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Shields MC, Bowers MR, Kramer HL, Fulcer MM, Perinet LC, Metz MJ, Reist NE. The role of the C2A domain of synaptotagmin 1 in asynchronous neurotransmitter release. PLoS One 2020; 15:e0232991. [PMID: 32407359 PMCID: PMC7224543 DOI: 10.1371/journal.pone.0232991] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Accepted: 04/24/2020] [Indexed: 11/22/2022] Open
Abstract
Following nerve stimulation, there are two distinct phases of Ca2+-dependent neurotransmitter release: a fast, synchronous release phase, and a prolonged, asynchronous release phase. Each of these phases is tightly regulated and mediated by distinct mechanisms. Synaptotagmin 1 is the major Ca2+ sensor that triggers fast, synchronous neurotransmitter release upon Ca2+ binding by its C2A and C2B domains. It has also been implicated in the inhibition of asynchronous neurotransmitter release, as blocking Ca2+ binding by the C2A domain of synaptotagmin 1 results in increased asynchronous release. However, the mutation used to block Ca2+ binding in the previous experiments (aspartate to asparagine mutations, sytD-N) had the unintended side effect of mimicking Ca2+ binding, raising the possibility that the increase in asynchronous release was directly caused by ostensibly constitutive Ca2+ binding. Thus, rather than modulating an asynchronous sensor, sytD-N may be mimicking one. To directly test the C2A inhibition hypothesis, we utilized an alternate C2A mutation that we designed to block Ca2+ binding without mimicking it (an aspartate to glutamate mutation, sytD-E). Analysis of both the original sytD-N mutation and our alternate sytD-E mutation at the Drosophila neuromuscular junction showed differential effects on asynchronous release, as well as on synchronous release and the frequency of spontaneous release. Importantly, we found that asynchronous release is not increased in the sytD-E mutant. Thus, our work provides new mechanistic insight into synaptotagmin 1 function during Ca2+-evoked synaptic transmission and demonstrates that Ca2+ binding by the C2A domain of synaptotagmin 1 does not inhibit asynchronous neurotransmitter release in vivo.
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Affiliation(s)
- Mallory C. Shields
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
- Molecular, Cellular, and Integrative Neuroscience Program, Colorado State University, Fort Collins, Colorado, United States of America
| | - Matthew R. Bowers
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
- Molecular, Cellular, and Integrative Neuroscience Program, Colorado State University, Fort Collins, Colorado, United States of America
| | - Hannah L. Kramer
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
| | - McKenzie M. Fulcer
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
| | - Lara C. Perinet
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
| | - Marissa J. Metz
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
- Molecular, Cellular, and Integrative Neuroscience Program, Colorado State University, Fort Collins, Colorado, United States of America
| | - Noreen E. Reist
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
- Molecular, Cellular, and Integrative Neuroscience Program, Colorado State University, Fort Collins, Colorado, United States of America
- * E-mail:
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Aquino-Martinez R, Farr JN, Weivoda MM, Negley BA, Onken JL, Thicke BS, Fulcer MM, Fraser DG, van Wijnen AJ, Khosla S, Monroe DG. miR-219a-5p Regulates Rorβ During Osteoblast Differentiation and in Age-related Bone Loss. J Bone Miner Res 2019; 34:135-144. [PMID: 30321475 PMCID: PMC6450079 DOI: 10.1002/jbmr.3586] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/25/2018] [Revised: 08/29/2018] [Accepted: 09/10/2018] [Indexed: 12/24/2022]
Abstract
Developing novel approaches to treat skeletal disorders requires an understanding of how critical molecular factors regulate osteoblast differentiation and bone remodeling. We have reported that (1) retinoic acid receptor-related orphan receptor beta (Rorβ) is upregulated in bone samples isolated from aged mice and humans in vivo; (2) Rorβ expression is inhibited during osteoblastic differentiation in vitro; and (3) genetic deletion of Rorβ in mice results in preservation of bone mass during aging. These data establish that Rorβ inhibits osteogenesis and that strict control of Rorβ expression is essential for bone homeostasis. Because microRNAs (miRNAs) are known to play important roles in the regulation of gene expression in bone, we explored whether a predicted subset of nine miRNAs regulates Rorβ expression during both osteoblast differentiation and aging. Mouse osteoblastic cells were differentiated in vitro and assayed for Rorβ and miRNA expression. As Rorβ levels declined with differentiation, the expression of many of these miRNAs, including miR-219a-5p, was increased. We further demonstrated that miR-219a-5p was decreased in bone samples from old (24-month) mice, as compared with young (6-month) mice, concomitant with increased Rorβ expression. Importantly, we also found that miR-219a-5p expression was decreased in aged human bone biopsies compared with young controls, demonstrating that this phenomenon also occurs in aging bone in humans. Inhibition of miR-219a-5p in mouse calvarial osteoblasts led to increased Rorβ expression and decreased alkaline phosphatase expression and activity, whereas a miR-219a-5p mimic decreased Rorβ expression and increased osteogenic activity. Finally, we demonstrated that miR-219a-5p physically interacts with Rorβ mRNA in osteoblasts, defining Rorβ as a true molecular target of miR-219a-5p. Overall, our findings demonstrate that miR-219a-5p is involved in the regulation of Rorβ in both mouse and human bone. © 2018 American Society for Bone and Mineral Research.
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Affiliation(s)
- Ruben Aquino-Martinez
- Department of Medicine, Division of Endocrinology, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Joshua N Farr
- Department of Medicine, Division of Endocrinology, Mayo Clinic College of Medicine, Rochester, MN, USA
- Robert and Arlene Kogod Center on Aging, Rochester, MN, USA
| | - Megan M Weivoda
- Department of Medicine, Division of Endocrinology, Mayo Clinic College of Medicine, Rochester, MN, USA
- Robert and Arlene Kogod Center on Aging, Rochester, MN, USA
| | - Brittany A Negley
- Department of Medicine, Division of Endocrinology, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Jennifer L Onken
- Department of Medicine, Division of Endocrinology, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Brianne S Thicke
- Department of Medicine, Division of Endocrinology, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - McKenzie M Fulcer
- Department of Medicine, Division of Endocrinology, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Daniel G Fraser
- Department of Medicine, Division of Endocrinology, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Andre J van Wijnen
- Department of Orthopedic Surgery, Mayo Clinic College of Medicine, Rochester, MN, USA
| | - Sundeep Khosla
- Department of Medicine, Division of Endocrinology, Mayo Clinic College of Medicine, Rochester, MN, USA
- Robert and Arlene Kogod Center on Aging, Rochester, MN, USA
| | - David G Monroe
- Department of Medicine, Division of Endocrinology, Mayo Clinic College of Medicine, Rochester, MN, USA
- Robert and Arlene Kogod Center on Aging, Rochester, MN, USA
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Shields MC, Bowers MR, Fulcer MM, Bollig MK, Rock PJ, Sutton BR, Vrailas-Mortimer AD, Lochmüller H, Whittaker RG, Horvath R, Reist NE. Drosophila studies support a role for a presynaptic synaptotagmin mutation in a human congenital myasthenic syndrome. PLoS One 2017; 12:e0184817. [PMID: 28953919 PMCID: PMC5617158 DOI: 10.1371/journal.pone.0184817] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2016] [Accepted: 08/31/2017] [Indexed: 12/04/2022] Open
Abstract
During chemical transmission, the function of synaptic proteins must be coordinated to efficiently release neurotransmitter. Synaptotagmin 2, the Ca2+ sensor for fast, synchronized neurotransmitter release at the human neuromuscular junction, has recently been implicated in a dominantly inherited congenital myasthenic syndrome associated with a non-progressive motor neuropathy. In one family, a proline residue within the C2B Ca2+-binding pocket of synaptotagmin is replaced by a leucine. The functional significance of this residue has not been investigated previously. Here we show that in silico modeling predicts disruption of the C2B Ca2+-binding pocket, and we examine the in vivo effects of the homologous mutation in Drosophila. When expressed in the absence of native synaptotagmin, this mutation is lethal, demonstrating for the first time that this residue plays a critical role in synaptotagmin function. To achieve expression similar to human patients, the mutation is expressed in flies carrying one copy of the wild type synaptotagmin gene. We now show that Drosophila carrying this mutation developed neurological and behavioral manifestations similar to those of human patients and provide insight into the mechanisms underlying these deficits. Our Drosophila studies support a role for this synaptotagmin point mutation in disease etiology.
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Affiliation(s)
- Mallory C. Shields
- Department of Biomedical Sciences, Colorado State University, Fort Collins, CO, United States of America
- Molecular, Cellular, and Integrative Neuroscience Program, Colorado State University, Fort Collins, CO, United States of America
| | - Matthew R. Bowers
- Department of Biomedical Sciences, Colorado State University, Fort Collins, CO, United States of America
- Molecular, Cellular, and Integrative Neuroscience Program, Colorado State University, Fort Collins, CO, United States of America
| | - McKenzie M. Fulcer
- Department of Biomedical Sciences, Colorado State University, Fort Collins, CO, United States of America
| | - Madelyn K. Bollig
- Department of Biomedical Sciences, Colorado State University, Fort Collins, CO, United States of America
| | - Patrick J. Rock
- School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas, United States of America
| | - Bryan R. Sutton
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, Texas, United States of America
| | - Alysia D. Vrailas-Mortimer
- Department of Biological Sciences, University of Denver, Denver, CO, United States of America
- School of Biological Sciences, Illinois State University, Normal, IL, United States of America
| | - Hanns Lochmüller
- John Walton Muscular Dystrophy Research Centre, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, NE1 3BZ, United Kingdom
| | - Roger G. Whittaker
- Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, NE2 4HH, United Kingdom
| | - Rita Horvath
- John Walton Muscular Dystrophy Research Centre, Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, NE1 3BZ, United Kingdom
| | - Noreen E. Reist
- Department of Biomedical Sciences, Colorado State University, Fort Collins, CO, United States of America
- Molecular, Cellular, and Integrative Neuroscience Program, Colorado State University, Fort Collins, CO, United States of America
- * E-mail:
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