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Lin Z, Shen Y, Li Y, Lu C, Zhu Y, He R, Cao Z, Yin Z, Gao H, Guo B, Ma X, Cao M, Luo M. Novel compound heterozygous variants in ARL13B lead to Joubert syndrome. J Cell Physiol 2024; 239:e31189. [PMID: 38219074 DOI: 10.1002/jcp.31189] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Revised: 12/07/2023] [Accepted: 12/22/2023] [Indexed: 01/15/2024]
Abstract
Joubert syndrome (JBTS) is a systematic developmental disorder mainly characterized by a pathognomonic mid-hindbrain malformation. All known JBTS-associated genes encode proteins involved in the function of antenna-like cellular organelle, primary cilium, which plays essential roles in cellular signal transduction and development. Here, we identified four unreported variants in ARL13B in two patients with the classical features of JBTS. ARL13B is a member of the Ras GTPase family and functions in ciliogenesis and cilia-related signaling. The two missense variants in ARL13B harbored the substitutions of amino acids at evolutionarily conserved positions. Using model cell lines, we found that the accumulations of the missense variants in cilia were impaired and the variants showed attenuated functions in ciliogenesis or the trafficking of INPP5E. Overall, these findings expanded the ARL13B pathogenetic variant spectrum of JBTS.
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Affiliation(s)
- Zaisheng Lin
- International Peace Maternity and Child Health Hospital, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Department of Pathophysiology, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Yue Shen
- National Human Genetic Resources Center, National Research Institute for Family Planning, Beijing, China
| | - Yan Li
- International Peace Maternity and Child Health Hospital, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Department of Pathophysiology, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Chao Lu
- National Human Genetic Resources Center, National Research Institute for Family Planning, Beijing, China
| | - Ying Zhu
- International Peace Maternity and Child Health Hospital, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Department of Pathophysiology, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Ruida He
- International Peace Maternity and Child Health Hospital, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Department of Pathophysiology, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Zongfu Cao
- National Human Genetic Resources Center, National Research Institute for Family Planning, Beijing, China
| | - Zhe Yin
- National Human Genetic Resources Center, National Research Institute for Family Planning, Beijing, China
| | - Huafang Gao
- National Human Genetic Resources Center, National Research Institute for Family Planning, Beijing, China
| | - Bin Guo
- International Peace Maternity and Child Health Hospital, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Department of Pathophysiology, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Xu Ma
- National Human Genetic Resources Center, National Research Institute for Family Planning, Beijing, China
| | - Muqing Cao
- International Peace Maternity and Child Health Hospital, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Department of Pathophysiology, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Minna Luo
- National Human Genetic Resources Center, National Research Institute for Family Planning, Beijing, China
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Gana S, Serpieri V, Valente EM. Genotype-phenotype correlates in Joubert syndrome: A review. AMERICAN JOURNAL OF MEDICAL GENETICS. PART C, SEMINARS IN MEDICAL GENETICS 2022; 190:72-88. [PMID: 35238134 PMCID: PMC9314610 DOI: 10.1002/ajmg.c.31963] [Citation(s) in RCA: 36] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/07/2022] [Revised: 02/04/2022] [Accepted: 02/15/2022] [Indexed: 01/20/2023]
Abstract
Joubert syndrome (JS) is a genetically heterogeneous primary ciliopathy characterized by a pathognomonic cerebellar and brainstem malformation, the “molar tooth sign,” and variable organ involvement. Over 40 causative genes have been identified to date, explaining up to 94% of cases. To date, gene‐phenotype correlates have been delineated only for a handful of genes, directly translating into improved counseling and clinical care. For instance, JS individuals harboring pathogenic variants in TMEM67 have a significantly higher risk of liver fibrosis, while pathogenic variants in NPHP1, RPGRIP1L, and TMEM237 are frequently associated to JS with renal involvement, requiring a closer monitoring of liver parameters, or renal functioning. On the other hand, individuals with causal variants in the CEP290 or AHI1 need a closer surveillance for retinal dystrophy and, in case of CEP290, also for chronic kidney disease. These examples highlight how an accurate description of the range of clinical symptoms associated with defects in each causative gene, including the rare ones, would better address prognosis and help guiding a personalized management. This review proposes to address this issue by assessing the available literature, to confirm known, as well as to propose rare gene‐phenotype correlates in JS.
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Affiliation(s)
- Simone Gana
- Neurogenetics Research Center, IRCCS Mondino Foundation, Pavia, Italy
| | | | - Enza Maria Valente
- Neurogenetics Research Center, IRCCS Mondino Foundation, Pavia, Italy.,Department of Molecular Medicine, University of Pavia, Pavia, Italy
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Suciu SK, Long AB, Caspary T. Smoothened and ARL13B are critical in mouse for superior cerebellar peduncle targeting. Genetics 2021; 218:6300527. [PMID: 34132778 PMCID: PMC8864748 DOI: 10.1093/genetics/iyab084] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2021] [Accepted: 06/15/2021] [Indexed: 01/07/2023] Open
Abstract
Patients with the ciliopathy Joubert syndrome present with physical anomalies, intellectual disability, and a hindbrain malformation described as the "molar tooth sign" due to its appearance on an MRI. This radiological abnormality results from a combination of hypoplasia of the cerebellar vermis and inappropriate targeting of the white matter tracts of the superior cerebellar peduncles. ARL13B is a cilia-enriched regulatory GTPase established to regulate cell fate, cell proliferation, and axon guidance through vertebrate Hedgehog signaling. In patients, mutations in ARL13B cause Joubert syndrome. To understand the etiology of the molar tooth sign, we used mouse models to investigate the role of ARL13B during cerebellar development. We found that ARL13B regulates superior cerebellar peduncle targeting and these fiber tracts require Hedgehog signaling for proper guidance. However, in mouse, the Joubert-causing R79Q mutation in ARL13B does not disrupt Hedgehog signaling nor does it impact tract targeting. We found a small cerebellar vermis in mice lacking ARL13B function but no cerebellar vermis hypoplasia in mice expressing the Joubert-causing R79Q mutation. In addition, mice expressing a cilia-excluded variant of ARL13B that transduces Hedgehog normally showed normal tract targeting and vermis width. Taken together, our data indicate that ARL13B is critical for the control of cerebellar vermis width as well as superior cerebellar peduncle axon guidance, likely via Hedgehog signaling. Thus, our work highlights the complexity of ARL13B in molar tooth sign etiology.
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Affiliation(s)
- Sarah K Suciu
- Genetics and Molecular Biology Graduate Program, Emory University, Atlanta, GA 30322, USA,Department of Human Genetics, Emory University, Atlanta, GA 30322, USA
| | - Alyssa B Long
- Department of Human Genetics, Emory University, Atlanta, GA 30322, USA
| | - Tamara Caspary
- Department of Human Genetics, Emory University, Atlanta, GA 30322, USA,Corresponding author: Department of Human Genetics, 615 Michael Street, Suite 301, Atlanta, GA 30322.
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Primary Cilia Signaling Promotes Axonal Tract Development and Is Disrupted in Joubert Syndrome-Related Disorders Models. Dev Cell 2020; 51:759-774.e5. [PMID: 31846650 DOI: 10.1016/j.devcel.2019.11.005] [Citation(s) in RCA: 53] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Revised: 08/08/2019] [Accepted: 11/10/2019] [Indexed: 12/18/2022]
Abstract
Appropriate axonal growth and connectivity are essential for functional wiring of the brain. Joubert syndrome-related disorders (JSRD), a group of ciliopathies in which mutations disrupt primary cilia function, are characterized by axonal tract malformations. However, little is known about how cilia-driven signaling regulates axonal growth and connectivity. We demonstrate that the deletion of related JSRD genes, Arl13b and Inpp5e, in projection neurons leads to de-fasciculated and misoriented axonal tracts. Arl13b deletion disrupts the function of its downstream effector, Inpp5e, and deregulates ciliary-PI3K/AKT signaling. Chemogenetic activation of ciliary GPCR signaling and cilia-specific optogenetic modulation of downstream second messenger cascades (PI3K, AKT, and AC3) commonly regulated by ciliary signaling receptors induce rapid changes in axonal dynamics. Further, Arl13b deletion leads to changes in transcriptional landscape associated with dysregulated PI3K/AKT signaling. These data suggest that ciliary signaling acts to modulate axonal connectivity and that impaired primary cilia signaling underlies axonal tract defects in JSRD.
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Ferent J, Constable S, Gigante ED, Yam PT, Mariani LE, Legué E, Liem KF, Caspary T, Charron F. The Ciliary Protein Arl13b Functions Outside of the Primary Cilium in Shh-Mediated Axon Guidance. Cell Rep 2019; 29:3356-3366.e3. [PMID: 31825820 PMCID: PMC6927553 DOI: 10.1016/j.celrep.2019.11.015] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2019] [Revised: 09/19/2019] [Accepted: 11/04/2019] [Indexed: 12/19/2022] Open
Abstract
The small GTPase Arl13b is enriched in primary cilia and regulates Sonic hedgehog (Shh) signaling. During neural development, Shh controls patterning and proliferation through a canonical, transcription-dependent pathway that requires the primary cilium. Additionally, Shh controls axon guidance through a non-canonical, transcription-independent pathway whose connection to the primary cilium is unknown. Here we show that inactivation of Arl13b results in defective commissural axon guidance in vivo. In vitro, we demonstrate that Arl13b functions autonomously in neurons for their Shh-dependent guidance response. We detect Arl13b protein in axons and growth cones, far from its well-established ciliary enrichment. To test whether Arl13b plays a non-ciliary function, we used an engineered, cilia-localization-deficient Arl13b variant and found that it was sufficient to mediate Shh axon guidance in vitro and in vivo. Together, these results indicate that, in addition to its ciliary role in canonical Shh signaling, Arl13b plays a cilia-independent role in Shh-mediated axon guidance.
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Affiliation(s)
- Julien Ferent
- Montreal Clinical Research Institute (IRCM), 110 Pine Avenue West, Montreal, QC H2W 1R7, Canada; Department of Neuroscience, University of Montreal, Montreal, QC H3T 1J4, Canada
| | - Sandii Constable
- Department of Human Genetics, 615 Michael St., Suite 301, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Eduardo D Gigante
- Department of Human Genetics, 615 Michael St., Suite 301, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Patricia T Yam
- Montreal Clinical Research Institute (IRCM), 110 Pine Avenue West, Montreal, QC H2W 1R7, Canada
| | - Laura E Mariani
- Department of Human Genetics, 615 Michael St., Suite 301, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Emilie Legué
- Vertebrate Developmental Biology Program and Department of Pediatrics, Yale School of Medicine, 333 Cedar St., New Haven, CT 06520, USA
| | - Karel F Liem
- Vertebrate Developmental Biology Program and Department of Pediatrics, Yale School of Medicine, 333 Cedar St., New Haven, CT 06520, USA
| | - Tamara Caspary
- Department of Human Genetics, 615 Michael St., Suite 301, Emory University School of Medicine, Atlanta, GA 30322, USA.
| | - Frédéric Charron
- Montreal Clinical Research Institute (IRCM), 110 Pine Avenue West, Montreal, QC H2W 1R7, Canada; Department of Neuroscience, University of Montreal, Montreal, QC H3T 1J4, Canada; Department of Anatomy and Cell Biology, Division of Experimental Medicine, McGill University, Montreal, QC H3A 0G4, Canada; Department of Medicine, University of Montreal, Montreal, QC H3T 1J4, Canada.
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Muñoz-Estrada J, Ferland RJ. Ahi1 promotes Arl13b ciliary recruitment, regulates Arl13b stability and is required for normal cell migration. J Cell Sci 2019; 132:jcs.230680. [PMID: 31391239 DOI: 10.1242/jcs.230680] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2019] [Accepted: 07/24/2019] [Indexed: 12/14/2022] Open
Abstract
Mutations in the Abelson-helper integration site 1 (AHI1) gene are associated with neurological/neuropsychiatric disorders, and cause the neurodevelopmental ciliopathy Joubert syndrome (JBTS). Here, we show that deletion of the transition zone (TZ) protein Ahi1 in mouse embryonic fibroblasts (MEFs) has a small effect on cilia formation. However, Ahi1 loss in these cells results in: (1) reduced localization of the JBTS-associated protein Arl13b to the ciliary membrane, (2) decreased sonic hedgehog signaling, (3) and an abnormally elongated ciliary axoneme accompanied by an increase in ciliary IFT88 concentrations. While no changes in Arl13b levels are detected in crude cell membrane extracts, loss of Ahi1 significantly reduced the level of non-membrane-associated Arl13b and its stability via the proteasome pathway. Exogenous expression of Ahi1-GFP in Ahi1-/- MEFs restored ciliary length, increased ciliary recruitment of Arl13b and augmented Arl13b stability. Finally, Ahi1-/- MEFs displayed defects in cell motility and Pdgfr-α-dependent migration. Overall, our findings support molecular mechanisms underlying JBTS etiology that involve: (1) disruptions at the TZ resulting in defects of membrane- and non-membrane-associated proteins to localize to primary cilia, and (2) defective cell migration.This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Jesús Muñoz-Estrada
- Department of Neuroscience and Experimental Therapeutics, Albany Medical College, Albany, NY 12208, USA
| | - Russell J Ferland
- Department of Neuroscience and Experimental Therapeutics, Albany Medical College, Albany, NY 12208, USA .,Department of Neurology, Albany Medical College, Albany, NY 12208, USA
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Sterpka A, Chen X. Neuronal and astrocytic primary cilia in the mature brain. Pharmacol Res 2018; 137:114-121. [PMID: 30291873 PMCID: PMC6410375 DOI: 10.1016/j.phrs.2018.10.002] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Revised: 09/28/2018] [Accepted: 10/01/2018] [Indexed: 12/17/2022]
Abstract
Primary cilia are tiny microtubule-based signaling devices that regulate a variety of physiological functions, including metabolism and cell division. Defects in primary cilia lead to a myriad of diseases in humans such as obesity and cancers. In the mature brain, both neurons and astrocytes contain a single primary cilium. Although neuronal primary cilia are not directly involved in synaptic communication, their pathophysiological impacts on obesity and mental disorders are well recognized. In contrast, research on astrocytic primary cilia lags far behind. Currently, little is known about their functions and molecular pathways in the mature brain. Unlike neurons, postnatal astrocytes retain the capacity of cell division and can become reactive and proliferate in response to various brain insults such as epilepsy, ischemia, traumatic brain injury, and neurodegenerative β-amyloid plaques. Since primary cilia derive from the mother centrioles, astrocyte proliferation must occur in coordination with the dismantling and ciliogenesis of astrocyte cilia. In this regard, the functions, signal pathways, and structural dynamics of neuronal and astrocytic primary cilia are fundamentally different. Here we discuss and compare the current understanding of neuronal and astrocytic primary cilia.
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Affiliation(s)
- Ashley Sterpka
- Department of Molecular, Cellular and Biomedical Sciences, University of New Hampshire, Durham, NH, 03824, United States
| | - Xuanmao Chen
- Department of Molecular, Cellular and Biomedical Sciences, University of New Hampshire, Durham, NH, 03824, United States.
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