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Zhou Y, Yang Z, Guo G, Guo Y. Microfilament dynamics is required for root growth under alkaline stress in Arabidopsis. JOURNAL OF INTEGRATIVE PLANT BIOLOGY 2010; 52:952-958. [PMID: 20977653 DOI: 10.1111/j.1744-7909.2010.00981.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The microfilament (MF) cytoskeleton has crucial functions in plant development. Recent studies have revealed the function of MFs in diverse stress response. Alkaline stress is harmful to plant growth; however, it remains unclear whether the MFs play a role in alkaline stress. In the present study, we find that blocking MF assembly with latrunculin B (Lat B) leads to inhibition of plant root growth, and stabilization of MFs with phalloidin does not significantly affect plant root growth under normal conditions. In high external pH conditions, MF de-polymerization is induced and that associates with the reduction of root growth; phalloidin treatment partially rescues this reduction. Moreover, Lat B treatment further decreases the survival rate of seedlings growing in high external pH conditions. However, a high external pH (8.0) does not affect MF stability in vitro. Taken together, our results suggest that alkaline stress may trigger a signal that leads the dynamics of MFs and in turn regulates root growth.
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Affiliation(s)
- Yue Zhou
- Institute of Cell Biology, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
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Pauls KP, Chan J, Woronuk G, Schulze D, Brazolot J. When microspores decide to become embryos — cellular and molecular changesThis review is one of a selection of papers published in the Special Issue on Plant Cell Biology. ACTA ACUST UNITED AC 2006. [DOI: 10.1139/b06-064] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cultured microspores can be induced to develop into fully functional haploid embryos instead of mature pollen. The ability of these cells to change their development in response to environmental stimuli is an exceptional example of totipotency in plants. Discovering the triggers of embryo development in microspore cultures could lead to a greater understanding of the early stages of embryogenesis in plants and might be used to increase the range of crop plants to which microspore culture can be applied for the production of double haploid homozygous lines. The information might also help to define the general characteristics of pluripotent cells in any organism. In this review, the changes that occur in cellular organization and gene expression in early-stage microspore cultures of several species are discussed. Responding cells in these cultures enlarge, their nuclei are repositioned to their cell centres, and their cytoplasms become filled with fragmented vacuoles. We used flow cytometry to track cellular changes in canola ( Brassica napus L.) microspore cultures as well as microarray analyses and real-time PCR to compare gene expression in embryogenic and nonembryogenic cells. A model for embryogenic cell activation in plants that involves alkalinization, Ca2+ signaling, and changes in GTPase activity that lead to significant changes in gene expression is discussed.
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Affiliation(s)
- K. Peter Pauls
- Department of Plant Agriculture, University of Guelph, Guelph, ON N1G 2W1, Canada
| | - John Chan
- Department of Plant Agriculture, University of Guelph, Guelph, ON N1G 2W1, Canada
| | - Grant Woronuk
- Department of Plant Agriculture, University of Guelph, Guelph, ON N1G 2W1, Canada
| | - Derek Schulze
- Department of Plant Agriculture, University of Guelph, Guelph, ON N1G 2W1, Canada
| | - Janice Brazolot
- Department of Plant Agriculture, University of Guelph, Guelph, ON N1G 2W1, Canada
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Squirrell JM, Lane M, Bavister BD. Altering intracellular pH disrupts development and cellular organization in preimplantation hamster embryos. Biol Reprod 2001; 64:1845-54. [PMID: 11369617 PMCID: PMC5087321 DOI: 10.1095/biolreprod64.6.1845] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
In early cleavage stage hamster embryos, the inability to regulate intracellular pH (pHi) properly is associated with reduced developmental competence in vitro. The disruption of mitochondrial organization is also correlated with reduced development in vitro. To determine the relationship between pHi and the disruption of cytoplasmic organization, we examined the effects of altering pHi on hamster embryo development, mitochondrial distribution, and cytoskeletal organization. The weak base trimethylamine was used to increase pHi and was found to reduce embryo development and disrupt the perinuclear organization of mitochondria. The weak acid 5,5-dimethyl-2,4-oxazolinedione was used to decrease pH(i) and was also found to reduce development and disrupt the perinuclear organization of mitochondria. With either treatment, the microfilament organization was perturbed, but the microtubule cytoskeleton was not. However, the temporal progression of the disruption of mitochondrial distribution was more rapid in alkalinized embryos than acidified embryos, as revealed by two-photon imaging of living embryos. Additionally, the disruption of the microfilament network by the two treatments was not identical. The cytoplasmic disruptions observed were not due to acute toxicity of the compounds because embryos recovered developmentally when the treatment compounds were removed. These observations link ionic homeostasis, structural integrity and developmental competence in preimplantation hamster embryos.
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Affiliation(s)
- J M Squirrell
- Department of Animal Health and Biomedical Sciences, University of Wisconsin, Madison, Wisconsin 53706, USA.
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Watanabe K, Hamaguchi MS, Hamaguchi Y. Effects of intracellular pH on the mitotic apparatus and mitotic stage in the sand dollar egg. CELL MOTILITY AND THE CYTOSKELETON 2000; 37:263-70. [PMID: 9227856 DOI: 10.1002/(sici)1097-0169(1997)37:3<263::aid-cm8>3.0.co;2-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The effect of change in intracellular pH (pHi) on mitosis was investigated in the sand dollar egg. The pHi in the fertilized egg of Scaphechinus mirabilis and Clypeaster japonicus, which was 7.34 and 7.31, respectively, changed by means of treating the egg at nuclear envelope breakdown with sea water containing acetate and/or ammonia at various values of pH. The mitotic apparatus at pHi 6.70 became larger than that of normal fertilized eggs; that is, the mitotic spindle had the maximal size, especially in length at pHi 6.70. The spindle length linearly decreased when pHi increased from 6.70 to 7.84. By polarization microscopy, the increase in birefringence retardation was detected at slightly acidic pHi, suggesting that the increase in size of the spindle is caused by the increase in the amount of microtubules in the spindle. At pHi 6.30, the organization of the mitotic apparatus was inhibited. Furthermore, slightly acidic pHi caused cleavage retardation or inhibition. By counting the number of the eggs at various mitotic stages with time after treating them with the media, it is found that metaphase was persistent and most of the S. mirabilis eggs were arrested at metaphase under the condition of pHi 6.70. It is concluded that at slightly acidic pH, the microtubules in the spindle are stabilized and more microtubules assembled than those in the normal eggs.
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Affiliation(s)
- K Watanabe
- Biological Laboratory, Faculty of Bioscience and Biotechnology, Tokyo Institute of Technology, Japan
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5
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Scott AC, Allen NS. Changes in cytosolic pH within Arabidopsis root columella cells play a key role in the early signaling pathway for root gravitropism. PLANT PHYSIOLOGY 1999; 121:1291-8. [PMID: 10594116 PMCID: PMC59496 DOI: 10.1104/pp.121.4.1291] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/1999] [Accepted: 08/19/1999] [Indexed: 05/20/2023]
Abstract
Ratiometric wide-field fluorescence microscopy with 1',7'- bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF)-dextran demonstrated that gravistimulation leads to rapid changes in cytoplasmic pH (pHc) in columella cells of Arabidopsis roots. The pHc of unstimulated columella cells in tiers 2 and 3, known sites of graviperception (E.B. Blancaflor, J.B. Fasano, S. Gilroy [1998] Plant Physiol 116: 213-222), was 7.22 +/- 0.02 pH units. Following gravistimulation, the magnitude and direction of pHc changes in these cells depended on their location in the columella. Cells in the lower side of tier 2 became more alkaline by 0.4 unit within 55 s of gravistimulation, whereas alkalinization of the cells on the upper side was slower (100 s). In contrast, all cells in tier 3 acidified by 0.4 pH unit within 480 s after gravistimulation. Disrupting these pHc changes in the columella cells using pHc modifiers at concentrations that do not affect root growth altered the gravitropic response. Acidifying agents, including bafilomycin A1, enhanced curvature, whereas alkalinizing agents disrupted gravitropic bending. These results imply that pHc changes in the gravisensing cells and the resultant pH gradients across the root cap are important at an early stage in the signal cascade leading to the gravitropic response.
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Affiliation(s)
- A C Scott
- Department of Botany, Box 7612, North Carolina State University, Raleigh, North Carolina 27695-7612, USA
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6
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Abstract
gamma-Tubulin is a conserved component of all microtubule-organizing centres and is required for these organelles to nucleate microtubule polymerization. However, the mechanism of nucleation is not known. In addition to its localization to organizing centres, a large pool of gamma-tubulin exists in the cytoplasm in a complex with other proteins. The size of the gamma-tubulin complex and number of associated proteins vary among organisms, and the functional significance of these differences is unknown. Recently, the nature of these gamma-tubulin complexes has been explored in different organisms, and this has led us closer to a molecular understanding of microtubule nucleation.
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Affiliation(s)
- R Jeng
- Dept of Biological Sciences, Stanford University, Stanford, CA 94305-5020, USA
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Palazzo RE, Vaisberg EA, Weiss DG, Kuznetsov SA, Steffen W. Dynein is required for spindle assembly in cytoplasmic extracts of Spisula solidissima oocytes. J Cell Sci 1999; 112 ( Pt 9):1291-302. [PMID: 10194408 DOI: 10.1242/jcs.112.9.1291] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Meiosis I spindle assembly is induced in lysate-extract mixtures prepared from clam (Spisula solidissima) oocytes. Unactivated lysate prepared from unactivated oocytes contain nuclei (germinal vesicles, GVs) which house condensed chromosomes. Treatment of unactivated lysate with clarified activated extract prepared from oocytes induced to complete meiosis by treatment with KCl induces GV breakdown (GVBD) and assembly of monopolar, bipolar, and multipolar aster-chromosome complexes. The process of in vitro meiosis I spindle assembly involves the assembly of microtubule asters and the association of these asters with the surfaces of the GVs, followed by GVBD and spindle assembly. Monoclonal antibody m74-1, known to react specifically with the N terminus of the intermediate chain of cytoplasmic dynein, recognizes Spisula oocyte dynein and inhibits in vitro meiosis I spindle assembly. Control antibody has no affect on spindle assembly. A similar inhibitory effect on spindle assembly was observed in the presence of orthovanadate, a known inhibitor of dynein ATPase activity. Neither m74-1 nor orthovanadate has any obvious affect on GVBD or aster formation. We propose that dynein function is required for the association of chromosomes with astral microtubules during in vitro meiosis I spindle assembly in these lysate-extract mixtures. However, we conclude that dynein function is not required for centrosome assembly and maturation or for centrosome-dependent aster formation.
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Affiliation(s)
- R E Palazzo
- The Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045, USA.
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8
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Brisch E, Ahrens DP, Suprenant KA. Phosphatase-sensitive regulators of microtubule assembly copurify with sea urchin egg microtubules. ACTA ACUST UNITED AC 1999. [DOI: 10.1002/(sici)1097-010x(19990215)283:3<258::aid-jez4>3.0.co;2-u] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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9
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Feijó JA, Sainhas J, Hackett GR, Kunkel JG, Hepler PK. Growing pollen tubes possess a constitutive alkaline band in the clear zone and a growth-dependent acidic tip. J Cell Biol 1999; 144:483-96. [PMID: 9971743 PMCID: PMC2132912 DOI: 10.1083/jcb.144.3.483] [Citation(s) in RCA: 241] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/1998] [Revised: 12/21/1998] [Indexed: 12/01/2022] Open
Abstract
Using both the proton selective vibrating electrode to probe the extracellular currents and ratiometric wide-field fluorescence microscopy with the indicator 2', 7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF)-dextran to image the intracellular pH, we have examined the distribution and activity of protons (H+) associated with pollen tube growth. The intracellular images reveal that lily pollen tubes possess a constitutive alkaline band at the base of the clear zone and an acidic domain at the extreme apex. The extracellular observations, in close agreement, show a proton influx at the extreme apex of the pollen tube and an efflux in the region that corresponds to the position of the alkaline band. The ability to detect the intracellular pH gradient is strongly dependent on the concentration of exogenous buffers in the cytoplasm. Thus, even the indicator dye, if introduced at levels estimated to be of 1.0 microM or greater, will dissipate the gradient, possibly through shuttle buffering. The apical acidic domain correlates closely with the process of growth, and thus may play a direct role, possibly in facilitating vesicle movement and exocytosis. The alkaline band correlates with the position of the reverse fountain streaming at the base of the clear zone, and may participate in the regulation of actin filament formation through the modulation of pH-sensitive actin binding proteins. These studies not only demonstrate that proton gradients exist, but that they may be intimately associated with polarized pollen tube growth.
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Affiliation(s)
- J A Feijó
- Department Biologia Vegetal, Faculdade de Ciências, Universidade de Lisboa, P-1749-016 Lisboa, Portugal.
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11
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Dubé F, Eckberg WR. Intracellular pH increase driven by an Na+/H+ exchanger upon activation of surf clam oocytes. Dev Biol 1997; 190:41-54. [PMID: 9331330 DOI: 10.1006/dbio.1997.8682] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Intracellular pH (pHi) measurements were performed in surf clam (Spisula solidissima) oocytes before and after artificial activation or fertilization [evidenced by germinal vesicle breakdown (GVBD)] by the dimethyloxazolidinedione (DMO) and 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF) methods. Results using both methods showed increases of pHi of 0.3 pH unit after activation by excess K+. Using BCECF, we found an increase of similar magnitude after fertilization or after the addition of serotonin. By contrast, GVBD did not occur when the pHi was increased to similar or even higher levels by exposing the oocytes to ammonia. In sodium-free seawater, excess K+ induced GVBD but the pHi of K+-activated oocytes decreased significantly below the resting level of unactivated oocytes. The pHi increases in K+-activated oocytes were otherwise proportional to the external Na+ concentration. The amiloride derivatives dimethylamiloride and hexamethylene amiloride (at 10-50 microM) efficiently inhibited the K+-induced increase of pHi but did not block GVBD. These two derivatives were able, however, to retard K+-induced GVBD, hexamethylene amiloride being the more efficient. This retardation of K+-induced GVBD could be abolished by the simultaneous addition of ammonia. Taken altogether, these results show that a pHi increase, driven by a typical Na+/H+ exchanger, follows activation of surf clam oocytes but that this pHi increase is neither sufficient nor required for GVBD, though it does allow its progression at an optimal rate.
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Affiliation(s)
- F Dubé
- Département d'Obstétrique-Gynécologie, Université de Montréal, Centre de Recherche du CHUM, Québec, Canada
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12
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Bachewich CL, Heath IB. The Cytoplasmic pH Influences Hyphal Tip Growth and Cytoskeleton-Related Organization. Fungal Genet Biol 1997; 21:76-91. [PMID: 9073482 DOI: 10.1006/fgbi.1997.0962] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The regulatory role of protons in hyphal tip growth was investigated by using membrane-permeant weak acids to acidify cytoplasm of the oomycete Saprolegnia ferax. Acetic acid decreased cytoplasmic pH from approximately pH 7.2 to 6.8, as shown by SNARF-1 measurements of cytoplasmic pH. Inhibition of growth in a dose-dependent manner by acetic, propionic, and isobutyric acid was accompanied by changes in positioning and morphology of mitochondria and nuclei, condensation of chromatin, disruptions in peripheral actin, and increases in hyphal diameter. These cellular alterations were fully reversible, and during recovery, major cytoplasmic movements and extensive apical vacuolations were observed. The results are consistent with proton regulation of the cytoskeleton, nuclear matrix, and/or chromosomes. However, a macroscopic cytoplasmic gradient of H+ in hyphae was not revealed by SNARF-1, indicating that if such a H+ gradient were required, it must occur at a finer level than we detected.
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Affiliation(s)
- CL Bachewich
- Department of Biology, York University, 4700 Keele St., North York, Ontario, M3J 1P3, Canada
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13
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Abstract
Cell duplication is characteristic of life. The coordination of cell growth with cell duplication and, specifically, the ordered steps necessary for this process are termed the cell cycle. Central to this process is the faithful replication and segregation of the chromosomes. The cycle consists of four phases: G1, where the decision to enter the cell cycle, which is known as Start, is made; S phase, during which the DNA is replicated; G2, during which controls assuring the completion of S phase operate; and M, or the mitotic phase, which is characterized by chromosome segregation, nuclear division, and cytokinesis. The budding yeast Saccharomyces cerevisiae has been developed into a model genetic system for the study of the cell division cycle (Hartwell et al. ["73] Genetics, 74:267-286). Here I review the basic processes by which chromosomes are segregated, with an emphasis on the physical structures fundamental to this process.
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Affiliation(s)
- S G Sobel
- Department of Cell Biology, Yale University, New Haven, Connecticut 06536-0812, USA
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Stephano JL, Gould MC. Parthenogenesis in Urechis caupo (Echiura). II. Role of intracellular pH in parthenogenesis induction. Dev Growth Differ 1997; 39:99-104. [PMID: 9079038 DOI: 10.1046/j.1440-169x.1997.00010.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
A peptide (P23) isolated from sperm acrosomal protein initiates development in eggs of the marine worm Urechis caupo. We have shown previously that eggs exposed to P23 for > or = 3 min complete meiosis but fail to cleave. However, a brief (1.5-2 min) exposure to P23 at pH 8, followed by either acidification of the seawater of pH 7 or dilution of P23 at pH 8 causes germinal vesicle breakdown (GVBD), but eggs fail to complete meiosis and many then later advance to mitosis. In the present study we investigated the hypothesis that partial activation leading to parthenogenesis occurs when there is a partial intracellular alkalinization. Measurements with the fluorescent pH indicator bis(carboxyethyl)-carboxyfluorescein (BCECF) showed that P23 induces a pHi increase similar to that occurring during fertilization and the parthenogenesis-inducing treatments interrupt this rise in pHi. In eggs exposed to P23 for > 3 min the pHi increase was 0.31-0.49 units, slightly higher than in fertilized eggs. In partially activated eggs exposed to P23 for 1.5-2 min at pH 8, pHi began to rise but then returned to control values or remained only partially elevated (< 0.2 pH units average increase). Electrophysiological measurements revealed that removal of P23 during the first few minutes of exposure caused the activation potential to terminate and experiments with [14C]-P23 confirmed that dilution results in a rapid unbinding of P23 from eggs. If proton export is driven by membrane potential as well as the pH gradient, these results explain why dilution of P23 at pH 8 also interrupts the pHi increase.
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Affiliation(s)
- J L Stephano
- Facultad de Ciencias, Universidad Autónoma de Baja California, Ensenada, México
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Spittle CS, Cassimeris L. Mechanisms blocking microtubule minus end assembly: evidence for a tubulin dimer-binding protein. CELL MOTILITY AND THE CYTOSKELETON 1996; 34:324-35. [PMID: 8871819 DOI: 10.1002/(sici)1097-0169(1996)34:4<324::aid-cm7>3.0.co;2-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
We have characterized an activity in sea urchin eggs which prevents microtubule assembly at minus ends. Using Chlamydomonas axoneme fragments to nucleate the assembly of plus and minus end microtubules, we find robust assembly at microtubule plus ends with negligible assembly at minus ends. The minus end assembly inhibitor does not co-pellet with microtubules when assembly is stimulated with DMSO while the resulting pellet of tubulin and microtubule associated proteins readily assembles from both plus and minus ends of axoneme fragments. Addition of increasing concentrations of porcine bran tubulin to the tubulin and MAP-depleted fraction eventually saturates the minus end inhibitory activity. Compared to purified tubulin, cytosolic fractions both increase the minus end critical concentration approximately 3 fold and decrease the plus end critical concentration. The inhibitory activity is removed by heating, trypsin, or by co-immunoprecipitation with tubulin. We hypothesize that a tubulin dimer binding protein is responsible for preventing assembly onto minus ends in our in vitro assays and speculate that this protein functions in vivo to prevent spontaneous nucleation, thus limiting assembly to nucleation sites.
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Affiliation(s)
- C S Spittle
- Department of Biological Sciences, Lehigh University, Bethlehem, Pennsylvania 18015, USA
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Eckberg WR, Anderson WA. Cytoskeleton, cellular signals, and cytoplasmic localization in Chaetopterus embryos. Curr Top Dev Biol 1996; 31:5-39. [PMID: 8746660 DOI: 10.1016/s0070-2153(08)60222-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- W R Eckberg
- Department of Biology, Howard University, Washington, DC 20059, USA
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18
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Affiliation(s)
- K A Suprenant
- Department of Physiology and Cell Biology, University of Kansas, Lawrence, Kansas 66045, USA
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19
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Kropf DL, Gibbon BC, Money NP. Role of cytosolic pH in axis establishment and tip growth. ACTA ACUST UNITED AC 1995. [DOI: 10.1139/b95-235] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The role of cytosolic pH (pHc) in determining the growth site and in tip elongation has been investigated by measuring and manipulating pHc. pHcacidifies by 0.1–0.2 units as the growth axis is established. Concomitantly, cells accumulate KCl, which increases the cellular osmotic pressure, resulting in the generation of turgor pressure. The K+taken up is apparently compartmentalized as the free cytosolic K+activity remains constant. At present, the relation between pHc, K+, and turgor pressure is not well understood. A small but statistically significant cytosolic pH gradient, acid at the future growth site, is also detectable during axis establishment. As growth is initiated the intensity of the gradient increases to approximately 0.3 pH units. The magnitude of the pH gradient correlates with the rate of tip elongation. The gradient may regulate tip elongation in a number of ways, including local control of the assembly and stability of cytoskeletal elements. Key words: cytosolic pH gradients, tip growth, turgor pressure, weak acids and bases, SNARF 1, pH-sensitive microelectrodes.
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20
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Cortassa S, Cáceres A, Aon MA. Microtubular protein in its polymerized or nonpolymerized states differentially modulates in vitro and intracellular fluxes catalyzed by enzymes of carbon metabolism. J Cell Biochem 1994; 55:120-32. [PMID: 8083293 DOI: 10.1002/jcb.240550114] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The fluxes through HK/G6PDH and PK/LDH coupled-enzymatic reactions were quantified in the presence of physiological concentrations (1-15 microM) of polymerized or non-polymerized microtubular protein (MTP) from rat brain and in a permeabilized yeast cell system. In vitro enzymatic fluxes were increased by either polymerized or nonpolymerized brain MTP mainly in the lower range of MTP concentration. At fixed MTP concentrations in the flux stimulatory range of HK/G6PDH (1 mg/ml MTP) or PK/LDH (0.4 mg/ml MTP), a hyperbolic and sigmoidal response to NADP and PEP, respectively, was detected. That dependence varied according to the polymeric status of MTP. The specificity of the phenomenon observed in vitro, was tested for the PK/LDH and HK/G6PDH enzymatic couples in the presence of neutral polymers such as glycogen (< or = 10 mg/ml), poly(ethylene glycol) (up to 10% w/w) or G-actin (< or = 1 mg/ml). In permeabilized Saccharomyces cerevisiae cells, the PK-catalyzed flux was sensitive to microtubule disruption by nocodazole (15 micrograms/ml). The HK/G6PDH system was not affected by nocodazole showing values of kinetic parameters close to those obtained in vitro in the presence of polymerized brain MTP. Indirect immunofluorescence with specific antibodies against tubulin allowed to confirm the microtubules disruption in the presence of nocodazole in permeabilized yeast cells under the same conditions in which enzymes were assayed intracellularly. The experimental evidence is in agreement with the observed phenomenon of increase in fluxes in the enzymatic reactions assayed to be specifically induced by MTP either in vitro or in situ. The results presented are discussed in terms of the assembly of large supramolecular structures as a supraregulatory mechanism of synchronization of systemic cellular processes such as metabolic fluxes.
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Affiliation(s)
- S Cortassa
- Instituto Superior de Investigaciones Biológicas (INSIBIO, CONICET-UNT), Departamento de Bioquímica de la Nutrición, Universidad Nacional de Tucumán, Argentina
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21
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Abstract
The presence of a cytosolic pH gradient and its relation to polar tip growth was investigated in rhizoid cells of Pelvetia embryos with the use of pH-sensitive microelectrodes and by ratio imaging. Growing rhizoid cells generated a longitudinal pH gradient in which the apical cytosol was 0.3 to 0.5 units more acidic than the cytosol at the base of the cell. Treatment with a membrane-permeant weak acid, propionic acid, dissipated the cytosolic pH gradient and inhibited growth. The magnitude of the pH gradient correlated well with the rate of tip elongation. The pH gradient spatially superimposed on the cytosolic calcium gradient, and inhibition of calcium fluxes by treatment with lanthanum abolished the pH gradient and inhibited growth.
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Stearns T, Kirschner M. In vitro reconstitution of centrosome assembly and function: the central role of gamma-tubulin. Cell 1994; 76:623-37. [PMID: 8124706 DOI: 10.1016/0092-8674(94)90503-7] [Citation(s) in RCA: 369] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The centrosome nucleates microtubule polymerization, affecting microtubule number, polarity, and structure. We use an in vitro system based on extracts of Xenopus eggs to examine the role of gamma-tubulin in centrosome assembly and function. gamma-Tubulin is present in the cytoplasm of frog eggs and vertebrate somatic cells in a large approximately 25S complex. The egg extracts assemble centrosomes around sperm centrioles. Formation of a centrosome in the extract requires both the gamma-tubulin complex and ATP and can take place in the absence of microtubules. gamma-Tubulin is not present on the sperm prior to incubation in extract, but is recruited from the cytoplasm during centrosome assembly. The gamma-tubulin complex also binds to microtubules, likely the minus end, independent of the centrosome. These results suggest that gamma-tubulin is an essential component of the link between the centrosome and the microtubule, probably playing a direct role in microtubule nucleation.
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Affiliation(s)
- T Stearns
- Department of Biochemistry and Biophysics, University of California Medical School, San Francisco 94143
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23
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Tiwari SC, Suprenant KA. pH-dependent solubility and assembly of microtubules in bovine brain extracts. CELL MOTILITY AND THE CYTOSKELETON 1994; 28:69-78. [PMID: 8044851 DOI: 10.1002/cm.970280107] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Alkaline pH favors the assembly of microtubules (MTs) in marine egg extracts [Suprenant and Marsh, 1987: J. Cell Sci. 184:167-180; Suprenant, 1989: Exp. Cell Res. 184:167-180; 1991: Cell Motil. Cytoskeleton 19:207-220] and mammalian brain extracts [Tiwari and Suprenant, 1993: Anal. Biochem. 215:96-103], even though the assembly of purified microtubule protein (MTP) from both of these sources is favored at slightly acidic pH. The present investigation examines whether alkaline pH has a direct or indirect effect on MT nucleation and growth in soluble brain extracts. Cell-free extracts were prepared from bovine cerebral cortex, and a nucleated assembly assay was used to demonstrate that MT assembly in brain extracts is favored at slightly acidic pH. The increase in MT mass found at alkaline pH is due to an increase in the solubility of tubulin not an increase in the extent of assembly. On average, 47.7 +/- 11.3% of the total tubulin is soluble at pH 7.2, while only 30.9 +/- 8.9% of the tubulin is soluble at pH 6.8. A model is proposed that indicates how microtubule proteins from both mammalian brain and marine eggs may be associated with pH-dependent factors.
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Affiliation(s)
- S C Tiwari
- Department of Physiology and Cell Biology, University of Kansas, Lawrence 66045
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Faruki S, Karsenti E. Purification of microtubule proteins from Xenopus egg extracts: identification of a 230K MAP4-like protein. CELL MOTILITY AND THE CYTOSKELETON 1994; 28:108-18. [PMID: 8087870 DOI: 10.1002/cm.970280203] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
We describe the purification of microtubule proteins from Xenopus egg extracts by temperature-dependent assembly and disassembly in the presence of dimethyl sulfoxide and identify a number of presumptive microtubule-associated proteins (MAPs). One of these proteins has a molecular weight of 230 kDa and is immunologically related to HeLa MAP4. We show that this MAP is heat stable and phosphorylated, and that it promotes elongation of microtubules from axonemes.
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Affiliation(s)
- S Faruki
- Cell Biology Program, European Molecular Biology Laboratory, Heidelberg, Germany
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Gliksman NR, Parsons SF, Salmon ED. Cytoplasmic extracts from the eggs of sea urchins and clams for the study of microtubule-associated motility and bundling. Methods Cell Biol 1993; 39:237-51. [PMID: 8246801 DOI: 10.1016/s0091-679x(08)60174-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- N R Gliksman
- Department of Biology, University of North Carolina, Chapel Hill 27599
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Gliksman NR, Parsons SF, Salmon ED. Okadaic acid induces interphase to mitotic-like microtubule dynamic instability by inactivating rescue. J Cell Biol 1992; 119:1271-6. [PMID: 1447301 PMCID: PMC2289736 DOI: 10.1083/jcb.119.5.1271] [Citation(s) in RCA: 100] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
We used high-resolution video microscopy to visualize microtubule dynamic instability in extracts of interphase sea urchin eggs and to analyze the changes that occur upon addition of 0.8-2.5 microM okadaic acid, an inhibitor of phosphatase 1 and 2A (PP1, PP2a) (Bialojan, D., and A. Takai. 1988. Biochem. J. 256:283-290). Microtubule plus-ends in these extracts oscillated between the elongation and shortening phases of dynamic instability at frequencies typical for interphase cells. Switching from elongation to shortening (catastrophe) was frequent, but microtubules persisted and grew long because of frequent switching back to elongation (rescue). Addition of okadaic acid to the extract induced rapid (< 5 min) conversion to short, dynamic microtubules typical of mitosis. The frequency of catastrophe doubled and the velocities of elongation and shortening increased slightly; however, the major change was an elimination of rescue. Thus, modulation of the rescue frequency by phosphorylation-dependent mechanisms may be a major regulatory pathway for selectively controlling microtubule dynamics without dramatically changing velocities of microtubule elongation and shortening.
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Affiliation(s)
- N R Gliksman
- Department of Biology, University of North Carolina, Chapel Hill 27599-3280
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Gildersleeve R, Cross A, Cullen K, Fagen A, Williams RC. Microtubules grow and shorten at intrinsically variable rates. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)42399-x] [Citation(s) in RCA: 86] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Baas PW, Ahmad FJ. The plus ends of stable microtubules are the exclusive nucleating structures for microtubules in the axon. J Cell Biol 1992; 116:1231-41. [PMID: 1740474 PMCID: PMC2289361 DOI: 10.1083/jcb.116.5.1231] [Citation(s) in RCA: 91] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Microtubules (MTs) in the axon have a uniform polarity orientation that is recapitulated during recovery from episodes of MT depolymerization (Heidemann, S. R., M. A. Hamborg, S. J. Thomas, B. Song, S. Lindley, and D. Chu. 1984. J. Cell Biol. 99:1289-1295). This tight regulation of their organization indicates that axonal MTs are spatially regulated by discrete nucleating structures comparable in function to the centrosome. Several authors have proposed that an especially stable class of MTs in the axon may serve as these nucleating structures. In a previous report (Baas, P. W., and M. M. Black. 1990. J. Cell Biol. 111:495-509), we determined that the axons of cultured sympathetic neurons contain two classes of MT polymer, stable and labile, that differ in their sensitivity to nocodazole by roughly 35-fold. The stable and labile polymer represent long-lived and recently assembled polymer, respectively. We also determined that these two classes of polymer can be visually distinguished at the immunoelectron microscopic level based on their content of tyrosinated alpha-tubulin: the labile polymer stains densely, while the stable polymer does not stain. In the present study, we have taken advantage of these observations to directly identify MT nucleating structures in the axon. Neuron cultures were treated with nocodazole for 6 h to completely depolymerize the labile polymer in the axon, and substantially shorten the stable polymer. The cultures were then rinsed free of the drug, permitted to reassemble polymer for various periods of time, and prepared for immunoelectron microscopic localization of tyrosinated alpha-tubulin. Serial reconstruction of consecutive thin sections was undertaken to determine the spatial relationship between the stable MTs and the newly assembled polymer. All of the new polymer assembled in direct continuity with the plus ends of stable MTs, indicating that these ends are assembly competent, and hence capable of acting as nucleating structures. Our results further indicate that no self-assembly of MTs occurs in the axon, nor do any MT nucleating structures exist in the axon other than the plus ends of stable MTs. Thus the plus ends of stable MTs are the exclusive nucleating structures for MTs in the axon.
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Affiliation(s)
- P W Baas
- Department of Anatomy, University of Wisconsin Medical School, Madison 53706
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