1
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Qiao X, Huang N, Meng W, Liu Y, Li J, Li C, Wang W, Lai Y, Zhao Y, Ma Z, Li J, Zhang X, Weng Z, Wu C, Li L, Li B. Beyond mitochondrial transfer, cell fusion rescues metabolic dysfunction and boosts malignancy in adenoid cystic carcinoma. Cell Rep 2024; 43:114652. [PMID: 39217612 DOI: 10.1016/j.celrep.2024.114652] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2023] [Revised: 06/05/2024] [Accepted: 08/01/2024] [Indexed: 09/04/2024] Open
Abstract
Cancer cells with mitochondrial dysfunction can be rescued by cells in the tumor microenvironment. Using human adenoid cystic carcinoma cell lines and fibroblasts, we find that mitochondrial transfer occurs not only between human cells but also between human and mouse cells both in vitro and in vivo. Intriguingly, spontaneous cell fusion between cancer cells and fibroblasts could also emerge; specific chromosome loss might be essential for nucleus reorganization and the post-hybrid selection process. Both mitochondrial transfer through tunneling nanotubes (TNTs) and cell fusion "selectively" revive cancer cells, with mitochondrial dysfunction as a key motivator. Beyond mitochondrial transfer, cell fusion significantly enhances cancer malignancy and promotes epithelial-mesenchymal transition. Mechanistically, mitochondrial dysfunction in cancer cells causes L-lactate secretion to attract fibroblasts to extend TNTs and TMEM16F-mediated phosphatidylserine externalization, facilitating TNT formation and cell-membrane fusion. Our findings offer insights into mitochondrial transfer and cell fusion, highlighting potential cancer therapy targets.
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Affiliation(s)
- Xianghe Qiao
- Department of Head and Neck Oncology, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China; State Key Laboratory of Oral Diseases, National Center for Stomatology, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China; Department of Oral and Maxillofacial Surgery, The First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, China
| | - Nengwen Huang
- Department of Head and Neck Oncology, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China; State Key Laboratory of Oral Diseases, National Center for Stomatology, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China
| | - Wanrong Meng
- Department of Head and Neck Oncology, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China; State Key Laboratory of Oral Diseases, National Center for Stomatology, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China
| | - Yunkun Liu
- Department of Head and Neck Oncology, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China; State Key Laboratory of Oral Diseases, National Center for Stomatology, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China
| | - Jinjin Li
- Department of Head and Neck Oncology, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China; State Key Laboratory of Oral Diseases, National Center for Stomatology, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China; Department of Oral and Maxillofacial Surgery, The First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, China
| | - Chunjie Li
- Department of Head and Neck Oncology, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China; State Key Laboratory of Oral Diseases, National Center for Stomatology, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China
| | - Wenxuan Wang
- Department of Head and Neck Oncology, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China; State Key Laboratory of Oral Diseases, National Center for Stomatology, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China
| | - Yi Lai
- Department of Medical Genetics/Prenatal Diagnostic Center, West China Second Hospital, Sichuan University, Chengdu 610041, China
| | - Yongjiang Zhao
- Genetics and Prenatal Diagnostic Center, The First Affiliated Hospital of Zhengzhou University, Henan Engineering Research Center for Gene Editing of Human Genetic Disease, Zhengzhou 450052, China
| | - Zhongkai Ma
- Department of Head and Neck Oncology, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China; State Key Laboratory of Oral Diseases, National Center for Stomatology, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China
| | - Jingya Li
- Department of Head and Neck Oncology, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China; State Key Laboratory of Oral Diseases, National Center for Stomatology, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China
| | - Xuan Zhang
- Department of Medical Genetics/Prenatal Diagnostic Center, West China Second Hospital, Sichuan University, Chengdu 610041, China
| | - Zhijie Weng
- Department of Head and Neck Oncology, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China; State Key Laboratory of Oral Diseases, National Center for Stomatology, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China
| | - Chenzhou Wu
- Department of Head and Neck Oncology, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China; State Key Laboratory of Oral Diseases, National Center for Stomatology, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China
| | - Longjiang Li
- Department of Head and Neck Oncology, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China; State Key Laboratory of Oral Diseases, National Center for Stomatology, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China.
| | - Bo Li
- State Key Laboratory of Oral Diseases, National Center for Stomatology, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China; Department of Orthodontics, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China.
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2
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Ruan ZR, Yu Z, Xing C, Chen EH. Inter-organ steroid hormone signaling promotes myoblast fusion via direct transcriptional regulation of a single key effector gene. Curr Biol 2024; 34:1438-1452.e6. [PMID: 38513654 PMCID: PMC11003854 DOI: 10.1016/j.cub.2024.02.056] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2023] [Revised: 12/24/2023] [Accepted: 02/23/2024] [Indexed: 03/23/2024]
Abstract
Steroid hormones regulate tissue development and physiology by modulating the transcription of a broad spectrum of genes. In insects, the principal steroid hormones, ecdysteroids, trigger the expression of thousands of genes through a cascade of transcription factors (TFs) to coordinate developmental transitions such as larval molting and metamorphosis. However, whether ecdysteroid signaling can bypass transcriptional hierarchies to exert its function in individual developmental processes is unclear. Here, we report that a single non-TF effector gene mediates the transcriptional output of ecdysteroid signaling in Drosophila myoblast fusion, a critical step in muscle development and differentiation. Specifically, we show that the 20-hydroxyecdysone (commonly referred to as "ecdysone") secreted from an extraembryonic tissue, amnioserosa, acts on embryonic muscle cells to directly activate the expression of antisocial (ants), which encodes an essential scaffold protein enriched at the fusogenic synapse. Not only is ants transcription directly regulated by the heterodimeric ecdysone receptor complex composed of ecdysone receptor (EcR) and ultraspiracle (USP) via ecdysone-response elements but also more strikingly, expression of ants alone is sufficient to rescue the myoblast fusion defect in ecdysone signaling-deficient mutants. We further show that EcR/USP and a muscle-specific TF Twist synergistically activate ants expression in vitro and in vivo. Taken together, our study provides the first example of a steroid hormone directly activating the expression of a single key non-TF effector gene to regulate a developmental process via inter-organ signaling and provides a new paradigm for understanding steroid hormone signaling in other developmental and physiological processes.
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Affiliation(s)
- Zhi-Rong Ruan
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Ze Yu
- McDermott Center for Human Growth and Development, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Chao Xing
- McDermott Center for Human Growth and Development, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Department of Bioinformatics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Elizabeth H Chen
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Hamon Center for Regenerative Science and Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Harold C. Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
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3
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Wherley TJ, Thomas S, Millay DP, Saunders T, Roy S. Molecular regulation of myocyte fusion. Curr Top Dev Biol 2024; 158:53-82. [PMID: 38670716 DOI: 10.1016/bs.ctdb.2024.01.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/28/2024]
Abstract
Myocyte fusion is a pivotal process in the development and regeneration of skeletal muscle. Failure during fusion can lead to a range of developmental as well as pathological consequences. This review aims to comprehensively explore the intricate processes underlying myocyte fusion, from the molecular to tissue scale. We shed light on key players, such as the muscle-specific fusogens - Myomaker and Myomixer, in addition to some lesser studied molecules contributing to myocyte fusion. Conserved across vertebrates, Myomaker and Myomixer play a crucial role in driving the merger of plasma membranes of fusing myocytes, ensuring the formation of functional muscle syncytia. Our multiscale approach also delves into broader cell and tissue dynamics that orchestrate the timing and positioning of fusion events. In addition, we explore the relevance of muscle fusogens to human health and disease. Mutations in fusogen genes have been linked to congenital myopathies, providing unique insights into the molecular basis of muscle diseases. We conclude with a discussion on potential therapeutic avenues that may emerge from manipulating the myocyte fusion process to remediate skeletal muscle disorders.
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Affiliation(s)
- Tanner J Wherley
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, United States
| | - Serena Thomas
- Warwick Medical School, University of Warwick, Coventry, United Kingdom; Institute of Molecular and Cell Biology, Agency for Science, Technology and Research, Proteos, Singapore, Singapore
| | - Douglas P Millay
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, United States; Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, United States.
| | - Timothy Saunders
- Warwick Medical School, University of Warwick, Coventry, United Kingdom; Institute of Molecular and Cell Biology, Agency for Science, Technology and Research, Proteos, Singapore, Singapore.
| | - Sudipto Roy
- Institute of Molecular and Cell Biology, Agency for Science, Technology and Research, Proteos, Singapore, Singapore; Department of Biological Sciences, National University of Singapore, Singapore, Singapore; Department of Pediatrics, National University of Singapore, Singapore, Singapore.
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4
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Kloc M, Tworzydło W, Szklarzewicz T. Germline and Somatic Cell Syncytia in Insects. Results Probl Cell Differ 2024; 71:47-63. [PMID: 37996672 DOI: 10.1007/978-3-031-37936-9_3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2023]
Abstract
Syncytia are common in the animal and plant kingdoms both under normal and pathological conditions. They form through cell fusion or division of a founder cell without cytokinesis. A particular type of syncytia occurs in invertebrate and vertebrate gametogenesis when the founder cell divides several times with partial cytokinesis producing a cyst (nest) of germ line cells connected by cytoplasmic bridges. The ultimate destiny of the cyst's cells differs between animal groups. Either all cells of the cyst become the gametes or some cells endoreplicate or polyploidize to become the nurse cells (trophocytes). Although many types of syncytia are permanent, the germ cell syncytium is temporary, and eventually, it separates into individual gametes. In this chapter, we give an overview of syncytium types and focus on the germline and somatic cell syncytia in various groups of insects. We also describe the multinuclear giant cells, which form through repetitive nuclear divisions and cytoplasm hypertrophy, but without cell fusion, and the accessory nuclei, which bud off the oocyte nucleus, migrate to its cortex and become included in the early embryonic syncytium.
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Affiliation(s)
- Malgorzata Kloc
- The Houston Methodist Research Institute, Houston, TX, USA.
- The Houston Methodist Hospital, Department of Surgery, Houston, TX, USA.
- Department of Genetics, MD Anderson Cancer Center, The University of Texas, Houston, TX, USA.
| | - Wacław Tworzydło
- Department of Developmental Biology and Invertebrate Morphology, Institute of Zoology and Biomedical Research, Faculty of Biology, Jagiellonian University in Krakow, Krakow, Poland
| | - Teresa Szklarzewicz
- Department of Developmental Biology and Invertebrate Morphology, Institute of Zoology and Biomedical Research, Faculty of Biology, Jagiellonian University in Krakow, Krakow, Poland
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5
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Long T, Zhang Y, Donnelly L, Li H, Pien YC, Liu N, Olson EN, Li X. Cryo-EM structures of Myomaker reveal a molecular basis for myoblast fusion. Nat Struct Mol Biol 2023; 30:1746-1754. [PMID: 37770716 DOI: 10.1038/s41594-023-01110-8] [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: 02/09/2023] [Accepted: 08/25/2023] [Indexed: 09/30/2023]
Abstract
The fusion of mononucleated myoblasts produces multinucleated muscle fibers leading to the formation of skeletal muscle. Myomaker, a skeletal muscle-specific membrane protein, is essential for myoblast fusion. Here we report the cryo-EM structures of mouse Myomaker (mMymk) and Ciona robusta Myomaker (cMymk). Myomaker contains seven transmembrane helices (TMs) that adopt a G-protein-coupled receptor-like fold. TMs 2-4 form a dimeric interface, while TMs 3 and 5-7 create a lipid-binding site that holds the polar head of a phospholipid and allows the alkyl tails to insert into Myomaker. The similarity of cMymk and mMymk suggests a conserved Myomaker-mediated cell fusion mechanism across evolutionarily distant species. Functional analyses demonstrate the essentiality of the dimeric interface and the lipid-binding site for fusogenic activity, and heterologous cell-cell fusion assays show the importance of transcellular interactions of Myomaker protomers for myoblast fusion. Together, our findings provide structural and functional insights into the process of myoblast fusion.
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Affiliation(s)
- Tao Long
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Yichi Zhang
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Linda Donnelly
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Hui Li
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Yu-Chung Pien
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Ning Liu
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Eric N Olson
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
| | - Xiaochun Li
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX, USA.
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA.
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6
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Dehn AS, Duhaime L, Gogna N, Nishina PM, Kelley K, Losick VP. Epithelial mechanics are maintained by inhibiting cell fusion with age in Drosophila. J Cell Sci 2023; 136:jcs260974. [PMID: 37732459 PMCID: PMC10651104 DOI: 10.1242/jcs.260974] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2023] [Accepted: 09/12/2023] [Indexed: 09/22/2023] Open
Abstract
A characteristic of normal aging and age-related diseases is the remodeling of the cellular organization of a tissue through polyploid cell growth. Polyploidy arises from an increase in nuclear ploidy or the number of nuclei per cell. However, it is not known whether age-induced polyploidy is an adaption to stressors or a precursor to degeneration. Here, we find that abdominal epithelium of the adult fruit fly becomes polyploid with age through generation of multinucleated cells by cell fusion. Inhibition of fusion does not improve the lifespan of the fly, but does enhance its biomechanical fitness, a measure of the healthspan of the animal. Remarkably, Drosophila can maintain their epithelial tension and abdominal movements with age when cell fusion is inhibited. Epithelial cell fusion also appears to be dependent on a mechanical cue, as knockdown of Rho kinase, E-cadherin or α-catenin is sufficient to induce multinucleation in young animals. Interestingly, mutations in α-catenin in mice result in retina pigment epithelial multinucleation associated with macular disease. Therefore, we have discovered that polyploid cells arise by cell fusion and contribute to the decline in the biomechanical fitness of the animal with age.
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Affiliation(s)
- Ari S. Dehn
- Boston College, 140 Commonwealth Ave, Chestnut Hill, MA 02467, USA
| | - Levi Duhaime
- Boston College, 140 Commonwealth Ave, Chestnut Hill, MA 02467, USA
| | - Navdeep Gogna
- The Jackson Laboratory, 600 Main Street, Bar Harbor, ME 04609, USA
| | - Patsy M. Nishina
- The Jackson Laboratory, 600 Main Street, Bar Harbor, ME 04609, USA
| | - Kristina Kelley
- Boston College, 140 Commonwealth Ave, Chestnut Hill, MA 02467, USA
| | - Vicki P. Losick
- Boston College, 140 Commonwealth Ave, Chestnut Hill, MA 02467, USA
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7
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Hindi SM, Petrany MJ, Greenfeld E, Focke LC, Cramer AAW, Whitt MA, Khairallah RJ, Ward CW, Chamberlain JS, Podbilewicz B, Prasad V, Millay DP. Enveloped viruses pseudotyped with mammalian myogenic cell fusogens target skeletal muscle for gene delivery. Cell 2023; 186:2062-2077.e17. [PMID: 37075755 PMCID: PMC11181154 DOI: 10.1016/j.cell.2023.03.033] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2022] [Revised: 02/08/2023] [Accepted: 03/28/2023] [Indexed: 04/21/2023]
Abstract
Entry of enveloped viruses into cells is mediated by viral fusogenic proteins that drive membrane rearrangements needed for fusion between viral and target membranes. Skeletal muscle development also requires membrane fusion events between progenitor cells to form multinucleated myofibers. Myomaker and Myomerger are muscle-specific cell fusogens but do not structurally or functionally resemble classical viral fusogens. We asked whether the muscle fusogens could functionally substitute for viral fusogens, despite their structural distinctiveness, and fuse viruses to cells. We report that engineering of Myomaker and Myomerger on the membrane of enveloped viruses leads to specific transduction of skeletal muscle. We also demonstrate that locally and systemically injected virions pseudotyped with the muscle fusogens can deliver μDystrophin to skeletal muscle of a mouse model of Duchenne muscular dystrophy and alleviate pathology. Through harnessing the intrinsic properties of myogenic membranes, we establish a platform for delivery of therapeutic material to skeletal muscle.
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Affiliation(s)
- Sajedah M Hindi
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
| | - Michael J Petrany
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
| | - Elena Greenfeld
- Department of Biology, Technion-Israel Institute of Technology, Haifa, Israel
| | - Leah C Focke
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
| | - Alyssa A W Cramer
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
| | - Michael A Whitt
- Department of Microbiology, Immunology, and Biochemistry, University of Tennessee Health Science Center, Memphis, TN, USA
| | | | - Christopher W Ward
- Department of Orthopedics and Center for Biomedical Engineering and Technology (BioMET), University of Maryland School of Medicine, Baltimore, MD, USA
| | - Jeffrey S Chamberlain
- Departments of Neurology, Medicine and Biochemistry, Wellstone Muscular Dystrophy Specialized Research Center, University of Washington School of Medicine, Seattle, WA, USA
| | | | - Vikram Prasad
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
| | - Douglas P Millay
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA; Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, USA.
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8
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Ali Moussa HY, Shin KC, Ponraj J, Kim SJ, Ryu J, Mansour S, Park Y. Requirement of Cholesterol for Calcium-Dependent Vesicle Fusion by Strengthening Synaptotagmin-1-Induced Membrane Bending. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2023; 10:e2206823. [PMID: 37058136 PMCID: PMC10214243 DOI: 10.1002/advs.202206823] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2022] [Revised: 02/09/2023] [Indexed: 05/27/2023]
Abstract
Cholesterol is essential for neuronal activity and function. Cholesterol depletion in the plasma membrane impairs synaptic transmission. However, the molecular mechanisms by which cholesterol deficiency leads to defects in vesicle fusion remain poorly understood. Here, it is shown that cholesterol is required for Ca2+ -dependent native vesicle fusion using the in vitro reconstitution of fusion and amperometry to monitor exocytosis in chromaffin cells. Purified native vesicles are crucial for the reconstitution of physiological Ca2+ -dependent fusion, because vesicle-mimicking liposomes fail to reproduce the cholesterol effect. Intriguingly, cholesterol has no effect on the membrane binding of synaptotagmin-1, a Ca2+ sensor for ultrafast fusion. Cholesterol strengthens local membrane deformation and bending induced by synaptotagmin-1, thereby lowering the energy barrier for Ca2+ -dependent fusion to occur. The data provide evidence that cholesterol depletion abolishes Ca2+ -dependent vesicle fusion by disrupting synaptotagmin-1-induced membrane bending, and suggests that cholesterol is an essential lipid regulator for Ca2+ -dependent fusion.
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Affiliation(s)
- Houda Yasmine Ali Moussa
- Neurological Disorders Research CenterQatar Biomedical Research Institute (QBRI)Hamad Bin Khalifa University (HBKU)Qatar FoundationDohaQatar
| | - Kyung Chul Shin
- Neurological Disorders Research CenterQatar Biomedical Research Institute (QBRI)Hamad Bin Khalifa University (HBKU)Qatar FoundationDohaQatar
| | | | - Soo Jin Kim
- Division of Molecular and Life SciencesPohang University of Science and TechnologyPohang790‐784Republic of Korea
| | - Je‐Kyung Ryu
- Department of Physics & AstronomySeoul National University. 1 Gwanak‐roGwanak‐guSeoul08826South Korea
| | - Said Mansour
- HBKU Core LabsHamad Bin Khalifa University (HBKU)DohaQatar
| | - Yongsoo Park
- Neurological Disorders Research CenterQatar Biomedical Research Institute (QBRI)Hamad Bin Khalifa University (HBKU)Qatar FoundationDohaQatar
- College of Health & Life Sciences (CHLS)Hamad Bin Khalifa University (HBKU)Qatar FoundationDohaQatar
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9
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Hindi SM, Petrany MJ, Greenfeld E, Focke LC, Cramer AA, Whitt MA, Prasad V, Chamberlain JS, Podbilewicz B, Millay DP. Enveloped viruses pseudotyped with mammalian myogenic cell fusogens target skeletal muscle for gene delivery. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.17.533157. [PMID: 36993357 PMCID: PMC10055243 DOI: 10.1101/2023.03.17.533157] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Entry of enveloped viruses into cells is mediated by fusogenic proteins that form a complex between membranes to drive rearrangements needed for fusion. Skeletal muscle development also requires membrane fusion events between progenitor cells to form multinucleated myofibers. Myomaker and Myomerger are muscle-specific cell fusogens, but do not structurally or functionally resemble classical viral fusogens. We asked if the muscle fusogens could functionally substitute for viral fusogens, despite their structural distinctiveness, and fuse viruses to cells. We report that engineering of Myomaker and Myomerger on the membrane of enveloped viruses leads to specific transduction of skeletal muscle. We also demonstrate that locally and systemically injected virions pseudotyped with the muscle fusogens can deliver micro-Dystrophin (μDys) to skeletal muscle of a mouse model of Duchenne muscular dystrophy. Through harnessing the intrinsic properties of myogenic membranes, we establish a platform for delivery of therapeutic material to skeletal muscle.
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Affiliation(s)
- Sajedah M. Hindi
- Division of Molecular Cardiovascular Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA
| | - Michael J. Petrany
- Division of Molecular Cardiovascular Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA
| | - Elena Greenfeld
- Department of Biology, Technion-Israel Institute of Technology, Haifa, Israel
| | - Leah C. Focke
- Division of Molecular Cardiovascular Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA
| | - Alyssa A.W. Cramer
- Division of Molecular Cardiovascular Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA
| | - Michael A. Whitt
- Department of Microbiology, Immunology, and Biochemistry, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Vikram Prasad
- Division of Molecular Cardiovascular Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA
| | - Jeffrey S. Chamberlain
- Departments of Neurology, Medicine and Biochemistry, Wellstone Muscular Dystrophy Specialized Research Center, University of Washington School of Medicine, Seattle, WA, USA
| | | | - Douglas P. Millay
- Division of Molecular Cardiovascular Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA
- Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, USA
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10
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Cell surface-bound La protein regulates the cell fusion stage of osteoclastogenesis. Nat Commun 2023; 14:616. [PMID: 36739273 PMCID: PMC9899215 DOI: 10.1038/s41467-023-36168-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Accepted: 01/16/2023] [Indexed: 02/06/2023] Open
Abstract
Multinucleated osteoclasts, essential for skeletal remodeling in health and disease, are formed by the fusion of osteoclast precursors, where each fusion event raises their bone-resorbing activity. Here we show that the nuclear RNA chaperone, La protein has an additional function as an osteoclast fusion regulator. Monocyte-to-osteoclast differentiation starts with a drastic decrease in La levels. As fusion begins, La reappears as a low molecular weight species at the osteoclast surface, where it promotes fusion. La's role in promoting osteoclast fusion is independent of canonical La-RNA interactions and involves direct interactions between La and Annexin A5, which anchors La to transiently exposed phosphatidylserine at the surface of fusing osteoclasts. Disappearance of cell-surface La, and the return of full length La to the nuclei of mature, multinucleated osteoclasts, acts as an off switch of their fusion activity. Targeting surface La in a novel explant model of fibrous dysplasia inhibits excessive osteoclast formation characteristic of this disease, highlighting La's potential as a therapeutic target.
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11
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Elson A, Anuj A, Barnea-Zohar M, Reuven N. The origins and formation of bone-resorbing osteoclasts. Bone 2022; 164:116538. [PMID: 36028118 DOI: 10.1016/j.bone.2022.116538] [Citation(s) in RCA: 31] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/09/2022] [Revised: 08/17/2022] [Accepted: 08/18/2022] [Indexed: 02/07/2023]
Abstract
Osteoclasts (OCLs) are hematopoietic cells whose physiological function is to degrade bone. OCLs are key players in the processes that determine and maintain the mass, shape, and physical properties of bone. OCLs adhere to bone tightly and degrade its matrix by secreting protons and proteases onto the underlying surface. The combination of low pH and proteases degrades the mineral and protein components of the matrix and forms a resorption pit; the degraded material is internalized by the cell and then secreted into the circulation. Insufficient or excessive activity of OCLs can lead to significant changes in bone and either cause or exacerbate symptoms of diseases, as in osteoporosis, osteopetrosis, and cancer-induced bone lysis. OCLs are derived from monocyte-macrophage precursor cells whose origins are in two distinct embryonic cell lineages - erythromyeloid progenitor cells of the yolk sac, and hematopoietic stem cells. OCLs are formed in a multi-stage process that is induced by the cytokines M-CSF and RANKL, during which the cells differentiate, fuse to form multi-nucleated cells, and then differentiate further to become mature, bone-resorbing OCLs. Recent studies indicate that OCLs can undergo fission in vivo to generate smaller cells, called "osteomorphs", that can be "re-cycled" by fusing with other cells to form new OCLs. In this review we describe OCLs and discuss their cellular origins and the cellular and molecular events that drive osteoclastogenesis.
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Affiliation(s)
- Ari Elson
- Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel.
| | - Anuj Anuj
- Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel
| | - Maayan Barnea-Zohar
- Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel
| | - Nina Reuven
- Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel
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12
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Gamage DG, Melikov K, Munoz-Tello P, Wherley TJ, Focke LC, Leikina E, Huffman E, Diao J, Kojetin DJ, Prasad V, Chernomordik LV, Millay DP. Phosphatidylserine orchestrates Myomerger membrane insertions to drive myoblast fusion. Proc Natl Acad Sci U S A 2022; 119:e2202490119. [PMID: 36095199 PMCID: PMC9499509 DOI: 10.1073/pnas.2202490119] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Accepted: 08/03/2022] [Indexed: 11/18/2022] Open
Abstract
Muscle cell fusion is a multistep process where the final step of the reaction drives progression beyond early hemifusion events to complete fusion. This step requires activity of the muscle-specific fusogen Myomerger, a single-pass transmembrane protein containing 84 amino acids with an ectodomain that includes two α-helices. Previous studies have demonstrated that Myomerger acts by destabilizing membranes through generation of elastic stresses in the outer leaflet of the plasma membrane. An obvious question is how such destabilizing activity might be regulated to avoid membrane and cellular damage, and how the two juxtaposed helices cooperate in fusion. Using cellular fusion assays and in vitro liposome assays, we report that the two helices possess unique characteristics, both of which are needed for full activity of the protein. We demonstrate that externalized phosphatidylserine (PS), a lipid previously implicated in myoblast fusion, has a determinant role in the regulation of Myomerger activity. The membrane-proximal, amphipathic Helix-1 is normally disordered and its α-helical structure is induced by PS, making membrane interactions more efficacious. The distal, more hydrophobic Helix-2 is intrinsically ordered, possesses an ability to insert into membranes, and augments the membrane-stressing effects of Helix-1. These data reveal that Myomerger fusogenic activity is an exquisitely orchestrated event involving its two ectodomain helices, which are controlled by membrane lipid composition, providing an explanation as to how its membrane-stressing activity is spatially and temporally regulated during the final step of myoblast fusion.
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Affiliation(s)
- Dilani G. Gamage
- Division of Molecular Cardiovascular Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229
| | - Kamran Melikov
- Section on Membrane Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892
| | - Paola Munoz-Tello
- Department of Integrative Structural and Computational Biology, University of Florida (UF) Scripps Biomedical Research, Jupiter, FL 33458
| | - Tanner J. Wherley
- Division of Molecular Cardiovascular Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229
| | - Leah C. Focke
- Division of Molecular Cardiovascular Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229
| | - Evgenia Leikina
- Section on Membrane Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892
| | - Elliana Huffman
- Section on Membrane Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892
| | - Jiajie Diao
- Department of Cancer Biology, University of Cincinnati College of Medicine, Cincinnati, OH 45229
| | - Douglas J. Kojetin
- Department of Integrative Structural and Computational Biology, University of Florida (UF) Scripps Biomedical Research, Jupiter, FL 33458
- Department of Molecular Medicine, UF Scripps Biomedical Research, Jupiter, FL 33458
| | - Vikram Prasad
- Division of Molecular Cardiovascular Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229
| | - Leonid V. Chernomordik
- Section on Membrane Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892
| | - Douglas P. Millay
- Division of Molecular Cardiovascular Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229
- Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH 45229
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13
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Rujano MA, Briand D, Ðelić B, Marc J, Spéder P. An interplay between cellular growth and atypical fusion defines morphogenesis of a modular glial niche in Drosophila. Nat Commun 2022; 13:4999. [PMID: 36008397 PMCID: PMC9411534 DOI: 10.1038/s41467-022-32685-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2021] [Accepted: 08/10/2022] [Indexed: 11/16/2022] Open
Abstract
Neural stem cells (NSCs) live in an intricate cellular microenvironment supporting their activity, the niche. Whilst shape and function are inseparable, the morphogenetic aspects of niche development are poorly understood. Here, we use the formation of a glial niche to investigate acquisition of architectural complexity. Cortex glia (CG) in Drosophila regulate neurogenesis and build a reticular structure around NSCs. We first show that individual CG cells grow tremendously to ensheath several NSC lineages, employing elaborate proliferative mechanisms which convert these cells into syncytia rich in cytoplasmic bridges. CG syncytia further undergo homotypic cell-cell fusion, using defined cell surface receptors and actin regulators. Cellular exchange is however dynamic in space and time. This atypical cell fusion remodels cellular borders, restructuring the CG syncytia. Ultimately, combined growth and fusion builds the multi-level architecture of the niche, and creates a modular, spatial partition of the NSC population. Our findings provide insights into how a niche forms and organises while developing intimate contacts with a stem cell population.
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Affiliation(s)
| | | | - Bojana Ðelić
- Institut Pasteur, CNRS UMR3738, Paris, France
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Cell Division and Neurogenesis, Ecole Normale Supérieure, CNRS, Inserm, PSL Université Paris, Paris, France
| | - Julie Marc
- Institut Pasteur, CNRS UMR3738, Paris, France
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14
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Kostow N, Welch MD. Plasma membrane protrusions mediate host cell-cell fusion induced by Burkholderia thailandensis. Mol Biol Cell 2022; 33:ar70. [PMID: 35594178 DOI: 10.1091/mbc.e22-02-0056] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Cell-cell fusion is important for biological processes including fertilization, development, immunity, and microbial pathogenesis. Bacteria in the pseudomallei group of the Burkholderia species, including B. thailandensis, spread between host cells by inducing cell-cell fusion. Previous work showed that B. thailandensis-induced cell-cell fusion requires intracellular bacterial motility and a bacterial protein secretion apparatus called the type VI secretion system-5 (T6SS-5), including the T6SS-5 protein VgrG5. However, the cellular-level mechanism of and T6SS-5 proteins important for bacteria-induced cell-cell fusion remained incompletely described. Using live-cell imaging, we found bacteria used actin-based motility to push on the host cell plasma membrane to form plasma membrane protrusions that extended into neighboring cells. Then, membrane fusion occurred within membrane protrusions either proximal to the bacterium at the tip or elsewhere within protrusions. Expression of VgrG5 by bacteria within membrane protrusions was required to promote cell-cell fusion. Furthermore, a second predicted T6SS-5 protein, TagD5, was also required for cell-cell fusion. In the absence of VgrG5 or TagD5, bacteria in plasma membrane protrusions were engulfed into neighboring cells. Our results suggest that the T6SS-5 effectors VgrG5 and TagD5 are secreted within membrane protrusions and act locally to promote membrane fusion.
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Affiliation(s)
- Nora Kostow
- Department of Molecular & Cell Biology, University of California, Berkeley, Berkeley, CA 94720
| | - Matthew D Welch
- Department of Molecular & Cell Biology, University of California, Berkeley, Berkeley, CA 94720
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15
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Millay DP. Regulation of the myoblast fusion reaction for muscle development, regeneration, and adaptations. Exp Cell Res 2022; 415:113134. [PMID: 35367215 PMCID: PMC9058940 DOI: 10.1016/j.yexcr.2022.113134] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Revised: 02/23/2022] [Accepted: 03/28/2022] [Indexed: 12/27/2022]
Abstract
Fusion of plasma membranes is essential for skeletal muscle development, regeneration, exercise-induced adaptations, and results in a cell that contains hundreds to thousands of nuclei within a shared cytoplasm. The differentiation process in myocytes culminates in their fusion to form a new myofiber or fusion to an existing myofiber thereby contributing more synthetic material to the syncytium. The choice for two cells to fuse and become one could be a dangerous event if the two cells are not committed to an allied function. Thus, fusion events are highly regulated with positive and negative factors to fine-tune the process, and requires muscle-specific fusogens (Myomaker and Myomerger) as well as general cellular machinery to achieve the union of membranes. While a unified vertebrate myoblast fusion pathway is not yet established, recent discoveries should make this pursuit attainable. Not only does myocyte fusion impact the normal biology of skeletal muscle, but new evidence indicates dysregulation of the process impacts pathologies of skeletal muscle. Here, I will highlight the molecular players and biochemical mechanisms that drive fusion events in muscle, and discuss how this key myogenic process impacts skeletal muscle diseases.
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Affiliation(s)
- Douglas P Millay
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, 45229, USA; Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, 45229, USA.
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16
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Brukman NG, Li X, Podbilewicz B. Fusexins, HAP2/GCS1 and Evolution of Gamete Fusion. Front Cell Dev Biol 2022; 9:824024. [PMID: 35083224 PMCID: PMC8784728 DOI: 10.3389/fcell.2021.824024] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2021] [Accepted: 12/21/2021] [Indexed: 12/14/2022] Open
Abstract
Gamete fusion is the climax of fertilization in all sexually reproductive organisms, from unicellular fungi to humans. Similarly to other cell-cell fusion events, gamete fusion is mediated by specialized proteins, named fusogens, that overcome the energetic barriers during this process. In recent years, HAPLESS 2/GENERATIVE CELL-SPECIFIC 1 (HAP2/GCS1) was identified as the fusogen mediating sperm-egg fusion in flowering plants and protists, being both essential and sufficient for the membrane merger in some species. The identification of HAP2/GCS1 in invertebrates, opens the possibility that a similar fusogen may be used in vertebrate fertilization. HAP2/GCS1 proteins share a similar structure with two distinct families of exoplasmic fusogens: the somatic Fusion Family (FF) proteins discovered in nematodes, and class II viral glycoproteins (e.g., rubella and dengue viruses). Altogether, these fusogens form the Fusexin superfamily. While some attributes are shared among fusexins, for example the overall structure and the possibility of assembly into trimers, some other characteristics seem to be specific, such as the presence or not of hydrophobic loops or helices at the distal tip of the protein. Intriguingly, HAP2/GCS1 or other fusexins have neither been identified in vertebrates nor in fungi, raising the question of whether these genes were lost during evolution and were replaced by other fusion machinery or a significant divergence makes their identification difficult. Here, we discuss the biology of HAP2/GCS1, its involvement in gamete fusion and the structural, mechanistic and evolutionary relationships with other fusexins.
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Affiliation(s)
- Nicolas G Brukman
- Department of Biology, Technion- Israel Institute of Technology, Haifa, Israel
| | - Xiaohui Li
- Department of Biology, Technion- Israel Institute of Technology, Haifa, Israel
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17
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Pinello JF, Clark TG. HAP2-Mediated Gamete Fusion: Lessons From the World of Unicellular Eukaryotes. Front Cell Dev Biol 2022; 9:807313. [PMID: 35071241 PMCID: PMC8777248 DOI: 10.3389/fcell.2021.807313] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Accepted: 11/15/2021] [Indexed: 01/29/2023] Open
Abstract
Most, if not all the cellular requirements for fertilization and sexual reproduction arose early in evolution and are retained in extant lineages of single-celled organisms including a number of important model organism species. In recent years, work in two such species, the green alga, Chlamydomonas reinhardtii, and the free-living ciliate, Tetrahymena thermophila, have lent important new insights into the role of HAP2/GCS1 as a catalyst for gamete fusion in organisms ranging from protists to flowering plants and insects. Here we summarize the current state of knowledge around how mating types from these algal and ciliate systems recognize, adhere and fuse to one another, current gaps in our understanding of HAP2-mediated gamete fusion, and opportunities for applying what we know in practical terms, especially for the control of protozoan parasites.
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Affiliation(s)
- Jennifer F. Pinello
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD, United States
| | - Theodore G. Clark
- Department of Microbiology and Immunology, Cornell University, Ithaca, NY, United States
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18
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Hu B, Liu R, Liu Q, Lin Z, Shi Y, Li J, Wang L, Li L, Xiao X, Wu Y. Engineering surface patterns on nanoparticles: New insights on nano-bio interactions. J Mater Chem B 2022; 10:2357-2383. [DOI: 10.1039/d1tb02549j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The surface properties of nanoparticles affect their fates in biological systems. Based on nanotechnology and methodology, pioneering works have explored the effects of chemical surface patterns on the behavior of...
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19
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Junion G, Jagla K. Diversification of muscle types in Drosophila embryos. Exp Cell Res 2022; 410:112950. [PMID: 34838813 DOI: 10.1016/j.yexcr.2021.112950] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Revised: 11/22/2021] [Accepted: 11/24/2021] [Indexed: 12/31/2022]
Abstract
Drosophila embryonic somatic muscles represent a simple and tractable model system to study the gene regulatory networks that control diversification of cell types. Somatic myogenesis in Drosophila is initiated by intrinsic action of the mesodermal master gene twist, which activates a cascade of transcriptional outputs including myogenic differentiation factor Mef2, which triggers all aspects of the myogenic differentiation program. In parallel, the expression of a combinatorial code of identity transcription factors (iTFs) defines discrete particular features of each muscle fiber, such as number of fusion events, and specific attachment to tendon cells or innervation, thus ensuring diversification of muscle types. Here, we take the example of a subset of lateral transverse (LT) muscles and discuss how the iTF code and downstream effector genes progressively define individual LT properties such as fusion program, attachment and innervation. We discuss new challenges in the field including the contribution of posttranscriptional and epitranscriptomic regulation of gene expression in the diversification of cell types.
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Affiliation(s)
- Guillaume Junion
- Genetics Reproduction and Development Institute (iGReD), CNRS UMR6293, INSERM U1103, University of Clermont Auvergne, Clermont-Ferrand, France
| | - Krzysztof Jagla
- Genetics Reproduction and Development Institute (iGReD), CNRS UMR6293, INSERM U1103, University of Clermont Auvergne, Clermont-Ferrand, France.
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20
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Eigler T, Zarfati G, Amzallag E, Sinha S, Segev N, Zabary Y, Zaritsky A, Shakked A, Umansky KB, Schejter ED, Millay DP, Tzahor E, Avinoam O. ERK1/2 inhibition promotes robust myotube growth via CaMKII activation resulting in myoblast-to-myotube fusion. Dev Cell 2021; 56:3349-3363.e6. [PMID: 34932950 PMCID: PMC8693863 DOI: 10.1016/j.devcel.2021.11.022] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2020] [Revised: 07/28/2021] [Accepted: 11/21/2021] [Indexed: 11/19/2022]
Abstract
Myoblast fusion is essential for muscle development and regeneration. Yet, it remains poorly understood how mononucleated myoblasts fuse with preexisting fibers. We demonstrate that ERK1/2 inhibition (ERKi) induces robust differentiation and fusion of primary mouse myoblasts through a linear pathway involving RXR, ryanodine receptors, and calcium-dependent activation of CaMKII in nascent myotubes. CaMKII activation results in myotube growth via fusion with mononucleated myoblasts at a fusogenic synapse. Mechanistically, CaMKII interacts with and regulates MYMK and Rac1, and CaMKIIδ/γ knockout mice exhibit smaller regenerated myofibers following injury. In addition, the expression of a dominant negative CaMKII inhibits the formation of large multinucleated myotubes. Finally, we demonstrate the evolutionary conservation of the pathway in chicken myoblasts. We conclude that ERK1/2 represses a signaling cascade leading to CaMKII-mediated fusion of myoblasts to myotubes, providing an attractive target for the cultivated meat industry and regenerative medicine.
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Affiliation(s)
- Tamar Eigler
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel
| | - Giulia Zarfati
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Emmanuel Amzallag
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel
| | - Sansrity Sinha
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Nadav Segev
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Yishaia Zabary
- Department of Software & Information Systems Engineering, Ben Gurion University, Be'er Sheva, Israel
| | - Assaf Zaritsky
- Department of Software & Information Systems Engineering, Ben Gurion University, Be'er Sheva, Israel
| | - Avraham Shakked
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel
| | - Kfir-Baruch Umansky
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel
| | - Eyal D Schejter
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Douglas P Millay
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA; Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, USA
| | - Eldad Tzahor
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel.
| | - Ori Avinoam
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel.
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21
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Muriel O, Michon L, Kukulski W, Martin SG. Ultrastructural plasma membrane asymmetries in tension and curvature promote yeast cell fusion. J Cell Biol 2021; 220:e202103142. [PMID: 34382996 PMCID: PMC8366684 DOI: 10.1083/jcb.202103142] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Revised: 07/15/2021] [Accepted: 07/26/2021] [Indexed: 12/24/2022] Open
Abstract
Cell-cell fusion is central for sexual reproduction, and generally involves gametes of different shapes and sizes. In walled fission yeast Schizosaccharomyces pombe, the fusion of h+ and h- isogametes requires the fusion focus, an actin structure that concentrates glucanase-containing vesicles for cell wall digestion. Here, we present a quantitative correlative light and electron microscopy (CLEM) tomographic dataset of the fusion site, which reveals the fusion focus ultrastructure. Unexpectedly, gametes show marked asymmetries: a taut, convex plasma membrane of h- cells progressively protrudes into a more slack, wavy plasma membrane of h+ cells. Asymmetries are relaxed upon fusion, with observations of ramified fusion pores. h+ cells have a higher exo-/endocytosis ratio than h- cells, and local reduction in exocytosis strongly diminishes membrane waviness. Reciprocally, turgor pressure reduction specifically in h- cells impedes their protrusions into h+ cells and delays cell fusion. We hypothesize that asymmetric membrane conformations, due to differential turgor pressure and exocytosis/endocytosis ratios between mating types, favor cell-cell fusion.
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Affiliation(s)
- Olivia Muriel
- Department of Fundamental Microbiology, University of Lausanne, Lausanne, Switzerland
| | - Laetitia Michon
- Department of Fundamental Microbiology, University of Lausanne, Lausanne, Switzerland
| | - Wanda Kukulski
- Medical Research Council Laboratory of Molecular Biology, Cambridge, UK
| | - Sophie G. Martin
- Department of Fundamental Microbiology, University of Lausanne, Lausanne, Switzerland
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22
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Dufrançais O, Mascarau R, Poincloux R, Maridonneau-Parini I, Raynaud-Messina B, Vérollet C. Cellular and molecular actors of myeloid cell fusion: podosomes and tunneling nanotubes call the tune. Cell Mol Life Sci 2021; 78:6087-6104. [PMID: 34296319 PMCID: PMC8429379 DOI: 10.1007/s00018-021-03875-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2021] [Revised: 05/25/2021] [Accepted: 06/05/2021] [Indexed: 12/22/2022]
Abstract
Different types of multinucleated giant cells (MGCs) of myeloid origin have been described; osteoclasts are the most extensively studied because of their importance in bone homeostasis. MGCs are formed by cell-to-cell fusion, and most types have been observed in pathological conditions, especially in infectious and non-infectious chronic inflammatory contexts. The precise role of the different MGCs and the mechanisms that govern their formation remain poorly understood, likely due to their heterogeneity. First, we will introduce the main populations of MGCs derived from the monocyte/macrophage lineage. We will then discuss the known molecular actors mediating the early stages of fusion, focusing on cell-surface receptors involved in the cell-to-cell adhesion steps that ultimately lead to multinucleation. Given that cell-to-cell fusion is a complex and well-coordinated process, we will also describe what is currently known about the evolution of F-actin-based structures involved in macrophage fusion, i.e., podosomes, zipper-like structures, and tunneling nanotubes (TNT). Finally, the localization and potential role of the key fusion mediators related to the formation of these F-actin structures will be discussed. This review intends to present the current status of knowledge of the molecular and cellular mechanisms supporting multinucleation of myeloid cells, highlighting the gaps still existing, and contributing to the proposition of potential disease-specific MGC markers and/or therapeutic targets.
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Affiliation(s)
- Ophélie Dufrançais
- Institut de Pharmacologie et Biologie Structurale, IPBS, Université de Toulouse, CNRS, UPS, Toulouse, France
| | - Rémi Mascarau
- Institut de Pharmacologie et Biologie Structurale, IPBS, Université de Toulouse, CNRS, UPS, Toulouse, France
- International Associated Laboratory (LIA) CNRS "IM-TB/HIV" (1167), Toulouse, France
- International Associated Laboratory (LIA) CNRS "IM-TB/HIV" (1167), Buenos Aires, Argentina
| | - Renaud Poincloux
- Institut de Pharmacologie et Biologie Structurale, IPBS, Université de Toulouse, CNRS, UPS, Toulouse, France
| | - Isabelle Maridonneau-Parini
- Institut de Pharmacologie et Biologie Structurale, IPBS, Université de Toulouse, CNRS, UPS, Toulouse, France
- International Associated Laboratory (LIA) CNRS "IM-TB/HIV" (1167), Toulouse, France
| | - Brigitte Raynaud-Messina
- Institut de Pharmacologie et Biologie Structurale, IPBS, Université de Toulouse, CNRS, UPS, Toulouse, France.
- International Associated Laboratory (LIA) CNRS "IM-TB/HIV" (1167), Toulouse, France.
- International Associated Laboratory (LIA) CNRS "IM-TB/HIV" (1167), Buenos Aires, Argentina.
| | - Christel Vérollet
- Institut de Pharmacologie et Biologie Structurale, IPBS, Université de Toulouse, CNRS, UPS, Toulouse, France.
- International Associated Laboratory (LIA) CNRS "IM-TB/HIV" (1167), Toulouse, France.
- International Associated Laboratory (LIA) CNRS "IM-TB/HIV" (1167), Buenos Aires, Argentina.
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23
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Lin SS, Su YA, Chuang MC, Liu YW. Probing invadosomes: technologies for the analysis of invadosomes. FEBS J 2021; 289:5850-5863. [PMID: 34196119 DOI: 10.1111/febs.16098] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2021] [Revised: 06/19/2021] [Accepted: 06/30/2021] [Indexed: 12/22/2022]
Abstract
Invadosomes are protrusive and mechanosensitive actin devices critical for cell migration, invasion, and extracellular matrix remodeling. The dynamic, proteolytic, and protrusive natures of invadosomes have made these structures fascinating and attracted many scientists to develop new technologies for their analysis. With these exciting methodologies, many biochemical and biophysical properties of invadosomes have been well characterized and appreciated, and those discoveries elegantly explained the biological and pathological effects of invadosomes in human health and diseases. In this review, we focus on these commonly used or newly developed methods for invadosome analysis and effort to reason some discrepancies among those assays. Finally, we explore the opposite regulatory mechanisms among invadosomes and focal adhesions, another actin-rich adhesive structures, and speculate a potential rule for their switch.
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Affiliation(s)
- Shan-Shan Lin
- Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - You-An Su
- Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Mei-Chun Chuang
- Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Ya-Wen Liu
- Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan.,Center of Precision Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan
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24
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Sanders DW, Jumper CC, Ackerman PJ, Bracha D, Donlic A, Kim H, Kenney D, Castello-Serrano I, Suzuki S, Tamura T, Tavares AH, Saeed M, Holehouse AS, Ploss A, Levental I, Douam F, Padera RF, Levy BD, Brangwynne CP. SARS-CoV-2 requires cholesterol for viral entry and pathological syncytia formation. eLife 2021; 10:e65962. [PMID: 33890572 PMCID: PMC8104966 DOI: 10.7554/elife.65962] [Citation(s) in RCA: 133] [Impact Index Per Article: 44.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Accepted: 04/01/2021] [Indexed: 12/27/2022] Open
Abstract
Many enveloped viruses induce multinucleated cells (syncytia), reflective of membrane fusion events caused by the same machinery that underlies viral entry. These syncytia are thought to facilitate replication and evasion of the host immune response. Here, we report that co-culture of human cells expressing the receptor ACE2 with cells expressing SARS-CoV-2 spike, results in synapse-like intercellular contacts that initiate cell-cell fusion, producing syncytia resembling those we identify in lungs of COVID-19 patients. To assess the mechanism of spike/ACE2-driven membrane fusion, we developed a microscopy-based, cell-cell fusion assay to screen ~6000 drugs and >30 spike variants. Together with quantitative cell biology approaches, the screen reveals an essential role for biophysical aspects of the membrane, particularly cholesterol-rich regions, in spike-mediated fusion, which extends to replication-competent SARS-CoV-2 isolates. Our findings potentially provide a molecular basis for positive outcomes reported in COVID-19 patients taking statins and suggest new strategies for therapeutics targeting the membrane of SARS-CoV-2 and other fusogenic viruses.
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Affiliation(s)
- David W Sanders
- Department of Chemical and Biological Engineering, Princeton University, Princeton, United States
| | - Chanelle C Jumper
- Department of Chemical and Biological Engineering, Princeton University, Princeton, United States
| | - Paul J Ackerman
- Department of Chemical and Biological Engineering, Princeton University, Princeton, United States
| | - Dan Bracha
- Department of Chemical and Biological Engineering, Princeton University, Princeton, United States
| | - Anita Donlic
- Department of Chemical and Biological Engineering, Princeton University, Princeton, United States
| | - Hahn Kim
- Princeton University Small Molecule Screening Center, Princeton University, Princeton, United States
- Department of Chemistry, Princeton University, Princeton, United States
| | - Devin Kenney
- Department of Microbiology, Boston University School of Medicine, Boston, United States
- National Emerging Infectious Diseases Laboratories, Boston University, Boston, United States
| | - Ivan Castello-Serrano
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, United States
| | - Saori Suzuki
- Department of Molecular Biology, Princeton University, Princeton, United States
| | - Tomokazu Tamura
- Department of Molecular Biology, Princeton University, Princeton, United States
| | - Alexander H Tavares
- National Emerging Infectious Diseases Laboratories, Boston University, Boston, United States
- Department of Biochemistry, Boston University School of Medicine, Boston, United States
| | - Mohsan Saeed
- National Emerging Infectious Diseases Laboratories, Boston University, Boston, United States
- Department of Biochemistry, Boston University School of Medicine, Boston, United States
| | - Alex S Holehouse
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, United States
| | - Alexander Ploss
- Department of Molecular Biology, Princeton University, Princeton, United States
| | - Ilya Levental
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, United States
| | - Florian Douam
- Department of Microbiology, Boston University School of Medicine, Boston, United States
- National Emerging Infectious Diseases Laboratories, Boston University, Boston, United States
| | - Robert F Padera
- Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, Boston, United States
| | - Bruce D Levy
- Pulmonary and Critical Care Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, United States
| | - Clifford P Brangwynne
- Department of Chemical and Biological Engineering, Princeton University, Princeton, United States
- Howard Hughes Medical Institute, Princeton, United States
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25
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Rodríguez-Pérez F, Manford AG, Pogson A, Ingersoll AJ, Martínez-González B, Rape M. Ubiquitin-dependent remodeling of the actin cytoskeleton drives cell fusion. Dev Cell 2021; 56:588-601.e9. [PMID: 33609460 DOI: 10.1016/j.devcel.2021.01.016] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Revised: 11/14/2020] [Accepted: 01/24/2021] [Indexed: 12/11/2022]
Abstract
Cell-cell fusion is a frequent and essential event during development, and its dysregulation causes diseases ranging from infertility to muscle weakness. Fusing cells need to repeatedly remodel their plasma membrane through orchestrated formation and disassembly of actin filaments, but how the dynamic reorganization of the cortical actin cytoskeleton is controlled is still poorly understood. Here, we identified a ubiquitin-dependent toggle switch that establishes reversible actin bundling during mammalian cell fusion. We found that EPS8-IRSp53 complexes stabilize cortical actin bundles at sites of cell contact to promote close membrane alignment. EPS8 monoubiquitylation by CUL3KCTD10 displaces EPS8-IRSp53 from membranes and counteracts actin bundling, a dual activity that restricts actin bundling to allow paired cells to progress with fusion. We conclude that cytoskeletal rearrangements during development are precisely controlled by ubiquitylation, raising the possibility of modulating the efficiency of cell-cell fusion for therapeutic benefit.
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Affiliation(s)
- Fernando Rodríguez-Pérez
- Howard Hughes Medical Institute, University of California at Berkeley, Berkeley, CA 94720, USA; Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA
| | - Andrew G Manford
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA
| | - Angela Pogson
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA
| | - Andrew J Ingersoll
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA
| | - Brenda Martínez-González
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA
| | - Michael Rape
- Howard Hughes Medical Institute, University of California at Berkeley, Berkeley, CA 94720, USA; Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA 94720, USA.
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26
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Flagging fusion: Phosphatidylserine signaling in cell-cell fusion. J Biol Chem 2021; 296:100411. [PMID: 33581114 PMCID: PMC8005811 DOI: 10.1016/j.jbc.2021.100411] [Citation(s) in RCA: 52] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2020] [Revised: 02/08/2021] [Accepted: 02/09/2021] [Indexed: 02/06/2023] Open
Abstract
Formations of myofibers, osteoclasts, syncytiotrophoblasts, and fertilized zygotes share a common step, cell–cell fusion. Recent years have brought about considerable progress in identifying some of the proteins involved in these and other cell-fusion processes. However, even for the best-characterized cell fusions, we still do not know the mechanisms that regulate the timing of cell-fusion events. Are they fully controlled by the expression of fusogenic proteins or do they also depend on some triggering signal that activates these proteins? The latter scenario would be analogous to the mechanisms that control the timing of exocytosis initiated by Ca2+ influx and virus-cell fusion initiated by low pH- or receptor interaction. Diverse cell fusions are accompanied by the nonapoptotic exposure of phosphatidylserine at the surface of fusing cells. Here we review data on the dependence of membrane remodeling in cell fusion on phosphatidylserine and phosphatidylserine-recognizing proteins and discuss the hypothesis that cell surface phosphatidylserine serves as a conserved “fuse me” signal regulating the time and place of cell-fusion processes.
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27
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Belardi B, Son S, Felce JH, Dustin ML, Fletcher DA. Cell-cell interfaces as specialized compartments directing cell function. Nat Rev Mol Cell Biol 2020; 21:750-764. [PMID: 33093672 DOI: 10.1038/s41580-020-00298-7] [Citation(s) in RCA: 42] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/09/2020] [Indexed: 12/14/2022]
Abstract
Cell-cell interfaces are found throughout multicellular organisms, from transient interactions between motile immune cells to long-lived cell-cell contacts in epithelia. Studies of immune cell interactions, epithelial cell barriers, neuronal contacts and sites of cell-cell fusion have identified a core set of features shared by cell-cell interfaces that critically control their function. Data from diverse cell types also show that cells actively and passively regulate the localization, strength, duration and cytoskeletal coupling of receptor interactions governing cell-cell signalling and physical connections between cells, indicating that cell-cell interfaces have a unique membrane organization that emerges from local molecular and cellular mechanics. In this Review, we discuss recent findings that support the emerging view of cell-cell interfaces as specialized compartments that biophysically constrain the arrangement and activity of their protein, lipid and glycan components. We also review how these biophysical features of cell-cell interfaces allow cells to respond with high selectivity and sensitivity to multiple inputs, serving as the basis for wide-ranging cellular functions. Finally, we consider how the unique properties of cell-cell interfaces present opportunities for therapeutic intervention.
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Affiliation(s)
- Brian Belardi
- Department of Bioengineering & Biophysics Program, UC Berkeley, Berkeley, CA, USA
| | - Sungmin Son
- Department of Bioengineering & Biophysics Program, UC Berkeley, Berkeley, CA, USA
| | | | | | - Daniel A Fletcher
- Department of Bioengineering & Biophysics Program, UC Berkeley, Berkeley, CA, USA.
- Division of Biological Systems & Engineering, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
- Chan Zuckerberg Biohub, San Francisco, CA, USA.
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28
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Takito J, Nakamura M. Heterogeneity and Actin Cytoskeleton in Osteoclast and Macrophage Multinucleation. Int J Mol Sci 2020; 21:ijms21186629. [PMID: 32927783 PMCID: PMC7554939 DOI: 10.3390/ijms21186629] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Revised: 09/08/2020] [Accepted: 09/09/2020] [Indexed: 02/07/2023] Open
Abstract
Osteoclast signatures are determined by two transcriptional programs, the lineage-determining transcription pathway and the receptor activator of nuclear factor kappa-B ligand (RANKL)-dependent differentiation pathways. During differentiation, mononuclear precursors become multinucleated by cell fusion. Recently, live-cell imaging has revealed a high level of heterogeneity in osteoclast multinucleation. This heterogeneity includes the difference in the differentiation states and the mobility of the fusion precursors, as well as the mode of fusion among the fusion precursors with different numbers of nuclei. In particular, fusion partners often form morphologically distinct actin-based linkages that allow two cells to exchange lipids and proteins before membrane fusion. However, the origin of this heterogeneity remains elusive. On the other hand, osteoclast multinucleation is sensitive to the environmental cues. Such cues promote the reorganization of the actin cytoskeleton, especially the formation and transformation of the podosome, an actin-rich punctate adhesion. This review covers the heterogeneity of osteoclast multinucleation at the pre-fusion stage with reference to the environment-dependent signaling pathway responsible for reorganizing the actin cytoskeleton. Furthermore, we compare osteoclast multinucleation with macrophage fusion, which results in multinucleated giant macrophages.
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Dynamin regulates the dynamics and mechanical strength of the actin cytoskeleton as a multifilament actin-bundling protein. Nat Cell Biol 2020; 22:674-688. [PMID: 32451441 PMCID: PMC7953826 DOI: 10.1038/s41556-020-0519-7] [Citation(s) in RCA: 48] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2019] [Accepted: 04/07/2020] [Indexed: 01/28/2023]
Abstract
The dynamin GTPase is known to bundle actin filaments, but the underlying molecular mechanism and physiological relevance remain unclear. Our genetic analyses revealed a function of dynamin in propelling invasive membrane protrusions during myoblast fusion in vivo. Using biochemistry, total internal reflection fluorescence microscopy, electron microscopy and cryo-electron tomography, we show that dynamin bundles actin while forming a helical structure. At its full capacity, each dynamin helix captures 12-16 actin filaments on the outer rim of the helix. GTP hydrolysis by dynamin triggers disassembly of fully assembled dynamin helices, releasing free dynamin dimers/tetramers and facilitating Arp2/3-mediated branched actin polymerization. The assembly/disassembly cycles of dynamin promote continuous actin bundling to generate mechanically stiff actin super-bundles. Super-resolution and immunogold platinum replica electron microscopy revealed dynamin along actin bundles at the fusogenic synapse. These findings implicate dynamin as a unique multifilament actin-bundling protein that regulates the dynamics and mechanical strength of the actin cytoskeletal network.
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