51
|
Zhang P, Abdelmohsen K, Liu Y, Tominaga-Yamanaka K, Yoon JH, Ioannis G, Martindale JL, Zhang Y, Becker KG, Yang IH, Gorospe M, Mattson MP. Novel RNA- and FMRP-binding protein TRF2-S regulates axonal mRNA transport and presynaptic plasticity. Nat Commun 2015; 6:8888. [PMID: 26586091 PMCID: PMC4673492 DOI: 10.1038/ncomms9888] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2015] [Accepted: 10/06/2015] [Indexed: 02/07/2023] Open
Abstract
Despite considerable evidence that RNA-binding proteins (RBPs) regulate mRNA transport and local translation in dendrites, roles for axonal RBPs are poorly understood. Here we demonstrate that a non-telomeric isoform of telomere repeat-binding factor 2 (TRF2-S) is a novel RBP that regulates axonal plasticity. TRF2-S interacts directly with target mRNAs to facilitate their axonal delivery. The process is antagonized by fragile X mental retardation protein (FMRP). Distinct from the current RNA-binding model of FMRP, we show that FMRP occupies the GAR domain of TRF2-S protein to block the assembly of TRF2-S–mRNA complexes. Overexpressing TRF2-S and silencing FMRP promotes mRNA entry to axons and enhances axonal outgrowth and neurotransmitter release from presynaptic terminals. Our findings suggest a pivotal role for TRF2-S in an axonal mRNA localization pathway that enhances axon outgrowth and neurotransmitter release. The molecular mechanisms regulating axonal mRNA transport are only partially understood. Here, Zhang et al. show a nontelomeric TRF2 splice variant interacts with FMRP to regulate the transport of several axonal mRNAs involved in axonal elongation and neurotransmitter release.
Collapse
Affiliation(s)
- Peisu Zhang
- Laboratory of Neurosciences, National Institute on Aging Intramural Research Program, National Institutes of Health, 251 Bayview Boulevard, Baltimore, Maryland 21224, USA
| | - Kotb Abdelmohsen
- Laboratory of Genetics, National Institute on Aging Intramural Research Program, National Institutes of Health, 251 Bayview Boulevard, Baltimore, Maryland 21224, USA
| | - Yong Liu
- Laboratory of Neurosciences, National Institute on Aging Intramural Research Program, National Institutes of Health, 251 Bayview Boulevard, Baltimore, Maryland 21224, USA
| | - Kumiko Tominaga-Yamanaka
- Laboratory of Genetics, National Institute on Aging Intramural Research Program, National Institutes of Health, 251 Bayview Boulevard, Baltimore, Maryland 21224, USA
| | - Je-Hyun Yoon
- Laboratory of Genetics, National Institute on Aging Intramural Research Program, National Institutes of Health, 251 Bayview Boulevard, Baltimore, Maryland 21224, USA
| | - Grammatikakis Ioannis
- Laboratory of Genetics, National Institute on Aging Intramural Research Program, National Institutes of Health, 251 Bayview Boulevard, Baltimore, Maryland 21224, USA
| | - Jennifer L Martindale
- Laboratory of Genetics, National Institute on Aging Intramural Research Program, National Institutes of Health, 251 Bayview Boulevard, Baltimore, Maryland 21224, USA
| | - Yongqing Zhang
- Laboratory of Genetics, National Institute on Aging Intramural Research Program, National Institutes of Health, 251 Bayview Boulevard, Baltimore, Maryland 21224, USA
| | - Kevin G Becker
- Laboratory of Genetics, National Institute on Aging Intramural Research Program, National Institutes of Health, 251 Bayview Boulevard, Baltimore, Maryland 21224, USA
| | - In Hong Yang
- Department of Biomedical Engineering, National University of Singapore, Singapore 117465, Singapore.,SINAPSE, National University of Singapore, Singapore 117465, Singapore
| | - Myriam Gorospe
- Laboratory of Genetics, National Institute on Aging Intramural Research Program, National Institutes of Health, 251 Bayview Boulevard, Baltimore, Maryland 21224, USA
| | - Mark P Mattson
- Laboratory of Neurosciences, National Institute on Aging Intramural Research Program, National Institutes of Health, 251 Bayview Boulevard, Baltimore, Maryland 21224, USA.,Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
| |
Collapse
|
52
|
Ruby K, Falvey K, Kulesza R. Abnormal neuronal morphology and neurochemistry in the auditory brainstem of Fmr1 knockout rats. Neuroscience 2015; 303:285-98. [DOI: 10.1016/j.neuroscience.2015.06.061] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2015] [Revised: 06/10/2015] [Accepted: 06/27/2015] [Indexed: 01/19/2023]
|
53
|
Guo W, Polich ED, Su J, Gao Y, Christopher DM, Allan AM, Wang M, Wang F, Wang G, Zhao X. Fragile X Proteins FMRP and FXR2P Control Synaptic GluA1 Expression and Neuronal Maturation via Distinct Mechanisms. Cell Rep 2015; 11:1651-66. [PMID: 26051932 DOI: 10.1016/j.celrep.2015.05.013] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2014] [Revised: 02/18/2015] [Accepted: 05/07/2015] [Indexed: 01/01/2023] Open
Abstract
Fragile X mental retardation protein (FMRP) and its autosomal paralog FXR2P are selective neuronal RNA-binding proteins, and mice that lack either protein exhibit cognitive deficits. Although double-mutant mice display more severe learning deficits than single mutants, the molecular mechanism behind this remains unknown. In the present study, we discovered that FXR2P (also known as FXR2) is important for neuronal dendritic development. FMRP and FXR2P additively promote the maturation of new neurons by regulating a common target, the AMPA receptor GluA1, but they do so via distinct mechanisms: FXR2P binds and stabilizes GluA1 mRNA and enhances subsequent protein expression, whereas FMRP promotes GluA1 membrane delivery. Our findings unveil important roles for FXR2P and GluA1 in neuronal development, uncover a regulatory mechanism of GluA1, and reveal a functional convergence between fragile X proteins in neuronal development.
Collapse
Affiliation(s)
- Weixiang Guo
- State Key Laboratory for Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China; Waisman Center, University of Wisconsin-Madison, Madison, WI 53705, USA; Department of Neuroscience, University of Wisconsin-Madison School of Medicine and Public Health, Madison, WI 53705, USA
| | - Eric D Polich
- Waisman Center, University of Wisconsin-Madison, Madison, WI 53705, USA; Department of Neuroscience, University of Wisconsin-Madison School of Medicine and Public Health, Madison, WI 53705, USA
| | - Juan Su
- Waisman Center, University of Wisconsin-Madison, Madison, WI 53705, USA; Department of Neuroscience, University of Wisconsin-Madison School of Medicine and Public Health, Madison, WI 53705, USA
| | - Yu Gao
- Waisman Center, University of Wisconsin-Madison, Madison, WI 53705, USA; Department of Neuroscience, University of Wisconsin-Madison School of Medicine and Public Health, Madison, WI 53705, USA
| | - Devin M Christopher
- Department of Neurosciences, University of New Mexico, Albuquerque, NM 87131, USA
| | - Andrea M Allan
- Department of Neurosciences, University of New Mexico, Albuquerque, NM 87131, USA
| | - Min Wang
- State Key Laboratory for Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
| | - Feifei Wang
- Waisman Center, University of Wisconsin-Madison, Madison, WI 53705, USA; Department of Neuroscience, University of Wisconsin-Madison School of Medicine and Public Health, Madison, WI 53705, USA
| | - Guangfu Wang
- Department of Pharmacology, School of Medicine, University of Virginia, Charlottesville, VA 22908, USA
| | - Xinyu Zhao
- Waisman Center, University of Wisconsin-Madison, Madison, WI 53705, USA; Department of Neuroscience, University of Wisconsin-Madison School of Medicine and Public Health, Madison, WI 53705, USA.
| |
Collapse
|
54
|
Schilit Nitenson A, Stackpole EE, Truszkowski TLS, Midroit M, Fallon JR, Bath KG. Fragile X mental retardation protein regulates olfactory sensitivity but not odorant discrimination. Chem Senses 2015; 40:345-50. [PMID: 25917509 DOI: 10.1093/chemse/bjv019] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Fragile X syndrome (FXS) is the most common cause of inherited intellectual disability and is characterized by cognitive impairments and altered sensory function. It is caused by absence of fragile X mental retardation protein (FMRP), an RNA-binding protein essential for normal synaptic plasticity and function. Animal models have provided important insights into mechanisms through which loss of FMRP impacts cognitive and sensory development and function. While FMRP is highly enriched in the developing and adult olfactory bulb (OB), its role in olfactory sensory function remains poorly understood. Here, we used a mouse model of FXS, the fmr1 (-/y) mouse, to test whether loss of FMRP impacts olfactory discrimination, habituation, or sensitivity using a spontaneous olfactory cross-habituation task at a range of odorant concentrations. We demonstrated that fmr1 (-/y) mice have a significant decrease in olfactory sensitivity compared with wild type controls. When we controlled for differences in sensitivity, we found no effect of loss of FMRP on the ability to habituate to or spontaneously discriminate between odorants. These data indicate that loss of FMRP significantly alters olfactory sensitivity, but not other facets of basal olfactory function. These findings have important implications for future studies aimed at understanding the role of FMRP on sensory functioning.
Collapse
Affiliation(s)
| | - Emily E Stackpole
- Department of Neuroscience, Brown University, 185 Meeting Street, Providence, RI 02912, USA
| | - Torrey L S Truszkowski
- Department of Neuroscience, Brown University, 185 Meeting Street, Providence, RI 02912, USA
| | - Maellie Midroit
- Universitie Claude Bernard Lyon, Universite de Lyon, Lyon, France
| | - Justin R Fallon
- Department of Neuroscience, Brown University, 185 Meeting Street, Providence, RI 02912, USA
| | - Kevin G Bath
- Department of Neuroscience, Brown University, 185 Meeting Street, Providence, RI 02912, USA, Department of Cognitive, Linguistic and Psychological Sciences, Brown University, 190 Thayer Street, Providence, RI 02912, USA
| |
Collapse
|
55
|
Wang GX, Smith SJ, Mourrain P. Fmr1 KO and fenobam treatment differentially impact distinct synapse populations of mouse neocortex. Neuron 2015; 84:1273-86. [PMID: 25521380 DOI: 10.1016/j.neuron.2014.11.016] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/18/2014] [Indexed: 02/07/2023]
Abstract
Cognitive deficits in fragile X syndrome (FXS) are attributed to molecular abnormalities of the brain's vast and heterogeneous synapse populations. Unfortunately, the density of synapses coupled with their molecular heterogeneity presents formidable challenges in understanding the specific contribution of synapse changes in FXS. We demonstrate powerful new methods for the large-scale molecular analysis of individual synapses that allow quantification of numerous specific changes in synapse populations present in the cortex of a mouse model of FXS. Analysis of nearly a million individual synapses reveals distinct, quantitative changes in synaptic proteins distributed across over 6,000 pairwise metrics. Some, but not all, of these synaptic alterations are reversed by treatment with the candidate therapeutic fenobam, an mGluR5 antagonist. These patterns of widespread, but diverse synaptic protein changes in response to global perturbation suggest that FXS and its treatment must be understood as a networked system at the synapse level.
Collapse
Affiliation(s)
- Gordon X Wang
- Center for Sleep Sciences and Medicine, Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, CA 94305, USA; Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305, USA.
| | - Stephen J Smith
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305, USA; Allen Institute for Brain Science, Seattle, WA 98103, USA
| | - Philippe Mourrain
- Center for Sleep Sciences and Medicine, Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, CA 94305, USA; INSERM 1024, Ecole Normale Supérieure Paris, 75005, France
| |
Collapse
|
56
|
Bonaccorso CM, Spatuzza M, Di Marco B, Gloria A, Barrancotto G, Cupo A, Musumeci SA, D'Antoni S, Bardoni B, Catania MV. Fragile X mental retardation protein (FMRP) interacting proteins exhibit different expression patterns during development. Int J Dev Neurosci 2015; 42:15-23. [PMID: 25681562 DOI: 10.1016/j.ijdevneu.2015.02.004] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2014] [Revised: 01/30/2015] [Accepted: 02/10/2015] [Indexed: 11/26/2022] Open
Abstract
Fragile X syndrome is caused by the lack of expression of fragile X mental retardation protein (FMRP), an RNA-binding protein involved in mRNA transport and translation. FMRP is a component of mRNA ribonucleoprotein complexes and it can interact with a range of proteins either directly or indirectly, as demonstrated by two-hybrid selection and co-immunoprecipitation, respectively. Most of FMRP-interacting proteins are RNA-binding proteins such as FXR1P, FXR2P and 82-FIP. Interestingly, FMRP can also interact directly with the cytoplasmic proteins CYFIP1 and CYFIP2, which do not bind RNA and link FMRP to the RhoGTPase pathway. The interaction with these different proteins may modulate the functions of FMRP by influencing its affinity to RNA and by affecting the FMRP ability of cytoskeleton remodeling through Rho/Rac GTPases. To better define the relationship of FMRP with its interacting proteins during brain development, we have analyzed the expression pattern of FMRP and its interacting proteins in the cortex, striatum, hippocampus and cerebellum at different ages in wild type (WT) mice. FMRP and FXR2P were strongly expressed during the first week and gradually decreased thereafter, more rapidly in the cerebellum than in the cortex. FXR1P was also expressed early and showed a reduction at later stages of development with a similar developmental pattern in these two regions. CYFIP1 was expressed at all ages and peaked in the third post-natal week. In contrast, CYFIP2 and 82-FIP (only in forebrain regions) were moderately expressed at P3 and gradually increased after P7. In general, the expression pattern of each protein was similar in the regions examined, except for 82-FIP, which exhibited a strong expression at P3 and low levels at later developmental stages in the cerebellum. Our data indicate that FMRP and its interacting proteins have distinct developmental patterns of expression and suggest that FMRP may be preferentially associated to certain proteins in early and late developmental periods. In particular, the RNA-binding and cytoskeleton remodeling functions of FMRP may be differently modulated during development.
Collapse
Affiliation(s)
| | - M Spatuzza
- Institute of Neurological Sciences, CNR, Catania, Italy
| | - B Di Marco
- Institute of Neurological Sciences, CNR, Catania, Italy; International PhD Program in Neuropharmacology, Department of Clinical and Molecular Biomedicine, University of Catania, Italy
| | - A Gloria
- IRCCS Oasi Maria SS, Troina, EN, Italy
| | | | - A Cupo
- CNRS UMR 7275, Institute of Molecular and Cellular Pharmacology, Valbonne Sophia-Antipolis, France; University of Nice Sophia-Antipolis, Nice, France
| | | | - S D'Antoni
- Institute of Neurological Sciences, CNR, Catania, Italy
| | - B Bardoni
- CNRS UMR 7275, Institute of Molecular and Cellular Pharmacology, Valbonne Sophia-Antipolis, France; University of Nice Sophia-Antipolis, Nice, France; CNRS LIA "NEOGENEX", Valbonne Sophia-Antipolis, France
| | - M V Catania
- IRCCS Oasi Maria SS, Troina, EN, Italy; Institute of Neurological Sciences, CNR, Catania, Italy.
| |
Collapse
|
57
|
Koga K, Liu MG, Qiu S, Song Q, O'Den G, Chen T, Zhuo M. Impaired presynaptic long-term potentiation in the anterior cingulate cortex of Fmr1 knock-out mice. J Neurosci 2015; 35:2033-43. [PMID: 25653361 PMCID: PMC6705363 DOI: 10.1523/jneurosci.2644-14.2015] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2014] [Revised: 11/24/2014] [Accepted: 12/18/2014] [Indexed: 01/08/2023] Open
Abstract
Fragile X syndrome is a common inherited form of mental impairment. Fragile X mental retardation protein (FMRP) plays important roles in the regulation of synaptic protein synthesis, and loss of FMRP leads to deficits in learning-related synaptic plasticity and behavioral disability. Previous studies mostly focus on postsynaptic long-term potentiation (LTP) in Fmr1 knock-out (KO) mice. Here, we investigate the role of FMRP in presynaptic LTP (pre-LTP) in the adult mouse anterior cingulate cortex (ACC). Low-frequency stimulation induced LTP in layer II/III pyramidal neurons under the voltage-clamp mode. Paired-pulse ratio, which is a parameter for presynaptic changes, was decreased after the low-frequency stimulation in Fmr1 wild-type (WT) mice. Cingulate pre-LTP was abolished in Fmr1 KO mice. We also used a 64-electrode array system for field EPSP recording and found that the combination of low-frequency stimulation paired with a GluK1-containing kainate receptor agonist induced NMDA receptor-independent and metabotropic glutamate receptor-dependent pre-LTP in the WT mice. This potentiation was blocked in Fmr1 KO mice. Biochemical experiments showed that Fmr1 KO mice displayed altered translocation of protein kinase A subunits in the ACC. Our results demonstrate that FMRP plays an important role in pre-LTP in the adult mouse ACC, and loss of this pre-LTP may explain some of the behavioral deficits in Fmr1 KO mice.
Collapse
Affiliation(s)
- Kohei Koga
- Department of Physiology, Faculty of Medicine, University of Toronto, Medical Science Building, Toronto, Ontario, M5S 1A8, Canada, Center for Neuron and Disease, Frontier Institutes of Science and Technology, Xi'an Jiaotong University, Xi'an, Shanxi 710049, China
| | - Ming-Gang Liu
- Department of Physiology, Faculty of Medicine, University of Toronto, Medical Science Building, Toronto, Ontario, M5S 1A8, Canada, Department of Anatomy and Histology and Embryology, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China, and
| | - Shuang Qiu
- Department of Physiology, Faculty of Medicine, University of Toronto, Medical Science Building, Toronto, Ontario, M5S 1A8, Canada, Center for Neuron and Disease, Frontier Institutes of Science and Technology, Xi'an Jiaotong University, Xi'an, Shanxi 710049, China
| | - Qian Song
- Department of Physiology, Faculty of Medicine, University of Toronto, Medical Science Building, Toronto, Ontario, M5S 1A8, Canada, Center for Neuron and Disease, Frontier Institutes of Science and Technology, Xi'an Jiaotong University, Xi'an, Shanxi 710049, China
| | - Gerile O'Den
- Center for Neuron and Disease, Frontier Institutes of Science and Technology, Xi'an Jiaotong University, Xi'an, Shanxi 710049, China
| | - Tao Chen
- Department of Physiology, Faculty of Medicine, University of Toronto, Medical Science Building, Toronto, Ontario, M5S 1A8, Canada, Center for Neuron and Disease, Frontier Institutes of Science and Technology, Xi'an Jiaotong University, Xi'an, Shanxi 710049, China, Department of Anatomy and KK Leung Brain Research Center, Fourth Military Medical University, Xi'an, Shanxi 710032, China
| | - Min Zhuo
- Department of Physiology, Faculty of Medicine, University of Toronto, Medical Science Building, Toronto, Ontario, M5S 1A8, Canada, Center for Neuron and Disease, Frontier Institutes of Science and Technology, Xi'an Jiaotong University, Xi'an, Shanxi 710049, China,
| |
Collapse
|
58
|
Independent role for presynaptic FMRP revealed by an FMR1 missense mutation associated with intellectual disability and seizures. Proc Natl Acad Sci U S A 2015; 112:949-56. [PMID: 25561520 DOI: 10.1073/pnas.1423094112] [Citation(s) in RCA: 90] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Fragile X syndrome (FXS) results in intellectual disability (ID) most often caused by silencing of the fragile X mental retardation 1 (FMR1) gene. The resulting absence of fragile X mental retardation protein 1 (FMRP) leads to both pre- and postsynaptic defects, yet whether the pre- and postsynaptic functions of FMRP are independent and have distinct roles in FXS neuropathology remain poorly understood. Here, we demonstrate an independent presynaptic function for FMRP through the study of an ID patient with an FMR1 missense mutation. This mutation, c.413G > A (R138Q), preserves FMRP's canonical functions in RNA binding and translational regulation, which are traditionally associated with postsynaptic compartments. However, neuronally driven expression of the mutant FMRP is unable to rescue structural defects at the neuromuscular junction in fragile x mental retardation 1 (dfmr1)-deficient Drosophila, suggesting a presynaptic-specific impairment. Furthermore, mutant FMRP loses the ability to rescue presynaptic action potential (AP) broadening in Fmr1 KO mice. The R138Q mutation also disrupts FMRP's interaction with the large-conductance calcium-activated potassium (BK) channels that modulate AP width. These results reveal a presynaptic- and translation-independent function of FMRP that is linked to a specific subset of FXS phenotypes.
Collapse
|
59
|
Gholizadeh S, Halder SK, Hampson DR. Expression of fragile X mental retardation protein in neurons and glia of the developing and adult mouse brain. Brain Res 2015; 1596:22-30. [DOI: 10.1016/j.brainres.2014.11.023] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2014] [Accepted: 11/10/2014] [Indexed: 01/20/2023]
|
60
|
Stackpole EE, Akins MR, Fallon JR. N-myristoylation regulates the axonal distribution of the Fragile X-related protein FXR2P. Mol Cell Neurosci 2014; 62:42-50. [PMID: 25109237 DOI: 10.1016/j.mcn.2014.08.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2014] [Revised: 07/21/2014] [Accepted: 08/06/2014] [Indexed: 12/20/2022] Open
Abstract
Fragile X syndrome, the leading cause of inherited intellectual disability and autism, is caused by loss of function of Fragile X mental retardation protein (FMRP). FMRP is an RNA binding protein that regulates local protein synthesis in the somatodendritic compartment. However, emerging evidence also indicates important roles for FMRP in axonal and presynaptic functions. In particular, FMRP and its homologue FXR2P localize axonally and presynaptically to discrete endogenous structures in the brain termed Fragile X granules (FXGs). FXR2P is a component of all FXGs and is necessary for the axonal and presynaptic localization of FMRP to these structures. We therefore sought to identify and characterize structural features of FXR2P that regulate its axonal localization. Sequence analysis reveals that FXR2P harbors a consensus N-terminal myristoylation sequence (MGXXXS) that is absent in FMRP. Using click chemistry with wild type and an unmyristoylatable G2A mutant we demonstrate that FXR2P is N-myristoylated on glycine 2, establishing it as a lipid-modified RNA binding protein. To investigate the role of FXR2P N-myristoylation in neurons we generated fluorescently tagged wild type and unmyristoylatable FXR2P (WT and G2A, respectively) and expressed them in primary cortical cultures. Both FXR2P(WT) and FXR2P(G2A) are expressed at equivalent overall levels and are capable of forming FMRP-containing axonal granules. However, FXR2P(WT) granules are largely restricted to proximal axonal segments while granules formed with unmyristoylatable FXR2P(G2A) are localized throughout the axonal arbor, including in growth cones. These studies indicate that N-terminal myristoylation of the RNA binding protein FXR2P regulates its localization within the axonal arbor. Moreover, since FMRP localization within axonal domains requires its association with FXR2P, these findings suggest that FXR2P lipid modification is a control point for the axonal and presynaptic distribution of FMRP.
Collapse
Affiliation(s)
- Emily E Stackpole
- Department of Neuroscience, Brown University, Providence, RI 02912, USA
| | - Michael R Akins
- Department of Neuroscience, Brown University, Providence, RI 02912, USA; Department of Biology, Drexel University, Philadelphia, PA 19104, USA
| | - Justin R Fallon
- Department of Neuroscience, Brown University, Providence, RI 02912, USA.
| |
Collapse
|
61
|
Li Y, Zhao X. Concise review: Fragile X proteins in stem cell maintenance and differentiation. Stem Cells 2014; 32:1724-33. [PMID: 24648324 PMCID: PMC4255947 DOI: 10.1002/stem.1698] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2014] [Revised: 02/18/2014] [Accepted: 03/01/2014] [Indexed: 12/15/2022]
Abstract
Fragile X syndrome (FXS), the most common genetic form of autism spectrum disorder, is caused by deficiency of the fragile X mental retardation protein (FMRP). Despite extensive research and scientific progress, understanding how FMRP regulates brain development and function remains a major challenge. FMRP is a neuronal RNA-binding protein that binds about a third of messenger RNAs in the brain and controls their translation, stability, and cellular localization. The absence of FMRP results in increased protein synthesis, leading to enhanced signaling in a number of intracellular pathways, including the mTOR, mGLuR5, ERK, Gsk3β, PI3K, and insulin pathways. Until recently, FXS was largely considered a deficit of mature neurons; however, a number of new studies have shown that FMRP may also play important roles in stem cells, among them neural stem cells, germline stem cells, and pluripotent stem cells. In this review, we will cover these newly discovered functions of FMRP, as well as the other two fragile X-related proteins, in stem cells. We will also discuss the literature on the use of stem cells, particularly neural stem cells and induced pluripotent stem cells, as model systems for studying the functions of FMRP in neuronal development.
Collapse
Affiliation(s)
- Yue Li
- Waisman Center and Department of Neuroscience, University of Wisconsin-Madison School of Medicine and Public Health, Madison, Wisconsin, USA
| | | |
Collapse
|
62
|
Beebe K, Wang Y, Kulesza R. Distribution of fragile X mental retardation protein in the human auditory brainstem. Neuroscience 2014; 273:79-91. [PMID: 24838064 DOI: 10.1016/j.neuroscience.2014.05.006] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2014] [Revised: 04/29/2014] [Accepted: 05/02/2014] [Indexed: 01/20/2023]
Abstract
Fragile X mental retardation protein (FMRP) binds select mRNAs, functions in intracellular transport of these mRNAs and represses their translation. FMRP is highly expressed in neurons and lack of FMRP has been shown to result in dendritic dysmorphology and altered synaptic function. FMRP is known to interact with mRNAs for the Kv3.1b potassium channel which is required for neurons to fire action potentials at high rates with remarkable temporal precision. Auditory brainstem neurons are known for remarkably high spike rates and expression of Kv3.1b potassium channels. Fragile X syndrome (FXS) is a genetic disorder caused by a mutation in the fragile X mental retardation 1 gene (Fmr1) resulting in decreased expression of FMRP and subsequent intellectual disability, seizures, attention deficit and hypersensitivity to auditory and other sensory stimuli. We therefore hypothesize that the auditory difficulties in FXS result, at least in part, from dysfunction of auditory brainstem neurons. To examine this hypothesis, we have studied normal human brainstem tissue with immunohistochemical techniques and confocal microscopy. Our results demonstrate that FMRP is widely expressed in cell bodies and dendritic arbors of neurons in the human cochlear nucleus and superior olivary complex and also that coincidence detector neurons of the medial superior olive colocalization of FMRP and Kv3.1b. We interpret these observations to suggest that the lower auditory brainstem is a potential site of dysfunction in FXS.
Collapse
Affiliation(s)
- K Beebe
- Lake Erie College of Osteopathic Medicine, Auditory Research Center, Erie, PA, USA
| | - Y Wang
- Virginia Merrill Bloedel Hearing Research Center, Department of Otolaryngology-Head and Neck Surgery, University of Washington School of Medicine, Seattle, WA, USA
| | - R Kulesza
- Lake Erie College of Osteopathic Medicine, Auditory Research Center, Erie, PA, USA.
| |
Collapse
|
63
|
Gomes C, Merianda TT, Lee SJ, Yoo S, Twiss JL. Molecular determinants of the axonal mRNA transcriptome. Dev Neurobiol 2014; 74:218-32. [PMID: 23959706 PMCID: PMC3933445 DOI: 10.1002/dneu.22123] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2013] [Revised: 08/05/2013] [Accepted: 08/13/2013] [Indexed: 12/12/2022]
Abstract
Axonal protein synthesis has been shown to play a role in developmental and regenerative growth, as well as in cell body responses to axotomy. Recent studies have begun to identify the protein products that contribute to these autonomous responses of axons. In the peripheral nervous system, intra-axonal protein synthesis has been implicated in the localized in vivo responses to neuropathic stimuli, and there is emerging evidence for protein synthesis in CNS axons in vivo. Despite that hundreds of mRNAs have now been shown to localize into the axonal compartment, knowledge of what RNA binding proteins are responsible for this is quite limited. Here, we review the current state of knowledge of RNA transport mechanisms and highlight recently uncovered mechanisms for dynamically altering the axonal transcriptome. Both changes in the levels or activities of components of the RNA transport apparatus and alterations in transcription of transported mRNAs can effectively shift the axonal mRNA population. Consistent with this, the axonal RNA population shifts with development, with changes in growth state, and in response to extracellular stimulation. Each of these events must impact the transcriptional and transport apparatuses of the neuron, thus directly and indirectly modifying the axonal transcriptome.
Collapse
Affiliation(s)
- Cynthia Gomes
- Department of Biology, Drexel University, Philadelphia, Pennsylvania 19104 USA
| | - Tanuja T. Merianda
- Department of Biology, Drexel University, Philadelphia, Pennsylvania 19104 USA
| | - Seung Joon Lee
- Department of Biology, Drexel University, Philadelphia, Pennsylvania 19104 USA
| | - Soonmoon Yoo
- Nemours Biomedical Research, Alfred I. duPont Hospital for Children, Wilmington, Delaware 19803 USA
| | - Jeffery L. Twiss
- Department of Biology, Drexel University, Philadelphia, Pennsylvania 19104 USA
- Department of Biological Sciences, University of South Carolina, Columbia, South Carolina 29201
| |
Collapse
|
64
|
Hsiao K, Bozdagi O, Benson DL. Axonal cap-dependent translation regulates presynaptic p35. Dev Neurobiol 2013; 74:351-64. [PMID: 24254883 DOI: 10.1002/dneu.22154] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2013] [Accepted: 11/14/2013] [Indexed: 01/19/2023]
Abstract
Axonal growth cones synthesize proteins during development and in response to injury in adult animals. Proteins locally translated in axons are used to generate appropriate responses to guidance cues, contribute to axon growth, and can serve as retrograde messengers. In addition to growth cones, mRNAs and translational machinery are also found along the lengths of axons where synapses form en passant, but contributions of intra-axonal translation to developing synapses are poorly understood. Here, we engineered a subcellular-targeting translational repressor to inhibit mRNA translation in axons, and we used this strategy to investigate presynaptic contributions of cap-dependent protein translation to developing CNS synapses. Our data show that intra-axonal mRNA translation restrains synaptic vesicle recycling pool size and that one target of this regulation is p35, a Cdk5 activating protein. Cdk5/p35 signaling regulates the size of vesicle recycling pools, p35 levels diminish when cap-dependent translation is repressed, and restoring p35 levels rescues vesicle recycling pools from the effects of spatially targeted translation repression. Together our findings show that intra-axonal synthesis of p35 is required for normal vesicle recycling in developing neurons, and that targeted translational repression provides a novel strategy to investigate extrasomal protein synthesis in neurons.
Collapse
Affiliation(s)
- Kuangfu Hsiao
- Department of Neuroscience, Friedman Brain Institute, Icahn School of Medicine and Graduate School of Biomedical Sciences at Mount Sinai, New York, New York, 10029
| | | | | |
Collapse
|
65
|
Wondolowski J, Dickman D. Emerging links between homeostatic synaptic plasticity and neurological disease. Front Cell Neurosci 2013; 7:223. [PMID: 24312013 PMCID: PMC3836049 DOI: 10.3389/fncel.2013.00223] [Citation(s) in RCA: 95] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2013] [Accepted: 11/03/2013] [Indexed: 01/22/2023] Open
Abstract
Homeostatic signaling systems are ubiquitous forms of biological regulation, having been studied for hundreds of years in the context of diverse physiological processes including body temperature and osmotic balance. However, only recently has this concept been brought to the study of excitatory and inhibitory electrical activity that the nervous system uses to establish and maintain stable communication. Synapses are a primary target of neuronal regulation with a variety of studies over the past 15 years demonstrating that these cellular junctions are under bidirectional homeostatic control. Recent work from an array of diverse systems and approaches has revealed exciting new links between homeostatic synaptic plasticity and a variety of seemingly disparate neurological and psychiatric diseases. These include autism spectrum disorders, intellectual disabilities, schizophrenia, and Fragile X Syndrome. Although the molecular mechanisms through which defective homeostatic signaling may lead to disease pathogenesis remain unclear, rapid progress is likely to be made in the coming years using a powerful combination of genetic, imaging, electrophysiological, and next generation sequencing approaches. Importantly, understanding homeostatic synaptic plasticity at a cellular and molecular level may lead to developments in new therapeutic innovations to treat these diseases. In this review we will examine recent studies that demonstrate homeostatic control of postsynaptic protein translation, retrograde signaling, and presynaptic function that may contribute to the etiology of complex neurological and psychiatric diseases.
Collapse
Affiliation(s)
- Joyce Wondolowski
- Department of Biology, University of Southern California Los Angeles, CA, USA
| | | |
Collapse
|
66
|
Perry RB, Fainzilber M. Local translation in neuronal processes-in vivotests of a “heretical hypothesis”. Dev Neurobiol 2013; 74:210-7. [DOI: 10.1002/dneu.22115] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2013] [Revised: 07/19/2013] [Accepted: 07/28/2013] [Indexed: 12/22/2022]
Affiliation(s)
- Rotem B. Perry
- Department of Biological Chemistry; Weizmann Institute of Science; 76100 Rehovot Israel
| | - Mike Fainzilber
- Department of Biological Chemistry; Weizmann Institute of Science; 76100 Rehovot Israel
| |
Collapse
|
67
|
Cook D, Nuro E, Murai KK. Increasing our understanding of human cognition through the study of Fragile X Syndrome. Dev Neurobiol 2013; 74:147-77. [PMID: 23723176 PMCID: PMC4216185 DOI: 10.1002/dneu.22096] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2013] [Accepted: 05/17/2013] [Indexed: 12/16/2022]
Abstract
Fragile X Syndrome (FXS) is considered the most common form of inherited intellectual disability. It is caused by reductions in the expression level or function of a single protein, the Fragile X Mental Retardation Protein (FMRP), a translational regulator which binds to approximately 4% of brain messenger RNAs. Accumulating evidence suggests that FXS is a complex disorder of cognition, involving interactions between genetic and environmental influences, leading to difficulties in acquiring key life skills including motor skills, language, and proper social behaviors. Since many FXS patients also present with one or more features of autism spectrum disorders (ASDs), insights gained from studying the monogenic basis of FXS could pave the way to a greater understanding of underlying features of multigenic ASDs. Here we present an overview of the FXS and FMRP field with the goal of demonstrating how loss of a single protein involved in translational control affects multiple stages of brain development and leads to debilitating consequences on human cognition. We also focus on studies which have rescued or improved FXS symptoms in mice using genetic or therapeutic approaches to reduce protein expression. We end with a brief description of how deficits in translational control are implicated in FXS and certain cases of ASDs, with many recent studies demonstrating that ASDs are likely caused by increases or decreases in the levels of certain key synaptic proteins. The study of FXS and its underlying single genetic cause offers an invaluable opportunity to study how a single gene influences brain development and behavior.
Collapse
Affiliation(s)
- Denise Cook
- Department of Neurology and Neurosurgery, Centre for Research in Neuroscience, The Research Institute of the McGill University Health Centre, Montreal General Hospital, Montreal, Quebec, Canada
| | | | | |
Collapse
|
68
|
Hörnberg H, Holt C. RNA-binding proteins and translational regulation in axons and growth cones. Front Neurosci 2013; 7:81. [PMID: 23734093 PMCID: PMC3661996 DOI: 10.3389/fnins.2013.00081] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2013] [Accepted: 05/06/2013] [Indexed: 01/11/2023] Open
Abstract
RNA localization and regulation play an important role in the developing and adult nervous system. In navigating axons, extrinsic cues can elicit rapid local protein synthesis that mediates directional or morphological responses. The mRNA repertoire in axons is large and dynamically changing, yet studies suggest that only a subset of these mRNAs are translated after cue stimulation, suggesting the need for a high level of translational regulation. Here, we review the role of RNA-binding proteins (RBPs) as local regulators of translation in developing axons. We focus on their role in growth, guidance, and synapse formation, and discuss the mechanisms by which they regulate translation in axons.
Collapse
Affiliation(s)
- Hanna Hörnberg
- Department of Physiology Development and Neuroscience, University of Cambridge Cambridge, UK
| | | |
Collapse
|
69
|
Deng PY, Rotman Z, Blundon JA, Cho Y, Cui J, Cavalli V, Zakharenko SS, Klyachko VA. FMRP regulates neurotransmitter release and synaptic information transmission by modulating action potential duration via BK channels. Neuron 2013; 77:696-711. [PMID: 23439122 DOI: 10.1016/j.neuron.2012.12.018] [Citation(s) in RCA: 257] [Impact Index Per Article: 23.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/11/2012] [Indexed: 01/06/2023]
Abstract
Loss of FMRP causes fragile X syndrome (FXS), but the physiological functions of FMRP remain highly debatable. Here we show that FMRP regulates neurotransmitter release in CA3 pyramidal neurons by modulating action potential (AP) duration. Loss of FMRP leads to excessive AP broadening during repetitive activity, enhanced presynaptic calcium influx, and elevated neurotransmitter release. The AP broadening defects caused by FMRP loss have a cell-autonomous presynaptic origin and can be acutely rescued in postnatal neurons. These presynaptic actions of FMRP are translation independent and are mediated selectively by BK channels via interaction of FMRP with BK channel's regulatory β4 subunits. Information-theoretical analysis demonstrates that loss of these FMRP functions causes marked dysregulation of synaptic information transmission. FMRP-dependent AP broadening is not limited to the hippocampus, but also occurs in cortical pyramidal neurons. Our results thus suggest major translation-independent presynaptic functions of FMRP that may have important implications for understanding FXS neuropathology.
Collapse
Affiliation(s)
- Pan-Yue Deng
- Departments of Biomedical Engineering and Cell Biology and Physiology, CIMED, Washington University, St. Louis, MO 63110, USA
| | | | | | | | | | | | | | | |
Collapse
|