how does a cell membrane repair itself


Failure or delay in these processes, as in chronic inflammatory conditions and conditions of regenerative deficit would lead to aberrant tissue remodeling resulting in fibrotic or adipogenic replacement of the lost tissue. This can limit the expansion of the wound area itself. When a crack moves from the scallops stiff material to the less stiff one, the latter reduces the force at the tip of the crack, thereby stopping it from spreadingfarther. Role of calcium-sensor proteins in cell membrane repair. While small injuries to the plasma membrane (on the nanometer scale) can be spontaneously resealed due to the line tension imposed by plasma membrane lipids alone (McNeil & Terasaki, 2001), larger membrane injuries (on the micron scale) require a series of coordinated mechanisms to undergo repair. Bissig C, Lenoir M, Velluz M-C, Kufareva I, Abagyan R, Overduin M, & Gruenberg J (2013). The major differences between normal cells and cancer cells relate to growth, communication, cell repair and death, "stickiness" and spread, appearance, maturation, evasion of the immune system, function and blood supply . Here we will discuss the current knowledge of how lipids facilitate plasma membrane repair by regulating membrane structure and signaling to coordinate the repair response, and will briefly note how lipid involvement extends beyond plasma membrane repair to the tissue repair response. Along with the annexins, which act quickly to physically manipulate the membrane itself, reassembly of the cytoskeleton plays a crucial role in restoring membrane tension in the later stages of repair. We use cookies to give you the best browsing experience. The .gov means its official. The signal to activate recruitment of MG53 to injury sites is not clear, but may relate to its role as a ubiquitin ligase to target substrate(s) damaged as a consequence of the membrane injury. Before Similar to the changes in tension described above, the fluidity of the plasma membrane is also dynamic after injury. Bethesda, MD 20894, Web Policies 2023 Feb 28;24(5):4707. doi: 10.3390/ijms24054707. Not only is the composition and organization of the plasma membrane in constant flux, the membrane itself also must interact with forces being applied to it from all directions. Sreetama SC, Chandra G, Van der Meulen JH, Ahmad MM, Suzuki P, Bhuvanendran S, Jaiswal JK (2018). The lipids in the membrane control the function of the membrane - keeping some products inside and some outside. Additional structural changes the plasma membrane must adopt for repair include molding the shape of the membrane to limit wound expansion as well as pulling in the membrane edges to close the wound. Caveolae internalization repairs wounded cells and muscle fibers, Regulation of endocytosis, exocytosis, and shape by membrane tension, Paper presented at the Cold Spring Harbor symposia on quantitative biology. official website and that any information you provide is encrypted However, these repair activities can also be observed at the single-cell level. This involves a series of distinct, but mutually dependent stages including inflammation, regeneration, and remodeling of the tissue (Gurtner, Werner, Barrandon, & Longaker, 2008). What feature of a cell membrane allows it to repair itself quickly? What's found inside a cell. While the structural importance of plasma membrane cholesterol is well appreciated, it can also play a role in signaling. Epub 2023 Mar 3. Bacterial pore-forming, What might membrane injury to muscle fibers look like? Potez S, Luginbhl M, Monastyrskaya K, Hostettler A, Draeger A, & Babiychuk EB (2011). Self-repairing cells: How single cells heal membrane ruptures and One model explaining membrane injury in dystrophin-deficient muscle fibers proposes that an initial injury causes a local influx of calcium and a local region of hypercontraction. Plasma membrane repair: Current Biology Accumulation of PS at the site of membrane injury allows it to act as a damage sensor, marking a key site for the recruitment of repair proteins such as annexins (Boye et al., 2017). and transmitted securely. This relies upon the coordinated action of the machinery that polarizes the repair response to the site of injury, resulting in resealing of the damaged membrane and subsequent remodeling to return the injured plasma membrane to its pre-injury state. Early observations of cells undergoing plasma membrane repair identified that membrane bound vesicles are involved in the process of membrane resealing (Bi, Alderton, & Steinhardt, 1995). Neurite transection produces cytosolic oxidation, which enhances plasmalemmal repair. Here we will discuss the current knowledge of how lipids facilitate plasma membrane repair by regulating membrane structure and signaling to coordinate the repair response, and will briefly note how lipid involvement extends beyond plasma membrane repair to the tissue repair response. What happens when cell membrane is damaged? - Studybuff This structural arrangement is important for the organization of cholesterol in biological membranes as it results in the hydroxyl group associating with the neighboring lipid head groups and water, while the majority of the cholesterol molecule resides within the hydrophobic core of the membrane. Gushchina LV, Bhattacharya S, McElhanon KE, Choi JH, Manring H, Beck EX, Weisleder N. (2017). One such mechanism is addition of more membrane via vesicle fusion (Fig 1B ). (C) Plasma membrane is dynamic and individual lipids have the capacity to move laterally within a leaflet (shown in pink) and between the leaflets (shown in blue). C-terminal di-arginine motif of Cdc42 protein is essential for binding to phosphatidylinositol 4, 5-bisphosphate-containing membranes and inducing cellular transformation, Plasma membraneCortical cytoskeleton interactions: A cell biology approach with biophysical considerations, Control of diverse subcellular processes by a single multi-functional lipid phosphatidylinositol 4, 5-bisphosphate [PI (4, 5) P2], The structural role of cholesterol in cell membranes: from condensed bilayers to lipid rafts. This is due to its protein-binding ability, resulting in protein translocation to the cholesterol-rich regions of plasma membrane (Sheng et al., 2012; Van Meer et al., 2008). the contents by NLM or the National Institutes of Health. Horn A, Van der Meulen JH, Defour A, Hogarth M, Sreetama SC, Reed A, Jaiswal JK. Van Meer G, Voelker DR, & Feigenson GW (2008). For example, lipid composition, distribution, and inter-lipid interactions actively control the rigidity and tension acting upon the plasma membrane, which in turn regulates cellular functions such as vesicle fusion, cell motility, and membrane resealing (Diz-Muoz, Fletcher, & Weiner, 2013; Gauthier, Fardin, Roca-Cusachs, & Sheetz, 2011; Togo, Krasieva, & Steinhardt, 2000). Yet the membrane is also a formidable barrier, allowing some dissolved substances, or solutes, to pass while blocking others. In some cases, these forces are benign, such as membrane protrusion driven by cortical actin polymerization (Pontes, Monzo, & Gauthier, 2017). Bethesda, MD 20894, Web Policies For example, PIP2 interacts with actin-associated proteins, resulting in a local strengthening of the plasma membrane-cytoskeleton interface. In bacterial and plant cells, a cell wall is attached to the plasma membrane on its outside surface. Phospholipid signalling through phospholipase D and phosphatidic acid. Cazzolli R, Shemon AN, Fang MQ, & Hughes WE (2006). Cell | Definition, Types, Functions, Diagram, Division, Theory, & Facts In addition to regulating the patterning and activity of Rho family GTPases, lipids also have a more direct role in regulating F-actin association with the plasma membrane. Semin Cell Dev Biol. Mitochondrial redox signaling enables repair of injured skeletal muscle cells. The long held dogma in the cardiac biology community was that these cells do not . This homeostatic process of vesicle fusion that maintains the plasma membrane at rest also enables plasma membrane repair through regulated fusion of vesicles triggered by calcium influx following plasma membrane injury (Horn & Jaiswal, 2018; McNeil & Steinhardt, 2003). Exocytosis of acid sphingomyelinase by wounded cells promotes endocytosis and plasma membrane repair. cell, in biology, the basic membrane-bound unit that contains the fundamental molecules of life and of which all living things are composed. What is membrane remodeling? - Studybuff The tension forces acting on the plasma membrane are generally applied by three sources: the difference in hydrostatic pressure between the cell interior and extracellular space, the cortical cytoskeletal network, and the extracellular matrix to which the cell is attached (Gauthier, Masters, & Sheetz, 2012; Kozlov & Chernomordik, 2015) (Figure 2B). Rather than these roles being separated from each other, they overlap significantly such that one can easily be an extension of the other. Plasma membrane damage caused by listeriolysin O is not repaired through endocytosis of the membrane pore. Sinha B, Kster D, Ruez R, Gonnord P, Bastiani M, Abankwa D, Johannes L (2011). Kinetic disruption of lipid rafts is a mechanosensor for phospholipase D, Conversion of phosphatidylcholine to phosphatidylglycerol with phospholipase D and glycerol, Journal of the American Oil Chemists Society. Healing of a punctured Xenopus oocyte, where the dark, The regeneration and reorganization of the oral apparatus (green) of Stentor coeruleus ., Wound healing studies in model cells such as Xenopus oocytes and muscle cells, Evidence that oral regeneration in Stentor can be triggered by the loss of, MeSH The wounded cell can survive if a rapid repair respons Membrane Repair: Mechanisms and Pathophysiology The discussion above illustrates several roles for lipids in changing biophysical properties of the injured plasma membrane during repair. What is cell membrane integrity? - Studybuff The signaling lipid PS is interesting in this regard due to its localization to the wound edge after injury. How does the cell membrane self heal? 2022 May 15;23(10):5525. doi: 10.3390/ijms23105525. When the cell is under stress, and the amount of ROS increases, the number of methionine "errors" is ramped up tenfold, allowing new proteins to be even more resistant to attack. A cartoon depicting the potential role of dysferlin-mediated vesicle fusion in membrane repair. These remodeling events actively promote plasma membrane repair; however, they also act as extensions of the repair response and may continue long after successful resealing in order to restore the plasma membrane to its pre-injury state. Being the most abundant component of the plasma membrane, lipids are also essential player in the process of plasma membrane repair; however, much of the research committed to identifying the mechanisms of plasma membrane repair has focused on the proteins associated with plasma membrane repair (Cooper & McNeil, 2015). This suggests the possibility that caveolae could act as mechanosensors that facilitate adaptation to membrane injury through gene transcription, although this remains to be explored. Self-repairing cells: How single cells heal membrane ruptures and The radiation could damage the DNA so badly that the cell dies. As she describes, a lesion is followed by a Ca2+-dependent movement of vesicles to the plasma membrane. Bookshelf This process is more efficient when GTPases and their regulatory proteins (which are themselves regulated by lipids) are clustered (Ligeti, Dagher, Hernandez, Koleske, & Settleman, 2004). Blood cells called platelets release clotting factors to stop the bleeding; white blood cells rid the area of foreign materials and release molecules to coordinate healing; cells called fibroblasts start rebuilding using proteins called collagen; new blood vessels form; and skin cells called keratinocytes create the newsurface. Treatment with Recombinant Human MG53 Protein Increases Membrane Integrity in a Mouse Model of Limb Girdle Muscular Dystrophy 2B. Thottacherry JJ, Kosmalska AJ, Kumar A, Vishen AS, Elosegui-Artola A, Pradhan S, Chaudhary N (2018). Thus, caveolae may serve a signaling function during membrane repair (see Section 4). Similar to PLC, phospholipase D (PLD) activity is also increased after injury and is required for repair (Arun et al., 2013). Exocytic fusion reduces membrane tension, and vesicle-vesicle fusion events provide a patch as a replacement for the membrane barrier missing at the disruption site. Membrane repair is a conserved physiologic process in multiple tissues Organ Type of mechanical force Principal cells stressed Cell wounding Charged phospholipids such as PIP2, PS, and PE are almost exclusively found on the inner leaflet, while the glycosphingolipids are only found on the outer leaflet. Disclaimer. Architectural and mechanistic insights into an EHD ATPase involved in membrane remodelling. Each of these lipids contributes their own qualities that affect the structural and signaling characteristics of the plasma membrane (Nicolson, 2014). Cells as part of multicellular systems rarely act alone, instead having ways to signal to start and complete simple to quite complex interactions. These roles of lipids in plasma membrane repair include both a structural role and a signaling role. Torrino S, Shen W-W, Blouin CM, Mani SK, de Lesegno CV, Bost P, Chambon V (2018). The lipids in the membrane are fluid, and therefore in motion, and are constantly adapting to the changing environment. The fatty membranes of cells are capable of self-repair using a mechanism that involves calcium-dependent exocytosis. Sealing holes in cellular membranes | The EMBO Journal Thus, local lipid peroxidation may provide transient membrane stabilization, while mechanisms such as redox-dependent MG53 binding may limit the spread of lipid peroxides. Bouter A, Gounou C, Brat R, Tan S, Gallois B, Granier T, Brisson AR. Cell damage. Structurally, the conical ceramide molecule results in negative membrane curvature associated with rapid nucleation of ESCRT complex proteins (Lee, Kai, Carlson, Groves, & Hurley, 2015). SM utilizes the ceramide (Cer) backbone and can be used to generate the signaling lipid sphingosine-1-phosphate (S1P). In the case of lipid mobility, this principle is exemplified by the observation that decreasing the excessive lipid mobility in LGMD2B patient cells using a membrane permeant modified glucocorticoid improves repair (Sreetama et al., 2018). There are mechanisms that allow some products to enter or leave the cell either actively or passively. This is in part achieved through the activity of lipid modifying enzymes, such as kinases, phosphatases, and phospholipases. Rapid actin-cytoskeletondependent recruitment of plasma membranederived dysferlin at wounds is critical for muscle membrane repair. Houang EM, Haman KJ, Filareto A, Perlingeiro RC, Bates FS, Lowe DA, & Metzger JM (2015). In addition to PA, PG is another lipid product of PLD activity relevant to membrane repair, and its synthesis has been implicated in the process of membrane repair and repair of epithelial wounds (Arun et al., 2013; Piazza & Marmer, 2007). McDade JR, Archambeau A, & Michele DE (2014). "Think of a . It also works extracellularly to improve repair of injured muscle and other cells (Gushchina et al., 2017; Weisleder et al., 2012). (2011). The plasma membrane, also called the cell membrane, is the membrane found in all cells that separates the interior of the cell from the outside environment. The basement membrane plays an important role in cellular functions, including those involved in healing, by controlling the binding of growth factors and their local concentrations between cell layers. There are many differences between cancer cells and normal cells in noncancerous (benign) or cancerous (malignant) tumors. A lysosome is a membrane-bound cell organelle that contains digestive enzymes. Plasma membrane lipids and proteins interact with the extracellular matrix (ECM) and the cortical actin network, both of which provide sources of tension that support the structure of the membrane. Interphase has three stages: G1, S and G2. Changing the head group attached to the DAG backbone creates different phospholipid species, which include phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), phosphatidylglycerol (PG), and PA (Oropeza, 2017) (Figure 1B). Careers. This dissociation has the effect of allowing Rho GTPase translocation to the membrane where it can interact with signaling lipids. Calcium can activate proteins directly, and ultimately is the initiator of many downstream repair pathways. Shear stress on the plasma membrane also results in the dissociation of the negative regulator RhoGDI and its binding partner Rho (Shao et al., 2018). Ligeti E, Dagher M-C, Hernandez SE, Koleske AJ, & Settleman J (2004). How quickly do different cells in the body replace themselves? Honeybee immune systems depend more on protein diversity thanquantity. Leikina E, Defour A, Melikov K, Van der Meulen JH, Nagaraju K, Bhuvanendran S, Jaiswal JK (2015). The observation, that endocytosis may not be required for resealing through the removal of pore-forming toxins but instead acts as a mechanosensor to buffer membrane tension, may also explain how endocytosis participates in the repair of mechanical damage, where no membrane-spanning pores need to be removed. During the S stage, the cell Given their integral role in forming the structural backbone of the membrane, lipids are ideally placed to act as damage sensors, initiating early signaling that sets the stage for subsequent repair machinery. At the population level, the composition of lipids in a membrane can result in formation of signaling platforms that can change the properties of an entire membrane, enabling the cell to finely tune tension, shape, and rigidity. Dysferlin is not detected at injury sites until 10 s postinjury, a delay we attribute to an intermediary step involving calpain cleavage. These functions also require modulating the membrane area, such as through the processes of exocytosis and endocytosis or by changing the existing membrane architecture (Kozlov & Chernomordik, 2015; Nassoy & Lamaze, 2012). J Cell Biol. Federal government websites often end in .gov or .mil. Similar to PS, DAG directly binds proteins to provide its signaling function; however, because it is generated de novo after injury, an additional temporal component to signaling is achieved. Plasma Membrane Repair: Norma Andrews - iBiology doi: 10.3791/50848. It can also be produced by methylation of existing PE, while PE can be produced by the decarboxylation of PS. When . Further, PE and PC head groups can be cleaved and replaced with serine to produce PS (Oropeza, 2017). This is especially important for membrane signaling functions as the liquid-ordered domains often serve to aggregate membrane-associated proteins (Cebecauer et al., 2018). Cell Calcium. Spontaneous resealing of plasma membrane, Spontaneous resealing of plasma membrane injuries in the nanometer range is opposed by, Calcium-activated exocytosis reduces membrane tension, Calcium-activated exocytosis reduces membrane tension and promotes spontaneous repair driven by lipid disorder, Very large plasma membrane disruptions (micron diameter) require membrane patching. Thus, each of these lipids contributes significantly to the organization, structure, and function of the plasma membrane as a whole. The goal of signaling during plasma membrane repair is to generate a polarized response such that the repair machinery can be spatially and temporally localized and activated at the repair site. If the cell is damaged beyond repair, lysosomes can help it to self-destruct in a process called programmed . Among these lipids, PC is the most abundant in the plasma membrane and is formed by adding choline to the DAG backbone. FOIA However, ceramide formation also changes membrane dynamics by forming rigid microdomains and potentially by displacing cholesterol from lipid rafts (London, 2004). Transient and local lipid peroxidation may affect membrane stabilization as peroxidation of polyunsaturated fatty acids changes head group separation and acyl chain interdigitation, increasing their molecular volume and causing formation of distinct cholesterol domains in the membrane, which increases the membrane rigidity (Jacob & Mason, 2005; Mason, Walter, & Mason, 1997). A different model for plasma membrane repair began to emerge when mammalian cells injured mechanically or by SLO pores were found to undergo massive endocytosis, after Ca 2+ -triggered exocytosis of lysosomes ( Figure 1 C). What might membrane injury to muscle fibers look like? . Would you like email updates of new search results? Modeling membrane shaping by proteins: Focus on EHD2 and NBAR domains. Saarikangas J, Zhao H, & Lappalainen P (2010). Similar inter-leaflet heterogeneity exists among sphingolipids, with the glycosphingolipids maintained exclusively in the outer leaflet. Caveolae protect endothelial cells from membrane rupture during increased cardiac output. Federal government websites often end in .gov or .mil. Membrane tension: A challenging but universal physical parameter in cell biology, Paper presented at the Seminars in cell & developmental biology. Gazzerro E, Sotgia F, Bruno C, Lisanti MP, & Minetti C (2010). 14.2: Cell Damage and Tissue Repair - Chemistry LibreTexts sharing sensitive information, make sure youre on a federal Self-repairing cells: How single cells heal membrane ruptures and restore lost structures Many organisms and tissues display the ability to heal and regenerate as needed for normal physiology and as a result of pathogenesis. S100A11 is required for efficient plasma membrane repair and survival of invasive cancer cells, S100 and annexin proteins identify cell membrane damage as the Achilles heel of metastatic cancer cells. Please enable it to take advantage of the complete set of features! Instead, there exists distinct inter- and intra-leaflet heterogeneity of lipids. Every cell has a fatty membrane that self-assembles when placed in water, then reassembles when a breach occurs. 2022 Dec 14;10(12):3256. doi: 10.3390/biomedicines10123256. How Phospholipids Help Hold a Cell Together - ThoughtCo This form of membrane remodeling maintains lipid homeostasis and plasma membrane functionality. Lipids also interact with plasma membrane localized proteins to regulate membrane tension and fluidity. Sci Rep. 2023 Mar 23;13(1):4763. doi: 10.1038/s41598-023-31973-2. Use of lipidomics during epidermal wound repair identified that several of the plasma membrane lipids discussed above are enriched during wound repair. Eukaryotic cells have been confronted throughout their evolution with potentially lethal plasma membrane injuries, including those caused by osmotic stress, by infection from bacterial toxins and parasites, and by mechanical and ischemic stress. The wounded cell can survive if a rapid repair response is mounted that restores boundary integrity. Below we describe the biochemical signaling role of lipids in facilitating plasma membrane repair. 2022 Aug 23;13(1):4950. doi: 10.1038/s41467-022-31277-5. How does the cell membrane self heal? In contrast, Annexin 1, one of the earliest responders to plasma membrane injury (Leikina et al., 2015; McNeil, Rescher, Gerke, & McNeil, 2006), does not appear to be essential for plasma membrane repair (Leikina et al., 2015; McNeil et al., 2006). Radiation Effects on Cells & DNA | Let's Talk Science In: StemBook [Internet]. Lipids act as signaling molecules through their ability to directly bind or otherwise alter the activity or localization of target proteins (Figure 2B, ,C).C). Nam D. Jan 28, 2018 Because it has the Golgi apparatus Explanation: Actually it doesn't heal by itself it is helped by a cell organelle named Golgi apparatus. Cheng JP, Mendoza-Topaz C, Howard G, Chadwick J, Shvets E, Cowburn AS, Nichols BJ (2015). Living systems must maintain a proper liquid balance, which is especially difficult in dry conditions. They include glycerophosphocholines, glycerophosphoglycerols, glycerophosphoinositols, as well as triacylglycerols (Taverna, Nanney, Pollins, Sindona, & Caprioli, 2011). What is Mitosis? | Let's Talk Science Shed microvesicles containing streptolysin-O have been shown to also contain annexins A1 and A6 (219). Membrane injury causes a local influx of calcium and activation of calpains. In mammalian cells, lipids formed upon the phosphate and glycerol (e.g. Very large plasma membrane disruptions (micron diameter) require membrane patching. The Biomimicry Institute empowers people to create nature-inspired solutions for a healthy planet. 2021 The Biomimicry Institute. Yet to be fully understood is whether core membrane repair machinery exists in all cells, or whether evolutionary adaptation has resulted in multiple compensatory repair pathways that specialize in different tissues and cells within our body. Their localization and function in response to injury is controlled by the patterning of anionic lipids such as PS, which is present at the wound edge and is a known binding partner of annexins (Gerke, Creutz, & Moss, 2005). The cell membrane is an extremely pliable structure composed primarily of two layers of phospholipids (a "bilayer"). Plasma membrane repair relies on the coordinated activity of repair machinery, which carries out vesicle fusion to the membrane, membrane shedding, and polymerization of F-actin at the site of repair (Horn & Jaiswal, 2018). Cancer Cells vs. Normal Cells: How Are They Different? - Verywell Health Two-way traffic on the road to plasma membrane repair. National Library of Medicine Furthermore, ASM activity at the injury site would locally produce ceramide from sphingomyelin. The role of lipids during plasma membrane repair goes far beyond a passive role in vesicle-mediated delivery of membrane lipids. Inclusion in an NLM database does not imply endorsement of, or agreement with, Physico-chemical and biological considerations for membrane wound evolution and repair in animal cells. Spontaneous formation of a self-healing carbon nanoskin at the liquid-liquid interface. Promotion of plasma membrane repair by vitamin E. Idone V, Tam C, Goss JW, Toomre D, Pypaert M, & Andrews NW (2008). Petersen EN, Chung H-W, Nayebosadri A, & Hansen SB (2016). 1Childrens National Health System, Center for Genetic Medicine Research, 111 Michigan Avenue NW, Washington, DC 20010-2970 USA, 2Department of Genomics and Precision Medicine, George Washington University School of Medicine and Health Sciences, Washington, DC USA. The PubMed wordmark and PubMed logo are registered trademarks of the U.S. Department of Health and Human Services (HHS). Tam C, Idone V, Devlin C, Fernandes MC, Flannery A, He X, Andrews NW (2010). In this case, cholesterol actually increases the fluidity among these lipids, which prevents them from forming a gel-like phase that is incompatible with the overall fluid nature of the plasma membrane (Krause & Regen, 2014). Alkaloid molecules protect plants from bacterial infections. Calcium-regulated exocytosis is required for cell membrane resealing. Plasma membrane wounding and repair in pulmonary diseases, American Journal of Physiology-Lung Cellular and Molecular Physiology, Membrane repair: mechanisms and pathophysiology. Live tracking of inter-organ communication by endogenous exosomes in vivo. A single cell is often a complete organism in itself, such as a bacterium or yeast. These same processes also work to dynamically control membrane fluidity by regulating the distribution of phospholipids, sphingolipids, and cholesterol in the membrane. Dysferlin regulates cell membrane repair by facilitating injury-triggered acid sphingomyelinase secretion, Demonbreun AR, & McNally EM (2016). The .gov means its official. During the G1 stage, the cell prepares for division by increasing its mass. FOIA Phospholipids in particular show inter-leaflet heterogeneity. Each of these pathways that facilitate repair through membrane remodeling also alter the local composition and distribution of plasma membrane lipids in healthy cells (van Meer, 1989) (Figure 2D).

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