The molecular mechanism of indoleamine-induced encystment in dinoflagellates

Tsim, Siu-Tai

doi:10.14711/thesis-b576774

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“…Another compounding effect is species variation. C. cohnii is less responsive to indoleamines as compared to G. polyedru [Tsim et al, 1996a[Tsim et al, ,1997. Even if IP formation and Ca" influx are associated with encystment, activation of other signaling pathways may also be required.…”

Section: Discussionmentioning

confidence: 99%

Regulation of calcium influx and phospholipase C activity by indoleamines in dinoflagellate Crypthecodiniurn cohnii

Tsim

Wong

1998

Journal of Pineal Research

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Exogenous indoleamines such as melatonin and 5-methoxytryptamine have been shown to induce cyst formation (encystment) in many species of dinoflagellate. Induction of inositol phosphates formation by indoleamine has previously been demonstrated in Crypthecodinium cohnii. In addition, depletion of extracellular Ca2+ blocks the indoleamine-induced encystment. In the present study, 12 indoleamines (including melatonin and related compounds) were examined for their abilities to induce Ca2+ influx, inositol phosphates formation, and encystment in C. cohnii. The results showed that melatonin, 5-methoxytryptamine, and the peptide toxin mastoparan stimulated 45Ca2+ influxes in dose- and time-dependent manners. The EC50 values of 5-methoxytrypramine and mastoparan to stimulate 45Ca2+ uptake were 2 mM and 35 microM, respectively. The 5-methoxytryptamine- and mastoparan-induced 45Ca2+ influx were partially attenuated by the calcium channel blockers, verapamil and ruthenium red. A series of indoleamines were examined for their structure-activity relationship on the induction of encystment and formation of inositol phosphates. Melatonin-induced inositol phosphates formation was completely blocked by U73122, indicating the possible involvement of phospholipase C. Taken together, we conclude that indoleamines may induce encystment of the dinoflagellate C. cohnii via parallel activation of phospholipase C and Ca2+ influx signaling pathways. However, activation of phospholipase C and Ca2+ influx are not always necessary or sufficient for inducing encystment. Also, these data provided the first direct evidence of a Ca2+ influx regulating mechanism in dinoflagellate C. cohnii.

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Section: Discussionmentioning

confidence: 99%