UC San Diego

Dinoflagellate bioluminescence represents a dramatic response to mechanical stress found in nature. The cellular mechanisms that govern this pathway, however, are not completely understood. The objective of this thesis is to build and expand from previous studies to explore the mechanosensitive properties of dinoflagellate bioluminescence. Chapter I tests the hypothesis that the signaling pathway involves a stretch-activated component. Chapter I uses two separate, measurable types of bioluminescence in the dinoflagellate Lingulodinium polyedrum - mechanically-stimulated and spontaneous - as reporter systems for pharmacological experiments that target specific areas of the pathway. Inhibition of both types of bioluminescence by the non-specific stretch- activated channel inhibitor gadolinium III and activation of bioluminescence by the membrane fluidizier benzyl alcohol suggest that a stretch-activated ion channel, in addition to a voltage-sensitive element, is involved in regulating dinoflagellate bioluminescence. Chapter II seeks to further characterize this stretch-activated ion channel, starting with a bioinformatic search of any existing dinoflagellates expressed sequence tags (ESTs) that represent mechanosensitive ion channels. This search resulted in partial sequences of a piezo-like mechanosensitive protein from Karenia brevis and a partial TRP-like channel from Symbiodinium sp. Furthermore, inhibition of bioluminescence and hypoosmotic cell- swelling by a TRP channel inhibitor, and activation of bioluminescence by a TRP channel activator, suggesting a role for TRP-like channels in the dinoflagellate bioluminescence signaling pathway. Based on these and previous studies, there are similar aspects of mechanosensory signaling seen between dinoflagellate bioluminescence and higher level eukaryotic mechanosensitive pathways, suggesting some level of conservation of mechanosensing proteins through eukaryotic evolution