1
|
Tetenborg S, Martinez-Soler E, O`Brien J. Characterizing ER Retention Defects of PDZ Binding Deficient Cx36 Mutants Using Confocal Microscopy. Bio Protoc 2024; 14:e5034. [PMID: 39100594 PMCID: PMC11292134 DOI: 10.21769/bioprotoc.5034] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2024] [Revised: 06/11/2024] [Accepted: 06/18/2024] [Indexed: 08/06/2024] Open
Abstract
Overexpression of proteins in transiently transfected cells is a simple way to study basic transport mechanisms and the underlying protein-protein interactions. While expression systems have obvious drawbacks compared to in vivo experiments, they allow a quick assessment of more conserved functions, for instance, ER export or sorting of proteins in the Golgi. In a previous study, our group described the formation of ER-derived removal vesicles for the gap junction protein Cx36 in transfected HEK293T cells. These removal vesicles, termed "whorls" because of their concentric structure, were formed by Cx36 channels that failed to escape the ER. In this article, we describe an imaging protocol that can be used to determine these ER retention defects for Cx36 expressed in cultured cells. The protocol we provide here employs regular confocal microscopy, which allows for sufficient resolution to reveal the characteristic shape of ER whorls.
Collapse
Affiliation(s)
| | | | - John O`Brien
- College of Optometry, University of Houston, Houston, TX, USA
| |
Collapse
|
2
|
Chan ICW, Chen N, Hernandez J, Meltzer H, Park A, Stahl A. Future avenues in Drosophila mushroom body research. Learn Mem 2024; 31:a053863. [PMID: 38862172 PMCID: PMC11199946 DOI: 10.1101/lm.053863.123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2023] [Accepted: 03/27/2024] [Indexed: 06/13/2024]
Abstract
How does the brain translate sensory information into complex behaviors? With relatively small neuronal numbers, readable behavioral outputs, and an unparalleled genetic toolkit, the Drosophila mushroom body (MB) offers an excellent model to address this question in the context of associative learning and memory. Recent technological breakthroughs, such as the freshly completed full-brain connectome, multiomics approaches, CRISPR-mediated gene editing, and machine learning techniques, led to major advancements in our understanding of the MB circuit at the molecular, structural, physiological, and functional levels. Despite significant progress in individual MB areas, the field still faces the fundamental challenge of resolving how these different levels combine and interact to ultimately control the behavior of an individual fly. In this review, we discuss various aspects of MB research, with a focus on the current knowledge gaps, and an outlook on the future methodological developments required to reach an overall view of the neurobiological basis of learning and memory.
Collapse
Affiliation(s)
- Ivy Chi Wai Chan
- Dynamics of Neuronal Circuits Group, German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany
- Department of Developmental Biology, RWTH Aachen University, Aachen, Germany
| | - Nannan Chen
- School of Life Science and Technology, Key Laboratory of Developmental Genes and Human Disease, Southeast University, Nanjing 210096, China
| | - John Hernandez
- Neuroscience Department, Brown University, Providence, Rhode Island 02906, USA
| | - Hagar Meltzer
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 7610001, Israel
- Department of Molecular Neuroscience, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Annie Park
- Department of Physiology, Anatomy and Genetics, Centre for Neural Circuits and Behaviour, University of Oxford, Oxford, United Kingdom
| | - Aaron Stahl
- Neuroscience and Pharmacology, University of Iowa, Iowa City, Iowa 52242, USA
| |
Collapse
|
3
|
Zhang D, Chen Z, Du Z, Bao B, Su N, Chen X, Ge Y, Lin Q, Yang L, Hua Y, Wang S, Hua X, Zuo F, Li N, Liu R, Jiang L, Bao C, Zhao Y, Loscalzo J, Yang Y, Zhu L. Design of a palette of SNAP-tag mimics of fluorescent proteins and their use as cell reporters. Cell Discov 2023; 9:56. [PMID: 37311750 DOI: 10.1038/s41421-023-00546-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2022] [Accepted: 03/18/2023] [Indexed: 06/15/2023] Open
Abstract
Naturally occurring fluorescent proteins (FPs) are the most widely used tools for tracking cellular proteins and sensing cellular events. Here, we chemically evolved the self-labeling SNAP-tag into a palette of SNAP-tag mimics of fluorescent proteins (SmFPs) that possess bright, rapidly inducible fluorescence ranging from cyan to infrared. SmFPs are integral chemical-genetic entities based on the same fluorogenic principle as FPs, i.e., induction of fluorescence of non-emitting molecular rotors by conformational locking. We demonstrate the usefulness of these SmFPs in real-time tracking of protein expression, degradation, binding interactions, trafficking, and assembly, and show that these optimally designed SmFPs outperform FPs like GFP in many important ways. We further show that the fluorescence of circularly permuted SmFPs is sensitive to the conformational changes of their fusion partners, and that these fusion partners can be used for the development of single SmFP-based genetically encoded calcium sensors for live cell imaging.
Collapse
Affiliation(s)
- Dasheng Zhang
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China
- Shanghai Frontiers Science Center of Optogenetic Techniques for Cell Metabolism, School of Pharmacy, East China University of Science and Technology, Shanghai, China
| | - Zhengda Chen
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China
- Shanghai Frontiers Science Center of Optogenetic Techniques for Cell Metabolism, School of Pharmacy, East China University of Science and Technology, Shanghai, China
| | - Zengmin Du
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China
- Shanghai Frontiers Science Center of Optogenetic Techniques for Cell Metabolism, School of Pharmacy, East China University of Science and Technology, Shanghai, China
| | - Bingkun Bao
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China
| | - Ni Su
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China
- Shanghai Frontiers Science Center of Optogenetic Techniques for Cell Metabolism, School of Pharmacy, East China University of Science and Technology, Shanghai, China
| | - Xianjun Chen
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China.
- Shanghai Frontiers Science Center of Optogenetic Techniques for Cell Metabolism, School of Pharmacy, East China University of Science and Technology, Shanghai, China.
| | - Yihui Ge
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China
- Shanghai Frontiers Science Center of Optogenetic Techniques for Cell Metabolism, School of Pharmacy, East China University of Science and Technology, Shanghai, China
| | - Qiuning Lin
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China
| | - Lipeng Yang
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China
| | - Yujie Hua
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China
| | - Shuo Wang
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China
- Shanghai Frontiers Science Center of Optogenetic Techniques for Cell Metabolism, School of Pharmacy, East China University of Science and Technology, Shanghai, China
| | - Xin Hua
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China
| | - Fangting Zuo
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China
- Shanghai Frontiers Science Center of Optogenetic Techniques for Cell Metabolism, School of Pharmacy, East China University of Science and Technology, Shanghai, China
| | - Ningfeng Li
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China
| | - Renmei Liu
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China
- Shanghai Frontiers Science Center of Optogenetic Techniques for Cell Metabolism, School of Pharmacy, East China University of Science and Technology, Shanghai, China
| | - Li Jiang
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China
| | - Chunyan Bao
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China
| | - Yuzheng Zhao
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China
- Shanghai Frontiers Science Center of Optogenetic Techniques for Cell Metabolism, School of Pharmacy, East China University of Science and Technology, Shanghai, China
| | - Joseph Loscalzo
- Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA
| | - Yi Yang
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China.
- Shanghai Frontiers Science Center of Optogenetic Techniques for Cell Metabolism, School of Pharmacy, East China University of Science and Technology, Shanghai, China.
| | - Linyong Zhu
- Optogenetics & Synthetic Biology Interdisciplinary Research Center, State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China.
- Shanghai Frontiers Science Center of Optogenetic Techniques for Cell Metabolism, School of Pharmacy, East China University of Science and Technology, Shanghai, China.
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China.
| |
Collapse
|
4
|
Kraujalis T, Gudaitis L, Kraujaliene L, Snipas M, Palacios-Prado N, Verselis VK. The Amino Terminal Domain and Modulation of Connexin36 Gap Junction Channels by Intracellular Magnesium Ions. Front Physiol 2022; 13:839223. [PMID: 35264979 PMCID: PMC8899287 DOI: 10.3389/fphys.2022.839223] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2021] [Accepted: 01/28/2022] [Indexed: 11/13/2022] Open
Abstract
Electrical synapses between neurons in the mammalian CNS are predominantly formed of the connexin36 (Cx36) gap junction (GJ) channel protein. Unique among GJs formed of a number of other members of the Cx gene family, Cx36 GJs possess a high sensitivity to intracellular Mg2+ that can robustly act to modulate the strength of electrical synaptic transmission. Although a putative Mg2+ binding site was previously identified to reside in the aqueous pore in the first extracellular (E1) loop domain, the involvement of the N-terminal (NT) domain in the atypical response of Cx36 GJs to pH was shown to depend on intracellular levels of Mg2+. In this study, we examined the impact of amino acid substitutions in the NT domain on Mg2+ modulation of Cx36 GJs, focusing on positions predicted to line the pore funnel, which constitutes the cytoplasmic entrance of the channel pore. We find that charge substitutions at the 8th, 13th, and 18th positions had pronounced effects on Mg2+ sensitivity, particularly at position 13 at which an A13K substitution completely abolished sensitivity to Mg2+. To assess potential mechanisms of Mg2+ action, we constructed and tested a series of mathematical models that took into account gating of the component hemichannels in a Cx36 GJ channel as well as Mg2+ binding to each hemichannel in open and/or closed states. Simultaneous model fitting of measurements of junctional conductance, gj, and transjunctional Mg2+ fluxes using a fluorescent Mg2+ indicator suggested that the most viable mechanism for Cx36 regulation by Mg2+ entails the binding of Mg2+ to and subsequent stabilization of the closed state in each hemichannel. Reduced permeability to Mg2+ was also evident, particularly for the A13K substitution, but homology modeling of all charge-substituted NT variants showed only a moderate correlation between a reduction in the negative electrostatic potential and a reduction in the permeability to Mg2+ ions. Given the reported role of the E1 domain in Mg2+ binding together with the impact of NT substitutions on gating and the apparent state-dependence of Mg2+ binding, this study suggests that the NT domain can be an integral part of Mg2+ modulation of Cx36 GJs likely through the coupling of conformational changes between NT and E1 domains.
Collapse
Affiliation(s)
- Tadas Kraujalis
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
- Department of Applied Informatics, Kaunas University of Technology, Kaunas, Lithuania
- *Correspondence: Tadas Kraujalis,
| | - Lukas Gudaitis
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Lina Kraujaliene
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Mindaugas Snipas
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
- Department of Mathematical Modelling, Kaunas University of Technology, Kaunas, Lithuania
| | - Nicolás Palacios-Prado
- Department of Physiology, Pontificia Universidad Católica de Chile, Santiago, Chile
- Centro Interdisciplinario de Neurociencias de Valparaíso, Universidad de Valparaiso, Valparaíso, Chile
| | - Vytas K. Verselis
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, NY, United States
| |
Collapse
|
5
|
Fusz K, Kovács-Öller T, Kóbor P, Szabó-Meleg E, Völgyi B, Buzás P, Telkes I. Regional Variation of Gap Junctional Connections in the Mammalian Inner Retina. Cells 2021; 10:2396. [PMID: 34572046 PMCID: PMC8466939 DOI: 10.3390/cells10092396] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2021] [Revised: 09/04/2021] [Accepted: 09/07/2021] [Indexed: 11/24/2022] Open
Abstract
The retinas of many species show regional specialisations that are evident in the differences in the processing of visual input from different parts of the visual field. Regional specialisation is thought to reflect an adaptation to the natural visual environment, optical constraints, and lifestyle of the species. Yet, little is known about regional differences in synaptic circuitry. Here, we were interested in the topographical distribution of connexin-36 (Cx36), the major constituent of electrical synapses in the retina. We compared the retinas of mice, rats, and cats to include species with different patterns of regional specialisations in the analysis. First, we used the density of Prox1-immunoreactive amacrine cells as a marker of any regional specialisation, with higher cell density signifying more central regions. Double-labelling experiments showed that Prox1 is expressed in AII amacrine cells in all three species. Interestingly, large Cx36 plaques were attached to about 8-10% of Prox1-positive amacrine cell somata, suggesting the strong electrical coupling of pairs or small clusters of cell bodies. When analysing the regional changes in the volumetric density of Cx36-immunoreactive plaques, we found a tight correlation with the density of Prox1-expressing amacrine cells in the ON, but not in the OFF sublamina in all three species. The results suggest that the relative contribution of electrical synapses to the ON- and OFF-pathways of the retina changes with retinal location, which may contribute to functional ON/OFF asymmetries across the visual field.
Collapse
Affiliation(s)
- Katalin Fusz
- Institute of Physiology, Medical School, University of Pécs, 7624 Pécs, Hungary; (K.F.); (P.K.); (I.T.)
- Szentágothai Research Centre, University of Pécs, 7624 Pécs, Hungary; (T.K.-Ö.); (E.S.-M.); (B.V.)
- Centre for Neuroscience, University of Pécs, 7624 Pécs, Hungary
| | - Tamás Kovács-Öller
- Szentágothai Research Centre, University of Pécs, 7624 Pécs, Hungary; (T.K.-Ö.); (E.S.-M.); (B.V.)
- Centre for Neuroscience, University of Pécs, 7624 Pécs, Hungary
- MTA-PTE NAP-2 Retinal Electrical Synapses Research Group, 7624 Pécs, Hungary
| | - Péter Kóbor
- Institute of Physiology, Medical School, University of Pécs, 7624 Pécs, Hungary; (K.F.); (P.K.); (I.T.)
- Szentágothai Research Centre, University of Pécs, 7624 Pécs, Hungary; (T.K.-Ö.); (E.S.-M.); (B.V.)
- Centre for Neuroscience, University of Pécs, 7624 Pécs, Hungary
| | - Edina Szabó-Meleg
- Szentágothai Research Centre, University of Pécs, 7624 Pécs, Hungary; (T.K.-Ö.); (E.S.-M.); (B.V.)
- Institute of Biophysics, Medical School, University of Pécs, 7624 Pécs, Hungary
| | - Béla Völgyi
- Szentágothai Research Centre, University of Pécs, 7624 Pécs, Hungary; (T.K.-Ö.); (E.S.-M.); (B.V.)
- Centre for Neuroscience, University of Pécs, 7624 Pécs, Hungary
- MTA-PTE NAP-2 Retinal Electrical Synapses Research Group, 7624 Pécs, Hungary
- Department of Experimental Zoology and Neurobiology, University of Pécs, 7624 Pécs, Hungary
| | - Péter Buzás
- Institute of Physiology, Medical School, University of Pécs, 7624 Pécs, Hungary; (K.F.); (P.K.); (I.T.)
- Szentágothai Research Centre, University of Pécs, 7624 Pécs, Hungary; (T.K.-Ö.); (E.S.-M.); (B.V.)
- Centre for Neuroscience, University of Pécs, 7624 Pécs, Hungary
| | - Ildikó Telkes
- Institute of Physiology, Medical School, University of Pécs, 7624 Pécs, Hungary; (K.F.); (P.K.); (I.T.)
- Szentágothai Research Centre, University of Pécs, 7624 Pécs, Hungary; (T.K.-Ö.); (E.S.-M.); (B.V.)
- Centre for Neuroscience, University of Pécs, 7624 Pécs, Hungary
| |
Collapse
|
6
|
Bhoi JD, Zhang Z, Janz R, You Y, Wei H, Wu J, Ribelayga CP. The SNARE regulator Complexin3 is a target of the cone circadian clock. J Comp Neurol 2021; 529:1066-1080. [PMID: 32783205 PMCID: PMC8190822 DOI: 10.1002/cne.25004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Revised: 08/03/2020] [Accepted: 08/05/2020] [Indexed: 01/07/2023]
Abstract
BMAL1 is a core component of the mammalian circadian clockwork. Removal of BMAL1 from the retina significantly affects visual information processing in both rod and cone pathways. To identify potential pathways and/or molecules through which BMAL1 alters signal transmission at the cone pedicle, we performed an RNA-seq differential expression analysis between cone-specific Bmal1 knockout cones (cone-Bmal1-/- ) and wild-type (WT) cones. We found 88 genes differentially expressed. Among these, Complexin3 (Cplx3), a SNARE regulator at ribbon synapses, was downregulated fivefold in the mutant cones. The purpose of this work was to determine whether BMAL1 and/or the cone clock controls CPLX3 protein expression at cone pedicles. We found that CPLX3 expression level was decreased twofold in cone-Bmal1-/- cones. Furthermore, CPLX3 expression was downregulated at night compared to the day in WT cones but remained constitutively low in mutant cones both day and night. The transcript and protein expression levels of Cplx4-the other complexin expressed in cones-were similar in WT and mutant cones; in WT cones, CPLX4 protein level did not change with the time of day. In silico analysis revealed four potential BMAL1:CLOCK binding sites upstream from exon one of Cplx3 and none upstream of exon one of Cplx4. Our results suggest that CPLX3 expression is regulated at the transcriptional level by the cone clock. The modulation of CPLX3 may be a mechanism by which the clock controls the cone synaptic transfer function to second-order cells and thereby impacts retinal signal processing during the day/night cycle.
Collapse
Affiliation(s)
- Jacob D. Bhoi
- Rice University, Undergraduate Program in Neuroscience, Houston, Texas
- Summer Research Program, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, Texas
| | - Zhijing Zhang
- Ruiz Department of Ophthalmology and Visual Science, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, Texas
| | - Roger Janz
- Department of Neurobiology and Anatomy, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, Texas
- MD Anderson UTHealth Graduate School of Biomedical Sciences, The University of Texas Health Science Center at Houston, Houston, Texas
- Program in Neuroscience, MD Anderson UTHealth Graduate School of Biomedical Sciences, The University of Texas Health Science Center at Houston, Houston, Texas
- Neuroscience Research Center, The University of Texas Health Science Center at Houston, Houston, Texas
| | - Yanan You
- The Vivian L. Smith Department of Neurosurgery, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, Texas
- Center for Stem Cell and Regenerative Medicine, The University of Texas Brown Foundation Institute of Molecular Medicine, Houston, Texas
| | - Haichao Wei
- The Vivian L. Smith Department of Neurosurgery, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, Texas
- Center for Stem Cell and Regenerative Medicine, The University of Texas Brown Foundation Institute of Molecular Medicine, Houston, Texas
| | - Jiaqian Wu
- MD Anderson UTHealth Graduate School of Biomedical Sciences, The University of Texas Health Science Center at Houston, Houston, Texas
- Program in Neuroscience, MD Anderson UTHealth Graduate School of Biomedical Sciences, The University of Texas Health Science Center at Houston, Houston, Texas
- Neuroscience Research Center, The University of Texas Health Science Center at Houston, Houston, Texas
- The Vivian L. Smith Department of Neurosurgery, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, Texas
- Center for Stem Cell and Regenerative Medicine, The University of Texas Brown Foundation Institute of Molecular Medicine, Houston, Texas
| | - Christophe P. Ribelayga
- Summer Research Program, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, Texas
- Ruiz Department of Ophthalmology and Visual Science, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, Texas
- MD Anderson UTHealth Graduate School of Biomedical Sciences, The University of Texas Health Science Center at Houston, Houston, Texas
- Program in Neuroscience, MD Anderson UTHealth Graduate School of Biomedical Sciences, The University of Texas Health Science Center at Houston, Houston, Texas
- Neuroscience Research Center, The University of Texas Health Science Center at Houston, Houston, Texas
- Program in Biochemistry and Cell Biology, MD Anderson UTHealth Graduate School of Biomedical Sciences, The University of Texas Health Science Center at Houston, Houston, Texas
- Bernice Weingarten Chair in Ophthalmology, Ruiz Department of Ophthalmology and Visual Science, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, Texas
| |
Collapse
|
7
|
Tetenborg S, Wang HY, Nemitz L, Depping A, Espejo AB, Aseervatham J, Bedford MT, Janssen-Bienhold U, O'Brien J, Dedek K. Phosphorylation of Connexin36 near the C-terminus switches binding affinities for PDZ-domain and 14-3-3 proteins in vitro. Sci Rep 2020; 10:18378. [PMID: 33110101 PMCID: PMC7592057 DOI: 10.1038/s41598-020-75375-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2020] [Accepted: 10/12/2020] [Indexed: 12/20/2022] Open
Abstract
Connexin36 (Cx36) is the most abundant connexin in central nervous system neurons. It forms gap junction channels that act as electrical synapses. Similar to chemical synapses, Cx36-containing gap junctions undergo activity-dependent plasticity and complex regulation. Cx36 gap junctions represent multimolecular complexes and contain cytoskeletal, regulatory and scaffolding proteins, which regulate channel conductance, assembly and turnover. The amino acid sequence of mammalian Cx36 harbors a phosphorylation site for the Ca2+/calmodulin-dependent kinase II at serine 315. This regulatory site is homologous to the serine 298 in perch Cx35 and in close vicinity to a PDZ binding domain at the very C-terminal end of the protein. We hypothesized that this phosphorylation site may serve as a molecular switch, influencing the affinity of the PDZ binding domain for its binding partners. Protein microarray and pulldown experiments revealed that this is indeed the case: phosphorylation of serine 298 decreased the binding affinity for MUPP1, a known scaffolding partner of connexin36, and increased the binding affinity for two different 14-3-3 proteins. Although we did not find the same effect in cell culture experiments, our data suggest that phosphorylation of serine 315/298 may serve to recruit different proteins to connexin36/35-containing gap junctions in an activity-dependent manner.
Collapse
Affiliation(s)
- Stephan Tetenborg
- Animal Navigation/Neurosensorics, Institute for Biology and Environmental Sciences, University of Oldenburg, Oldenburg, Germany
- Ruiz Department of Ophthalmology & Visual Science, The University of Texas Health Science Center at Houston, Houston, TX, 77030, USA
| | - Helen Y Wang
- Ruiz Department of Ophthalmology & Visual Science, The University of Texas Health Science Center at Houston, Houston, TX, 77030, USA
| | - Lena Nemitz
- Visual Neuroscience, Dept. of Neuroscience, University of Oldenburg, Oldenburg, Germany
| | - Anne Depping
- Animal Navigation/Neurosensorics, Institute for Biology and Environmental Sciences, University of Oldenburg, Oldenburg, Germany
| | - Alexsandra B Espejo
- Department of Epigenetics and Molecular Carcinogenesis, University of Texas M.D. Anderson Cancer Center, Smithville, TX, 78957, USA
| | - Jaya Aseervatham
- Ruiz Department of Ophthalmology & Visual Science, The University of Texas Health Science Center at Houston, Houston, TX, 77030, USA
| | - Mark T Bedford
- Department of Epigenetics and Molecular Carcinogenesis, University of Texas M.D. Anderson Cancer Center, Smithville, TX, 78957, USA
| | - Ulrike Janssen-Bienhold
- Visual Neuroscience, Dept. of Neuroscience, University of Oldenburg, Oldenburg, Germany
- Research Center Neurosensory Science, University of Oldenburg, Oldenburg, Germany
| | - John O'Brien
- Ruiz Department of Ophthalmology & Visual Science, The University of Texas Health Science Center at Houston, Houston, TX, 77030, USA
| | - Karin Dedek
- Animal Navigation/Neurosensorics, Institute for Biology and Environmental Sciences, University of Oldenburg, Oldenburg, Germany.
- Research Center Neurosensory Science, University of Oldenburg, Oldenburg, Germany.
| |
Collapse
|
8
|
McCutcheon S, Stout RF, Spray DC. The dynamic Nexus: gap junctions control protein localization and mobility in distinct and surprising ways. Sci Rep 2020; 10:17011. [PMID: 33046777 PMCID: PMC7550573 DOI: 10.1038/s41598-020-73892-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2020] [Accepted: 09/23/2020] [Indexed: 12/24/2022] Open
Abstract
Gap junction (GJ) channels permit molecules, such as ions, metabolites and second messengers, to transfer between cells. Their function is critical for numerous cellular interactions, providing exchange of metabolites, signaling molecules, and ionic currents. GJ channels are composed of Connexin (Cx) hexamers paired across extracellular space and typically form large rafts of clustered channels, called plaques, at cell appositions. Cxs together with molecules that interact with GJ channels make up a supramolecular structure known as the GJ Nexus. While the stability of connexin localization in GJ plaques has been studied, mobility of other Nexus components has yet to be addressed. Colocalization analysis of several nexus components and other membrane proteins reveal that certain molecules are excluded from the GJ plaque (Aquaporin 4, EAAT2b), while others are quite penetrant (lipophilic molecules, Cx30, ZO-1, Occludin). Fluorescence recovery after photobleaching of tagged Nexus-associated proteins showed that mobility in plaque domains is affected by mobility of the Cx proteins. These novel findings indicate that the GJ Nexus is a dynamic membrane organelle, with cytoplasmic and membrane-embedded proteins binding and diffusing according to distinct parameters.
Collapse
Affiliation(s)
- Sean McCutcheon
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, 1410 Pelham Parkway South, Bronx, NY, 10461, USA.
| | - Randy F Stout
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, 1410 Pelham Parkway South, Bronx, NY, 10461, USA.,Department of Biomedical Sciences, The New York Institute of Technology College of Osteopathic Medicine, 101 Northern Blvd., Old Westbury, NY, 11586, USA
| | - David C Spray
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, 1410 Pelham Parkway South, Bronx, NY, 10461, USA
| |
Collapse
|
9
|
Kotova A, Timonina K, Zoidl GR. Endocytosis of Connexin 36 is Mediated by Interaction with Caveolin-1. Int J Mol Sci 2020; 21:E5401. [PMID: 32751343 PMCID: PMC7432810 DOI: 10.3390/ijms21155401] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2020] [Revised: 07/25/2020] [Accepted: 07/28/2020] [Indexed: 12/22/2022] Open
Abstract
The gap junctional protein connexin 36 (Cx36) has been co-purified with the lipid raft protein caveolin-1 (Cav-1). The relevance of an interaction between the two proteins is unknown. In this study, we explored the significance of Cav-1 interaction in the context of intracellular and membrane transport of Cx36. Coimmunoprecipitation assays and Förster resonance energy transfer analysis (FRET) were used to confirm the interaction between the two proteins in the Neuro 2a cell line. We found that the Cx36 and Cav-1 interaction was dependent on the intracellular calcium levels. By employing different microscopy techniques, we demonstrated that Cav-1 enhances the vesicular transport of Cx36. Pharmacological interventions coupled with cell surface biotinylation assays and FRET analysis revealed that Cav-1 regulates membrane localization of Cx36. Our data indicate that the interaction between Cx36 and Cav-1 plays a role in the internalization of Cx36 by a caveolin-dependent pathway.
Collapse
Affiliation(s)
- Anna Kotova
- Department of Biology, York University, Toronto, ON M3J 1P3, Canada; (A.K.); (K.T.)
| | - Ksenia Timonina
- Department of Biology, York University, Toronto, ON M3J 1P3, Canada; (A.K.); (K.T.)
| | - Georg R. Zoidl
- Department of Biology, York University, Toronto, ON M3J 1P3, Canada; (A.K.); (K.T.)
- Department of Psychology, York University, Toronto, ON M3J 1P3, Canada
| |
Collapse
|
10
|
Cohen LD, Boulos A, Ziv NE. A non-fluorescent HaloTag blocker for improved measurement and visualization of protein synthesis in living cells. F1000Res 2020; 9. [PMID: 32518633 PMCID: PMC7255903 DOI: 10.12688/f1000research.23289.2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 06/03/2020] [Indexed: 11/20/2022] Open
Abstract
Background: HaloTag is a modified bacterial enzyme that binds rapidly and irreversibly to an array of synthetic ligands, including chemical dyes. When expressed in live cells in conjunction with a protein of interest, HaloTag can be used to study protein trafficking, synthesis, and degradation. For instance, sequential HaloTag labeling with spectrally separable dyes can be used to separate preexisting protein pools from proteins newly synthesized following experimental manipulations or the passage of time. Unfortunately, incomplete labeling by the first dye, or labeling by residual, trapped dye pools can confound interpretation. Methods: Labeling specificity of newly synthesized proteins could be improved by blocking residual binding sites. To that end, we synthesized a non-fluorescent, cell permeable blocker (1-chloro-6-(2-propoxyethoxy)hexane; CPXH), essentially the HaloTag ligand backbone without the reactive amine used to attach fluorescent groups. Results: High-content imaging was used to quantify the ability of CPXH to block HaloTag ligand binding in live HEK cells expressing a fusion protein of mTurquoise2 and HaloTag. Full saturation was observed at CPXH concentrations of 5-10 µM at 30 min. No overt effects on cell viability were observed at any concentration or treatment duration. The ability of CPXH to improve the reliability of newly synthesized protein detection was then demonstrated in live cortical neurons expressing the mTurquoise2-HaloTag fusion protein, in both single and dual labeling time lapse experiments. Practically no labeling was observed after blocking HaloTag binding sites with CPXH when protein synthesis was suppressed with cycloheximide, confirming the identification of newly synthesized protein copies as such, while providing estimates of protein synthesis suppression in these experiments. Conclusions: CPXH is a reliable (and inexpensive) non-fluorescent ligand for improving assessment of protein-of-interest metabolism in live cells using HaloTag technology.
Collapse
Affiliation(s)
- Laurie D Cohen
- Faculty of Medicine, Rappaport Institute and Network Biology Research Laboratories, Technion - Israel Institute of Technology, Haifa, 32000, Israel
| | - Ayub Boulos
- Faculty of Medicine, Rappaport Institute and Network Biology Research Laboratories, Technion - Israel Institute of Technology, Haifa, 32000, Israel
| | - Noam E Ziv
- Faculty of Medicine, Rappaport Institute and Network Biology Research Laboratories, Technion - Israel Institute of Technology, Haifa, 32000, Israel
| |
Collapse
|
11
|
Lynn KS, Peterson RJ, Koval M. Ruffles and spikes: Control of tight junction morphology and permeability by claudins. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1862:183339. [PMID: 32389670 DOI: 10.1016/j.bbamem.2020.183339] [Citation(s) in RCA: 43] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2020] [Revised: 04/24/2020] [Accepted: 05/01/2020] [Indexed: 02/06/2023]
Abstract
Epithelial barrier function is regulated by a family of transmembrane proteins known as claudins. Functional tight junctions are formed when claudins interact with other transmembrane proteins, cytosolic scaffold proteins and the actin cytoskeleton. The predominant scaffold protein, zonula occludens-1 (ZO-1), directly binds to most claudin C-terminal domains, crosslinking them to the actin cytoskeleton. When imaged by immunofluorescence microscopy, tight junctions most frequently are linear structures that form between tricellular junctions. However, tight junctions also adapt non-linear architectures exhibiting either a ruffled or spiked morphology, which both are responses to changes in claudin engagement of actin filaments. Other terms for ruffled tight junctions include wavy, tortuous, undulating, serpentine or zig-zag junctions. Ruffling is under the control of hypoxia induced factor (HIF) and integrin-mediated signaling, as well as direct mechanical stimulation. Tight junction ruffling is specifically enhanced by claudin-2, antagonized by claudin-1 and requires claudin binding to ZO-1. Tight junction spikes are sites of active vesicle budding and fusion that appear as perpendicular projections oriented towards the nucleus. Spikes share molecular features with focal adherens junctions and tubulobulbar complexes found in Sertoli cells. Lung epithelial cells under stress form spikes due to an increase in claudin-5 expression that directly disrupts claudin-18/ZO-1 interactions. Together this suggests that claudins are not simply passive cargoes controlled by scaffold proteins. We propose a model where claudins specifically influence tight junction scaffold proteins to control interactions with the cytoskeleton as a mechanism that regulates tight junction assembly and function.
Collapse
Affiliation(s)
- K Sabrina Lynn
- Division of Pulmonary, Allergy Critical Care and Sleep Medicine, Department of Medicine, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Raven J Peterson
- Division of Pulmonary, Allergy Critical Care and Sleep Medicine, Department of Medicine, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Michael Koval
- Division of Pulmonary, Allergy Critical Care and Sleep Medicine, Department of Medicine, Emory University School of Medicine, Atlanta, GA 30322, USA; Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA.
| |
Collapse
|
12
|
Cohen LD, Boulos A, Ziv NE. A non-fluorescent HaloTag blocker for improved measurement and visualization of protein synthesis in living cells. F1000Res 2020; 9:ISF-302. [PMID: 32518633 PMCID: PMC7255903 DOI: 10.12688/f1000research.23289.1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 06/03/2020] [Indexed: 12/24/2023] Open
Abstract
Background: HaloTag is a modified bacterial enzyme that binds rapidly and irreversibly to an array of synthetic ligands, including chemical dyes. When expressed in live cells in conjunction with a protein of interest, HaloTag can be used to study protein trafficking, synthesis, and degradation. For instance, sequential HaloTag labeling with spectrally separable dyes can be used to separate preexisting protein pools from proteins newly synthesized following experimental manipulations or the passage of time. Unfortunately, incomplete labeling by the first dye, or labeling by residual, trapped dye pools can confound interpretation. Methods: Labeling specificity of newly synthesized proteins could be improved by blocking residual binding sites. To that end, we synthesized a non-fluorescent, cell permeable blocker (1-chloro-6-(2-propoxyethoxy)hexane; CPXH), essentially the HaloTag ligand backbone without the reactive amine used to attach fluorescent groups. Results: High-content imaging was used to quantify the ability of CPXH to block HaloTag ligand binding in live HEK cells expressing a fusion protein of mTurquoise2 and HaloTag. Full saturation was observed at CPXH concentrations of 5-10 µM at 30 min. No overt effects on cell viability were observed at any concentration or treatment duration. The ability of CPXH to improve the reliability of newly synthesized protein detection was then demonstrated in live cortical neurons expressing the mTurquoise2-HaloTag fusion protein, in both single and dual labeling time lapse experiments. Practically no labeling was observed after blocking HaloTag binding sites with CPXH when protein synthesis was suppressed with cycloheximide, confirming the identification of newly synthesized protein copies as such, while providing estimates of protein synthesis suppression in these experiments. Conclusions: CPXH is a reliable (and inexpensive) non-fluorescent ligand for improving assessment of protein-of-interest metabolism in live cells using HaloTag technology.
Collapse
Affiliation(s)
- Laurie D. Cohen
- Faculty of Medicine, Rappaport Institute and Network Biology Research Laboratories, Technion - Israel Institute of Technology, Haifa, 32000, Israel
| | - Ayub Boulos
- Faculty of Medicine, Rappaport Institute and Network Biology Research Laboratories, Technion - Israel Institute of Technology, Haifa, 32000, Israel
| | - Noam E. Ziv
- Faculty of Medicine, Rappaport Institute and Network Biology Research Laboratories, Technion - Israel Institute of Technology, Haifa, 32000, Israel
| |
Collapse
|
13
|
Martin EA, Lasseigne AM, Miller AC. Understanding the Molecular and Cell Biological Mechanisms of Electrical Synapse Formation. Front Neuroanat 2020; 14:12. [PMID: 32372919 PMCID: PMC7179694 DOI: 10.3389/fnana.2020.00012] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2019] [Accepted: 03/09/2020] [Indexed: 12/20/2022] Open
Abstract
In this review article, we will describe the recent advances made towards understanding the molecular and cell biological mechanisms of electrical synapse formation. New evidence indicates that electrical synapses, which are gap junctions between neurons, can have complex molecular compositions including protein asymmetries across joined cells, diverse morphological arrangements, and overlooked similarities with other junctions, all of which indicate new potential roles in neurodevelopmental disease. Aquatic organisms, and in particular the vertebrate zebrafish, have proven to be excellent models for elucidating the molecular mechanisms of electrical synapse formation. Zebrafish will serve as our main exemplar throughout this review and will be compared with other model organisms. We highlight the known cell biological processes that build neuronal gap junctions and compare these with the assemblies of adherens junctions, tight junctions, non-neuronal gap junctions, and chemical synapses to explore the unknown frontiers remaining in our understanding of the critical and ubiquitous electrical synapse.
Collapse
Affiliation(s)
- E Anne Martin
- Department of Biology, Institute of Neuroscience, University of Oregon, Eugene, OR, United States
| | - Abagael M Lasseigne
- Department of Biology, Institute of Neuroscience, University of Oregon, Eugene, OR, United States
| | - Adam C Miller
- Department of Biology, Institute of Neuroscience, University of Oregon, Eugene, OR, United States
| |
Collapse
|
14
|
Brown CA, Del Corsso C, Zoidl C, Donaldson LW, Spray DC, Zoidl G. Tubulin-Dependent Transport of Connexin-36 Potentiates the Size and Strength of Electrical Synapses. Cells 2019; 8:E1146. [PMID: 31557934 PMCID: PMC6829524 DOI: 10.3390/cells8101146] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Revised: 09/17/2019] [Accepted: 09/20/2019] [Indexed: 12/12/2022] Open
Abstract
Connexin-36 (Cx36) electrical synapses strengthen transmission in a calcium/calmodulin (CaM)/calmodulin-dependent kinase II (CaMKII)-dependent manner similar to a mechanism whereby the N-methyl-D-aspartate (NMDA) receptor subunit NR2B facilitates chemical transmission. Since NR2B-microtubule interactions recruit receptors to the cell membrane during plasticity, we hypothesized an analogous modality for Cx36. We determined that Cx36 binding to tubulin at the carboxy-terminal domain was distinct from Cx43 and NR2B by binding a motif overlapping with the CaM and CaMKII binding motifs. Dual patch-clamp recordings demonstrated that pharmacological interference of the cytoskeleton and deleting the binding motif at the Cx36 carboxyl-terminal (CT) reversibly abolished Cx36 plasticity. Mechanistic details of trafficking to the gap-junction plaque (GJP) were probed pharmacologically and through mutational analysis, all of which affected GJP size and formation between cell pairs. Lys279, Ile280, and Lys281 positions were particularly critical. This study demonstrates that tubulin-dependent transport of Cx36 potentiates synaptic strength by delivering channels to GJPs, reinforcing the role of protein transport at chemical and electrical synapses to fine-tune communication between neurons.
Collapse
Affiliation(s)
- Cherie A Brown
- Department of Biology, York University, Toronto, ON M3J 1P3, Canada.
| | - Cristiane Del Corsso
- Department of Biophysics and Physiology, Federal University of Rio de Janeiro-RJ, Rio de Janeiro 21941-901, Brazil.
| | - Christiane Zoidl
- Department of Biology, York University, Toronto, ON M3J 1P3, Canada.
| | - Logan W Donaldson
- Department of Biology, York University, Toronto, ON M3J 1P3, Canada.
| | - David C Spray
- Department of Neuroscience, Albert Einstein College, Bronx, NY 10461, USA.
- Department of Medicine, Albert Einstein College, Bronx, NY 10461, USA.
| | - Georg Zoidl
- Department of Biology, York University, Toronto, ON M3J 1P3, Canada.
- Department of Psychology, York University, Toronto, ON M3J 1P3, Canada.
| |
Collapse
|
15
|
Merrill RA, Song J, Kephart RA, Klomp AJ, Noack CE, Strack S. A robust and economical pulse-chase protocol to measure the turnover of HaloTag fusion proteins. J Biol Chem 2019; 294:16164-16171. [PMID: 31511325 DOI: 10.1074/jbc.ra119.010596] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2019] [Revised: 08/25/2019] [Indexed: 11/06/2022] Open
Abstract
The self-labeling protein HaloTag has been used extensively to determine the localization and turnover of proteins of interest at the single-cell level. To this end, halogen-substituted alkanes attached to diverse fluorophores are commercially available that allow specific, irreversible labeling of HaloTag fusion proteins; however, measurement of protein of interest half-life by pulse-chase of HaloTag ligands is not widely employed because residual unbound ligand continues to label newly synthesized HaloTag fusions even after extensive washing. Excess unlabeled HaloTag ligand can be used as a blocker of undesired labeling, but this is not economical. In this study, we screened several inexpensive, low-molecular-weight haloalkanes as blocking agents in pulse-chase labeling experiments with the cell-permeable tetramethylrhodamine HaloTag ligand. We identified 7-bromoheptanol as a high-affinity, low-toxicity HaloTag-blocking agent that permits protein turnover measurements at both the cell population (by blotting) and single-cell (by imaging) levels. We show that the HaloTag pulse-chase approach is a nontoxic alternative to inhibition of protein synthesis with cycloheximide and extend protein turnover assays to long-lived proteins.
Collapse
Affiliation(s)
- Ronald A Merrill
- Department of Neuroscience and Pharmacology, and Iowa Neuroscience Institute, University of Iowa, Iowa City, Iowa 52242
| | - Jianing Song
- Department of Neuroscience and Pharmacology, and Iowa Neuroscience Institute, University of Iowa, Iowa City, Iowa 52242
| | - Rikki A Kephart
- Department of Neuroscience and Pharmacology, and Iowa Neuroscience Institute, University of Iowa, Iowa City, Iowa 52242
| | - Annette J Klomp
- Department of Neuroscience and Pharmacology, and Iowa Neuroscience Institute, University of Iowa, Iowa City, Iowa 52242
| | - Claire E Noack
- Department of Neuroscience and Pharmacology, and Iowa Neuroscience Institute, University of Iowa, Iowa City, Iowa 52242
| | - Stefan Strack
- Department of Neuroscience and Pharmacology, and Iowa Neuroscience Institute, University of Iowa, Iowa City, Iowa 52242
| |
Collapse
|
16
|
Telkes I, Kóbor P, Orbán J, Kovács-Öller T, Völgyi B, Buzás P. Connexin-36 distribution and layer-specific topography in the cat retina. Brain Struct Funct 2019; 224:2183-2197. [PMID: 31172263 PMCID: PMC6591202 DOI: 10.1007/s00429-019-01876-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Accepted: 04/11/2019] [Indexed: 11/29/2022]
Abstract
Connexin-36 (Cx36) is the major constituent of mammalian retinal gap junctions positioned in key signal pathways. Here, we examined the laminar and large-scale topographical distribution of Cx36 punctate immunolabels in the retina of the cat, a classical model of the mammalian visual system. Calretinin-immunoreactive (CaR-IR) cell populations served to outline the nuclear and plexiform layers and to stain specific neuronal populations. CaR-IR cells included horizontal cells in the outer retina, numerous amacrine cells, and scattered cells in the ganglion cell layer. Cx36-IR plaques were found among horizontal cell dendrites albeit without systematic colocalization of the two labels. Diffuse Cx36 immunoreactivity was found in the cytoplasm of AII amacrine cells, but no colocalization of Cx36 plaques was observed with either the perikarya or the long varicose dendrites of the CaR-IR non-AII amacrine cells. Cx36 puncta were seen throughout the entire inner plexiform layer showing their highest density in the ON sublamina. The densities of AII amacrine cell bodies and Cx36 plaques in the ON sublamina were strongly correlated across a wide range of eccentricities suggesting their anatomical association. However, the high number of plaques per AII cell suggests that a considerable fraction of Cx36 gap junctions in the ON sublamina is formed by other cell types than AII amacrine cells drawing attention to extensive but less studied electrically coupled networks.
Collapse
Affiliation(s)
- Ildikó Telkes
- Institute of Physiology, Medical School, University of Pécs, Szigeti út 12, Pécs, 7624, Hungary
- Szentágothai Research Centre, University of Pécs, Pécs, 7624, Hungary
- Centre for Neuroscience, University of Pécs, Pécs, 7624, Hungary
| | - Péter Kóbor
- Institute of Physiology, Medical School, University of Pécs, Szigeti út 12, Pécs, 7624, Hungary
- Szentágothai Research Centre, University of Pécs, Pécs, 7624, Hungary
- Centre for Neuroscience, University of Pécs, Pécs, 7624, Hungary
| | - József Orbán
- Szentágothai Research Centre, University of Pécs, Pécs, 7624, Hungary
- Department of Biophysics, Medical School, University of Pécs, Pécs, 7624, Hungary
| | - Tamás Kovács-Öller
- Szentágothai Research Centre, University of Pécs, Pécs, 7624, Hungary
- Department of Experimental Zoology and Neurobiology, University of Pécs, Pécs, 7624, Hungary
- Retinal Electrical Synapses Research Group, MTA-PTE NAP-2, University of Pécs, Pécs, 7624, Hungary
- Centre for Neuroscience, University of Pécs, Pécs, 7624, Hungary
| | - Béla Völgyi
- Szentágothai Research Centre, University of Pécs, Pécs, 7624, Hungary
- Department of Experimental Zoology and Neurobiology, University of Pécs, Pécs, 7624, Hungary
- Retinal Electrical Synapses Research Group, MTA-PTE NAP-2, University of Pécs, Pécs, 7624, Hungary
- Centre for Neuroscience, University of Pécs, Pécs, 7624, Hungary
| | - Péter Buzás
- Institute of Physiology, Medical School, University of Pécs, Szigeti út 12, Pécs, 7624, Hungary.
- Szentágothai Research Centre, University of Pécs, Pécs, 7624, Hungary.
- Centre for Neuroscience, University of Pécs, Pécs, 7624, Hungary.
| |
Collapse
|
17
|
Alcamí P, Pereda AE. Beyond plasticity: the dynamic impact of electrical synapses on neural circuits. Nat Rev Neurosci 2019; 20:253-271. [DOI: 10.1038/s41583-019-0133-5] [Citation(s) in RCA: 64] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
|
18
|
Farnsworth NL, Walter R, Piscopio RA, Schleicher WE, Benninger RKP. Exendin-4 overcomes cytokine-induced decreases in gap junction coupling via protein kinase A and Epac2 in mouse and human islets. J Physiol 2019; 597:431-447. [PMID: 30412665 PMCID: PMC6332825 DOI: 10.1113/jp276106] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2018] [Accepted: 11/07/2018] [Indexed: 12/21/2022] Open
Abstract
KEY POINTS The pancreatic islets of Langerhans maintain glucose homeostasis through insulin secretion, where insulin secretion dynamics are regulated by intracellular Ca2+ signalling and electrical coupling of the insulin producing β-cells in the islet. We have previously shown that cytokines decrease β-cell coupling and that compounds which increase cAMP can increase coupling. In both mouse and human islets exendin-4, which increases cAMP, protected against cytokine-induced decreases in coupling and in mouse islets preserved glucose-stimulated calcium signalling by increasing connexin36 gap junction levels on the plasma membrane. Our data indicate that protein kinase A regulates β-cell coupling through a fast mechanism, such as channel gating or membrane organization, while Epac2 regulates slower mechanisms of regulation, such as gap junction turnover. Increases in β-cell coupling with exendin-4 may protect against cytokine-mediated β-cell death as well as preserve insulin secretion dynamics during the development of diabetes. ABSTRACT The pancreatic islets of Langerhans maintain glucose homeostasis. Insulin secretion from islet β-cells is driven by glucose metabolism, depolarization of the cell membrane and an influx of calcium, which initiates the release of insulin. Gap junctions composed of connexin36 (Cx36) electrically couple β-cells, regulating calcium signalling and insulin secretion dynamics. Cx36 coupling is decreased in pre-diabetic mice, suggesting a role for altered coupling in diabetes. Our previous work has shown that pro-inflammatory cytokines decrease Cx36 coupling and that compounds which increase cAMP can increase Cx36 coupling. The goal of this study was to determine if exendin-4, which increases cAMP, can protect against cytokine-induced decreases in Cx36 coupling and altered islet function. In both mouse and human islets, exendin-4 protected against cytokine-induced decreases in coupling and preserved glucose-stimulated calcium signalling. Exendin-4 also protected against protein kinase Cδ-mediated decreases in Cx36 coupling. Exendin-4 preserved coupling in mouse islets by preserving Cx36 levels on the plasma membrane. Exendin-4 regulated Cx36 coupling via both protein kinase A (PKA)- and Epac2-mediated mechanisms in cytokine-treated islets. In mouse islets, modulating Epac2 had a greater impact in mediating Cx36 coupling, while in human islets modulating PKA had a greater impact on Cx36 coupling. Our data indicate that PKA regulates Cx36 coupling through a fast mechanism, such as channel gating, while Epac2 regulates slower mechanisms of regulation, such as Cx36 turnover in the membrane. Increases in Cx36 coupling with exendin-4 may protect against cytokine-mediated β-cell dysfunction to insulin secretion dynamics during the development of diabetes.
Collapse
Affiliation(s)
- Nikki L. Farnsworth
- Barbara Davis Center for Childhood DiabetesUniversity of Colorado Anschutz Medical CampusAuroraCO80045USA
| | - Rachelle Walter
- Department of BioengineeringUniversity of Colorado Anschutz Medical CampusAuroraCO80045USA
| | - Robert A. Piscopio
- Department of BioengineeringUniversity of Colorado Anschutz Medical CampusAuroraCO80045USA
| | - Wolfgang E. Schleicher
- Department of BioengineeringUniversity of Colorado Anschutz Medical CampusAuroraCO80045USA
| | - Richard K. P. Benninger
- Barbara Davis Center for Childhood DiabetesUniversity of Colorado Anschutz Medical CampusAuroraCO80045USA
- Department of BioengineeringUniversity of Colorado Anschutz Medical CampusAuroraCO80045USA
| |
Collapse
|
19
|
Wang P, Wang SC, Li D, Li T, Yang HP, Wang L, Wang YF, Parpura V. Role of Connexin 36 in Autoregulation of Oxytocin Neuronal Activity in Rat Supraoptic Nucleus. ASN Neuro 2019; 11:1759091419843762. [PMID: 31091986 PMCID: PMC6535915 DOI: 10.1177/1759091419843762] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2018] [Revised: 02/10/2019] [Accepted: 02/26/2019] [Indexed: 12/24/2022] Open
Abstract
In the supraoptic nucleus (SON), the incidence of dye coupling among oxytocin (OT) neurons increases significantly in nursing mothers. However, the type(s) of connexin (Cx) involved is(are) unknown. In this study, we specifically investigated whether Cx36 plays a functional role in the coupling between OT neurons in the SON of lactating rats. In this brain region, Cx36 was mainly coimmunostained with vasopressin neurons in virgin female rats, whereas in lactating rats, Cx36 was primarily colocalized with OT neurons. In brain slices from lactating rats, application of quinine (0.1 mM), a selective blocker of Cx36, significantly reduced dye coupling among OT neurons as well as the discharge/firing frequency of spikes/action potentials and their amplitude, and transiently depolarized the membrane potential of OT neurons in whole-cell patch-clamp recordings. However, quinine significantly reduced the amplitude, but not frequency, of inhibitory postsynaptic currents in OT neurons; the duration of excitatory postsynaptic currents was reduced but not their frequency and amplitude. Furthermore, the excitatory effect of OT (1 pM) on OT neurons was significantly weakened and delayed by quinine, and burst firing was absent in the presence of this inhibitor. Lastly, Western blotting analysis revealed that the presence of combined, but not alone, quinine and OT significantly reduced the amount of Cx36 in the SON. Thus, Cx36-mediated junctional communication plays a crucial role in autoregulatory control of OT neuronal activity, likely by acting at the postsynaptic sites. The level of Cx36 is modulated by its own activity and the presence of OT.
Collapse
Affiliation(s)
- Ping Wang
- Department of Genetics, School of Basic Medical Sciences, Harbin Medical University, China
| | | | - Dongyang Li
- Department of Physiology, School of Basic Medical Sciences, Harbin Medical University, China
| | - Tong Li
- Department of Physiology, School of Basic Medical Sciences, Harbin Medical University, China
| | - Hai-Peng Yang
- The Fourth Affiliated Hospital, Harbin Medical University, China
| | - Liwei Wang
- The Fourth Affiliated Hospital, Harbin Medical University, China
| | - Yu-Feng Wang
- Department of Physiology, School of Basic Medical Sciences, Harbin Medical University, China
| | - Vladimir Parpura
- Department of Neurobiology, The University of Alabama at Birmingham, AL, USA
| |
Collapse
|
20
|
Lee YH, Zhang S, Mitchell CK, Lin YP, O’Brien J. Calcium Imaging with Super-Resolution Radial Fluctuations. BIOSCIENCE AND BIOENGINEERING (BOSTON, MASS.) 2018; 4:78-84. [PMID: 33005746 PMCID: PMC7526954] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Calcium signals act as a ubiquitous secondary messenger in regulating many body functions. The detection of calcium microdomain signals is greatly facilitated by the existence of biomarker-targeted fluorescent probes. In this study, SRRF (super-resolution radial fluctuations) algorithm were used to compare the loci and the intensity of fluorescent probes before and after SRRF analysis. The implementation of SRRF algorithm was aimed for automatically resolving delicate and small calcium signals (to avoid the overlapped loci) on original images. For assessing the spatial accuracy of image intensity, immunofluorescence staining of retina cryostat slice for connexin 36 (Cx36) was microscopically imaged with or without the successive SRRF reconstruction. For characterizing the temporal association between SRRF and non-SRRF images, the changes of Cx36-GCaMP calcium indicator were recorded from transfected HeLa cells in response to the transient puffing of ionomycin. Image processing and analyses were conducted with Image J and Matlab. Through this study, SRRF reconstruction was found to confer an accurate measure for the identification of subcellular molecules, such as gap junctions. Compared with the conventional imaging, SRRF reconstruction generated better image resolution for the precise registration of individual signals. Temporally, the ratios of change in fluorescence intensity between SRRF and non-SRRF images were significantly correlated in the presence or absence of the subtraction of high background intensity. Quantitatively, the ratios of change in fluorescence intensity between SRRF and non-SRRF images with or without background subtraction were also significantly correlated. The merit of SRRF application on calcium live imaging was validated with the reporter gene system we worked on.
Collapse
Affiliation(s)
- Yuan-Hao Lee
- Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, USA,Corresponding author: (Yuan-Hao Lee)
| | - Shuo Zhang
- Department of Ophthalmology, Emory University, School of Medicine, Atlanta, USA,Department of Ophthalmology, Xiangya Hospital, Central South University, Changsha, P. R. of China
| | - Cheryl Kyles Mitchell
- Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, USA
| | - Ya-Ping Lin
- Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, USA
| | - John O’Brien
- Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, USA,The MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, Houston, USA
| |
Collapse
|
21
|
Lynn BD, Li X, Hormuzdi SG, Griffiths EK, McGlade CJ, Nagy JI. E3 ubiquitin ligases LNX1 and LNX2 localize at neuronal gap junctions formed by connexin36 in rodent brain and molecularly interact with connexin36. Eur J Neurosci 2018; 48:3062-3081. [PMID: 30295974 DOI: 10.1111/ejn.14198] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Revised: 08/31/2018] [Accepted: 09/25/2018] [Indexed: 12/31/2022]
Abstract
Electrical synapses in the mammalian central nervous system (CNS) are increasingly recognized as highly complex structures for mediation of neuronal communication, both with respect to their capacity for dynamic short- and long-term modification in efficacy of synaptic transmission and their multimolecular regulatory and structural components. These two characteristics are inextricably linked, such that understanding of mechanisms that contribute to electrical synaptic plasticity requires knowledge of the molecular composition of electrical synapses and the functions of proteins associated with these synapses. Here, we provide evidence that the key component of gap junctions that form the majority of electrical synapses in the mammalian CNS, namely connexin36 (Cx36), directly interacts with the related E3 ubiquitin ligase proteins Ligand of NUMB protein X1 (LNX1) and Ligand of NUMB protein X2 (LNX2). This is based on immunofluorescence colocalization of LNX1 and LNX2 with Cx36-containing gap junctions in adult mouse brain versus lack of such coassociation in LNX null mice, coimmunoprecipitation of LNX proteins with Cx36, and pull-down of Cx36 with the second PDZ domain of LNX1 and LNX2. Furthermore, cotransfection of cultured cells with Cx36 and E3 ubiquitin ligase-competent LNX1 and LNX2 isoforms led to loss of Cx36-containing gap junctions between cells, whereas these junctions persisted following transfection with isoforms of these proteins that lack ligase activity. Our results suggest that a LNX protein mediates ubiquitination of Cx36 at neuronal gap junctions, with consequent Cx36 internalization, and may thereby contribute to intracellular mechanisms that govern the recently identified modifiability of synaptic transmission at electrical synapses.
Collapse
Affiliation(s)
- Bruce D Lynn
- Department of Physiology and Pathophysiology, Max Rady College of Medicine, Rady Faculty of Health Science, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Xinbo Li
- Casey Eye Institute, Oregon Health and Science University, Portland, Oregon
| | - Sheriar G Hormuzdi
- D'Arcy Thompson Unit, School of Life Sciences, University of Dundee, Dundee, UK
| | - Emily K Griffiths
- Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada
- The Arthur and Sonia Labatt Brain Tumour Research Centre, Hospital for Sick Children, Toronto, Ontario, Canada
| | - C Jane McGlade
- Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada
- The Arthur and Sonia Labatt Brain Tumour Research Centre, Hospital for Sick Children, Toronto, Ontario, Canada
| | - James I Nagy
- Department of Physiology and Pathophysiology, Max Rady College of Medicine, Rady Faculty of Health Science, University of Manitoba, Winnipeg, Manitoba, Canada
| |
Collapse
|
22
|
Welzel G, Schuster S. Long-term potentiation in an innexin-based electrical synapse. Sci Rep 2018; 8:12579. [PMID: 30135467 PMCID: PMC6105662 DOI: 10.1038/s41598-018-30966-w] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2018] [Accepted: 08/09/2018] [Indexed: 11/08/2022] Open
Abstract
Electrical synapses are formed by two unrelated gap junction protein families, the primordial innexins (invertebrates) or the connexins (vertebrates). Although molecularly different, innexin- and connexin-based electrical synapses are strikingly similar in their membrane topology. However, it remains unclear if this similarity extends also to more sophisticated functions such as long-term potentiation which is only known in connexin-based synapses. Here we show that this capacity is not unique to connexin-based synapses. Using a method that allowed us to quantitatively measure gap-junction conductance we provide the first and unequivocal evidence of long-term potentiation in an innexin-based electrical synapse. Our findings suggest that long-term potentiation is a property that has likely existed already in ancestral gap junctions. They therefore could provide a highly potent system to dissect shared molecular mechanisms of electrical synapse plasticity.
Collapse
Affiliation(s)
- Georg Welzel
- Department of Animal Physiology, University of Bayreuth, 95440, Bayreuth, Germany.
| | - Stefan Schuster
- Department of Animal Physiology, University of Bayreuth, 95440, Bayreuth, Germany.
| |
Collapse
|
23
|
Nagy JI, Lynn BD. Structural and Intermolecular Associations Between Connexin36 and Protein Components of the Adherens Junction-Neuronal Gap Junction Complex. Neuroscience 2018; 384:241-261. [PMID: 29879437 DOI: 10.1016/j.neuroscience.2018.05.026] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2018] [Revised: 05/17/2018] [Accepted: 05/18/2018] [Indexed: 11/20/2022]
Abstract
Intimate structural and functional relationships between gap junctions and adherens junctions have been demonstrated in peripheral tissues, but have not been thoroughly examined in the central nervous system, where adherens junctions are often found in close proximity to neuronal gap junctions. Here, we used immunofluorescence approaches to document the localization of various protein components of adherens junctions in relation to those that we have previously reported to occur at electrical synapses formed by neuronal gap junctions composed of connexin36 (Cx36). The adherens junction constituents N-cadherin and nectin-1 were frequently found to localize near or overlap with Cx36-containing gap junctions in several brain regions examined. This was also true of the adherens junction-associated proteins α-catenin and β-catenin, as well as the proteins zonula occludens-1 and AF6 (aka, afadin) that were reported constituents of both adherens junctions and gap junctions. The deployment of the protein constituents of these junctions was especially striking at somatic contacts between primary afferent neurons in the mesencephalic trigeminal nucleus (MesV), where the structural components of adherens junctions appeared to be maintained in connexin36 null mice. These results support emerging views concerning the multi-molecular composition of electrical synapses and raise possibilities for various structural and functional protein-protein interactions at what now can be considered the adherens junction-neuronal gap junction complex. Further, the results point to intracellular signaling pathways that could potentially contribute to the assembly, maintenance and turnover of this complex, as well as to the dynamic nature of neuronal communication at electrical synapses.
Collapse
Affiliation(s)
- J I Nagy
- Department of Physiology and Pathophysiology, Max Rady College of Medicine, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Canada.
| | - B D Lynn
- Department of Physiology and Pathophysiology, Max Rady College of Medicine, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Canada
| |
Collapse
|
24
|
Aasen T, Johnstone S, Vidal-Brime L, Lynn KS, Koval M. Connexins: Synthesis, Post-Translational Modifications, and Trafficking in Health and Disease. Int J Mol Sci 2018; 19:ijms19051296. [PMID: 29701678 PMCID: PMC5983588 DOI: 10.3390/ijms19051296] [Citation(s) in RCA: 62] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Revised: 04/20/2018] [Accepted: 04/21/2018] [Indexed: 02/06/2023] Open
Abstract
Connexins are tetraspan transmembrane proteins that form gap junctions and facilitate direct intercellular communication, a critical feature for the development, function, and homeostasis of tissues and organs. In addition, a growing number of gap junction-independent functions are being ascribed to these proteins. The connexin gene family is under extensive regulation at the transcriptional and post-transcriptional level, and undergoes numerous modifications at the protein level, including phosphorylation, which ultimately affects their trafficking, stability, and function. Here, we summarize these key regulatory events, with emphasis on how these affect connexin multifunctionality in health and disease.
Collapse
Affiliation(s)
- Trond Aasen
- Translational Molecular Pathology, Vall d'Hebron Institute of Research (VHIR), Autonomous University of Barcelona, CIBERONC, 08035 Barcelona, Spain.
| | - Scott Johnstone
- Robert M. Berne Cardiovascular Research Center, University of Virginia School of Medicine, P.O. Box 801394, Charlottesville, VI 22908, USA.
- Institute of Cardiovascular and Medical Sciences, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8TT, UK.
| | - Laia Vidal-Brime
- Translational Molecular Pathology, Vall d'Hebron Institute of Research (VHIR), Autonomous University of Barcelona, CIBERONC, 08035 Barcelona, Spain.
| | - K Sabrina Lynn
- Division of Pulmonary, Allergy, Critical Care and Sleep Medicine, Department of Medicine, Emory University School of Medicine, Atlanta, GA 30322, USA.
| | - Michael Koval
- Division of Pulmonary, Allergy, Critical Care and Sleep Medicine, Department of Medicine, Emory University School of Medicine, Atlanta, GA 30322, USA.
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA.
| |
Collapse
|
25
|
Lotze J, Wolf P, Reinhardt U, Seitz O, Mörl K, Beck-Sickinger AG. Time-Resolved Tracking of Separately Internalized Neuropeptide Y 2 Receptors by Two-Color Pulse-Chase. ACS Chem Biol 2018; 13:618-627. [PMID: 29268018 DOI: 10.1021/acschembio.7b00999] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Internalization and intracellular trafficking of G protein-coupled receptors (GPCR) plays an important role in the signal transduction. These processes are often highly dynamic and take place rapidly. In the past 10 years, it became obvious that internalized GPCRs are also capable of signaling via arrestin or heterotrimeric G proteins within the endosomal compartment. Real-time imaging of receptors in living cells can help to evaluate the temporal and spatial localization. We achieved a two-color pulse-chase labeling approach, which allowed the tracking of the human neuropeptide Y2 receptor (hY2R) in the same cell at different times. The ability to visualize the internalization pathway of two separately labeled and separately stimulated subsets of hY2R in a time-resolved manner revealed a rapid trafficking. Fusion of the two hY2R subsets was already observed 10 min after stimulation in the early endosomal compartment without subsequent separation of the fused receptor populations. The results demonstrate that the cells do not discriminate between receptors that were stimulated and internalized at different time points.
Collapse
Affiliation(s)
- Jonathan Lotze
- Institute of Biochemistry, Leipzig University, 04103 Leipzig, Germany
| | - Philipp Wolf
- Institute of Biochemistry, Leipzig University, 04103 Leipzig, Germany
| | - Ulrike Reinhardt
- Institute of Chemistry, Humboldt-University Berlin, 12489 Berlin, Germany
| | - Oliver Seitz
- Institute of Chemistry, Humboldt-University Berlin, 12489 Berlin, Germany
| | - Karin Mörl
- Institute of Biochemistry, Leipzig University, 04103 Leipzig, Germany
| | | |
Collapse
|
26
|
Abstract
Cortical oscillations are thought to be involved in many cognitive functions and processes. Several mechanisms have been proposed to regulate oscillations. One prominent but understudied mechanism is gap junction coupling. Gap junctions are ubiquitous in cortex between GABAergic interneurons. Moreover, recent experiments indicate their strength can be modified in an activity-dependent manner, similar to chemical synapses. We hypothesized that activity-dependent gap junction plasticity acts as a mechanism to regulate oscillations in the cortex. We developed a computational model of gap junction plasticity in a recurrent cortical network based on recent experimental findings. We showed that gap junction plasticity can serve as a homeostatic mechanism for oscillations by maintaining a tight balance between two network states: asynchronous irregular activity and synchronized oscillations. This homeostatic mechanism allows for robust communication between neuronal assemblies through two different mechanisms: transient oscillations and frequency modulation. This implies a direct functional role for gap junction plasticity in information transmission in cortex.
Collapse
Affiliation(s)
- Guillaume Pernelle
- Bioengineering Department, Imperial College London, London, United Kingdom
| | - Wilten Nicola
- Bioengineering Department, Imperial College London, London, United Kingdom
| | - Claudia Clopath
- Bioengineering Department, Imperial College London, London, United Kingdom
- * E-mail:
| |
Collapse
|
27
|
Coulon P, Landisman CE. The Potential Role of Gap Junctional Plasticity in the Regulation of State. Neuron 2017; 93:1275-1295. [PMID: 28334604 DOI: 10.1016/j.neuron.2017.02.041] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2016] [Revised: 01/20/2017] [Accepted: 02/22/2017] [Indexed: 11/19/2022]
Abstract
Electrical synapses are the functional correlate of gap junctions and allow transmission of small molecules and electrical current between coupled neurons. Instead of static pores, electrical synapses are actually plastic, similar to chemical synapses. In the thalamocortical system, gap junctions couple inhibitory neurons that are similar in their biochemical profile, morphology, and electrophysiological properties. We postulate that electrical synaptic plasticity among inhibitory neurons directly interacts with the switching between different firing patterns in a state-dependent and type-dependent manner. In neuronal networks, electrical synapses may function as a modifiable resonance feedback system that enables stable oscillations. Furthermore, the plasticity of electrical synapses may play an important role in regulation of state, synchrony, and rhythmogenesis in the mammalian thalamocortical system, similar to chemical synaptic plasticity. Based on their plasticity, rich diversity, and specificity, electrical synapses are thus likely to participate in the control of consciousness and attention.
Collapse
Affiliation(s)
- Philippe Coulon
- Seattle Children's Research Institute, Center for Integrative Brain Research, Seattle, WA 98101, USA.
| | - Carole E Landisman
- Seattle Children's Research Institute, Center for Integrative Brain Research, Seattle, WA 98101, USA.
| |
Collapse
|
28
|
O'Brien J. Design principles of electrical synaptic plasticity. Neurosci Lett 2017; 695:4-11. [PMID: 28893590 DOI: 10.1016/j.neulet.2017.09.003] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2017] [Revised: 08/09/2017] [Accepted: 09/01/2017] [Indexed: 01/19/2023]
Abstract
Essentially all animals with nervous systems utilize electrical synapses as a core element of communication. Electrical synapses, formed by gap junctions between neurons, provide rapid, bidirectional communication that accomplishes tasks distinct from and complementary to chemical synapses. These include coordination of neuron activity, suppression of voltage noise, establishment of electrical pathways that define circuits, and modulation of high order network behavior. In keeping with the omnipresent demand to alter neural network function in order to respond to environmental cues and perform tasks, electrical synapses exhibit extensive plasticity. In some networks, this plasticity can have dramatic effects that completely remodel circuits or remove the influence of certain cell types from networks. Electrical synaptic plasticity occurs on three distinct time scales, ranging from milliseconds to days, with different mechanisms accounting for each. This essay highlights principles that dictate the properties of electrical coupling within networks and the plasticity of the electrical synapses, drawing examples extensively from retinal networks.
Collapse
Affiliation(s)
- John O'Brien
- McGovern Medical School, The University of Texas Health Science Center at Houston, 6431 Fannin St., MSB 7.024, Houston, TX 77030, USA.
| |
Collapse
|
29
|
Stout RF, Spray DC. Cysteine residues in the cytoplasmic carboxy terminus of connexins dictate gap junction plaque stability. Mol Biol Cell 2017; 28:2757-2764. [PMID: 28835376 PMCID: PMC5638580 DOI: 10.1091/mbc.e17-03-0206] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2017] [Revised: 07/21/2017] [Accepted: 08/14/2017] [Indexed: 01/01/2023] Open
Abstract
Cysteine residues within the cytoplasmic carboxyl-terminus of gap junction–forming proteins are required to stabilize gap junction plaque organization. The stability of gap junction plaque organization can be modified. Gap junction stability may provide a stable supramolecular platform for modulation of gap junction functions. Gap junctions are cellular contact sites composed of clustered connexin transmembrane proteins that act in dual capacities as channels for direct intercellular exchange of small molecules and as structural adhesion complexes known as gap junction nexuses. Depending on the connexin isoform, the cluster of channels (the gap junction plaque) can be stably or fluidly arranged. Here we used confocal microscopy and mutational analysis to identify the residues within the connexin proteins that determine gap junction plaque stability. We found that stability is altered by changing redox balance using a reducing agent—indicating gap junction nexus stability is modifiable. Stability of the arrangement of connexins is thought to regulate intercellular communication by establishing an ordered supramolecular platform. By identifying the residues that establish plaque stability, these studies lay the groundwork for exploration of mechanisms by which gap junction nexus stability modulates intercellular communication.
Collapse
Affiliation(s)
- Randy F Stout
- Department of Biomedical Sciences, New York Institute of Technology College of Osteopathic Medicine, Old Westbury, NY 11568-8000 .,Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461
| | - David C Spray
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461
| |
Collapse
|
30
|
Corsini S, Tortora M, Rauti R, Nistri A. Nicotine protects rat hypoglossal motoneurons from excitotoxic death via downregulation of connexin 36. Cell Death Dis 2017; 8:e2881. [PMID: 28617431 PMCID: PMC5520892 DOI: 10.1038/cddis.2017.232] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2016] [Revised: 04/21/2017] [Accepted: 04/26/2017] [Indexed: 01/01/2023]
Abstract
Motoneuron disease including amyotrophic lateral sclerosis may be due, at an early stage, to deficit in the extracellular clearance of the excitatory transmitter glutamate. A model of glutamate-mediated excitotoxic cell death based on pharmacological inhibition of its uptake was used to investigate how activation of neuronal nicotinic receptors by nicotine may protect motoneurons. Hypoglossal motoneurons (HMs) in neonatal rat brainstem slices were exposed to the glutamate uptake blocker DL-threo-β-benzyloxyaspartate (TBOA) that evoked large Ca2+ transients time locked among nearby HMs, whose number fell by about 30% 4 h later. As nicotine or the gap junction blocker carbenoxolone suppressed bursting, we studied connexin 36 (Cx36), which constitutes gap junctions in neurons and found it largely expressed by HMs. Cx36 was downregulated when nicotine or carbenoxolone was co-applied with TBOA. Expression of Cx36 was preferentially observed in cytosolic rather than membrane fractions after nicotine and TBOA, suggesting protein redistribution with no change in synthesis. Nicotine raised the expression of heat shock protein 70 (Hsp70), a protective factor that binds the apoptotic-inducing factor (AIF) whose nuclear translocation is a cause of cell death. TBOA increased intracellular AIF, an effect blocked by nicotine. These results indicate that activation of neuronal nicotinic receptors is an early tool for protecting motoneurons from excitotoxicity and that this process is carried out via the combined decrease in Cx36 activity, overexpression of Hsp70 and fall in AIF translocation. Thus, retarding or inhibiting HM death may be experimentally achieved by targeting one of these processes leading to motoneuron death.
Collapse
Affiliation(s)
- Silvia Corsini
- Department of Neuroscience, International School for Advanced Studies (SISSA), Trieste, Italy
| | - Maria Tortora
- Department of Neuroscience, International School for Advanced Studies (SISSA), Trieste, Italy
| | - Rossana Rauti
- Department of Neuroscience, International School for Advanced Studies (SISSA), Trieste, Italy
| | - Andrea Nistri
- Department of Neuroscience, International School for Advanced Studies (SISSA), Trieste, Italy
| |
Collapse
|
31
|
Miller AC, Pereda AE. The electrical synapse: Molecular complexities at the gap and beyond. Dev Neurobiol 2017; 77:562-574. [PMID: 28170151 DOI: 10.1002/dneu.22484] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Revised: 01/04/2017] [Accepted: 01/04/2017] [Indexed: 12/21/2022]
Abstract
Gap junctions underlie electrical synaptic transmission between neurons. Generally perceived as simple intercellular channels, "electrical synapses" have demonstrated to be more functionally sophisticated and structurally complex than initially anticipated. Electrical synapses represent an assembly of multiple molecules, consisting of channels, adhesion complexes, scaffolds, regulatory machinery, and trafficking proteins, all required for their proper function and plasticity. Additionally, while electrical synapses are often viewed as strictly symmetric structures, emerging evidence has shown that some components forming electrical synapses can be differentially distributed at each side of the junction. We propose that the molecular complexity and asymmetric distribution of proteins at the electrical synapse provides rich potential for functional diversity. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 562-574, 2017.
Collapse
Affiliation(s)
- Adam C Miller
- Institute of Neuroscience, Department of Biology, University of Oregon, Eugene, Oregon
| | - Alberto E Pereda
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York
| |
Collapse
|
32
|
Yoshikawa S, Vila A, Segelken J, Lin YP, Mitchell CK, Nguyen D, O'Brien J. Zebrafish connexin 79.8 (Gja8a): A lens connexin used as an electrical synapse in some neurons. Dev Neurobiol 2016; 77:548-561. [PMID: 27402207 DOI: 10.1002/dneu.22418] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2016] [Revised: 06/23/2016] [Accepted: 07/05/2016] [Indexed: 11/07/2022]
Abstract
In the mammalian central nervous system, a remarkably small number of connexins is used in electrical synapses, with the majority formed from Cx36. A larger number has been detected in teleosts, with some seeming to serve restricted roles. Here, we report the discovery of a new connexin expressed in the zebrafish lens and a limited set of neurons. Zebrafish cx79.8 (gja8a), previously annotated incorrectly as cx50.5 based on a partial cDNA sequence, is a homologue of mammalian Cx50 (Gja8). We examined its expression through transgenic promoter-reporter constructs, in situ hybridization, and immunolabeling, and examined regulation of coupling in transfected HeLa cells. cx79.8 was expressed most strongly in the lens, but expression was also found in several groups of neurons in the cerebellum and related areas at the midbrain-hindbrain boundary, in cone photoreceptors, and in neurons in the retinal inner nuclear and ganglion cell layers. Labeling in the retina with antibodies against two C-terminal epitopes revealed numerous small punctate spots in the inner plexiform layer and along the somata of cones. Abundant gap junctions were labeled in the outer 1/3 of the lens, but were absent from the center, suggesting that the epitopes or the entire protein was absent from the center. Cx79.8 tracer coupling was strongly regulated by phosphorylation, and was extremely low in control conditions in HeLa cells due to protein phosphatase 2A activity. These properties allow coupling to be strongly restricted in situ, a frequently observed property for electrical synapses. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 548-561, 2017.
Collapse
Affiliation(s)
- Shunichi Yoshikawa
- Richard S. Ruiz M.D., Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, Texas
| | - Alejandro Vila
- Richard S. Ruiz M.D., Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, Texas.,University of Texas Graduate School of Biomedical Sciences at Houston, Houston, Texas
| | - Jasmin Segelken
- Visual Neuroscience, Faculty of Medicine and Health Sciences, University of Oldenburg, Oldenburg, Germany
| | - Ya-Ping Lin
- Richard S. Ruiz M.D., Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, Texas
| | - Cheryl K Mitchell
- Richard S. Ruiz M.D., Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, Texas
| | - Duc Nguyen
- Richard S. Ruiz M.D., Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, Texas
| | - John O'Brien
- Richard S. Ruiz M.D., Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, Texas.,University of Texas Graduate School of Biomedical Sciences at Houston, Houston, Texas
| |
Collapse
|
33
|
Arroyo DA, Kirkby LA, Feller MB. Retinal Waves Modulate an Intraretinal Circuit of Intrinsically Photosensitive Retinal Ganglion Cells. J Neurosci 2016; 36:6892-905. [PMID: 27358448 PMCID: PMC4926237 DOI: 10.1523/jneurosci.0572-16.2016] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Revised: 05/11/2016] [Accepted: 05/16/2016] [Indexed: 02/07/2023] Open
Abstract
UNLABELLED Before the maturation of rod and cone photoreceptors, the developing retina relies on light detection by intrinsically photosensitive retinal ganglion cells (ipRGCs) to drive early light-dependent behaviors. ipRGCs are output neurons of the retina; however, they also form functional microcircuits within the retina itself. Whether ipRGC microcircuits exist during development and whether they influence early light detection remain unknown. Here, we investigate the neural circuit that underlies the ipRGC-driven light response in developing mice. We use a combination of calcium imaging, tracer coupling, and electrophysiology experiments to show that ipRGCs form extensive gap junction networks that strongly contribute to the overall light response of the developing retina. Interestingly, we found that gap junction coupling was modulated by spontaneous retinal waves, such that acute blockade of waves dramatically increased the extent of coupling and hence increased the number of light-responsive neurons. Moreover, using an optical sensor, we found that this wave-dependent modulation of coupling is driven by dopamine that is phasically released by retinal waves. Our results demonstrate that ipRGCs form gap junction microcircuits during development that are modulated by retinal waves; these circuits determine the extent of the light response and thus potentially impact the processing of early visual information and light-dependent developmental functions. SIGNIFICANCE STATEMENT Light-dependent functions in early development are mediated by intrinsically photosensitive retinal ganglion cells (ipRGCs). Here we show that ipRGCs form an extensive gap junction network with other retinal neurons, including other ipRGCs, which shapes the retina's overall light response. Blocking cholinergic retinal waves, which are the primary source of neural activity before maturation of photoreceptors, increased the extent of ipRGC gap junction networks, thus increasing the number of light-responsive cells. We determined that this modulation of ipRGC gap junction networks occurs via dopamine released by waves. These results demonstrate that retinal waves mediate dopaminergic modulation of gap junction networks to regulate pre-vision light responses.
Collapse
Affiliation(s)
| | | | - Marla B Feller
- Department of Molecular and Cell Biology, Helen Wills Neuroscience Institute, University of California-Berkeley, Berkeley, California 94720-3200
| |
Collapse
|
34
|
Falk MM, Bell CL, Kells Andrews RM, Murray SA. Molecular mechanisms regulating formation, trafficking and processing of annular gap junctions. BMC Cell Biol 2016; 17 Suppl 1:22. [PMID: 27230503 PMCID: PMC4896261 DOI: 10.1186/s12860-016-0087-7] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
Internalization of gap junction plaques results in the formation of annular gap junction vesicles. The factors that regulate the coordinated internalization of the gap junction plaques to form annular gap junction vesicles, and the subsequent events involved in annular gap junction processing have only relatively recently been investigated in detail. However it is becoming clear that while annular gap junction vesicles have been demonstrated to be degraded by autophagosomal and endo-lysosomal pathways, they undergo a number of additional processing events. Here, we characterize the morphology of the annular gap junction vesicle and review the current knowledge of the processes involved in their formation, fission, fusion, and degradation. In addition, we address the possibility for connexin protein recycling back to the plasma membrane to contribute to gap junction formation and intercellular communication. Information on gap junction plaque removal from the plasma membrane and the subsequent processing of annular gap junction vesicles is critical to our understanding of cell-cell communication as it relates to events regulating development, cell homeostasis, unstable proliferation of cancer cells, wound healing, changes in the ischemic heart, and many other physiological and pathological cellular phenomena.
Collapse
Affiliation(s)
- Matthias M Falk
- Department of Biological Sciences, Lehigh University, Bethlehem, PA, 18049, USA.
| | - Cheryl L Bell
- Department of Cell Biology and Physiology, University of Pittsburgh, School of Medicine, Pittsburgh, PA, l5261, USA
| | | | - Sandra A Murray
- Department of Cell Biology and Physiology, University of Pittsburgh, School of Medicine, Pittsburgh, PA, l5261, USA.
| |
Collapse
|