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Sequence variants in different genes underlying Bardet-Biedl syndrome in four consanguineous families. Mol Biol Rep 2023; 50:9963-9970. [PMID: 37897612 DOI: 10.1007/s11033-023-08816-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2023] [Accepted: 09/11/2023] [Indexed: 10/30/2023]
Abstract
BACKGROUND Bardet-Biedl Syndrome (BBS) is a rare (1:13,500-1-160,000) heterogeneous congenital disorder, characterized by postaxial polydactyly, obesity, hypogonadism, rod-cone dystrophy, cognitive impairment, and renal abnormalities (renal cystic dysplasia, anatomical malformation). To date about twenty-five genes have been identified to cause BBS, which accounts for about 80% of BBS diagnosis. METHODS In the current study, we have performed mutational screening of four Pakistani consanguineous families (A-D) with clinical manifestation of BBS by microsatellite-based genotyping and whole exome sequencing. RESULTS Analysis of the data revealed four variants, including a novel/unique inheritance pattern of compound heterozygous variants, p.(Ser40*) and p.(Thr259Leufs*21), in MKKS gene, novel homozygous variant, p.(Gly251Val)] in BBS7 gene and two previously reported p.(Thr259Leufs*21) in MKKS and p.(Met1Lys) in BBS5 gene. The variants were found segregated with the disorder within the families. CONCLUSION The study not only expanded mutations spectrum in the BBS genes, but this will facilitate diagnosis and genetic counselling of families carrying BBS related phenotypes in Pakistani population.
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Retinal nerve fibre layer thinning and corneal nerve loss in patients with Bardet-Biedl syndrome. BMC Med Genomics 2023; 16:301. [PMID: 37996899 PMCID: PMC10666305 DOI: 10.1186/s12920-023-01739-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2023] [Accepted: 11/13/2023] [Indexed: 11/25/2023] Open
Abstract
BACKGROUND Bardet-Biedl syndrome (BBS) is an autosomal recessive, genetically heterogeneous, pleiotropic disorder caused by variants in genes involved in the function of the primary cilium. We have harnessed genomics to identify BBS and ophthalmic technologies to describe novel features of BBS. CASE PRESENTATION A patient with an unclear diagnosis of syndromic type 2 diabetes mellitus, another affected sibling and unaffected siblings and parents were sequenced using DNA extracted from saliva samples. Corneal confocal microscopy (CCM) and retinal spectral domain optical coherence tomography (SD-OCT) were used to identify novel ophthalmic features in these patients. The two affected individuals had a homozygous variant in C8orf37 (p.Trp185*). SD-OCT and CCM demonstrated a marked and patchy reduction in the retinal nerve fiber layer thickness and loss of corneal nerve fibers, respectively. CONCLUSION This report highlights the use of ophthalmic imaging to identify novel retinal and corneal abnormalities that extend the phenotype of BBS in a patient with syndromic type 2 diabetes.
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Mediastinal lipomatosis in a patient with Bardet-Biedl syndrome: more diverse than previously thought. Pan Afr Med J 2023; 45:82. [PMID: 37663628 PMCID: PMC10474804 DOI: 10.11604/pamj.2023.45.82.35582] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Accepted: 06/07/2023] [Indexed: 09/05/2023] Open
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Neofunctionalization of ciliary BBS proteins to nuclear roles is likely a frequent innovation across eukaryotes. iScience 2023; 26:106410. [PMID: 37034981 PMCID: PMC10074162 DOI: 10.1016/j.isci.2023.106410] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2022] [Revised: 07/20/2022] [Accepted: 03/10/2023] [Indexed: 03/17/2023] Open
Abstract
The eukaryotic BBSome is a transport complex within cilia and assembled by chaperonin-like BBS proteins. Recent work indicates nuclear functions for BBS proteins in mammals, but it is unclear how common these are in extant proteins or when they evolved. We screened for BBS orthologues across a diverse set of eukaryotes, consolidated nuclear association via signal sequence predictions and permutation analysis, and validated nuclear localization in mammalian cells via fractionation and immunocytochemistry. BBS proteins are-with exceptions-conserved as a set in ciliated species. Predictions highlight five most likely nuclear proteins and suggest that nuclear roles evolved independently of nuclear access during mitosis. Nuclear localization was confirmed in human cells. These findings suggest that nuclear BBS functions are potentially not restricted to mammals, but may be a common frequently co-opted eukaryotic feature. Understanding the functional spectrum of BBS proteins will help elucidating their role in gene regulation, development, and disease.
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Kidney Failure in Bardet-Biedl Syndrome. Clin Genet 2022; 101:429-441. [PMID: 35112343 PMCID: PMC9311438 DOI: 10.1111/cge.14119] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2021] [Revised: 01/29/2022] [Accepted: 01/30/2022] [Indexed: 11/29/2022]
Abstract
The aim of this study was to explore kidney failure (KF) in Bardet–Biedl syndrome (BBS), focusing on high‐risk gene variants, demographics, and morbidity. We employed the Clinical Registry Investigating BBS (CRIBBS) to identify 44 (7.2%) individuals with KF out of 607 subjects. Molecularly confirmed BBS was identified in 37 KF subjects and 364 CRIBBS registrants. KF was concomitant with recessive causal variants in 12 genes, with BBS10 the most predominant causal gene (26.6%), while disease penetrance was highest in SDCCAG8 (100%). Two truncating variants were present in 67.6% of KF cases. KF incidence was increased in genes not belonging to the BBSome or chaperonin‐like genes (p < 0.001), including TTC21B, a new candidate BBS gene. Median age of KF was 12.5 years, with the vast majority of KF occurring by 30 years (86.3%). Females were disproportionately affected (77.3%). Diverse uropathies were identified, but were not more common in the KF group (p = 0.672). Kidney failure was evident in 11 of 15 (73.3%) deaths outside infancy. We conclude that KF poses a significant risk for premature morbidity in BBS. Risk factors for KF include female sex, truncating variants, and genes other than BBSome/chaperonin‐like genes highlighting the value of comprehensive genetic investigation.
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Bardet-Biedl Syndrome ciliopathy is linked to altered hematopoiesis and dysregulated self-tolerance. EMBO Rep 2021; 22:e50785. [PMID: 33426789 DOI: 10.15252/embr.202050785] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2020] [Revised: 12/04/2020] [Accepted: 12/09/2020] [Indexed: 12/19/2022] Open
Abstract
Bardet-Biedl Syndrome (BBS) is a pleiotropic genetic disease caused by the dysfunction of primary cilia. The immune system of patients with ciliopathies has not been investigated. However, there are multiple indications that the impairment of the processes typically associated with cilia may have influence on the hematopoietic compartment and immunity. In this study, we analyze clinical data of BBS patients and corresponding mouse models carrying mutations in Bbs4 or Bbs18. We find that BBS patients have a higher prevalence of certain autoimmune diseases. Both BBS patients and animal models have altered red blood cell and platelet compartments, as well as elevated white blood cell levels. Some of the hematopoietic system alterations are associated with BBS-induced obesity. Moreover, we observe that the development and homeostasis of B cells in mice is regulated by the transport complex BBSome, whose dysfunction is a common cause of BBS. The BBSome limits canonical WNT signaling and increases CXCL12 levels in bone marrow stromal cells. Taken together, our study reveals a connection between a ciliopathy and dysregulated immune and hematopoietic systems.
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The BBSome assembly is spatially controlled by BBS1 and BBS4 in human cells. J Biol Chem 2020; 295:14279-14290. [PMID: 32759308 DOI: 10.1074/jbc.ra120.013905] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Revised: 08/04/2020] [Indexed: 12/18/2022] Open
Abstract
Bardet-Biedl syndrome (BBS) is a pleiotropic ciliopathy caused by dysfunction of primary cilia. More than half of BBS patients carry mutations in one of eight genes encoding for subunits of a protein complex, the BBSome, which mediates trafficking of ciliary cargoes. In this study, we elucidated the mechanisms of the BBSome assembly in living cells and how this process is spatially regulated. We generated a large library of human cell lines deficient in a particular BBSome subunit and expressing another subunit tagged with a fluorescent protein. We analyzed these cell lines utilizing biochemical assays, conventional and expansion microscopy, and quantitative fluorescence microscopy techniques: fluorescence recovery after photobleaching and fluorescence correlation spectroscopy. Our data revealed that the BBSome formation is a sequential process. We show that the pre-BBSome is nucleated by BBS4 and assembled at pericentriolar satellites, followed by the translocation of the BBSome into the ciliary base mediated by BBS1. Our results provide a framework for elucidating how BBS-causative mutations interfere with the biogenesis of the BBSome.
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Clinical and exome sequencing findings in seven children with Bardet-Biedl syndrome from Turkey. Ann Hum Genet 2020; 85:27-36. [PMID: 32686083 DOI: 10.1111/ahg.12401] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2020] [Revised: 07/02/2020] [Accepted: 07/02/2020] [Indexed: 12/14/2022]
Abstract
BACKGROUND Bardet-Biedl syndrome (BBS) is a very-rare autosomal recessive genetic disorder with severe multisystem manifestations. Genetic testing plays an important role in the early diagnosis of the disease. In this study, while trying to elucidate the genetic etiology of seven individuals with clinical BBS diagnosis from six different families, we also aimed to examine the distribution of BBS variations in this region of Turkey. METHODS AND MATERIALS Exome sequencing analysis is performed for clinically diagnosed patients with BBS in the present study followed by parental segregation. The unreported and previously described clinical features are presented. RESULTS Homozygous variants, four of which are unreported, in BBS-related genes (BBS5 [c.682-2A > G], MKKS [c.775del], BBS7 [c.849+1G > T], BBS9 [c.965G > A], BBS10 [c.145C > T], LZTFL1[c.384G > A]) are detected for all the seven individuals included in the study. The most common clinical finding is polydactyly followed by renal anomalies. The clinical features not previously described are correlated to the unreported variant. CONCLUSIONS In this study, exome sequencing findings are discussed and four previously unreported disease-associated variants are described including the fifth BBS-implicated LZTFL1 change and possible genotype-phenotype correlation is described.
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Near-atomic structures of the BBSome reveal the basis for BBSome activation and binding to GPCR cargoes. eLife 2020; 9:55954. [PMID: 32510327 PMCID: PMC7311171 DOI: 10.7554/elife.55954] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Accepted: 06/08/2020] [Indexed: 02/07/2023] Open
Abstract
Dynamic trafficking of G protein-coupled receptors (GPCRs) out of cilia is mediated by the BBSome. In concert with its membrane recruitment factor, the small GTPase ARL6/BBS3, the BBSome ferries GPCRs across the transition zone, a diffusion barrier at the base of cilia. Here, we present the near-atomic structures of the BBSome by itself and in complex with ARL6GTP, and we describe the changes in BBSome conformation induced by ARL6GTP binding. Modeling the interactions of the BBSome with membranes and the GPCR Smoothened (SMO) reveals that SMO, and likely also other GPCR cargoes, must release their amphipathic helix 8 from the membrane to be recognized by the BBSome.
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Identification of A Novel Compound Heterozygous Mutation in BBS12 in An Iranian Family with Bardet-Biedl Syndrome Using Targeted Next Generation Sequencing. CELL JOURNAL 2018; 20:284-289. [PMID: 29633607 PMCID: PMC5893301 DOI: 10.22074/cellj.2018.5012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/08/2017] [Accepted: 03/21/2017] [Indexed: 01/27/2023]
Abstract
Bardet-Biedl syndrome (BBS) is a pleiotropic and multisystemic disorder characterized by rod-cone dystrophy, polydactyly,
learning difficulties, renal abnormalities, obesity and hypogonadism. This disorder is genetically heterogeneous. Until
now, a total of nineteen genes have been identified for BBS whose mutations explain more than 80% of diagnosed
cases. Recently, the development of next generation sequencing (NGS) technology has accelerated mutation screening
of target genes, resulting in lower cost and less time consumption. Here, we screened the most common BBS genes
(BBS1-BBS13) using NGS in an Iranian family of a proposita displaying symptoms of BBS. Among the 18 mutations
identified in the proposita, one (BBS12 c.56T>G and BBS12 c.1156C>T) was novel. This compound heterozygosity
was confirmed by Sanger sequencing in the proposita and her parents. Although our data were presented as a case
report, however, we suggest a new probable genetic mechanism other than the conventional autosomal recessive
inheritance of BBS. Additionally, given that in some Iranian provinces, like Khuzestan, consanguineous marriages
are common, designing mutational panels for genetic diseases is strongly recommended, especially for those with an
autosomal recessive inheritance pattern.
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Sleep disordered breathing in Bardet-Biedl Syndrome. Int J Pediatr Otorhinolaryngol 2017; 102:127-132. [PMID: 29106859 DOI: 10.1016/j.ijporl.2017.09.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Revised: 09/01/2017] [Accepted: 09/02/2017] [Indexed: 12/24/2022]
Abstract
INTRODUCTION Bardet-Biedl Syndrome (BBS) is an autosomal recessive ciliopathy, and obesity is among its defining characteristics. Consequently, the incidence of sleep disordered breathing (SDB) in this population is expected to be high. Due to its relative rarity, the nature of SDB in this population is poorly described. The objective of this study was to review a single institutional experience in the assessment and management of SDB in patients with BBS. METHODS Retrospective chart review of tertiary care, academic pediatric hospital. RESULTS 20 patients with BBS were evaluated over a 25-year period. Median age at initial consultation was 69 months; half of these patients were referred before the diagnosis of BBS was made. Eighteen of twenty patients had symptoms of sleep-disordered breathing. Median follow-up duration was 17.5 months. A wide range of polysomnographic outcomes was observed, including obstructive apnea-hypopnea indexes of 0-195 events/hour. Patients were managed with adenotonsillectomy and/or non-invasive positive pressure ventilation. CONCLUSIONS SDB is commonly seen in BBS. These patients should be routinely screened for OSA and if present, a polysomnogram should be obtained. Based on patient characteristics, the failure rate of primary surgical intervention, namely adenotonsillectomy, is expected to be high. Further investigation into the role of ancillary diagnostic testing is still needed.
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[Patho-physiology of renal dysfunction in Bardet-Biedl Syndrome]. GIORNALE ITALIANO DI NEFROLOGIA : ORGANO UFFICIALE DELLA SOCIETA ITALIANA DI NEFROLOGIA 2017; 34:62-72. [PMID: 28963828] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Bardet-Biedl Syndrome (BBS) is a rare autosomal recessive disorder with renal and extra-renal involvement. The wide spectrum of clinical manifestations is associated to the high genetic heterogeneity. To date 21 genes have been identified in humans and the majority of them encode proteins located on the basal body of the primary cilium. For this reason the disease is has been included among the 'ciliopathies'. The renal involvement is extremely heterogeneous in BBS and is considered the main cause of morbidity and mortality. Recent evidences have suggested that mutations in BBS6, 10 and 12 are associated with a more severe renal dysfunction. The most common renal dysfunction is the urine concentrating defect, even though the underlying mechanism is not completely known. Recently we have demonstrated that hyposthenuria in BBS patients has a renal origin, and depends on desmopessin resistance. The majority of hyposthenuric BBS patients have a combined defect to both concentrate and dilute the urine. The combined defect is associated with a blunted increased urine Aquaproine-2 (u-AQP2) excretion in antidiuresis. A ccordingly, in vitro BBS10 silencing prevented AQP2 trafficking to the apical plasma membrane. However, after long term water restriction hyposthenuric BBS patients showed the same u-AQP2 excretion compared with controls, suggesting that other mechanisms are implicated into the pathogenesis of hyposhtenuria. The complete molecular mechanism underlying hyposhtenuria remains largely unknown in BBS. Whether this defect may represent a predictor factor for poor renal outcome remains to be elucidated.
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Bardet-Biedl syndrome 3 regulates the development of cranial base midline structures. Bone 2017; 101:179-190. [PMID: 27170093 PMCID: PMC5519131 DOI: 10.1016/j.bone.2016.02.017] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Revised: 02/21/2016] [Accepted: 02/24/2016] [Indexed: 11/22/2022]
Abstract
Bardet-Biedl Syndrome (BBS) is an autosomal recessive disorder and is classified as one of the ciliopathy. The patients manifest a characteristic craniofacial dysmorphology but the effects of Bbs3 deficiency in the developmental process during the craniofacial pathogenesis are still incompletely understood. Here, we analyzed a cranial development of a BBS model Bbs3-/- mouse. It was previously reported that these mutant mice exhibit a dome-shape cranium. We show that Bbs3-/- mouse embryos present mid-facial hypoplasia and solitary central upper incisor. Morphologically, these mutant mice show synchondrosis of the cranial base midline due to the failure to fuse in association with loss of intrasphenoidal synchondrosis. The cranial base was laterally expanded and longitudinally shortened. In the developing cartilaginous primordium of cranial base, cells present in the midline were less in Bbs3-/- embryos. Expression of BBS3 was observed specifically in a cell population lying between condensed ectomesenchyme in the midline and the ventral midbrain at this stage. Finally, siRNA-based knockdown of Bbs3 in ATDC5 cells impaired migration in culture. Our data suggest that BBS3 is required for the development of cranial base via regulation of cell migration toward the midline where they promote the condensation of ectomesenchyme and form the future cartilaginous templates of cranial base.
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Exploring genotype-phenotype relationships in Bardet-Biedl syndrome families. J Med Genet 2015; 52:503-13. [PMID: 26082521 DOI: 10.1136/jmedgenet-2015-103099] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2015] [Accepted: 05/26/2015] [Indexed: 11/03/2022]
Abstract
BACKGROUND Bardet-Biedl syndrome (BBS) is a pleiotropic autosomal recessive ciliopathy that displays retinal dystrophy, obesity, polydactyly, cognitive impairment, urogenital anomalies and renal abnormalities as primary clinical features. To date, 19 causative genes (BBS1-19) have been involved, whose mutations would explain over 80% of patients. The overlapping phenotypes among ciliopathies, in addition to the high intrafamilial and interfamilial variability in clinical presentation, further complicate the diagnosis of this syndrome. Thus, the main purpose of this study was to elucidate some genotype-phenotype trends that could be helpful to focus the molecular diagnosis of patients with BBS. METHODS Thirty-seven families (52 cases) with mutations in BBS1 or chaperonin-like BBS genes (BBS6, BBS10, BBS12) from our Spanish cohort were enrolled. Systemic and ocular features were documented as comprehensively as possible. RESULTS Comparing BBS1 versus chaperonin-like genes phenotypes we found more severe clinical features in the second group, since they displayed higher prevalence of all primary features, remarkable being the frequency of cognitive impairment (75%) in BBS12 and urogenital anomalies (83%) in patients with BBS10. With regards to p.(Met390Arg) cases, homozygotes showed a relatively more severe ocular phenotype than compound heterozygotes, since more severe fundus alterations and higher frequency of cataracts and dyschromatopsia (not previously described) were documented in the first group. The phenotypes observed frequently overlapped with Alström syndrome and, in the case of chaperonin-like genes, McKusick-Kauffman syndrome overlapping was detected. CONCLUSIONS We provide the first evidence of BBS12 mutations related to severe phenotypes as previously described for patients with BBS10, while BBS1 ocular phenotype should not be considered as mild as generally reported when compared with other BBS phenotypes.
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Abstract
PURPOSE While some evidence suggests an essential role for the chaperonin containing t-complex protein 1 (CCT) in ciliogenesis, this function remains poorly understood mechanistically. We used transgenic mice, previously generated in our lab, and characterized by a genetically-induced suppression of CCT in rod photoreceptors as well as a malformation of the rod sensory cilia, the outer segments, to gain new insights into this underlying molecular mechanism. METHODS The CCT activity in rod photoreceptors of mice was suppressed by overexpressing the chaperonin inhibitor, phosducin-like protein short, and the ensuing changes of cellular morphology were analyzed by light and electron microscopy. Protein expression levels were studied by fluorescent microscopy and Western blotting. RESULTS Suppressing the chaperonin made the photoreceptors incompetent to build their outer segments. Specifically, the CCT-deficient rods appeared unable to expand the outer segment plasma membrane, and accommodate growth of this compartment. Seeking the molecular mechanisms underlying such a shortcoming, we found that the affected rods could not express normal levels of Bardet-Biedl Syndrome (BBS) proteins 2, 5, and 7 and, owing to that deficiency, were unable to assemble the BBSome, a multisubunit complex responsible for ciliary trafficking. A similar effect in response to the chaperonin suppression was also observed in cultured ciliated cells. CONCLUSIONS Our data provide new evidence indicating the essential role of the chaperonin CCT in the biogenesis of vertebrate photoreceptor sensory cilia, and suggest that it may be due to the direct participation of the chaperonin in the posttranslational processing of selected BBS proteins and assembly of the BBSome.
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Abstract
Proteins associated with primary cilia and basal bodies mediate numerous signaling pathways, but little is known about their role in Notch signaling. Here, we report that loss of the Bardet-Biedl syndrome proteins BBS1 or BBS4 produces increased Notch-directed transcription in a zebrafish reporter line and in human cell lines. Pathway overactivation is accompanied by reduced localization of Notch receptor at both the plasma membrane and the cilium. In Drosophila mutants, overactivation of Notch can result from receptor accumulation in endosomes, and recent studies implicate ciliary proteins in endosomal trafficking, suggesting a possible mechanism by which overactivation occurs in BBS mutants. Consistent with this, we observe genetic interaction of BBS1 and BBS4 with the endosomal sorting complexes required for transport (ESCRT) gene TSG101 and accumulation of receptor in late endosomes, reduced endosomal recycling and reduced receptor degradation in lysosomes. We observe similar defects with disruption of BBS3. Loss of another basal body protein, ALMS1, also enhances Notch activation and the accumulation of receptor in late endosomes, but does not disrupt recycling. These findings suggest a role for these proteins in the regulation of Notch through endosomal trafficking of the receptor.
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Interaction with the Bardet-Biedl gene product TRIM32/BBS11 modifies the half-life and localization of Glis2/NPHP7. J Biol Chem 2014; 289:8390-401. [PMID: 24500717 DOI: 10.1074/jbc.m113.534024] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Although the two ciliopathies Bardet-Biedl syndrome and nephronophthisis share multiple clinical manifestations, the molecular basis for this overlap remains largely unknown. Both BBS11 and NPHP7 are unusual members of their respective gene families. Although BBS11/TRIM32 represents a RING finger E3 ubiquitin ligase also involved in hereditary forms of muscular dystrophy, NPHP7/Glis2 is a Gli-like transcriptional repressor that localizes to the nucleus, deviating from the ciliary localization of most other ciliopathy-associated gene products. We found that BBS11/TRIM32 and NPHP7/Glis2 can physically interact with each other, suggesting that both proteins form a functionally relevant protein complex in vivo. This hypothesis was further supported by the genetic interaction and synergist cyst formation in the zebrafish pronephros model. However, contrary to our expectation, the E3 ubiquitin ligase BBS11/TRIM32 was not responsible for the short half-life of NPHP7/Glis2 but instead promoted the accumulation of mixed Lys(48)/Lys(63)-polyubiquitylated NPHP7/Glis2 species. This modification not only prolonged the half-life of NPHP7/Glis2, but also altered the subnuclear localization and the transcriptional activity of NPHP7/Glis2. Thus, physical and functional interactions between NPHP and Bardet-Biedl syndrome gene products, demonstrated for Glis2 and TRIM32, may help to explain the phenotypic similarities between these two syndromes.
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Molecular complexes that direct rhodopsin transport to primary cilia. Prog Retin Eye Res 2013; 38:1-19. [PMID: 24135424 DOI: 10.1016/j.preteyeres.2013.08.004] [Citation(s) in RCA: 101] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2013] [Revised: 08/13/2013] [Accepted: 08/19/2013] [Indexed: 11/27/2022]
Abstract
Rhodopsin is a key molecular constituent of photoreceptor cells, yet understanding of how it regulates photoreceptor membrane trafficking and biogenesis of light-sensing organelles, the rod outer segments (ROS) is only beginning to emerge. Recently identified sequence of well-orchestrated molecular interactions of rhodopsin with the functional networks of Arf and Rab GTPases at multiple stages of intracellular targeting fits well into the complex framework of the biogenesis and maintenance of primary cilia, of which the ROS is one example. This review will discuss the latest progress in dissecting the molecular complexes that coordinate rhodopsin incorporation into ciliary-targeted carriers with the recruitment and activation of membrane tethering complexes and regulators of fusion with the periciliary plasma membrane. In addition to revealing the fundamental principals of ciliary membrane renewal, recent advances also provide molecular insight into the ways by which disruptions of the exquisitely orchestrated interactions lead to cilia dysfunction and result in human retinal dystrophies and syndromic diseases that affect multiple organs, including the eyes.
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