant for individual MKS genes fail to recruit other MKS proteins to the TZ, whereas Cep290 seems to be recruited normally. Although there are abnormalities in microtubule and membrane organisation in developing MKS mutant cilia, these defects are less apparent in adults, where sensory cilia and sperm flagella seem to function quite normally. Thus, localising MKS proteins to the cilium or flagellum is not essential for viability or fertility in flies.
Abstract.
Author URL.
Martin-Urdiroz M, Deeks MJ, Horton CG, Dawe HR, Jourdain I (2016). The Exocyst Complex in Health and Disease. Frontiers in Cell and Developmental Biology, 4
Barker AR, Renzaglia KS, Fry K, Dawe HR (2014). Bioinformatic analysis of ciliary transition zone proteins reveals insights into the evolution of ciliopathy networks.
BMC Genomics,
15Abstract:
Bioinformatic analysis of ciliary transition zone proteins reveals insights into the evolution of ciliopathy networks.
BACKGROUND: Cilia are critical for diverse functions, from motility to signal transduction, and ciliary dysfunction causes inherited diseases termed ciliopathies. Several ciliopathy proteins influence developmental signalling and aberrant signalling explains many ciliopathy phenotypes. Ciliary compartmentalisation is essential for function, and the transition zone (TZ), found at the proximal end of the cilium, has recently emerged as a key player in regulating this process. Ciliary compartmentalisation is linked to two protein complexes, the MKS and NPHP complexes, at the TZ that consist largely of ciliopathy proteins, leading to the hypothesis that ciliopathy proteins affect signalling by regulating ciliary content. However, there is no consensus on complex composition, formation, or the contribution of each component. RESULTS: Using bioinformatics, we examined the evolutionary patterns of TZ complex proteins across the extant eukaryotic supergroups, in both ciliated and non-ciliated organisms. We show that TZ complex proteins are restricted to the proteomes of ciliated organisms and identify a core conserved group (TMEM67, CC2D2A, B9D1, B9D2, AHI1 and a single TCTN, plus perhaps MKS1) which are present in >50% of all ciliate/flagellate organisms analysed in each supergroup. The smaller NPHP complex apparently evolved later than the larger MKS complex; this result may explain why RPGRIP1L, which forms the linker between the two complexes, is not one of the core conserved proteins. We also uncovered a striking correlation between lack of TZ proteins in non-seed land plants and loss of TZ-specific ciliary Y-links that link microtubule doublets to the membrane, consistent with the interpretation that these proteins are structural components of Y-links, or regulators of their formation. CONCLUSIONS: This bioinformatic analysis represents the first systematic analysis of the cohort of TZ complex proteins across eukaryotic evolution. Given the near-ubiquity of only 6 proteins across ciliated eukaryotes, we propose that the MKS complex represents a dynamic complex built around these 6 proteins and implicated in Y-link formation and ciliary permeability.
Abstract.
Author URL.
Barker AR, Thomas R, Dawe HR (2014). Meckel-Gruber syndrome and the role of primary cilia in kidney, skeleton, and central nervous system development.
Organogenesis,
10(1), 96-107.
Abstract:
Meckel-Gruber syndrome and the role of primary cilia in kidney, skeleton, and central nervous system development.
The ciliopathies are a group of related inherited diseases characterized by malformations in organ development. The diseases affect multiple organ systems, with kidney, skeleton, and brain malformations frequently observed. Research over the last decade has revealed that these diseases are due to defects in primary cilia, essential sensory organelles found on most cells in the human body. Here we discuss the genetic and cell biological basis of one of the most severe ciliopathies, Meckel-Gruber syndrome, and explain how primary cilia contribute to the development of the affected organ systems.
Abstract.
Author URL.
Adams M, Simms RJ, Abdelhamed Z, Dawe HR, Szymanska K, Logan CV, Wheway G, Pitt E, Gull K, Knowles MA, et al (2012). A meckelin-filamin a interaction mediates ciliogenesis.
Human Molecular Genetics,
21(6), 1272-1286.
Abstract:
A meckelin-filamin a interaction mediates ciliogenesis
MKS3, encoding the transmembrane receptor meckelin, is mutated in Meckel-Gruber syndrome (MKS), an autosomal-recessive ciliopathy. Meckelin localizes to the primary cilium, basal body and elsewhere within the cell. Here, we found that the cytoplasmic domain of meckelin directly interacts with the actin-binding protein filamin A, potentially at the apical cell surface associated with the basal body. Mutations in FLNA, the gene for filamin A, cause periventricular heterotopias. We identified a single consanguineous patient with an MKS-like ciliopathy that presented with both MKS and cerebellar heterotopia, caused by an unusual in-frame deletion mutation in the meckelin C-terminus at the region of interaction with filamin A. We modelled this mutation and found it to abrogate the meckelin-filamin a interaction. Furthermore, we found that loss of filamin a by siRNA knockdown, in patient cells, and in tissues from Flna Dilp2 null mouse embryos results in cellular phenotypes identical to those caused by meckelin loss, namely basal body positioning and ciliogenesis defects. In addition, morpholino knockdown of flna in zebrafish embryos significantly increases the frequency of dysmorphology and severity of ciliopathy developmental defects caused by mks3 knockdown. Our results suggest that meckelin forms a functional complex with filamin a that is disrupted in MKS and causes defects in neuronal migration and Wnt signalling. Furthermore, filamin a has a crucial role in the normal processes of ciliogenesis and basal body positioning. Concurrent with these processes, the meckelin-filamin a signalling axis may be a key regulator in maintaining correct, normal levels of Wnt signalling. © the Author 2011. Published by Oxford University Press. All rights reserved.
Abstract.
Publications by year
2016
Barker AR, McIntosh KV, Dawe HR (2016). Centrosome positioning in non-dividing cells.
Protoplasma,
253(4), 1007-1021.
Abstract:
Centrosome positioning in non-dividing cells.
Centrioles and centrosomes are found in almost all eukaryotic cells, where they are important for organising the microtubule cytoskeleton in both dividing and non-dividing cells. The spatial location of centrioles and centrosomes is tightly controlled and, in non-dividing cells, plays an important part in cell migration, ciliogenesis and immune cell functions. Here, we examine some of the ways that centrosomes are connected to other organelles and how this impacts on cilium formation, cell migration and immune cell function in metazoan cells.
Abstract.
Author URL.
Pratt MB, Titlow JS, Davis I, Barker AR, Dawe HR, Raff JW, Roque H (2016). Drosophila sensory cilia lacking MKS proteins exhibit striking defects in development but only subtle defects in adults.
J Cell Sci,
129(20), 3732-3743.
Abstract:
Drosophila sensory cilia lacking MKS proteins exhibit striking defects in development but only subtle defects in adults.
Cilia are conserved organelles that have important motility, sensory and signalling roles. The transition zone (TZ) at the base of the cilium is crucial for cilia function, and defects in several TZ proteins are associated with human congenital ciliopathies such as nephronophthisis (NPHP) and Meckel-Gruber syndrome (MKS). In several species, MKS and NPHP proteins form separate complexes that cooperate with Cep290 to assemble the TZ, but flies seem to lack core components of the NPHP module. We show that MKS proteins in flies are spatially separated from Cep290 at the TZ, and that flies mutant for individual MKS genes fail to recruit other MKS proteins to the TZ, whereas Cep290 seems to be recruited normally. Although there are abnormalities in microtubule and membrane organisation in developing MKS mutant cilia, these defects are less apparent in adults, where sensory cilia and sperm flagella seem to function quite normally. Thus, localising MKS proteins to the cilium or flagellum is not essential for viability or fertility in flies.
Abstract.
Author URL.
Martin-Urdiroz M, Deeks MJ, Horton CG, Dawe HR, Jourdain I (2016). The Exocyst Complex in Health and Disease. Frontiers in Cell and Developmental Biology, 4
2014
Barker AR, Renzaglia KS, Fry K, Dawe HR (2014). Bioinformatic analysis of ciliary transition zone proteins reveals insights into the evolution of ciliopathy networks.
BMC Genomics,
15Abstract:
Bioinformatic analysis of ciliary transition zone proteins reveals insights into the evolution of ciliopathy networks.
BACKGROUND: Cilia are critical for diverse functions, from motility to signal transduction, and ciliary dysfunction causes inherited diseases termed ciliopathies. Several ciliopathy proteins influence developmental signalling and aberrant signalling explains many ciliopathy phenotypes. Ciliary compartmentalisation is essential for function, and the transition zone (TZ), found at the proximal end of the cilium, has recently emerged as a key player in regulating this process. Ciliary compartmentalisation is linked to two protein complexes, the MKS and NPHP complexes, at the TZ that consist largely of ciliopathy proteins, leading to the hypothesis that ciliopathy proteins affect signalling by regulating ciliary content. However, there is no consensus on complex composition, formation, or the contribution of each component. RESULTS: Using bioinformatics, we examined the evolutionary patterns of TZ complex proteins across the extant eukaryotic supergroups, in both ciliated and non-ciliated organisms. We show that TZ complex proteins are restricted to the proteomes of ciliated organisms and identify a core conserved group (TMEM67, CC2D2A, B9D1, B9D2, AHI1 and a single TCTN, plus perhaps MKS1) which are present in >50% of all ciliate/flagellate organisms analysed in each supergroup. The smaller NPHP complex apparently evolved later than the larger MKS complex; this result may explain why RPGRIP1L, which forms the linker between the two complexes, is not one of the core conserved proteins. We also uncovered a striking correlation between lack of TZ proteins in non-seed land plants and loss of TZ-specific ciliary Y-links that link microtubule doublets to the membrane, consistent with the interpretation that these proteins are structural components of Y-links, or regulators of their formation. CONCLUSIONS: This bioinformatic analysis represents the first systematic analysis of the cohort of TZ complex proteins across eukaryotic evolution. Given the near-ubiquity of only 6 proteins across ciliated eukaryotes, we propose that the MKS complex represents a dynamic complex built around these 6 proteins and implicated in Y-link formation and ciliary permeability.
Abstract.
Author URL.
Locke JM, Da Silva Xavier G, Dawe HR, Rutter GA, Harries LW (2014). Increased expression of miR-187 in human islets from individuals with type 2 diabetes is associated with reduced glucose-stimulated insulin secretion.
Diabetologia,
57(1), 122-128.
Abstract:
Increased expression of miR-187 in human islets from individuals with type 2 diabetes is associated with reduced glucose-stimulated insulin secretion
Aims/hypothesis: Type 2 diabetes is characterised by progressive beta cell dysfunction, with changes in gene expression playing a crucial role in its development. MicroRNAs (miRNAs) are post-transcriptional regulators of gene expression and therefore alterations in miRNA levels may be involved in the deterioration of beta cell function. Methods: Global TaqMan arrays and individual TaqMan assays were used to measure islet miRNA expression in discovery (n = 20) and replication (n = 20) cohorts from individuals with and without type 2 diabetes. The role of specific dysregulated miRNAs in regulating insulin secretion, content and apoptosis was subsequently investigated in primary rat islets and INS-1 cells. Identification of miRNA targets was assessed using luciferase assays and by measuring mRNA levels. Results: in the discovery and replication cohorts miR-187 expression was found to be significantly increased in islets from individuals with type 2 diabetes compared with matched controls. An inverse correlation between miR-187 levels and glucose-stimulated insulin secretion (GSIS) was observed in islets from normoglycaemic donors. This correlation paralleled findings in primary rat islets and INS-1 cells where overexpression of miR-187 markedly decreased GSIS without affecting insulin content or apoptotic index. Finally, the gene encoding homeodomain-interacting protein kinase-3 (HIPK3), a known regulator of insulin secretion, was identified as a direct target of miR-187 and displayed reduced expression in islets from individuals with type 2 diabetes. Conclusions/interpretation: Our findings suggest a role for miR-187 in the blunting of insulin secretion, potentially involving regulation of HIPK3, which occurs during the pathogenesis of type 2 diabetes. © 2013 the Author(s).
Abstract.
Barker AR, Thomas R, Dawe HR (2014). Meckel-Gruber syndrome and the role of primary cilia in kidney, skeleton, and central nervous system development.
Organogenesis,
10(1), 96-107.
Abstract:
Meckel-Gruber syndrome and the role of primary cilia in kidney, skeleton, and central nervous system development.
The ciliopathies are a group of related inherited diseases characterized by malformations in organ development. The diseases affect multiple organ systems, with kidney, skeleton, and brain malformations frequently observed. Research over the last decade has revealed that these diseases are due to defects in primary cilia, essential sensory organelles found on most cells in the human body. Here we discuss the genetic and cell biological basis of one of the most severe ciliopathies, Meckel-Gruber syndrome, and explain how primary cilia contribute to the development of the affected organ systems.
Abstract.
Author URL.
2013
Barker AR, McIntosh K, Dawe HR (2013). Meckel-Gruber syndrome proteins are required for actin cytoskeleton organisation and directional cell migration.
MOLECULAR BIOLOGY OF THE CELL,
24 Author URL.
2012
Adams M, Simms RJ, Abdelhamed Z, Dawe HR, Szymanska K, Logan CV, Wheway G, Pitt E, Gull K, Knowles MA, et al (2012). A meckelin-filamin a interaction mediates ciliogenesis.
Hum Mol Genet,
21(6), 1272-1286.
Abstract:
A meckelin-filamin a interaction mediates ciliogenesis.
MKS3, encoding the transmembrane receptor meckelin, is mutated in Meckel-Gruber syndrome (MKS), an autosomal-recessive ciliopathy. Meckelin localizes to the primary cilium, basal body and elsewhere within the cell. Here, we found that the cytoplasmic domain of meckelin directly interacts with the actin-binding protein filamin A, potentially at the apical cell surface associated with the basal body. Mutations in FLNA, the gene for filamin A, cause periventricular heterotopias. We identified a single consanguineous patient with an MKS-like ciliopathy that presented with both MKS and cerebellar heterotopia, caused by an unusual in-frame deletion mutation in the meckelin C-terminus at the region of interaction with filamin A. We modelled this mutation and found it to abrogate the meckelin-filamin a interaction. Furthermore, we found that loss of filamin a by siRNA knockdown, in patient cells, and in tissues from Flna(Dilp2) null mouse embryos results in cellular phenotypes identical to those caused by meckelin loss, namely basal body positioning and ciliogenesis defects. In addition, morpholino knockdown of flna in zebrafish embryos significantly increases the frequency of dysmorphology and severity of ciliopathy developmental defects caused by mks3 knockdown. Our results suggest that meckelin forms a functional complex with filamin a that is disrupted in MKS and causes defects in neuronal migration and Wnt signalling. Furthermore, filamin a has a crucial role in the normal processes of ciliogenesis and basal body positioning. Concurrent with these processes, the meckelin-filamin a signalling axis may be a key regulator in maintaining correct, normal levels of Wnt signalling.
Abstract.
Author URL.
Adams M, Simms RJ, Abdelhamed Z, Dawe HR, Szymanska K, Logan CV, Wheway G, Pitt E, Gull K, Knowles MA, et al (2012). A meckelin-filamin a interaction mediates ciliogenesis.
Human Molecular Genetics,
21(6), 1272-1286.
Abstract:
A meckelin-filamin a interaction mediates ciliogenesis
MKS3, encoding the transmembrane receptor meckelin, is mutated in Meckel-Gruber syndrome (MKS), an autosomal-recessive ciliopathy. Meckelin localizes to the primary cilium, basal body and elsewhere within the cell. Here, we found that the cytoplasmic domain of meckelin directly interacts with the actin-binding protein filamin A, potentially at the apical cell surface associated with the basal body. Mutations in FLNA, the gene for filamin A, cause periventricular heterotopias. We identified a single consanguineous patient with an MKS-like ciliopathy that presented with both MKS and cerebellar heterotopia, caused by an unusual in-frame deletion mutation in the meckelin C-terminus at the region of interaction with filamin A. We modelled this mutation and found it to abrogate the meckelin-filamin a interaction. Furthermore, we found that loss of filamin a by siRNA knockdown, in patient cells, and in tissues from Flna Dilp2 null mouse embryos results in cellular phenotypes identical to those caused by meckelin loss, namely basal body positioning and ciliogenesis defects. In addition, morpholino knockdown of flna in zebrafish embryos significantly increases the frequency of dysmorphology and severity of ciliopathy developmental defects caused by mks3 knockdown. Our results suggest that meckelin forms a functional complex with filamin a that is disrupted in MKS and causes defects in neuronal migration and Wnt signalling. Furthermore, filamin a has a crucial role in the normal processes of ciliogenesis and basal body positioning. Concurrent with these processes, the meckelin-filamin a signalling axis may be a key regulator in maintaining correct, normal levels of Wnt signalling. © the Author 2011. Published by Oxford University Press. All rights reserved.
Abstract.
Cheng Y-Z, Eley L, Hynes A-M, Overman LM, Simms RJ, Barker A, Dawe HR, Lindsay S, Sayer JA (2012). Investigating embryonic expression patterns and evolution of AHI1 and CEP290 genes, implicated in Joubert syndrome.
PLoS One,
7(9).
Abstract:
Investigating embryonic expression patterns and evolution of AHI1 and CEP290 genes, implicated in Joubert syndrome.
Joubert syndrome and related diseases (JSRD) are developmental cerebello-oculo-renal syndromes with phenotypes including cerebellar hypoplasia, retinal dystrophy and nephronophthisis (a cystic kidney disease). We have utilised the MRC-Wellcome Trust Human Developmental Biology Resource (HDBR), to perform in-situ hybridisation studies on embryonic tissues, revealing an early onset neuronal, retinal and renal expression pattern for AHI1. An almost identical pattern of expression is seen with CEP290 in human embryonic and fetal tissue. A novel finding is that both AHI1 and CEP290 demonstrate strong expression within the developing choroid plexus, a ciliated structure important for central nervous system development. To test if AHI1 and CEP290 may have co-evolved, we carried out a genomic survey of a large group of organisms across eukaryotic evolution. We found that, in animals, ahi1 and cep290 are almost always found together; however in other organisms either one may be found independent of the other. Finally, we tested in murine epithelial cells if Ahi1 was required for recruitment of Cep290 to the centrosome. We found no obvious differences in Cep290 localisation in the presence or absence of Ahi1, suggesting that, while Ahi1 and Cep290 may function together in the whole organism, they are not interdependent for localisation within a single cell. Taken together these data support a role for AHI1 and CEP290 in multiple organs throughout development and we suggest that this accounts for the wide phenotypic spectrum of AHI1 and CEP290 mutations in man.
Abstract.
Author URL.
Simms RJ, Hynes AM, Eley L, Inglis D, Chaudhry B, Dawe HR, Sayer JA (2012). Modelling a ciliopathy: Ahi1 knockdown in model systems reveals an essential role in brain, retinal, and renal development.
Cellular and Molecular Life Sciences,
69(6), 993-1009.
Abstract:
Modelling a ciliopathy: Ahi1 knockdown in model systems reveals an essential role in brain, retinal, and renal development
Joubert syndrome and related diseases (JSRD) are cerebello-oculo-renal syndromes with phenotypes including cerebellar hypoplasia, retinal dystrophy, and nephronophthisis (a cystic kidney disease). Mutations in AHI1 are the most common genetic cause of JSRD, with developmental hindbrain anomalies and retinal degeneration being prominent features. We demonstrate that Ahi1, a WD40 domain-containing protein, is highly conserved throughout evolution and its expression associates with ciliated organisms. In zebrafish ahi1 morphants, the phenotypic spectrum of JSRD is modeled, with embryos showing brain, eye, and ear abnormalities, together with renal cysts and cloacal dilatation. Following ahi1 knockdown in zebrafish, we demonstrate loss of cilia at Kupffer's vesicle and subsequently defects in cardiac left- right asymmetry. Finally, using siRNAin renal epithelial cells we demonstrate a role for Ahi1 in both ciliogenesis and cell- cell junction formation. These data support a role for Ahi1 in epithelial cell organization and ciliary formation and explain the ciliopathy phenotype of AHI1 mutations in man. © 2011 Springer Basel AG.
Abstract.
Simms RJ, Hynes AM, Eley L, Inglis D, Chaudhry B, Dawe HR, Sayer JA (2012). Modelling a ciliopathy: Ahi1 knockdown in model systems reveals an essential role in brain, retinal, and renal development.
Cell Mol Life Sci,
69(6), 993-1009.
Abstract:
Modelling a ciliopathy: Ahi1 knockdown in model systems reveals an essential role in brain, retinal, and renal development.
Joubert syndrome and related diseases (JSRD) are cerebello-oculo-renal syndromes with phenotypes including cerebellar hypoplasia, retinal dystrophy, and nephronophthisis (a cystic kidney disease). Mutations in AHI1 are the most common genetic cause of JSRD, with developmental hindbrain anomalies and retinal degeneration being prominent features. We demonstrate that Ahi1, a WD40 domain-containing protein, is highly conserved throughout evolution and its expression associates with ciliated organisms. In zebrafish ahi1 morphants, the phenotypic spectrum of JSRD is modeled, with embryos showing brain, eye, and ear abnormalities, together with renal cysts and cloacal dilatation. Following ahi1 knockdown in zebrafish, we demonstrate loss of cilia at Kupffer's vesicle and subsequently defects in cardiac left-right asymmetry. Finally, using siRNA in renal epithelial cells we demonstrate a role for Ahi1 in both ciliogenesis and cell-cell junction formation. These data support a role for Ahi1 in epithelial cell organization and ciliary formation and explain the ciliopathy phenotype of AHI1 mutations in man.
Abstract.
Author URL.
Thompson H, Shaw MK, Dawe HR, Shimeld SM (2012). The formation and positioning of cilia in Ciona intestinalis embryos in relation to the generation and evolution of chordate left-right asymmetry.
Dev Biol,
364(2), 214-223.
Abstract:
The formation and positioning of cilia in Ciona intestinalis embryos in relation to the generation and evolution of chordate left-right asymmetry.
In the early mouse embryo monocilia on the ventral node rotate to generate a leftward flow of fluid. This nodal flow is essential for the left-sided expression of nodal and pitx2, and for subsequent asymmetric organ patterning. Equivalent left fluid flow has been identified in other vertebrates, including Xenopus and zebrafish, indicating it is an ancient vertebrate mechanism. Asymmetric nodal and Pitx expression have also been identified in several invertebrates, including the vertebrates' nearest relatives, the urochordates. However whether cilia regulate this asymmetric gene expression remains unknown, and previous studies in urochordates have not identified any cilia prior to the larval stage, when asymmetry is already long established. Here we use Scanning and Transmission Electron Microscopy and immunofluorescence to investigate cilia in the urochordate Ciona intestinalis. We show that single cilia are transiently present on each ectoderm cell of the late neurula/early tailbud stage embryo, a time point just before onset of asymmetric nodal expression. Mapping the position of each cilium on these cells shows they are posteriorly positioned, something also described for mouse node cilia. The C. intestinalis cilia have a 9+0 ring ultrastructure, however we find no evidence of structures associated with motility such as dynein arms, radial spokes or nexin. Furthermore the 9+0 ring structure becomes disorganised immediately after the cilia have exited the cell, indicative of cilia which are not capable of motility. Our results indicate that although cilia are present prior to molecular asymmetries, they are not motile and hence cannot be operating in the same way as the flow-generating cilia of the vertebrate node. We conclude that the cilia may have a role in the development of C. intestinalis left-right asymmetry but that this would have to be in a sensory capacity, perhaps as mechanosensors as hypothesised in two-cilia physical models of vertebrate cilia-driven asymmetry.
Abstract.
Author URL.
2011
Vaughan S, Dawe HR (2011). Common themes in centriole and centrosome movements.
Trends Cell Biol,
21(1), 57-66.
Abstract:
Common themes in centriole and centrosome movements.
Centrioles are found in nearly all eukaryotic cells and are required for growth and maintenance of the radial array of microtubules, the mitotic spindle, and cilia and flagella. Different types of microtubule structures are often required at different places in a given cell; centrioles must move around to nucleate these varied structures. Here, we draw together recent data on diverse centriole movements to decipher common themes in how centrioles move. Par proteins establish and maintain the required cellular asymmetry. The actin cytoskeleton facilitates movement of multiple basal bodies. Microtubule forces acting on the cell cortex, and nuclear-cytoskeletal links, are important for positioning individual centrosomes, and during cell division. Knowledge of these common mechanisms can inform the study of centriole movements across biology.
Abstract.
Author URL.
2010
Gluenz E, Höög JL, Smith AE, Dawe HR, Shaw MK, Gull K (2010). Beyond 9+0: noncanonical axoneme structures characterize sensory cilia from protists to humans.
FASEB J,
24(9), 3117-3121.
Abstract:
Beyond 9+0: noncanonical axoneme structures characterize sensory cilia from protists to humans.
The intracellular amastigote stages of parasites such as Leishmania are often referred to as aflagellate. They do, however, possess a short axoneme of cryptic function. Here, our examination of the structure of this axoneme leads to a testable hypothesis of its role in the cell biology of pathogenicity. We show a striking similarity between the microtubule axoneme structure of the Leishmania mexicana parasite infecting a macrophage and vertebrate primary cilia. In both, the 9-fold microtubule doublet symmetry is broken by the incursion of one or more microtubule doublets into the axoneme core, giving rise to an architecture that we term here the 9v (variable) axoneme. Three-dimensional reconstructions revealed that no particular doublet initiated the symmetry break, and moreover it often involved 2 doublets. The tip of the L. mexicana flagellum was frequently intimately associated with the macrophage vacuole membrane. We propose that the main function of the amastigote flagellum is to act as a sensory organelle with important functions in host-parasite interactions and signaling in the intracellular stage of the L. mexicana life cycle.
Abstract.
Author URL.
2009
Dawe HR, Adams M, Wheway G, Szymanska K, Logan CV, Noegel AA, Gull K, Johnson CA (2009). Nesprin-2 interacts with meckelin and mediates ciliogenesis via remodelling of the actin cytoskeleton.
J Cell Sci,
122(Pt 15), 2716-2726.
Abstract:
Nesprin-2 interacts with meckelin and mediates ciliogenesis via remodelling of the actin cytoskeleton.
Meckel-Gruber syndrome (MKS) is a severe autosomal recessively inherited disorder caused by mutations in genes that encode components of the primary cilium and basal body. Here we show that two MKS proteins, MKS1 and meckelin, that are required for centrosome migration and ciliogenesis interact with actin-binding isoforms of nesprin-2 (nuclear envelope spectrin repeat protein 2, also known as Syne-2 and NUANCE). Nesprins are important scaffold proteins for maintenance of the actin cytoskeleton, nuclear positioning and nuclear-envelope architecture. However, in ciliated-cell models, meckelin and nesprin-2 isoforms colocalized at filopodia prior to the establishment of cell polarity and ciliogenesis. Loss of nesprin-2 and nesprin-1 shows that both mediate centrosome migration and are then essential for ciliogenesis, but do not otherwise affect apical-basal polarity. Loss of meckelin (by siRNA and in a patient cell-line) caused a dramatic remodelling of the actin cytoskeleton, aberrant localization of nesprin-2 isoforms to actin stress-fibres and activation of RhoA signalling. These findings further highlight the important roles of the nesprins during cellular and developmental processes, particularly in general organelle positioning, and suggest that a mechanistic link between centrosome positioning, cell polarity and the actin cytoskeleton is required for centrosomal migration and is essential for early ciliogenesis.
Abstract.
Author URL.
Dawe HR, Gluenz E (2009). The tale of the trypanosome tail. Biologist, 56(4), 216-220.
2007
Dawe HR, Farr H, Gull K (2007). Centriole/basal body morphogenesis and migration during ciliogenesis in animal cells.
J Cell Sci,
120(Pt 1), 7-15.
Abstract:
Centriole/basal body morphogenesis and migration during ciliogenesis in animal cells.
Cilia, either motile or immotile, exist on most cells in the human body. There are several different mechanisms of ciliogenesis, which enable the production of many kinds of cilia and flagella: motile and immotile, transient and long-lived. These can be linked to the cell cycle or associated with differentiation. A primary cilium is extended from a basal body analogous to the mitotic centrioles, whereas the several hundred centrioles needed to form the cilia of a multi-ciliated cell can be generated by centriolar or acentriolar pathways. Little is known about the molecular control of these pathways and most of our knowledge comes from ultrastructural studies. The increasing number of genetic diseases linked to dysfunctional cilia and basal bodies has renewed interest in this area, and recent proteomic and cell biological studies in model organisms have helped to shed light on the molecular components of these enigmatic organelles.
Abstract.
Author URL.
Dawe HR, Smith UM, Cullinane AR, Gerrelli D, Cox P, Badano JL, Blair-Reid S, Sriram N, Katsanis N, Attie-Bitach T, et al (2007). The Meckel-Gruber Syndrome proteins MKS1 and meckelin interact and are required for primary cilium formation.
Hum Mol Genet,
16(2), 173-186.
Abstract:
The Meckel-Gruber Syndrome proteins MKS1 and meckelin interact and are required for primary cilium formation.
Meckel-Gruber syndrome (MKS) is an autosomal recessive lethal malformation syndrome characterized by renal cystic dysplasia, central nervous system malformations (typically, posterior occipital encephalocele), and hepatic developmental defects. Two MKS genes, MKS1 and MKS3, have been identified recently. The present study describes the cellular, sub-cellular and functional characterization of the novel proteins, MKS1 and meckelin, encoded by these genes. In situ hybridization studies for MKS3 in early human embryos showed transcript localizations in agreement with the tissue phenotype of MKS patients. Both MKS proteins predominantly localized to epithelial cells, including proximal renal tubules and biliary epithelial cells. MKS1 localized to basal bodies, while meckelin localized both to the primary cilium and to the plasma membrane in ciliated cell-lines and primary cells. Meckelin protein with the Q376P missense mutation was unable to localize at the cell membrane. siRNA-mediated reduction of Mks1 and Mks3 expression in a ciliated epithelial cell-line blocked centriole migration to the apical membrane and consequent formation of the primary cilium. Co-immunoprecipitation experiments show that wild-type meckelin and MKS1 interact and, in three-dimensional tissue culture assays, epithelial branching morphogenesis was severely impaired. These results suggest that MKS proteins mediate a fundamental developmental stage of ciliary formation and epithelial morphogenesis.
Abstract.
Author URL.
Dawe HR, Shaw MK, Farr H, Gull K (2007). The hydrocephalus inducing gene product, Hydin, positions axonemal central pair microtubules.
BMC Biol,
5Abstract:
The hydrocephalus inducing gene product, Hydin, positions axonemal central pair microtubules.
BACKGROUND: Impairment of cilia and flagella function underlies a growing number of human genetic diseases. Mutations in hydin in hy3 mice cause lethal communicating hydrocephalus with early onset. Hydin was recently identified as an axonemal protein; however, its function is as yet unknown. RESULTS: Here we use RNAi in Trypanosoma brucei to address this issue and demonstrate that loss of Hydin causes slow growth and a loss of cell motility. We show that two separate defects in newly-formed flagellar central pair microtubules underlie the loss of cell motility. At early time-points after RNAi induction, the central pair becomes mispositioned, while at later time points the central pair is lost. While the basal body is unaffected, both defects originate at the basal plate, reflecting a role for TbHydin throughout the length of the central pair. CONCLUSION: Our data provide the first evidence of Hydin's role within the trypanosome axoneme, and reveal central pair anomalies and thus impairment of ependymal ciliary motility as the likely cause of the hydrocephalus observed in the hy3 mouse.
Abstract.
Author URL.
2006
Broadhead R, Dawe HR, Farr H, Griffiths S, Hart SR, Portman N, Shaw MK, Ginger ML, Gaskell SJ, McKean PG, et al (2006). Flagellar motility is required for the viability of the bloodstream trypanosome.
Nature,
440(7081), 224-227.
Abstract:
Flagellar motility is required for the viability of the bloodstream trypanosome.
The 9 + 2 microtubule axoneme of flagella and cilia represents one of the most iconic structures built by eukaryotic cells and organisms. Both unity and diversity are present among cilia and flagella on the evolutionary as well as the developmental scale. Some cilia are motile, whereas others function as sensory organelles and can variously possess 9 + 2 and 9 + 0 axonemes and other associated structures. How such unity and diversity are reflected in molecular repertoires is unclear. The flagellated protozoan parasite Trypanosoma brucei is endemic in sub-Saharan Africa, causing devastating disease in humans and other animals. There is little hope of a vaccine for African sleeping sickness and a desperate need for modern drug therapies. Here we present a detailed proteomic analysis of the trypanosome flagellum. RNA interference (RNAi)-based interrogation of this proteome provides functional insights into human ciliary diseases and establishes that flagellar function is essential to the bloodstream-form trypanosome. We show that RNAi-mediated ablation of various proteins identified in the trypanosome flagellar proteome leads to a rapid and marked failure of cytokinesis in bloodstream-form (but not procyclic insect-form) trypanosomes, suggesting that impairment of flagellar function may provide a method of disease control. A postgenomic meta-analysis, comparing the evolutionarily ancient trypanosome with other eukaryotes including humans, identifies numerous trypanosome-specific flagellar proteins, suggesting new avenues for selective intervention.
Abstract.
Author URL.
2005
Dawe HR, Farr H, Portman N, Shaw MK, Gull K (2005). The Parkin co-regulated gene product, PACRG, is an evolutionarily conserved axonemal protein that functions in outer-doublet microtubule morphogenesis.
J Cell Sci,
118(Pt 23), 5421-5430.
Abstract:
The Parkin co-regulated gene product, PACRG, is an evolutionarily conserved axonemal protein that functions in outer-doublet microtubule morphogenesis.
Eukaryotic cilia and flagella are highly conserved structures composed of a canonical 9+2 microtubule axoneme. Comparative genomics of flagellated and non-flagellated eukaryotes provides one way to identify new putative flagellar proteins. We identified the Parkin co-regulated gene, or PACRG, from such a screen. Male mice deficient in PACRG are sterile, but its function has been little explored. The flagellated protozoan parasite Trypanosoma brucei possesses two homologues of PACRG. We performed RNA interference knockdown experiments of the two genes independently and both together. Simultaneous ablation of both proteins produced slow growth and paralysis of the flagellum with consequent effects on organelle segregation. Moreover, using transmission electron microscopy, structural defects were seen in the axoneme, with microtubule doublets missing from the canonical 9+2 formation. The occurrence of missing doublets increased toward the distal end of the flagellum and sequential loss of doublets was observed along individual axonemes. GFP fusion proteins of both PACRG homologues localised along the full length of the axoneme. Our results provide the first evidence for PACRG function within the axoneme, where we suggest that PACRG acts to maintain functional stability of the axonemal outer doublets of both motile and sensory cilia and flagella.
Abstract.
Author URL.
2004
Mseka T, Dawe HR, Bamburg JR, Cramer LP (2004). Actin filament depolymerization and microtubules control sequential actin dynamic steps to initiate cell polarity.
Author URL.
2003
Dawe HR, Minamide LS, Bamburg JR, Cramer LP (2003). ADF/cofilin controls cell polarity during fibroblast migration.
Curr Biol,
13(3), 252-257.
Abstract:
ADF/cofilin controls cell polarity during fibroblast migration.
To migrate, normally a cell must establish morphological polarity and continuously protrude a single lamellipodium, polarized in the direction of migration. We have previously shown that actin filament disassembly is necessary for protrusion of the lamellipodium during fibroblast migration. As ADF/cofilin (AC) proteins are essential for the catalysis of filament disassembly in cells, we assessed their role in polarized lamellipodium protrusion in migrating fibroblasts. We compared the spatial distribution of AC and the inactive, phosphorylated AC (pAC) in migrating cells. AC, but not pAC, localized to the lamellipodium. To investigate a role for AC in cell polarity, we increased the proportion of pAC in migrating fibroblasts by overexpressing constitutively active (CA) LIM kinase 1. In 87% of cells expressing CA LIM kinase, cell polarity was abolished. In such cells, the single polarized lamellipodium was replaced by multiple nonpolarized lamellipodia, which, in contrast to nonexpressing migrating cells, stained for pAC. Cell polarity was rescued by coexpressing an active, nonphosphorylatable Xenopus AC (CA XAC) with the CA LIMK. Furthermore, overexpressing a pseudophosphorylated (less active) XAC by itself also abolished cell polarity. We conclude that locally maintaining ADF/cofilin in the active, nonphosphorylated state within the lamellipodium is necessary to maintain polarized protrusion during cell migration.
Abstract.
Author URL.
2002
Cramer LP, Briggs LJ, Dawe HR (2002). Use of fluorescently labelled deoxyribonuclease I to spatially measure G-actin levels in migrating and non-migrating cells.
Cell Motil Cytoskeleton,
51(1), 27-38.
Abstract:
Use of fluorescently labelled deoxyribonuclease I to spatially measure G-actin levels in migrating and non-migrating cells.
Lamellipodium protrusion is linked to actin filament disassembly in migrating fibroblasts [Cramer, 1999: Curr. Biol. 9:1095-1105]. To further study this relationship, we have identified a method to specifically and sensitively detect G-actin in distinct spatial locations in motile cells using deoxyribonuclease I (DNase I). Although DNase I can bind both G- and F-actin in vitro [Mannherz et al. 1980: Eur. J. Biochem. 95:377-385], when cells were fixed in formaldehyde and permeabilized in detergent, fluorescently-labelled DNase I specifically stained G-actin and not F-actin. 92-98% of actin molecules were stably retained in cells during fixation and permeabilization. Further, increasing or decreasing cellular G-actin concentration by treating live cells with latrunculin-A or jasplakinolide, respectively, caused a respective increase and decrease in DNase I cell-staining intensity as expected. These changes in DNase I fluorescence intensity accurately reflected increases and decreases in cellular G-actin concentration independently measured in lysates prepared from drug-treated live cells (regression coefficient = 0.98). This shows that DNase I cell-staining is very sensitive using this method. Applying this method, we found that the ratio of G-/F-actin is lower in both the lamellipodium and in a broad band immediately behind the lamellipodium in migrating compared to non-migrating fibroblasts. Thus, we predict that protrusion of the lamellipodium in migrating fibroblasts requires tight coupling to filament disassembly at least in part because G-actin is relatively limited within and behind the lamellipodium. This is the first report to directly demonstrate high sensitivity of cell-staining for any G-actin probe and this, together with the ready commercial accessibility of fluorescently-labelled DNase I, make it a simple, convenient, and sensitive tool for cell-staining of G-actin.
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