1
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Xie L, Kang F, Qin T, Kang Y, Liang T, Xie H, Froese CD, Xie H, Au A, Yip CM, Trimble WS, Gaisano HY. Septin5 deletion enhances β-cell exocytosis by releasing microtubule-tethered insulin granules onto plasma membrane. Nat Commun 2025; 16:2725. [PMID: 40108136 PMCID: PMC11923188 DOI: 10.1038/s41467-025-57421-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2024] [Accepted: 02/19/2025] [Indexed: 03/22/2025] Open
Abstract
Septin5 interacts with SNARE proteins to regulate exocytosis in neurons, but its role in pancreatic β-cells is unknown. Here, we report that Septin5 is abundant in rodent and human β-cells, deletion of which dramatically enhances biphasic glucose-stimulated insulin secretion, including in type 2 diabetes (T2D). Super-resolution imaging shows that Septin5 is preferentially assembled in microtubule-plasma membrane contact sites in a microtubule-dependent manner, which provides discrete harbor for secretory granule anchoring. By decreasing the stability of the cortical microtubule meshwork, Septin5 depletion increases insulin granule dynamics and access to the plasma membrane. Analysis of spatiotemporal coupling of fusion events and localized Ca2+ influx through L-type Ca2+ channels show that Septin5 depletion increases releasable granule pool clustering on Ca2+ channels, previously shown to be impaired in T2D, thus rectifying this T2D defect. Hence, inhibition of Septin5 can improve insulin secretion.
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Affiliation(s)
- Li Xie
- Department of Medicine, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, Canada.
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON, Canada.
| | - Fei Kang
- Department of Medicine, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, Canada.
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON, Canada.
| | - Tairan Qin
- Department of Medicine, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, Canada
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON, Canada
| | - Youhou Kang
- Department of Medicine, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, Canada
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON, Canada
| | - Tao Liang
- Department of Medicine, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, Canada
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON, Canada
| | - Huanli Xie
- Department of Medicine, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, Canada
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON, Canada
| | - Carol D Froese
- The program in Cell Biology, Department of Biochemistry, Hospital for Sick Children, University of Toronto, Toronto, ON, Canada
| | - Hong Xie
- The program in Cell Biology, Department of Biochemistry, Hospital for Sick Children, University of Toronto, Toronto, ON, Canada
| | - Aaron Au
- Institute of Biomedical Engineering, University of Toronto, Toronto, ON, Canada
- Donnelly Centre for Cellular & Biomolecular Research, University of Toronto, Toronto, ON, Canada
| | - Christopher M Yip
- Institute of Biomedical Engineering, University of Toronto, Toronto, ON, Canada
- Donnelly Centre for Cellular & Biomolecular Research, University of Toronto, Toronto, ON, Canada
| | - William S Trimble
- The program in Cell Biology, Department of Biochemistry, Hospital for Sick Children, University of Toronto, Toronto, ON, Canada
| | - Herbert Y Gaisano
- Department of Medicine, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, Canada.
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON, Canada.
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2
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Omar-Hmeadi M, Guček A, Barg S. Local PI(4,5)P 2 signaling inhibits fusion pore expansion during exocytosis. Cell Rep 2023; 42:112036. [PMID: 36701234 DOI: 10.1016/j.celrep.2023.112036] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Revised: 11/04/2022] [Accepted: 01/11/2023] [Indexed: 01/26/2023] Open
Abstract
Phosphatidylinositol(4,5)bisphosphate (PI(4,5)P2) is an important signaling phospholipid that is required for regulated exocytosis and some forms of endocytosis. The two processes share a topologically similar pore structure that connects the vesicle lumen with the outside. Widening of the fusion pore during exocytosis leads to cargo release, while its closure initiates kiss&run or cavicapture endocytosis. We show here, using live-cell total internal reflection fluorescence (TIRF) microscopy of insulin granule exocytosis, that transient accumulation of PI(4,5)P2 at the release site recruits components of the endocytic fission machinery and stalls the late fusion pore expansion that is required for peptide release. The absence of clathrin differentiates this mechanism from clathrin-mediated endocytosis. Knockdown of phosphatidylinositol-phosphate-5-kinase-1c or optogenetic recruitment of 5-phosphatase reduces PI(4,5)P2 transients and accelerates fusion pore expansion, suggesting that acute PI(4,5)P2 synthesis is involved. Thus, local phospholipid signaling inhibits fusion pore expansion and peptide release through an unconventional endocytic mechanism.
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Affiliation(s)
- Muhmmad Omar-Hmeadi
- Department of Medical Cell Biology, Uppsala University, BMC Box 571, 751 23 Uppsala, Sweden
| | - Alenka Guček
- Department of Medical Cell Biology, Uppsala University, BMC Box 571, 751 23 Uppsala, Sweden
| | - Sebastian Barg
- Department of Medical Cell Biology, Uppsala University, BMC Box 571, 751 23 Uppsala, Sweden.
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3
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Bracey KM, Gu G, Kaverina I. Microtubules in Pancreatic β Cells: Convoluted Roadways Toward Precision. Front Cell Dev Biol 2022; 10:915206. [PMID: 35874834 PMCID: PMC9305484 DOI: 10.3389/fcell.2022.915206] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2022] [Accepted: 06/14/2022] [Indexed: 11/18/2022] Open
Abstract
Pancreatic islet β cells regulate glucose homeostasis via glucose-stimulated insulin secretion (GSIS). Cytoskeletal polymers microtubules (MTs) serve as tracks for the transport and positioning of secretory insulin granules. MT network in β cells has unique morphology with several distinct features, which support granule biogenesis (via Golgi-derived MT array), net non-directional transport (via interlocked MT mesh), and control availability of granules at secretion sites (via submembrane MT bundle). The submembrane MT array, which is parallel to the plasma membrane and serves to withdraw excessive granules from the secretion hot spots, is destabilized and fragmented downstream of high glucose stimulation, allowing for regulated secretion. The origin of such an unusual MT network, the features that define its functionality, and metabolic pathways that regulate it are still to a large extent elusive and are a matter of active investigation and debate. Besides the MT network itself, it is important to consider the interplay of molecular motors that drive and fine-tune insulin granule transport. Importantly, activity of kinesin-1, which is the major MT-dependent motor in β cells, transports insulin granules, and has a capacity to remodel MT network, is also regulated by glucose. We discuss yet unknown potential avenues toward understanding how MT network and motor proteins provide control for secretion in coordination with other GSIS-regulating mechanisms.
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4
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Noordstra I, van den Berg CM, Boot FWJ, Katrukha EA, Yu KL, Tas RP, Portegies S, Viergever BJ, de Graaff E, Hoogenraad CC, de Koning EJP, Carlotti F, Kapitein LC, Akhmanova A. Organization and dynamics of the cortical complexes controlling insulin secretion in β-cells. J Cell Sci 2022; 135:274234. [PMID: 35006275 PMCID: PMC8918791 DOI: 10.1242/jcs.259430] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2021] [Accepted: 12/21/2021] [Indexed: 11/20/2022] Open
Abstract
Insulin secretion in pancreatic β-cells is regulated by cortical complexes that are enriched at the sites of adhesion to extracellular matrix facing the vasculature. Many components of these complexes, including bassoon, RIM, ELKS and liprins, are shared with neuronal synapses. Here, we show that insulin secretion sites also contain the non-neuronal proteins LL5β (also known as PHLDB2) and KANK1, which, in migrating cells, organize exocytotic machinery in the vicinity of integrin-based adhesions. Depletion of LL5β or focal adhesion disassembly triggered by myosin II inhibition perturbed the clustering of secretory complexes and attenuated the first wave of insulin release. Although previous analyses in vitro and in neurons have suggested that secretory machinery might assemble through liquid–liquid phase separation, analysis of endogenously labeled ELKS in pancreatic islets indicated that its dynamics is inconsistent with such a scenario. Instead, fluorescence recovery after photobleaching and single-molecule imaging showed that ELKS turnover is driven by binding and unbinding to low-mobility scaffolds. Both the scaffold movements and ELKS exchange were stimulated by glucose treatment. Our findings help to explain how integrin-based adhesions control spatial organization of glucose-stimulated insulin release. Summary: Characterization of the composition of cortical complexes controlling insulin secretion, showing that their dynamics is inconsistent with assembly through liquid–liquid phase separation.
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Affiliation(s)
- Ivar Noordstra
- Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.,Division of Cell and Developmental Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Cyntha M van den Berg
- Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Fransje W J Boot
- Department of Internal Medicine, Nephrology, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, The Netherlands
| | - Eugene A Katrukha
- Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Ka Lou Yu
- Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Roderick P Tas
- Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Sybren Portegies
- Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Bastiaan J Viergever
- Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Esther de Graaff
- Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Casper C Hoogenraad
- Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Eelco J P de Koning
- Department of Internal Medicine, Nephrology, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, The Netherlands
| | - Françoise Carlotti
- Department of Internal Medicine, Nephrology, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, The Netherlands
| | - Lukas C Kapitein
- Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Anna Akhmanova
- Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
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5
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Trogden KP, Lee J, Bracey KM, Ho KH, McKinney H, Zhu X, Arpag G, Folland TG, Osipovich AB, Magnuson MA, Zanic M, Gu G, Holmes WR, Kaverina I. Microtubules regulate pancreatic β-cell heterogeneity via spatiotemporal control of insulin secretion hot spots. eLife 2021; 10:59912. [PMID: 34783306 PMCID: PMC8635970 DOI: 10.7554/elife.59912] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2020] [Accepted: 11/08/2021] [Indexed: 12/25/2022] Open
Abstract
Heterogeneity of glucose-stimulated insulin secretion (GSIS) in pancreatic islets is physiologically important but poorly understood. Here, we utilize mouse islets to determine how microtubules (MTs) affect secretion toward the vascular extracellular matrix at single cell and subcellular levels. Our data indicate that MT stability in the β-cell population is heterogenous, and that GSIS is suppressed in cells with highly stable MTs. Consistently, MT hyper-stabilization prevents, and MT depolymerization promotes the capacity of single β-cell for GSIS. Analysis of spatiotemporal patterns of secretion events shows that MT depolymerization activates otherwise dormant β-cells via initiation of secretion clusters (hot spots). MT depolymerization also enhances secretion from individual cells, introducing both additional clusters and scattered events. Interestingly, without MTs, the timing of clustered secretion is dysregulated, extending the first phase of GSIS and causing oversecretion. In contrast, glucose-induced Ca2+ influx was not affected by MT depolymerization yet required for secretion under these conditions, indicating that MT-dependent regulation of secretion hot spots acts in parallel with Ca2+ signaling. Our findings uncover a novel MT function in tuning insulin secretion hot spots, which leads to accurately measured and timed response to glucose stimuli and promotes functional β-cell heterogeneity.
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Affiliation(s)
- Kathryn P Trogden
- Department of Cell and Developmental Biology and Program in Developmental Biology, Vanderbilt University, Nashville, United States
| | - Justin Lee
- Department of Cell and Developmental Biology and Program in Developmental Biology, Vanderbilt University, Nashville, United States
| | - Kai M Bracey
- Department of Cell and Developmental Biology and Program in Developmental Biology, Vanderbilt University, Nashville, United States
| | - Kung-Hsien Ho
- Department of Cell and Developmental Biology and Program in Developmental Biology, Vanderbilt University, Nashville, United States
| | - Hudson McKinney
- Department of Cell and Developmental Biology and Program in Developmental Biology, Vanderbilt University, Nashville, United States
| | - Xiaodong Zhu
- Department of Cell and Developmental Biology and Program in Developmental Biology, Vanderbilt University, Nashville, United States.,Department of Medicine, Vanderbilt University, Nashville, United States
| | - Goker Arpag
- Department of Cell and Developmental Biology and Program in Developmental Biology, Vanderbilt University, Nashville, United States
| | - Thomas G Folland
- Department of Mechanical Engineering, Vanderbilt University, Nashville, United States
| | - Anna B Osipovich
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, United States.,Center for Stem Cell Biology, Vanderbilt University, Nashville, United States
| | - Mark A Magnuson
- Department of Cell and Developmental Biology and Program in Developmental Biology, Vanderbilt University, Nashville, United States.,Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, United States.,Center for Stem Cell Biology, Vanderbilt University, Nashville, United States
| | - Marija Zanic
- Department of Cell and Developmental Biology and Program in Developmental Biology, Vanderbilt University, Nashville, United States.,Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, United States.,Department of Biochemistry, Vanderbilt University, Nashville, United States
| | - Guoqiang Gu
- Department of Cell and Developmental Biology and Program in Developmental Biology, Vanderbilt University, Nashville, United States
| | - William R Holmes
- Department of Physics and Astronomy, Vanderbilt University, Nashville, United States.,Department of Mathematics, Vanderbilt University, Nashville, United States.,Quantitative Systems Biology Center, Vanderbilt University, Nashville, United States
| | - Irina Kaverina
- Department of Cell and Developmental Biology and Program in Developmental Biology, Vanderbilt University, Nashville, United States
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6
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Xing J, Duan Z, Zhang L, Zhang X, Lin J. 3D Imaging of Lipid-Guided Vesicle Trafficking Along the Cytoskeleton. TRENDS IN PLANT SCIENCE 2021; 26:421-422. [PMID: 33478815 DOI: 10.1016/j.tplants.2020.12.019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2020] [Accepted: 12/23/2020] [Indexed: 06/12/2023]
Affiliation(s)
- Jingjing Xing
- State Key Laboratory of Crop Stress Adaptation and Improvement, School of Life Sciences, Henan University, Kaifeng 475004, China.
| | - Zhikun Duan
- State Key Laboratory of Crop Stress Adaptation and Improvement, School of Life Sciences, Henan University, Kaifeng 475004, China
| | - Liang Zhang
- College of Life Science, Henan Normal University, Xinxiang 453007, China
| | - Xi Zhang
- Beijing Advanced Innovation Center for Tree Breeding by Molecular Design, Beijing Forestry University, Beijing 100083, China; College of Biological Sciences and Technology, Beijing Forestry University, Beijing 100083, China
| | - Jinxing Lin
- Beijing Advanced Innovation Center for Tree Breeding by Molecular Design, Beijing Forestry University, Beijing 100083, China; College of Biological Sciences and Technology, Beijing Forestry University, Beijing 100083, China.
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7
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Activity and Cytosolic Na + Regulate Synaptic Vesicle Endocytosis. J Neurosci 2020; 40:6112-6120. [PMID: 32605936 DOI: 10.1523/jneurosci.0119-20.2020] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2020] [Revised: 06/18/2020] [Accepted: 06/24/2020] [Indexed: 11/21/2022] Open
Abstract
Retrieval of synaptic vesicles via endocytosis is essential for maintaining sustained synaptic transmission, especially for neurons that fire action potentials at high frequencies. However, how neuronal activity regulates synaptic vesicle recycling is largely unknown. Here we report that Na+ substantially accumulated in the mouse calyx of Held terminals of either sex during repetitive high-frequency spiking. Elevated presynaptic Na+ accelerated both slow and rapid forms of endocytosis and facilitated endocytosis overshoot, but did not affect the readily releasable pool size, Ca2+ influx, or exocytosis. To examine whether this facilitation of endocytosis is related to the Na+-dependent vesicular content change, we dialyzed glutamate into the presynaptic cytosol or blocked the vesicular glutamate uptake with bafilomycin and found that the rate of endocytosis was not affected by regulating the vesicular glutamate content. Endocytosis is critically dependent on intracellular Ca2+, and the activity of Na+/Ca2+ exchanger (NCX) may be altered when the Na+ gradient is changed. However, neither NCX inhibitor nor change of extracellular Na+ concentration affected the endocytosis rate. Moreover, two-photon Ca2+ imaging showed that presynaptic Na+ did not affect the action potential-evoked intracellular Ca2+ transient and decay. Therefore, we revealed a novel mechanism of cytosolic Na+ in accelerating vesicle endocytosis. During high-frequency synaptic transmission, when large numbers of synaptic vesicles were fused, the rapid buildup of presynaptic cytosolic Na+ promoted vesicle recycling and sustained synaptic transmission.SIGNIFICANCE STATEMENT High-frequency firing neurons are widely distributed in the CNS. A large number of synaptic vesicles are released during high-frequency synaptic transmission; accordingly, synaptic vesicles need to be recycled rapidly to replenish the vesicle pool. Synaptic vesicle exocytosis and endocytosis are tightly coupled, and their coupling is essential for synaptic function and structural stability. We showed here that intracellular Na+ concentration at the calyx of Held terminal increased rapidly during spike activity and the increased Na+ accelerated endocytosis. Thus, when large numbers of synaptic vesicles are released during high-frequency synaptic transmission, Na+ accumulated in terminals and facilitated vesicle recycling. These findings represent a novel cellular mechanism that supports reliable synaptic transmission at high frequency in the CNS.
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8
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Abstract
Background Insulin is stored within large dense-core granules in pancreatic beta (β)-cells and is released by Ca2+-triggered exocytosis with increasing blood glucose levels. Polarized and targeted secretion of insulin from β-cells in pancreatic islets into the vasculature has been proposed; however, the mechanisms related to cellular and molecular localization remain largely unknown. Within nerve terminals, the Ca2+-dependent release of a polarized transmitter is limited to the active zone, a highly specialized area of the presynaptic membrane. Several active zone-specific proteins have been characterized; among them, the CAST/ELKS protein family members have the ability to form large protein complexes with other active zone proteins to control the structure and function of the active zone for tight regulation of neurotransmitter release. Notably, ELKS but not CAST is also expressed in β-cells, implying that ELKS may be involved in polarized insulin secretion from β-cells. Scope of review This review provides an overview of the current findings regarding the role(s) of ELKS and other active zone proteins in β-cells and focuses on the molecular mechanism underlying ELKS regulation within polarized insulin secretion from islets. Major conclusions ELKS localizes at the vascular-facing plasma membrane of β-cells in mouse pancreatic islets. ELKS forms a potent insulin secretion complex with L-type voltage-dependent Ca2+ channels on the vascular-facing plasma membrane of β-cells, enabling polarized Ca2+ influx and first-phase insulin secretion from islets. This model provides novel insights into the functional polarity observed during insulin secretion from β-cells within islets at the molecular level. This active zone-like region formed by ELKS at the vascular side of the plasma membrane is essential for coordinating physiological insulin secretion and may be disrupted in diabetes.
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Affiliation(s)
- Mica Ohara-Imaizumi
- Department of Cellular Biochemistry, Kyorin University School of Medicine, Tokyo 181-8611, Japan.
| | - Kyota Aoyagi
- Department of Cellular Biochemistry, Kyorin University School of Medicine, Tokyo 181-8611, Japan
| | - Toshihisa Ohtsuka
- Department of Biochemistry, Graduate School of Medicine, University of Yamanashi, Yamanashi 409-3898, Japan
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9
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Ma W, Chang J, Tong J, Ho U, Yau B, Kebede MA, Thorn P. Arp2/3 nucleates F-actin coating of fusing insulin granules in pancreatic β cells to control insulin secretion. J Cell Sci 2020; 133:jcs236794. [PMID: 32079655 DOI: 10.1242/jcs.236794] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2019] [Accepted: 02/05/2020] [Indexed: 01/11/2023] Open
Abstract
F-actin dynamics are known to control insulin secretion, but the point of intersection with the stimulus-secretion cascade is unknown. Here, using multiphoton imaging of β cells isolated from Lifeact-GFP transgenic mice, we show that glucose stimulation does not cause global changes in subcortical F-actin. Instead, we observe spatially discrete and transient F-actin changes around each fusing granule. This F-actin remodelling is dependent on actin nucleation and is observed for granule fusion induced by either glucose or high potassium stimulation. Using GFP-labelled proteins, we identify local enrichment of Arp3, dynamin 2 and clathrin, all occurring after granule fusion, suggesting early recruitment of an endocytic complex to the fusing granules. Block of Arp2/3 activity with drugs or shRNA inhibits F-actin coating, traps granules at the cell membrane and reduces insulin secretion. Block of formin-mediated actin nucleation also blocks F-actin coating, but has no effect on insulin secretion. We conclude that local Arp2/3-dependent actin nucleation at the sites of granule fusion plays an important role in post-fusion granule dynamics and in the regulation of insulin secretion.
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Affiliation(s)
- Wei Ma
- Discipline of Physiology, School of Medical Sciences, Charles Perkins Centre, University of Sydney, Camperdown 2006, Australia
| | - Jenny Chang
- School of Biomedical Sciences, University of Queensland, St Lucia 4072, Australia
| | - Jason Tong
- Discipline of Physiology, School of Medical Sciences, Charles Perkins Centre, University of Sydney, Camperdown 2006, Australia
| | - Uda Ho
- School of Biomedical Sciences, University of Queensland, St Lucia 4072, Australia
| | - Belinda Yau
- Discipline of Physiology, School of Medical Sciences, Charles Perkins Centre, University of Sydney, Camperdown 2006, Australia
| | - Melkam A Kebede
- Discipline of Physiology, School of Medical Sciences, Charles Perkins Centre, University of Sydney, Camperdown 2006, Australia
| | - Peter Thorn
- Discipline of Physiology, School of Medical Sciences, Charles Perkins Centre, University of Sydney, Camperdown 2006, Australia
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10
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Zhang X, Cui Y, Yu M, Lin J. Single-Molecule Techniques for Imaging Exo-Endocytosis Coupling in Cells. TRENDS IN PLANT SCIENCE 2019; 24:879-880. [PMID: 31279733 DOI: 10.1016/j.tplants.2019.05.013] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/17/2019] [Accepted: 05/27/2019] [Indexed: 06/09/2023]
Affiliation(s)
- Xi Zhang
- Beijing Advanced Innovation Center for Tree Breeding by Molecular Design, Beijing Forestry University, Beijing 100083, China; College of Biological Sciences and Biotechnology, Beijing Forestry University, Beijing 10083, China
| | - Yaning Cui
- Beijing Advanced Innovation Center for Tree Breeding by Molecular Design, Beijing Forestry University, Beijing 100083, China; College of Biological Sciences and Biotechnology, Beijing Forestry University, Beijing 10083, China
| | - Meng Yu
- Beijing Advanced Innovation Center for Tree Breeding by Molecular Design, Beijing Forestry University, Beijing 100083, China; College of Biological Sciences and Biotechnology, Beijing Forestry University, Beijing 10083, China
| | - Jinxing Lin
- Beijing Advanced Innovation Center for Tree Breeding by Molecular Design, Beijing Forestry University, Beijing 100083, China; College of Biological Sciences and Biotechnology, Beijing Forestry University, Beijing 10083, China.
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11
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E-syt1 Re-arranges STIM1 Clusters to Stabilize Ring-shaped ER-PM Contact Sites and Accelerate Ca 2+ Store Replenishment. Sci Rep 2019; 9:3975. [PMID: 30850711 PMCID: PMC6408583 DOI: 10.1038/s41598-019-40331-0] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2018] [Accepted: 01/31/2019] [Indexed: 12/02/2022] Open
Abstract
In many non-excitable cells, the depletion of endoplasmic reticulum (ER) Ca2+ stores leads to the dynamic formation of membrane contact sites (MCSs) between the ER and the plasma membrane (PM), which activates the store-operated Ca2+ entry (SOCE) to refill the ER store. Two different Ca2+-sensitive proteins, STIM1 and extended synaptotagmin-1 (E-syt1), are activated during this process. Due to the lack of live cell super-resolution imaging, how MCSs are dynamically regulated by STIM1 and E-syt1 coordinately during ER Ca2+ store depletion and replenishment remain unknown. With home-built super-resolution microscopes that provide superior axial and lateral resolution in live cells, we revealed that extracellular Ca2+ influx via SOCE activated E-syt1s to move towards the PM by ~12 nm. Unexpectedly, activated E-syt1s did not constitute the MCSs per se, but re-arranged neighboring ER structures into ring-shaped MCSs (230~280 nm in diameter) enclosing E-syt1 puncta, which helped to stabilize MCSs and accelerate local ER Ca2+ replenishment. Overall, we have demonstrated different roles of STIM1 and E-syt1 in MCS formation regulation, SOCE activation and ER Ca2+ store replenishment.
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12
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Fan J, Huang X, Li L, Chen L, Tan S. One-step deconvolution for multi-angle TIRF microscopy with enhanced resolution. BIOMEDICAL OPTICS EXPRESS 2019; 10:1097-1110. [PMID: 30891332 PMCID: PMC6420288 DOI: 10.1364/boe.10.001097] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2018] [Revised: 01/08/2019] [Accepted: 01/11/2019] [Indexed: 06/09/2023]
Abstract
Total internal reflection fluorescence microscopy (TIRF microscopy) uses a rapid decay of evanescent waves to excite fluorophores within several hundred nanometers (nm) beneath the plasma membrane, which can effectively suppress excitation of fluorescence signals in the deep layers. From image stacks obtained with a plurality of different incident angles, a three-dimensional spatial structure of the observed sample can be reconstructed by a Multi-Angle-TIRF (MA-TIRF) algorithm that provides an axial resolution of ~50 nm. Taking into account the point spread function (PSF) of the TIRF microscopes, we further increase its lateral resolution by introducing a fast deconvolution algorithm into the reconstruction of MA-TIRF data (DMA-TIRF), which is approached in just one step of minimizing the reconstruction function. We also introduce a TV regularization term in the deconvolution algorithm to suppress artifacts induced by the excessive noise. Therefore, based on the hardware of existing MA-TIRF microscopes, the proposed DMA-TIRF algorithm has achieved lateral and axial resolutions of ~200 and ~50 nm, respectively.
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Affiliation(s)
- Junchao Fan
- Key Laboratory of Image Processing and Intelligent Control of Ministry of Education of China, School of Automation, Huazhong University of Science and Technology, Wuhan 430074, China
- J.F., X. H. and L.L. contributed equally to this work
| | - Xiaoshuai Huang
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking University, Beijing 100871, China
- J.F., X. H. and L.L. contributed equally to this work
| | - Liuju Li
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking University, Beijing 100871, China
- J.F., X. H. and L.L. contributed equally to this work
| | - Liangyi Chen
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking University, Beijing 100871, China
| | - Shan Tan
- Key Laboratory of Image Processing and Intelligent Control of Ministry of Education of China, School of Automation, Huazhong University of Science and Technology, Wuhan 430074, China
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13
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Xie B, Nguyen PM, Idevall-Hagren O. Feedback regulation of insulin secretion by extended synaptotagmin-1. FASEB J 2018; 33:4716-4728. [PMID: 30589572 DOI: 10.1096/fj.201801878r] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Endoplasmic reticulum (ER)-plasma membrane (PM) contacts are dynamic structures with important roles in the regulation of calcium (Ca2+) and lipid homeostasis. The extended synaptotagmins (E-Syts) are ER-localized lipid transport proteins that interact with PM phosphatidylinositol 4,5-bisphosphate in a Ca2+-dependent manner. E-Syts bidirectionally transfer glycerolipids, including diacylglycerol (DAG), between the 2 juxtaposed membranes, but the biologic significance of this transport is still unclear. Using insulin-secreting cells and live-cell imaging, we now show that Ca2+-triggered exocytosis of insulin granules is followed, in sequence, by PM DAG formation and E-Syt1 recruitment. E-Syt1 counteracted the depolarization-induced DAG formation through a mechanism that required both voltage-dependent Ca2+ influx and Ca2+ release from the ER. E-Syt1 knockdown resulted in prolonged accumulation of DAG in the PM, resulting in increased glucose-stimulated insulin secretion. We conclude that Ca2+-triggered exocytosis is temporally coupled to Ca2+-triggered E-Syt1 PM recruitment and removal of DAG to negatively regulate the same process.-Xie, B., Nguyen, P. M., Idevall-Hagren, O. Feedback regulation of insulin secretion by extended synaptotagmin-1.
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Affiliation(s)
- Beichen Xie
- Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
| | - Phuoc My Nguyen
- Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
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14
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Minimizing ATP depletion by oxygen scavengers for single-molecule fluorescence imaging in live cells. Proc Natl Acad Sci U S A 2018; 115:E5706-E5715. [PMID: 29866842 DOI: 10.1073/pnas.1717724115] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The stability of organic dyes against photobleaching is critical in single-molecule tracking and localization microscopy. Since oxygen accelerates photobleaching of most organic dyes, glucose oxidase is commonly used to slow dye photobleaching by depleting oxygen. As demonstrated here, pyranose-2-oxidase slows bleaching of Alexa647 dye by ∼20-fold. However, oxygen deprivation may pose severe problems for live cells by reducing mitochondrial oxidative phosphorylation and ATP production. We formulate a method to sustain intracellular ATP levels in the presence of oxygen scavengers. Supplementation with metabolic intermediates including glyceraldehyde, glutamine, and α-ketoisocaproate maintained the intracellular ATP level for at least 10 min by balancing between FADH2 and NADH despite reduced oxygen levels. Furthermore, those metabolites supported ATP-dependent synthesis of phosphatidylinositol 4,5-bisphosphate and internalization of PAR2 receptors. Our method is potentially relevant to other circumstances that involve acute drops of oxygen levels, such as ischemic damage in the brain or heart or tissues for transplantation.
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15
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Fast, long-term, super-resolution imaging with Hessian structured illumination microscopy. Nat Biotechnol 2018; 36:451-459. [PMID: 29644998 DOI: 10.1038/nbt.4115] [Citation(s) in RCA: 302] [Impact Index Per Article: 43.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2017] [Accepted: 03/01/2018] [Indexed: 01/13/2023]
Abstract
To increase the temporal resolution and maximal imaging time of super-resolution (SR) microscopy, we have developed a deconvolution algorithm for structured illumination microscopy based on Hessian matrixes (Hessian-SIM). It uses the continuity of biological structures in multiple dimensions as a priori knowledge to guide image reconstruction and attains artifact-minimized SR images with less than 10% of the photon dose used by conventional SIM while substantially outperforming current algorithms at low signal intensities. Hessian-SIM enables rapid imaging of moving vesicles or loops in the endoplasmic reticulum without motion artifacts and with a spatiotemporal resolution of 88 nm and 188 Hz. Its high sensitivity allows the use of sub-millisecond excitation pulses followed by dark recovery times to reduce photobleaching of fluorescent proteins, enabling hour-long time-lapse SR imaging of actin filaments in live cells. Finally, we observed the structural dynamics of mitochondrial cristae and structures that, to our knowledge, have not been observed previously, such as enlarged fusion pores during vesicle exocytosis.
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16
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Liang K, Wei L, Chen L. Exocytosis, Endocytosis, and Their Coupling in Excitable Cells. Front Mol Neurosci 2017; 10:109. [PMID: 28469555 PMCID: PMC5395637 DOI: 10.3389/fnmol.2017.00109] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2017] [Accepted: 03/31/2017] [Indexed: 11/13/2022] Open
Abstract
Evoked exocytosis in excitable cells is fast and spatially confined and must be followed by coupled endocytosis to enable sustained exocytosis while maintaining the balance of the vesicle pool and the plasma membrane. Various types of exocytosis and endocytosis exist in these excitable cells, as those has been found from different types of experiments conducted in different cell types. Correlating these diversified types of exocytosis and endocytosis is problematic. By providing an outline of different exocytosis and endocytosis processes and possible coupling mechanisms here, we emphasize that the endocytic pathway may be pre-determined at the time the vesicle chooses to fuse with the plasma membrane in one specific mode. Therefore, understanding the early intermediate stages of vesicle exocytosis may be instrumental in exploring the mechanism of tailing endocytosis.
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Affiliation(s)
- Kuo Liang
- Department of General Surgery, XuanWu Hospital, Capital Medical UniversityBeijing, China
| | - Lisi Wei
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking UniversityBeijing, China
| | - Liangyi Chen
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking UniversityBeijing, China
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17
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Zyxin regulates endothelial von Willebrand factor secretion by reorganizing actin filaments around exocytic granules. Nat Commun 2017; 8:14639. [PMID: 28256511 PMCID: PMC5338022 DOI: 10.1038/ncomms14639] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2016] [Accepted: 01/17/2017] [Indexed: 12/13/2022] Open
Abstract
Endothelial exocytosis of Weibel-Palade body (WPB) is one of the first lines of defence against vascular injury. However, the mechanisms that control WPB exocytosis in the final stages (including the docking, priming and fusion of granules) are poorly understood. Here we show that the focal adhesion protein zyxin is crucial in this process. Zyxin downregulation inhibits the secretion of von Willebrand factor (VWF), the most abundant cargo in WPBs, from human primary endothelial cells (ECs) induced by cAMP agonists. Zyxin-deficient mice exhibit impaired epinephrine-stimulated VWF release, prolonged bleeding time and thrombosis, largely due to defective endothelial secretion of VWF. Using live-cell super-resolution microscopy, we visualize previously unappreciated reorganization of pre-existing actin filaments around WPBs before fusion, dependent on zyxin and an interaction with the actin crosslinker α-actinin. Our findings identify zyxin as a physiological regulator of endothelial exocytosis through reorganizing local actin network in the final stage of exocytosis.
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18
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Diagonally Scanned Light-Sheet Microscopy for Fast Volumetric Imaging of Adherent Cells. Biophys J 2016; 110:1456-65. [PMID: 27028654 PMCID: PMC4816690 DOI: 10.1016/j.bpj.2016.01.029] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Revised: 12/31/2015] [Accepted: 01/28/2016] [Indexed: 11/23/2022] Open
Abstract
In subcellular light-sheet fluorescence microscopy (LSFM) of adherent cells, glass substrates are advantageously rotated relative to the excitation and emission light paths to avoid glass-induced optical aberrations. Because cells are spread across the sample volume, three-dimensional imaging requires a light-sheet with a long propagation length, or rapid sample scanning. However, the former degrades axial resolution and/or optical sectioning, while the latter mechanically perturbs sensitive biological specimens on pliant biomimetic substrates (e.g., collagen and basement membrane). Here, we use aberration-free remote focusing to diagonally sweep a narrow light-sheet along the sample surface, enabling multicolor imaging with high spatiotemporal resolution. Further, we implement a dithered Gaussian lattice to minimize sample-induced illumination heterogeneities, significantly improving signal uniformity. Compared with mechanical sample scanning, we drastically reduce sample oscillations, allowing us to achieve volumetric imaging at speeds of up to 3.5 Hz for thousands of Z-stacks. We demonstrate the optical performance with live-cell imaging of microtubule and actin cytoskeletal dynamics, phosphoinositide signaling, clathrin-mediated endocytosis, polarized blebbing, and endocytic vesicle sorting. We achieve three-dimensional particle tracking of clathrin-associated structures with velocities up to 4.5 μm/s in a dense intracellular environment, and show that such dynamics cannot be recovered reliably at lower volumetric image acquisition rates using experimental data, numerical simulations, and theoretical modeling.
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19
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Raben DM, Barber CN. Phosphatidic acid and neurotransmission. Adv Biol Regul 2016; 63:15-21. [PMID: 27671966 DOI: 10.1016/j.jbior.2016.09.004] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Revised: 09/15/2016] [Accepted: 09/19/2016] [Indexed: 12/31/2022]
Abstract
Lipids play a vital role in the health and functioning of neurons and interest in the physiological role of neuronal lipids is certainly increasing. One neuronal function in which neuronal lipids appears to play key roles in neurotransmission. Our understanding of the role of lipids in the synaptic vesicle cycle and neurotransmitter release is becoming increasingly more important. Much of the initial research in this area has highlighted the major roles played by the phosphoinositides (PtdIns), diacylglycerol (DAG), and phosphatidic acid (PtdOH). Of these, PtdOH has not received as much attention as the other lipids although its role and metabolism appears to be extremely important. This lipid has been shown to play a role in modulating both exocytosis and endocytosis although its precise role in either process is not well defined. The currently evidence suggest this lipid likely participates in key processes by altering membrane architecture necessary for membrane fusion, mediating the penetration of membrane proteins, serving as a precursor for other important SV cycling lipids, or activating essential enzymes. In this review, we address the sources of PtdOH, the enzymes involved in its production, the regulation of these enzymes, and its potential roles in neurotransmission in the central nervous system.
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Affiliation(s)
- Daniel M Raben
- The Department of Biological Chemistry, The Johns Hopkins University, School of Medicine, Baltimore, MD 21205, USA.
| | - Casey N Barber
- The Department of Biological Chemistry, The Johns Hopkins University, School of Medicine, Baltimore, MD 21205, USA
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20
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Tanguy E, Carmon O, Wang Q, Jeandel L, Chasserot-Golaz S, Montero-Hadjadje M, Vitale N. Lipids implicated in the journey of a secretory granule: from biogenesis to fusion. J Neurochem 2016; 137:904-12. [PMID: 26877188 DOI: 10.1111/jnc.13577] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2015] [Revised: 01/20/2016] [Accepted: 02/03/2016] [Indexed: 01/01/2023]
Abstract
The regulated secretory pathway begins with the formation of secretory granules by budding from the Golgi apparatus and ends by their fusion with the plasma membrane leading to the release of their content into the extracellular space, generally following a rise in cytosolic calcium. Generation of these membrane-bound transport carriers can be classified into three steps: (i) cargo sorting that segregates the cargo from resident proteins of the Golgi apparatus, (ii) membrane budding that encloses the cargo and depends on the creation of appropriate membrane curvature, and (iii) membrane fission events allowing the nascent carrier to separate from the donor membrane. These secretory vesicles then mature as they are actively transported along microtubules toward the cortical actin network at the cell periphery. The final stage known as regulated exocytosis involves the docking and the priming of the mature granules, necessary for merging of vesicular and plasma membranes, and the subsequent partial or total release of the secretory vesicle content. Here, we review the latest evidence detailing the functional roles played by lipids during secretory granule biogenesis, recruitment, and exocytosis steps. In this review, we highlight evidence supporting the notion that lipids play important functions in secretory vesicle biogenesis, maturation, recruitment, and membrane fusion steps. These effects include regulating various protein distribution and activity, but also directly modulating membrane topology. The challenges ahead to understand the pleiotropic functions of lipids in a secretory granule's journey are also discussed. This article is part of a mini review series on Chromaffin cells (ISCCB Meeting, 2015).
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Affiliation(s)
- Emeline Tanguy
- Institut des Neurosciences Cellulaires et Intégratives (INCI), UPR-3212 Centre National de la Recherche Scientifique & Université de Strasbourg, Strasbourg, France
| | - Ophélie Carmon
- INSERM U982, Laboratoire de Différenciation et Communication Neuronale et Neuroendocrine, Institut de Recherche et d'Innovation Biomédicale, Université de Rouen, Mont-Saint-Aignan, France
| | - Qili Wang
- Institut des Neurosciences Cellulaires et Intégratives (INCI), UPR-3212 Centre National de la Recherche Scientifique & Université de Strasbourg, Strasbourg, France
| | - Lydie Jeandel
- INSERM U982, Laboratoire de Différenciation et Communication Neuronale et Neuroendocrine, Institut de Recherche et d'Innovation Biomédicale, Université de Rouen, Mont-Saint-Aignan, France
| | - Sylvette Chasserot-Golaz
- Institut des Neurosciences Cellulaires et Intégratives (INCI), UPR-3212 Centre National de la Recherche Scientifique & Université de Strasbourg, Strasbourg, France
| | - Maité Montero-Hadjadje
- INSERM U982, Laboratoire de Différenciation et Communication Neuronale et Neuroendocrine, Institut de Recherche et d'Innovation Biomédicale, Université de Rouen, Mont-Saint-Aignan, France
| | - Nicolas Vitale
- Institut des Neurosciences Cellulaires et Intégratives (INCI), UPR-3212 Centre National de la Recherche Scientifique & Université de Strasbourg, Strasbourg, France
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ZHANG XIUJUAN, WU CHANGLI, XIONG WEI, CHEN CHUNLING, LI RONG, ZHOU GUANGJI. Knockdown of p54nrb inhibits migration, invasion and TNF-α release of human acute monocytic leukemia THP1 cells. Oncol Rep 2016; 35:3742-8. [DOI: 10.3892/or.2016.4756] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2015] [Accepted: 02/22/2016] [Indexed: 11/06/2022] Open
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22
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Hopping Pits Catch Fusing Granules. Dev Cell 2016; 35:10-1. [PMID: 26460943 DOI: 10.1016/j.devcel.2015.09.026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In excitable cells, regulated exocytosis is coupled to endocytic membrane retrieval. Yuan et al. (2015) in this issue of Developmental Cell report a possible mechanism for such exo-endocytic coupling that is based on stimulation-induced hopping of clathrin-containing endocytic structures to nascent sites of insulin granule fusion.
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