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Paudel S, Yue M, Nalamalapu R, Saha MS. Deciphering the Calcium Code: A Review of Calcium Activity Analysis Methods Employed to Identify Meaningful Activity in Early Neural Development. Biomolecules 2024; 14:138. [PMID: 38275767 PMCID: PMC10813340 DOI: 10.3390/biom14010138] [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: 12/14/2023] [Revised: 01/16/2024] [Accepted: 01/18/2024] [Indexed: 01/27/2024] Open
Abstract
The intracellular and intercellular flux of calcium ions represents an ancient and universal mode of signaling that regulates an extensive array of cellular processes. Evidence for the central role of calcium signaling includes various techniques that allow the visualization of calcium activity in living cells. While extensively investigated in mature cells, calcium activity is equally important in developing cells, particularly the embryonic nervous system where it has been implicated in a wide variety array of determinative events. However, unlike in mature cells, where the calcium dynamics display regular, predictable patterns, calcium activity in developing systems is far more sporadic, irregular, and diverse. This renders the ability to assess calcium activity in a consistent manner extremely challenging, challenges reflected in the diversity of methods employed to analyze calcium activity in neural development. Here we review the wide array of calcium detection and analysis methods used across studies, limiting the extent to which they can be comparatively analyzed. The goal is to provide investigators not only with an overview of calcium activity analysis techniques currently available, but also to offer suggestions for future work and standardization to enable informative comparative evaluations of this fundamental and important process in neural development.
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Affiliation(s)
- Sudip Paudel
- Wyss Institute, Harvard University, Boston, MA 02215, USA; (S.P.); (M.Y.)
| | - Michelle Yue
- Wyss Institute, Harvard University, Boston, MA 02215, USA; (S.P.); (M.Y.)
| | - Rithvik Nalamalapu
- School of Medicine, Virginia Commonwealth University, Richmond, VA 23298, USA;
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2
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Gao DD, Lan CF, Cao XN, Chen L, Lei TL, Peng L, Xu JW, Qiu ZE, Wang LL, Sun Q, Huang ZY, Zhu YX, Zhou WL, Zhang YL. G protein-coupled estrogen receptor promotes acrosome reaction via regulation of Ca2+ signaling in mouse sperm. Biol Reprod 2022; 107:1026-1034. [PMID: 35774023 DOI: 10.1093/biolre/ioac136] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Revised: 05/18/2022] [Accepted: 06/22/2022] [Indexed: 11/13/2022] Open
Abstract
G protein-coupled estrogen receptor (GPER), a seven-transmembrane G protein-coupled receptor, mediates the rapid pre-genomic signaling actions of estrogen and derivatives thereof. The expression of GPER is extensive in mammal male reproductive system. However, the functional role of GPER in mouse sperm has not yet been well recognized. This study revealed that GPER was expressed at the acrosome and the mid-flagellum of the mouse sperm. The endogenous GPER ligand 17β-estradiol and the selective GPER agonist G1 increased intracellular Ca2+ concentration ([Ca2+]i) in mouse sperm, which could be abolished by G15, an antagonist of GPER. In addition, the G1-stimulated Ca2+ response was attenuated by interference with the phospholipase C (PLC) signaling pathways or by blocking the cation sperm channel (CatSper). Chlortetracycline staining assay showed that the activation of GPER increased the incidence of acrosome-reacted sperm. Conclusively, GPER was located at the acrosome and mid-flagellum of the mouse sperm. Activation of GPER triggered the elevation of [Ca2+]i through PLC-dependent Ca2+ mobilization and CatSper-mediated Ca2+ influx, which promoted the acrosome reaction in mouse sperm.
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Affiliation(s)
- Dong-Dong Gao
- School of Life Sciences, Sun Yat-sen University, Guangzhou, P.R. China.,Guangdong Provincial Key Laboratory of Physical Activity and Health Promotion, Scientific Research Center, Guangzhou Sport University, Guangzhou, P.R. China
| | - Chong-Feng Lan
- School of Life Sciences, Sun Yat-sen University, Guangzhou, P.R. China
| | - Xiao-Nian Cao
- School of Life Sciences, Sun Yat-sen University, Guangzhou, P.R. China
| | - Lei Chen
- School of Life Sciences, Sun Yat-sen University, Guangzhou, P.R. China
| | - Tian-Lun Lei
- School of Life Sciences, Sun Yat-sen University, Guangzhou, P.R. China
| | - Lei Peng
- School of Life Sciences, Sun Yat-sen University, Guangzhou, P.R. China
| | - Jia-Wen Xu
- School of Life Sciences, Sun Yat-sen University, Guangzhou, P.R. China
| | - Zhuo-Er Qiu
- School of Life Sciences, Sun Yat-sen University, Guangzhou, P.R. China
| | - Long-Long Wang
- School of Life Sciences, Sun Yat-sen University, Guangzhou, P.R. China
| | - Qing Sun
- School of Life Sciences, Sun Yat-sen University, Guangzhou, P.R. China
| | - Zi-Yang Huang
- School of Life Sciences, Sun Yat-sen University, Guangzhou, P.R. China
| | - Yun-Xin Zhu
- School of Life Sciences, Sun Yat-sen University, Guangzhou, P.R. China
| | - Wen-Liang Zhou
- School of Life Sciences, Sun Yat-sen University, Guangzhou, P.R. China
| | - Yi-Lin Zhang
- School of Life Sciences, Sun Yat-sen University, Guangzhou, P.R. China
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3
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Mostafa S, Nader N, Machaca K. Lipid Signaling During Gamete Maturation. Front Cell Dev Biol 2022; 10:814876. [PMID: 36204680 PMCID: PMC9531329 DOI: 10.3389/fcell.2022.814876] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2021] [Accepted: 05/30/2022] [Indexed: 01/24/2023] Open
Abstract
Cell lipids are differentially distributed in distinct organelles and within the leaflets of the bilayer. They can further form laterally defined sub-domains within membranes with important signaling functions. This molecular and spatial complexity offers optimal platforms for signaling with the associated challenge of dissecting these pathways especially that lipid metabolism tends to be highly interconnected. Lipid signaling has historically been implicated in gamete function, however the detailed signaling pathways involved remain obscure. In this review we focus on oocyte and sperm maturation in an effort to consolidate current knowledge of the role of lipid signaling and set the stage for future directions.
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Affiliation(s)
- Sherif Mostafa
- Medical Program, WCMQ, Education City, Qatar Foundation, Doha, Qatar
| | - Nancy Nader
- Calcium Signaling Group, Research Department, Weill Cornell Medicine Qatar (WCMQ), Education City, Qatar Foundation, Doha, Qatar
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY, United States
| | - Khaled Machaca
- Calcium Signaling Group, Research Department, Weill Cornell Medicine Qatar (WCMQ), Education City, Qatar Foundation, Doha, Qatar
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY, United States
- *Correspondence: Khaled Machaca,
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Abstract
Mammalian oocytes undergo major changes in zinc content and localization to be fertilized, the most striking being the rapid exocytosis of over 10 billion zinc ions in what are known as zinc sparks. Here, we report that fertilization of amphibian Xenopus laevis eggs also initiates a zinc spark that progresses across the cell surface in coordination with dynamic calcium waves. This zinc exocytosis is accompanied by a newly recognized loss of intracellular manganese. Synchrotron-based X-ray fluorescence and analytical electron microscopy reveal that zinc and manganese are sequestered in a system of cortical granules that are abundant at the animal pole. Through electron-nuclear double-resonance studies, we rule out Mn2+ complexation with phosphate or nitrogenous ligands in intact eggs, but the data are consistent with a carboxylate coordination environment. Our observations suggest that zinc and manganese fluxes are a conserved feature of fertilization in vertebrates and that they function as part of a physiological block to polyspermy.
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5
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Szlasa W, Zendran I, Zalesińska A, Tarek M, Kulbacka J. Lipid composition of the cancer cell membrane. J Bioenerg Biomembr 2020; 52:321-342. [PMID: 32715369 PMCID: PMC7520422 DOI: 10.1007/s10863-020-09846-4] [Citation(s) in RCA: 184] [Impact Index Per Article: 46.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2020] [Accepted: 07/10/2020] [Indexed: 12/12/2022]
Abstract
Cancer cell possesses numerous adaptations to resist the immune system response and chemotherapy. One of the most significant properties of the neoplastic cells is the altered lipid metabolism, and consequently, the abnormal cell membrane composition. Like in the case of phosphatidylcholine, these changes result in the modulation of certain enzymes and accumulation of energetic material, which could be used for a higher proliferation rate. The changes are so prominent, that some lipids, such as phosphatidylserines, could even be considered as the cancer biomarkers. Additionally, some changes of biophysical properties of cell membranes lead to the higher resistance to chemotherapy, and finally to the disturbances in signalling pathways. Namely, the increased levels of certain lipids, like for instance phosphatidylserine, lead to the attenuation of the immune system response. Also, changes in lipid saturation prevent the cells from demanding conditions of the microenvironment. Particularly interesting is the significance of cell membrane cholesterol content in the modulation of metastasis. This review paper discusses the roles of each lipid type in cancer physiology. The review combined theoretical data with clinical studies to show novel therapeutic options concerning the modulation of cell membranes in oncology.
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Affiliation(s)
- Wojciech Szlasa
- Faculty of Medicine, Wroclaw Medical University, Wrocław, Poland
| | - Iga Zendran
- Faculty of Medicine, Wroclaw Medical University, Wrocław, Poland
| | | | - Mounir Tarek
- Université de Lorraine, CNRS, LPCT, F-54000, Nancy, France
| | - Julita Kulbacka
- Department of Molecular and Cellular Biology, Faculty of Pharmacy, Wroclaw Medical University, Wrocław, Poland.
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Zhukovsky MA, Filograna A, Luini A, Corda D, Valente C. Phosphatidic acid in membrane rearrangements. FEBS Lett 2019; 593:2428-2451. [PMID: 31365767 DOI: 10.1002/1873-3468.13563] [Citation(s) in RCA: 106] [Impact Index Per Article: 21.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Revised: 07/25/2019] [Accepted: 07/26/2019] [Indexed: 12/16/2022]
Abstract
Phosphatidic acid (PA) is the simplest cellular glycerophospholipid characterized by unique biophysical properties: a small headgroup; negative charge; and a phosphomonoester group. Upon interaction with lysine or arginine, PA charge increases from -1 to -2 and this change stabilizes protein-lipid interactions. The biochemical properties of PA also allow interactions with lipids in several subcellular compartments. Based on this feature, PA is involved in the regulation and amplification of many cellular signalling pathways and functions, as well as in membrane rearrangements. Thereby, PA can influence membrane fusion and fission through four main mechanisms: it is a substrate for enzymes producing lipids (lysophosphatidic acid and diacylglycerol) that are involved in fission or fusion; it contributes to membrane rearrangements by generating negative membrane curvature; it interacts with proteins required for membrane fusion and fission; and it activates enzymes whose products are involved in membrane rearrangements. Here, we discuss the biophysical properties of PA in the context of the above four roles of PA in membrane fusion and fission.
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Affiliation(s)
- Mikhail A Zhukovsky
- Institute of Protein Biochemistry and Institute of Biochemistry and Cell Biology, National Research Council, Naples, Italy
| | - Angela Filograna
- Institute of Protein Biochemistry and Institute of Biochemistry and Cell Biology, National Research Council, Naples, Italy
| | - Alberto Luini
- Institute of Protein Biochemistry and Institute of Biochemistry and Cell Biology, National Research Council, Naples, Italy
| | - Daniela Corda
- Institute of Protein Biochemistry and Institute of Biochemistry and Cell Biology, National Research Council, Naples, Italy
| | - Carmen Valente
- Institute of Protein Biochemistry and Institute of Biochemistry and Cell Biology, National Research Council, Naples, Italy
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7
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Fees CP, Stith BJ. Insemination or phosphatidic acid induces an outwardly spiraling disk of elevated Ca 2+ to produce the Ca 2+ wave during Xenopus laevis fertilization. Dev Biol 2019; 448:59-68. [PMID: 30641042 DOI: 10.1016/j.ydbio.2019.01.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Revised: 01/03/2019] [Accepted: 01/04/2019] [Indexed: 02/06/2023]
Abstract
During Xenopus fertilization, the initial intracellular calcium ((Ca2+)i) release at the sperm-egg binding site (hot spot) has not been described without the use of inhibitors, nor related to underlying ER structure. Without inhibitors, we now report that sperm induce an initial hot spot after sperm addition to Xenopus eggs that was ~25 µm. This area is consistent with the size of ER patches and clusters of IP3 receptors that have enhanced activity. Furthermore, we find a new mechanism for the fertilization (Ca2+)i wave; instead of outward diffusion of inositol 1,4,5-trisphosphate (IP3), we find that the wave was generated by an outward, clockwise rotation of a ~63 µm disk of elevated (Ca2+)i moving very rapidly at ~65 µm/s. We also suggest a new mechanism for the acceleration of the fertilization (Ca2+)i wave as the disk accelerated and was joined by other rotating disks (some rotating counterclockwise) at a time when the speed of the (Ca2+)i wave increases. To examine the role of phosphatidic acid (PA) in the release of (Ca2+)i during Xenopus fertilization, we find that two inhibitors of PA production delayed the appearance of fertilization hot spots by ~9-12 min but did not reduce the size of hot spots and actually accelerated the later (Ca2+)i wave. Surprisingly, global addition of PA to Xenopus eggs induced localized hot spots at a time and size that was similar to those induced after sperm addition. In contrast, sperm induce a rapid (Ca2+)i wave (~4 µm/s) within ~30 s after hot spot appearance, whereas hot spots induced by PA required an ~32 min to induce a very slow (~1 µm/s) (Ca2+)i wave with a lower peak of (Ca2+)i. Thus, PA may not be required for the initial release of (Ca2+)i at the sperm-egg binding site, but mimics sperm by inducing a similarly sized localized (Ca2+)i release. As compared with sperm, PA may induce a weak, slow (Ca2+)i wave by slowly increasing IP3 receptor clustering. Addition of PA to Xenopus oocytes, or Ca2+ ionophore to either Xenopus oocytes or eggs, did not induce hot spots but a global (Ca2+)i wave that rapidly moved at ~12 µm/s.
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Watabe M, Izaki K, Fujino S, Maruyama M, Kojima C, Hiraiwa A, Ueno S, Iwao Y. The electrical block to polyspermy induced by an intracellular Ca
2+
increase at fertilization of the clawed frogs,
Xenopus laevis
and
Xenopus tropicalis. Mol Reprod Dev 2019; 86:387-403. [DOI: 10.1002/mrd.23115] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Revised: 12/26/2018] [Accepted: 01/09/2019] [Indexed: 11/08/2022]
Affiliation(s)
- Mami Watabe
- Laboratory of Reproductive Developmental BiologyGraduate School of Sciences and Technology for Innovation, Yamaguchi University Yamaguchi Japan
| | - Kenta Izaki
- Laboratory of Reproductive Developmental BiologyGraduate School of Sciences and Technology for Innovation, Yamaguchi University Yamaguchi Japan
| | - Shohei Fujino
- Laboratory of Reproductive Developmental BiologyGraduate School of Sciences and Technology for Innovation, Yamaguchi University Yamaguchi Japan
| | - Mei Maruyama
- Laboratory of Reproductive Developmental BiologyGraduate School of Sciences and Technology for Innovation, Yamaguchi University Yamaguchi Japan
| | - Chiho Kojima
- Laboratory of Reproductive Developmental BiologyGraduate School of Sciences and Technology for Innovation, Yamaguchi University Yamaguchi Japan
| | - Azusa Hiraiwa
- Laboratory of Reproductive Developmental BiologyGraduate School of Sciences and Technology for Innovation, Yamaguchi University Yamaguchi Japan
| | - Shuichi Ueno
- Laboratory of Reproductive Developmental BiologyGraduate School of Sciences and Technology for Innovation, Yamaguchi University Yamaguchi Japan
| | - Yasuhiro Iwao
- Laboratory of Reproductive Developmental BiologyGraduate School of Sciences and Technology for Innovation, Yamaguchi University Yamaguchi Japan
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Abstract
Extracellular vesicles (EVs), and exosomes in particular, were initially considered as "garbage bags" for secretion of undesired cellular components. This view has changed considerably over the last two decades, and exosomes have now emerged as important organelles controlling cell-to-cell signaling. They are present in biological fluids and have important roles in the communication between cells in physiological and pathological processes. They are envisioned for clinical use as carriers of biomarkers, therapeutic targets, and vehicles for drug delivery. Important efforts are being made to characterize the contents of these vesicles and to understand the mechanisms that govern their biogenesis and modes of action. This chapter aims to recapitulate the place given to lipids in our understanding of exosome biology. Besides their structural role and their function as carriers, certain lipids and lipid-modifying enzymes seem to exert privileged functions in this mode of cellular communication. By extension, the use of selective "lipid inhibitors" might turn out to be interesting modulators of exosomal-based cell signaling.
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Affiliation(s)
- Antonio Luis Egea-Jimenez
- Centre de Recherche en Cancérologie de Marseille, Equipe labellisée Ligue 2018, Aix-Marseille Université, Inserm, CNRS, Institut Paoli Calmettes, Marseille, France.,Department of Human Genetics, K. U. Leuven, Leuven, Belgium
| | - Pascale Zimmermann
- Centre de Recherche en Cancérologie de Marseille, Equipe labellisée Ligue 2018, Aix-Marseille Université, Inserm, CNRS, Institut Paoli Calmettes, Marseille, France. .,Department of Human Genetics, K. U. Leuven, Leuven, Belgium.
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10
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Anguita E, Villalobo A. Ca 2+ signaling and Src-kinases-controlled cellular functions. Arch Biochem Biophys 2018; 650:59-74. [DOI: 10.1016/j.abb.2018.05.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2018] [Revised: 04/26/2018] [Accepted: 05/07/2018] [Indexed: 12/16/2022]
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Egea-Jimenez AL, Zimmermann P. Phospholipase D and phosphatidic acid in the biogenesis and cargo loading of extracellular vesicles. J Lipid Res 2018; 59:1554-1560. [PMID: 29853529 DOI: 10.1194/jlr.r083964] [Citation(s) in RCA: 53] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2018] [Revised: 05/09/2018] [Indexed: 12/30/2022] Open
Abstract
Extracellular vesicles released by viable cells (exosomes and microvesicles) have emerged as important organelles supporting cell-cell communication. Because of their potential therapeutic significance, important efforts are being made toward characterizing the contents of these vesicles and the mechanisms that govern their biogenesis. It has been recently demonstrated that the lipid modifying enzyme, phospholipase D (PLD)2, is involved in exosome production and acts downstream of the small GTPase, ARF6. This review aims to recapitulate our current knowledge of the role of PLD2 and its product, phosphatidic acid, in the biogenesis of exosomes and to propose hypotheses for further investigation of a possible central role of these molecules in the biology of these organelles.
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Affiliation(s)
- Antonio Luis Egea-Jimenez
- Centre de Recherche en Cancérologie de Marseille (CRCM), Equipe labellisée LIGUE 2018, Aix-Marseille Université, Marseille F-13284, France and Inserm U1068, Institut Paoli-Calmettes, and CNRS UMR7258, Marseille F-13009, France
| | - Pascale Zimmermann
- Centre de Recherche en Cancérologie de Marseille (CRCM), Equipe labellisée LIGUE 2018, Aix-Marseille Université, Marseille F-13284, France and Inserm U1068, Institut Paoli-Calmettes, and CNRS UMR7258, Marseille F-13009, France; Department of Human Genetics, University of Leuven, B-3000 Leuven, Belgium.
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12
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Universality and Diversity of a Fast, Electrical Block to Polyspermy During Fertilization in Animals. DIVERSITY AND COMMONALITY IN ANIMALS 2018. [DOI: 10.1007/978-4-431-56609-0_24] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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13
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Belmonte SA, Mayorga LS, Tomes CN. The Molecules of Sperm Exocytosis. ADVANCES IN ANATOMY EMBRYOLOGY AND CELL BIOLOGY 2016; 220:71-92. [PMID: 27194350 DOI: 10.1007/978-3-319-30567-7_4] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Exocytosis is a fundamental process used by eukaryotic cells to release biological compounds and to insert lipids and proteins in the plasma membrane. Specialized secretory cells undergo regulated exocytosis in response to physiological signals. Sperm exocytosis or acrosome reaction (AR) is essentially a regulated secretion with special characteristics. We will focus here on some of these unique features, covering the topology, kinetics, and molecular mechanisms that prepare, drive, and regulate membrane fusion during the AR. Last, we will compare acrosomal release with exocytosis in other model systems.
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Affiliation(s)
- Silvia A Belmonte
- Laboratorio de Biología Celular y Molecular, Instituto de Histología y Embriología, IHEM-CONICET, Facultad de Ciencias Médicas, Universidad Nacional de Cuyo, 5500, Mendoza, Mendoza, Argentina
| | - Luis S Mayorga
- Laboratorio de Biología Celular y Molecular, Instituto de Histología y Embriología, IHEM-CONICET, Facultad de Ciencias Médicas, Universidad Nacional de Cuyo, 5500, Mendoza, Mendoza, Argentina
| | - Claudia N Tomes
- Laboratorio de Biología Celular y Molecular, Instituto de Histología y Embriología, IHEM-CONICET, Facultad de Ciencias Médicas, Universidad Nacional de Cuyo, 5500, Mendoza, Mendoza, Argentina.
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Phosphoinositide 5- and 3-phosphatase activities of a voltage-sensing phosphatase in living cells show identical voltage dependence. Proc Natl Acad Sci U S A 2016; 113:E3686-95. [PMID: 27222577 DOI: 10.1073/pnas.1606472113] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Voltage-sensing phosphatases (VSPs) are homologs of phosphatase and tensin homolog (PTEN), a phosphatidylinositol 3,4-bisphosphate [PI(3,4)P2] and phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P3] 3-phosphatase. However, VSPs have a wider range of substrates, cleaving 3-phosphate from PI(3,4)P2 and probably PI(3,4,5)P3 as well as 5-phosphate from phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] and PI(3,4,5)P3 in response to membrane depolarization. Recent proposals say these reactions have differing voltage dependence. Using Förster resonance energy transfer probes specific for different PIs in living cells with zebrafish VSP, we quantitate both voltage-dependent 5- and 3-phosphatase subreactions against endogenous substrates. These activities become apparent with different voltage thresholds, voltage sensitivities, and catalytic rates. As an analytical tool, we refine a kinetic model that includes the endogenous pools of phosphoinositides, endogenous phosphatase and kinase reactions connecting them, and four exogenous voltage-dependent 5- and 3-phosphatase subreactions of VSP. We show that apparent voltage threshold differences for seeing effects of the 5- and 3-phosphatase activities in cells are not due to different intrinsic voltage dependence of these reactions. Rather, the reactions have a common voltage dependence, and apparent differences arise only because each VSP subreaction has a different absolute catalytic rate that begins to surpass the respective endogenous enzyme activities at different voltages. For zebrafish VSP, our modeling revealed that 3-phosphatase activity against PI(3,4,5)P3 is 55-fold slower than 5-phosphatase activity against PI(4,5)P2; thus, PI(4,5)P2 generated more slowly from dephosphorylating PI(3,4,5)P3 might never accumulate. When 5-phosphatase activity was counteracted by coexpression of a phosphatidylinositol 4-phosphate 5-kinase, there was accumulation of PI(4,5)P2 in parallel to PI(3,4,5)P3 dephosphorylation, emphasizing that VSPs can cleave the 3-phosphate of PI(3,4,5)P3.
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