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HgCl2-sensitive aquaporins are not involved in melanosome aggregation in Xenopus laevis melanophores
Linköping University, Department of Molecular and Clinical Medicine, Medical Microbiology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Molecular and Clinical Medicine, Medical Microbiology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Medicine and Care, Pharmacology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Molecular and Clinical Medicine, Medical Microbiology. Linköping University, Faculty of Health Sciences.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Melanophores are cells specialized for transport of pigment-filled organelles called melanosomes. Melanosomes are aggregated in the center of a melanophore or dispersed throughout the cytoplasm by motor proteins moving along the actin and microtubule cytoskeleton. In angelfish (Pterophyllum scalare), aggregation of melanosomes (as compared to dispersion) increases the height of the central part of melanophores by 300%. Our objective was to detennine whether such a height increase also occurs in frog (Xenopus laevis) melanophores. In analogy with theories explaining the leading edge of migrating cells, we investigated the possibility that elevation of the melanophore plasma membrane is due to local swelling caused by influx of water through HgCl2-sensitive aquaporins and subsequent polymerization of actin. Confocal microscopy revealed a 30% increase in height in X. laevis melanophores during melatonin-induced aggregation. This was not due to actin polymerization, because it also occurred when aggregation was induced by the polymerization inhibitor latrunculin B. The nitric oxide (NO) synthase inhibitor L-NAME induced dispersion and lowered the plasma membrane, which suggests that NO is involved in the upward movement. Furthermore, neither dispersion nor aggregation was affected by inhibition of water flux through HgCl2 sensitive aquaporins. Together, these observations imply that melanosomes in X. laevis melanophores are driven upwards during aggregation by a mechanism other than actin polymerization, possibly involving microtubules, intermediate filaments, or a motor protein that may be regulated by NO. Furthermore, influx of water through HgCl2-sensitive aquaporins is probably not necessary for aggregation-induced elevation of the cell membrane, because both aggregation and dispersion can occur in the presence of HgCl2.

National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-80030OAI: oai:DiVA.org:liu-80030DiVA: diva2:545073
Available from: 2012-08-17 Created: 2012-08-17 Last updated: 2015-09-18Bibliographically approved
In thesis
1. The role of nitric oxide in cytoskeleton-mediated organelle transport and cell adhesion
Open this publication in new window or tab >>The role of nitric oxide in cytoskeleton-mediated organelle transport and cell adhesion
2001 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nitric oxide (NO) is a signaling molecule that is produced by many different kinds of cells, and it is known to mediate actions such as blood vessel dilation, communication between nerve cells, and killing of bacteria in infections. The cytoskeleton is involved in many important cellular functions, among them intracellular transport of organelles, migration, and cell division. The aim of the present studies was to examine the effects of NO on some of the indicated functions. Homotypic adhesion of human neutrophils, which is mediated by ß2 integrins, is an early step in the inflammatory process. Addition of L-argiriine (the substrate of NO production) to fMLP-stimulated neutrophils increased and prolonged aggregation of the cells. Stimulation of L-arginine-pretreated neutrophils by cross-linking of ß2 integrins attenuated the increase in F-actin, as compared to control cells. These results suggest that the aggregation is prolonged by activation of ß2 integrins and endogenous NO production, two events that together seem to inhibit actin polymerization, possibly via ADP ribosylation.

The effect of NO on intracellular translocation of organelles along the cytoskeleton was studied in Xenopus laevis pigment cells. Inhibition of NO production induced by the drug L-NAME was found to inhibit aggregation of the pigment organelles (melanosomes) and to induce dispersion. Activation of PKC, MEK, and ERKl, but not PKA, was associated with the dispersion, thus NO may negatively regulate these kinases, which, when activated, would induce movement of melanosomes. During melanosome aggregation, the cell center increases in height by approximately 30%. Experiments were performed to determine whether the cell membrane is pushed upwards by actin polymerization and water influx through HgCl2-sensitive aquaporins. The results gave no evidence that either two of these mechanisms affects the upward movement. However, L-NAME caused dispersion and a decrease in cell height, thus NO may play a role in maintaining an aggregated, elevated state. In conclusion, many factors regulate both homotypic aggregation and intracellular organelle transport, and NO seems to prolong homotypic aggregation of neutrophils and regulate melanosome transport by inhibiting PKC, MEK and ERKl.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2001. 48 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 660
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-28614 (URN)13769 (Local ID)91-7219-761-7 (ISBN)13769 (Archive number)13769 (OAI)
Public defence
2001-03-02, Elsa Brändströmssalen, Universitetssjukhuset, Linköping, 09:00 (Swedish)
Opponent
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2015-09-18Bibliographically approved

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Nilsson, Harriet M.Holmgren Peterson, KajsaSvensson, Samuel P. S.Sundqvist, Tommy

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