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Calcium ion dependency and the role of inositol phosphates in melatonin-induced encystment of dinoflagellates

Authors Tsim, ST
Wong, JTY
Wong, YH
Issue Date 1997
Source Journal of cell science , v. 110, (Part 12), 1997, JUN, p. 1387-1393
Summary 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 greater than or equal to melatonin much greater than 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 dinaflagellates.
ISSN 0021-9533
Rights Permission is granted by the Company of Biologists Ltd. The paper was published in J Cell Sci 1997 110 : 1387-1393
Language English
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