Brefeldin A disturbs Golgi complex integrity but does not impair ecdysis in the dinoflagellates Prorocentrum cordatum

Summary The marine planktonic dinoflagellate Prorocentrum cordatum (syn. Prorocentrum minimum ) is a thecate species capable of ecdysis, i.e. rearrangement of the cell covering in response to different stressors. During the process of ecdysis, P. cordatum cells shed the plasma membrane and outer amphiesmal vesicle membrane, and become immotile, covered only by thecal plates and the new plasma membrane. At this stage, the cells can be considered as thecal cysts. Then, they complete ecdysis by leaving the old thecal plates and restoring motility, i.e. excyst. To elucidate the role of vesicular transport in the cell covering rearrangement, we tested the effect of brefeldin A, the inhibitor of vesicular transport from the endoplasmic reticulum to the Golgi complex widely used in cell biology, on the cellular structure of P. cordatum and its ability to ecdyse. We found out that brefeldin A blocked vesicular trafficking from the endoplasmic reticulum to the Golgi complex, since we observed disassembly of the Golgi complex in cells treated by brefeldin A at 0.1 µg/ml for 1 h. Moreover, such a treatment did not increase mortality in P. cordatum culture at the time scale of 6 h. Nevertheless, our experiments demonstrated that brefeldin A affected neither shedding of outer membranes nor discarding of thecal plates during the stressor-induced ecdysis. Based on our findings, we conclude that vesicle trafficking from the endoplasmic reticulum to the Golgi complex and further to the plasma membrane is not essential to the process of membrane and theca shedding. However, this route still can be involved in the process of new amphiesma’ maturation, which is discussed in this work.