Cellular growth can be regulated through a number of pathways. The second messenger cyclic AMP is a key regulator of growth in many cells. Previous studies have demonstrated that CAMP could reverse the growth inhibition of indoleamines in the dinoflagellate Crypthecodinium cohnii....[ Read more ]

Cellular growth can be regulated through a number of pathways. The second messenger cyclic AMP is a key regulator of growth in many cells. Previous studies have demonstrated that CAMP could reverse the growth inhibition of indoleamines in the dinoflagellate Crypthecodinium cohnii.

The purpose of this study is to investigate the possible role of CAMP in the growth and cell cycle progression of C.cohnii. Indoleamines were reported to inhibit cell growth in dinoflagellates. Our lab also isolated a mutant mtrl, that was indoleamine resistant in C.cohnii. The growth, cell cycle progression and the levels of CAMP in this mutant were studied. The mutant was demonstrated to be non-responsive to CAMP-stimulated growth. Synchronous populations were used and cell cycle progression was analyzed by flow cytometry. The internal cAMP levels were measured by competitive binding assay.

It was observed that Bt₂-cAMP directly stimulates the growth of C.cohnii and promotes early entry to the next cell cycle. Moreover, the intracellular cAMP levels vary during the cell cycle. In normal C.cohnii, the intracellular cAMP levels peak during the G_l phase. This is the first measurement of intracellular cAMP levels in dinoflagellates. Mutant mtrl cells have higher intracellular cAMP levels than normal cells. The intracellular cAMP levels were observed to increase in the presence of Bt₂-cAMP, while they decreased in the presence of 5-methoxytryptamine. Variation of cAMP-dependent protein kinase activities was observed throughout the cell cycle. 5-methoxytryptamine was shown not only to inhibit cell proliferation but also to arrest cells at G1G0 phase of cell cycle. This may reflect the fact that more than one pathways are involved in the regulation of growth and cell cycle progression of the dinoflagellate C.cohnii.