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| Title: | Calcium ion dependency and the role of inositol phosphates in melatonin-induced encystment of dinoflagellates |
| Authors: | Tsim, Siu-Tai
Wong, Joseph T. Y.
Wong, Yung-Hou |
| Keywords: | Dinoflagellate
Encystment
Melatonin
5-Methoxytryptamine
Calcium
Inositol phosphate |
| Issue Date: | 1997 |
| Citation: | Journal of cell science, v. 110, no. 12, Jun. 1997, p. 1387-1393 |
| Abstract: | The unicellular eukaryotic dinoflagellates shed their flagella and form a new pellicle cyst wall in response to environmental stress. This encystment process can also be induced by indoleamines such as melatonin and 5-methoxytryptamine. To decipher the complex signaling events which lead to encystment, we have investigated the functional roles of Ca2+ and inositol phosphates in indoleamine-induced encystment of the dinoflagellates Alexandrium catenella and Crypthecodinium cohnii. Pretreatment with EGTA, but not with EDTA, effectively blocked the indoleamine-induced encystment of A. catenella in a dose-dependent manner. Conversely, agents that facilitate the influx of Ca2+ (Bay K 8644, A23187 and ionomycin) dose-dependently induced encystment of A. catenella. Endoplasmic Ca2+-ATPase inhibitors such as thapsigargin and the peptide toxin melittin also induced encystment of A. catenella. These results suggest that an elevation of intracellular [Ca2+] may be involved in the encystment response. In terms of the regulation of phospholipase C, melatonin dose- and time-dependently stimulated the formation of inositol phosphates in C. cohnii. The rank order of potency for several indoleamines to stimulate inositol phosphates formation was 2-iodomelatonin > 5-methoxytryptamine ≥ melatonin >> N-acetylserotonin > 5-hydroxytryptamine. This rank order was the same as for the indoleamine-induced encystment of C. cohnii as previously reported. Our results indicate that indoleamine-induced activation of phospholipase C and elevation of intracellular [Ca2+] may be proximal steps in the signal transduction pathway leading to encystment in dinoflagellates. Moreover, this is the first demonstration of the possible involvement of Ca2+ and inositol phosphates as second messengers in dinoflagellates. |
| Rights: | Permission is granted by the Company of Biologists Ltd. The paper was published in J Cell Sci 1997 110 : 1387-1393 |
| URI: | http://hdl.handle.net/1783.1/1605 |
| Appears in Collections: | BIOL Journal/Magazine Articles
BICH Journal/Magazine Articles
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| 1387.pdf | | 106Kb | Adobe PDF | View/Open |
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