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York-Andersen AH, Hu Q, Wood BW, Wolfner MF, Weil TT. A calcium-mediated actin redistribution at egg activation in Drosophila. Mol Reprod Dev 2019; 87:293-304. [PMID: 31880382 PMCID: PMC7044060 DOI: 10.1002/mrd.23311] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Accepted: 12/12/2019] [Indexed: 12/24/2022]
Abstract
Egg activation is the essential process in which mature oocytes gain the competency to proceed into embryonic development. Many events of egg activation are conserved, including an initial rise of intracellular calcium. In some species, such as echinoderms and mammals, changes in the actin cytoskeleton occur around the time of fertilization and egg activation. However, the interplay between calcium and actin during egg activation remains unclear. Here, we use imaging, genetics, pharmacological treatment, and physical manipulation to elucidate the relationship between calcium and actin in living Drosophila eggs. We show that, before egg activation, actin is smoothly distributed between ridges in the cortex of the dehydrated mature oocytes. At the onset of egg activation, we observe actin spreading out as the egg swells though the intake of fluid. We show that a relaxed actin cytoskeleton is required for the intracellular rise of calcium to initiate and propagate. Once the swelling is complete and the calcium wave is traversing the egg, it leads to a reorganization of actin in a wavelike manner. After the calcium wave, the actin cytoskeleton has an even distribution of foci at the cortex. Together, our data show that calcium resets the actin cytoskeleton at egg activation, a model that we propose to be likely conserved in other species.
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Affiliation(s)
| | - Qinan Hu
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York
| | - Benjamin W Wood
- Department of Zoology, University of Cambridge, Cambridge, UK
| | - Mariana F Wolfner
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York
| | - Timothy T Weil
- Department of Zoology, University of Cambridge, Cambridge, UK
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Brannen KC, Chapin RE, Jacobs AC, Green ML. Alternative Models of Developmental and Reproductive Toxicity in Pharmaceutical Risk Assessment and the 3Rs. ILAR J 2017; 57:144-156. [DOI: 10.1093/ilar/ilw026] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2016] [Revised: 01/01/2016] [Accepted: 01/01/2016] [Indexed: 01/21/2023] Open
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3
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Eno C, Solanki B, Pelegri F. aura (mid1ip1l) regulates the cytoskeleton at the zebrafish egg-to-embryo transition. Development 2016; 143:1585-99. [PMID: 26965374 PMCID: PMC4986165 DOI: 10.1242/dev.130591] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2015] [Accepted: 03/01/2016] [Indexed: 12/11/2022]
Abstract
Embryos from females homozygous for a recessive maternal-effect mutation in the gene aura exhibit defects including reduced cortical integrity, defective cortical granule (CG) release upon egg activation, failure to complete cytokinesis, and abnormal cell wound healing. We show that the cytokinesis defects are associated with aberrant cytoskeletal reorganization during furrow maturation, including abnormal F-actin enrichment and microtubule reorganization. Cortical F-actin prior to furrow formation fails to exhibit a normal transition into F-actin-rich arcs, and drug inhibition is consistent with aura function promoting F-actin polymerization and/or stabilization. In mutants, components of exocytic and endocytic vesicles, such as Vamp2, Clathrin and Dynamin, are sequestered in unreleased CGs, indicating a need for CG recycling in the normal redistribution of these factors. However, the exocytic targeting factor Rab11 is recruited to the furrow plane normally at the tip of bundling microtubules, suggesting an alternative anchoring mechanism independent of membrane recycling. A positional cloning approach indicates that the mutation in aura is associated with a truncation of Mid1 interacting protein 1 like (Mid1ip1l), previously identified as an interactor of the X-linked Opitz G/BBB syndrome gene product Mid1. A Cas9/CRISPR-induced mutant allele in mid1ip1l fails to complement the originally isolated aura maternal-effect mutation, confirming gene assignment. Mid1ip1l protein localizes to cortical F-actin aggregates, consistent with a direct role in cytoskeletal regulation. Our studies indicate that maternally provided aura (mid1ip1l) acts during the reorganization of the cytoskeleton at the egg-to-embryo transition and highlight the importance of cytoskeletal dynamics and membrane recycling during this developmental period.
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Affiliation(s)
- Celeste Eno
- Laboratory of Genetics, University of Wisconsin - Madison, 425-G Henry Mall, Room 2455 Genetics, Madison, WI 53706, USA
| | - Bharti Solanki
- Laboratory of Genetics, University of Wisconsin - Madison, 425-G Henry Mall, Room 2455 Genetics, Madison, WI 53706, USA
| | - Francisco Pelegri
- Laboratory of Genetics, University of Wisconsin - Madison, 425-G Henry Mall, Room 2455 Genetics, Madison, WI 53706, USA
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Distinct and separable activities of the endocytic clathrin-coat components Fcho1/2 and AP-2 in developmental patterning. Nat Cell Biol 2012; 14:488-501. [PMID: 22484487 PMCID: PMC3354769 DOI: 10.1038/ncb2473] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2011] [Accepted: 02/29/2012] [Indexed: 12/13/2022]
Abstract
Clathrin-mediated endocytosis occurs at multiple independent import sites on the plasma membrane, but how these positions are selected and how different cargo is simultaneously recognized is obscure. FCHO1 and FCHO2 are early-arriving proteins at surface clathrin assemblies and are speculated to act as compulsory coat nucleators, preceding the core clathrin adaptor AP-2. Here, we show the μ-homology domain (μHD) of FCHO1/2 represents a novel endocytic interaction hub. Translational silencing of fcho1 in zebrafish embryos causes strong dorsoventral patterning defects analogous to Bmp signal failure. The Fcho1 μHD interacts with the Bmp receptor Alk8, uncovering a new endocytic component that positively modulates Bmp signal transmission. Still, the fcho1 morphant phenotype is distinct from severe embryonic defects apparent when AP-2 is depleted. Our data thus contradict the primacy of FCHO1/2 in coat initiation.
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Henn K, Braunbeck T. Dechorionation as a tool to improve the fish embryo toxicity test (FET) with the zebrafish (Danio rerio). Comp Biochem Physiol C Toxicol Pharmacol 2011; 153:91-8. [PMID: 20869464 DOI: 10.1016/j.cbpc.2010.09.003] [Citation(s) in RCA: 99] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/24/2010] [Revised: 09/14/2010] [Accepted: 09/14/2010] [Indexed: 11/26/2022]
Abstract
Prior to hatching, the zebrafish embryo is surrounded by an acellular envelope, the chorion. Despite repeated speculations, it could not be clarified unequivocally whether the chorion represents an effective barrier and, thus, protects the embryo from exposure to distinct chemicals. Potentially, there is a risk of generating false negative results in developmental toxicity studies due to limited permeability of the chorion for some compounds. The simplest way to exclude this is to remove the chorion and expose the "naked" embryo. In the context of ecotoxicity testing, standardized protocols do not exist for fish embryo dechorionation, and survival rates of dechorionated embryos have usually not been subjected to statistical analysis. Since reproducibly high survival rates are of fundamental importance for chemical toxicity assessment, the present study was designed to develop and optimize a dechorionation procedure. With appropriate modifications of the fish embryo test protocol, embryos can be dechorionated at 24h post-fertilization (hpf) with survival rates of ≥90%. However, for fish embryo tests with dechorionated embryos, the standard positive control test substance, 3,4-dichloroaniline, should be replaced by another compound, e.g., acetone, since 3,4-dichloroaniline exerts its effects during the first 24h of development. Dechorionation of younger stages (<24 hpf) is generally possible, however with lower survival rates. The effect of dechorionation was demonstrated with the cationic polymer Luviquat HM 552, which is blocked by the chorion non-dechorionated embryos due to its molecular weight of ~400,000 Dalton, but becomes strongly toxic after dechorionation.
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Affiliation(s)
- Kirsten Henn
- Aquatic Ecology and Toxicology Section, Department of Zoology, University of Heidelberg, Im Neuenheimer Feld 230, D-69120 Heidelberg, Germany
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Sharma D, Kinsey WH. Fertilization triggers localized activation of Src-family protein kinases in the zebrafish egg. Dev Biol 2006; 295:604-14. [PMID: 16698010 PMCID: PMC4324460 DOI: 10.1016/j.ydbio.2006.03.041] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2006] [Revised: 03/28/2006] [Accepted: 03/29/2006] [Indexed: 11/28/2022]
Abstract
Fertilization triggers activation of Src-family kinases in eggs of various species including marine invertebrates and lower vertebrates. While immunofluorescence studies have localized Src-family kinases to the plasma membrane or cortical cytoplasm, no information is available regarding the extent to which these kinases are activated in different regions of the zygote. The objective of the present study was to detect the subcellular distribution of activated Src-family kinases in the fertilized zebrafish egg. An antibody specific for the active, non-phosphorylated form of Src-family PTKs was used to detect these activated kinases by immunofluorescence. The results demonstrate that Fyn, and possibly other Src family members are activated by dephosphorylation of the C-terminal tyrosine at fertilization. The activated Src-family kinases are asymmetrically distributed around the egg cortex with an area of higher kinase activity localized adjacent to the micropyle near the presumptive animal pole. Fertilization initially caused elevation of kinase activity in the cytoplasm underlying the micropyle, but this quickly spread to involve the entire zygote cortex. Later, during egg activation, formation of the blastodisc involved concentration of active Src-family kinase in the blastodisc cortex. As cytokinesis began, activated Src-family kinases were no longer limited to the cortex, but became more evenly distributed in the clear apical cytoplasm of the blastomeres. The results demonstrate that the cortex of the zebrafish egg is functionally differentiated and that fertilization triggers localized activation of Src-family kinases at the point of sperm entry, which subsequently progresses through the entire egg cortex.
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Affiliation(s)
| | - William H. Kinsey
- To whom correspondence should be addressed: Department of Anatomy and Cell Biology, University of Kansas Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160., Tel.: 913-588-2721; Fax: 913-588-2710.
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7
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Abstract
Fertilization is the union of a single sperm and an egg, an event that results in a diploid embryo. Animals use many mechanisms to achieve this ratio; the most prevalent involves physically blocking the fusion of subsequent sperm. Selective pressures to maintain monospermy have resulted in an elaboration of diverse egg and sperm structures. The processes employed for monospermy are as diverse as the animals that result from this process. Yet, the fundamental molecular requirements for successful monospermic fertilization are similar, implying that animals may have a common ancestral block to polyspermy. Here, we explore this hypothesis, reviewing biochemical, molecular, and genetic discoveries that lend support to a common ancestral mechanism. We also consider the evolution of alternative or radical techniques, including physiological polyspermy, with respect to our ability to describe a parsimonious guide to fertilization.
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Affiliation(s)
- Julian L Wong
- Department of Molecular Biology, Cellular Biology, and Biochemistry, Brown University, Providence, Rhode Island 02912, USA
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Pelegri F, Schulte-Merker S. A gynogenesis-based screen for maternal-effect genes in the zebrafish, Danio rerio. Methods Cell Biol 1999; 60:1-20. [PMID: 9891328 DOI: 10.1016/s0091-679x(08)61891-9] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- F Pelegri
- Max-Planck Institut für Entwicklungsbiologie, Tübingen, Germany
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Becker KA, Hart NH. Reorganization of filamentous actin and myosin-II in zebrafish eggs correlates temporally and spatially with cortical granule exocytosis. J Cell Sci 1999; 112 ( Pt 1):97-110. [PMID: 9841907 DOI: 10.1242/jcs.112.1.97] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The zebrafish egg provides a useful experimental system to study events of fertilization, including exocytosis. We show by differential interference contrast videomicroscopy that cortical granules are: (1) released nonsynchronously over the egg surface and (2) mobilized to the plasma membrane in two phases, depending upon vesicle size and location. Turbidometric assay measurements of the timing and extent of exocytosis revealed a steady release of small granules during the first 30 seconds of egg activation. This was followed by an explosive discharge of large granules, beginning at 30 seconds and continuing for 1–2 minutes. Stages of single granule exocytosis and subsequent remodeling of the egg surface were imaged by either real-time or time-lapse videomicroscopy as well as scanning electron microscopy. Cortical granule translocation and fusion with the plasma membrane were followed by the concurrent expansion of a fusion pore and release of granule contents. A dramatic rearrangement of the egg surface followed exocytosis. Cortical crypts (sites of evacuated granules) displayed a purse-string-like contraction, resulting in their gradual flattening and disappearance from the egg surface. We tested the hypothesis that subplasmalemmal filamentous (F-) actin acts as a physical barrier to secretion and is locally disassembled prior to granule release. Experimental results showed a reduction of rhodamine-phalloidin and antimyosin staining at putative sites of secretion, acceleration of the timing and extent of granule release in eggs pretreated with cytochalasin D, and dose-dependent inhibition of exocytosis in permeabilized eggs preincubated with phalloidin. An increase in assembled actin was detected by fluorometric assay during the period of exocytosis. Localization studies showed that F-actin and myosin-II codistributed with an inward-moving, membrane-delimited zone of cytoplasm that circumscribed cortical crypts during their transformation. Furthermore, cortical crypts displayed a distinct delay in transformation when incubated continuously with cytochalasin D following egg activation. We propose that closure of cortical crypts is driven by a contractile ring whose forces depend upon dynamic actin filaments and perhaps actomyosin interactions.
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Affiliation(s)
- K A Becker
- Rutgers University, Department of Cell Biology and Neuroscience, Busch Campus, Nelson Biology Laboratories, Piscataway, NJ 08854-8082, USA
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Bonsignorio D, Perego L, Del Giacco L, Cotelli F. Structure and macromolecular composition of the zebrafish egg chorion. ZYGOTE 1996; 4:101-8. [PMID: 8913023 DOI: 10.1017/s0967199400002975] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The chorion is the acellular envelope surrounding mature eggs of teleostean fish. The macromolecular composition of the zebrafish (Danio rerio) egg chorion, organised as a three-layered structure, has been analysed. SDS-PAGE analysis, under reducing conditions, of isolated and purified chorions revealed a reproducible pattern of four major polypeptides (116, 97, 50 and 43 kDa) and several minor bands. Lectin binding assays showed that both the 116 kDa and 50 kDa proteins were recognised by concanavalin agglutinin (Con A), Galanthus nivalis agglutinin (GNA), Sambucus nigra bark agglutinin (SNA) and Ricinus communis agglutinin (RCA 120), suggesting that these polypeptides are N-linked glycoproteins. By contrast, neither the 97 kDa nor the 43 kDa polypeptides were stained by these lectins, indicating that these polypeptides are not glycosylated. Amino acid analysis also showed significant differences in the average content of some amino acids, for example serine and proline, when compared with previous reports.
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11
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Becker KA, Hart NH. The cortical actin cytoskeleton of unactivated zebrafish eggs: spatial organization and distribution of filamentous actin, nonfilamentous actin, and myosin-II. Mol Reprod Dev 1996; 43:536-47. [PMID: 9052946 DOI: 10.1002/(sici)1098-2795(199604)43:4<536::aid-mrd17>3.0.co;2-x] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Actin and nonmuscle myosin heavy chain (myosin-II) have been identified and localized in the cortex of unfertilized zebrafish eggs using techniques of SDS-polyacrylamide gel electrophoresis, immunoblotting, and fluorescence microscopy. Whole egg mounts, egg fragments, cryosections, and cortical membrane patches probed with rhodamine phalloidin, fluorescent DNase-I, or anti-actin antibody showed the cortical cytoskeleton to contain two domains of actin: filamentous and nonfilamentous. Filamentous actin was restricted to microplicae and the cytoplasmic face of the plasma membrane where it was organized as an extensive meshwork of interconnecting filaments. The cortical cytoplasm deep to the plasma membrane contained cortical granules and sequestered actin in nonfilamentous form. The cytoplasmic surface (membrane?) of cortical granules displayed an enrichment of nonfilamentous actin. An antibody against human platelet myosin was used to detect myosin-II in whole mounts and egg fragments. Myosin-II colocalized with both filamentous and nonfilamentous actin domains of the cortical cytoskeleton. It was not determined if egg myosin was organized into filaments. Similar to nonfilamentous actin, myosin-II appeared to be concentrated over the surface of cortical granules where staining was in the form of patches and punctate foci. The identification of organized and interconnected domains of filamentous actin, nonfilamentous actin, and myosin-II provides insight into possible functions of these proteins before and after fertilization.
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Affiliation(s)
- K A Becker
- Department of Biological Sciences, Nelson Biological Laboratory, Rutgers University, Piscataway, New Jersey 08855-1059, USA
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Hart NH, Fluck RA. Cytoskeleton in teleost eggs and early embryos: contributions to cytoarchitecture and motile events. Curr Top Dev Biol 1996; 31:343-81. [PMID: 8746670 DOI: 10.1016/s0070-2153(08)60233-1] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- N H Hart
- Department of Biological Sciences, Rutgers University, Piscataway, New Jersey 08855, USA
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Selman K, Wallace RA, Sarka A, Qi X. Stages of oocyte development in the zebrafish,Brachydanio rerio. J Morphol 1993; 218:203-224. [DOI: 10.1002/jmor.1052180209] [Citation(s) in RCA: 477] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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