Role of TRP Channels in Dinoflagellate Mechanotransduction

Abstract

Transient receptor potential (TRP) ion channels are common components of mechanosensing pathways, mainly described in mammals and other multicellular organisms. To gain insight into the evolutionary origins of eukaryotic mechanosensory proteins, we investigated the involvement of TRP channels in mechanosensing in a unicellular eukaryotic protist, the dinoflagellate Lingulodinium polyedra. BLASTP analysis of the protein sequences predicted from the L. polyedra transcriptome revealed six sequences with high similarity to human TRPM2, TRPM8, TRPML2, TRPP1, and TRPP2; and characteristic TRP domains were identified in all sequences. In a phylogenetic tree including all mammalian TRP subfamilies and TRP channel sequences from unicellular and multicellular organisms, the L. polyedra sequences grouped with the TRPM, TPPML, and TRPP clades. In pharmacological experiments, we used the intrinsic bioluminescence of L. polyedra as a reporter of mechanoresponsivity. Capsaicin and RN1734, agonists of mammalian TRPV, and arachidonic acid, an agonist of mammalian TRPV, TRPA, TRPM, and Drosophila TRP, all stimulated bioluminescence in L. polyedra. Mechanical stimulation of bioluminescence, but not capsaicin-stimulated bioluminescence, was inhibited by gadolinium (Gd), a general inhibitor of mechanosensitive ion channels, and the phospholipase C (PLC) inhibitor U73122. These pharmacological results are consistent with the involvement of TRP-like channels in mechanosensing by L. polyedra. The TRP channels do not appear to be mechanoreceptors but rather are components of the mechanotransduction signaling pathway and may be activated via a PLC-dependent mechanism. The presence and function of TRP channels in a dinoflagellate emphasize the evolutionary conservation of both the channel structures and their functions.

Evolutionary Aspects of TRPMLs and TPCs

“…Only TRPP and TRPML have been reported for euglenozoans, Leishmania (e.g., Leishmania major) and Trypanosoma and the alveolate protist Paramecium tetraurelia, which evolved around 700 million years ago. In another unicellular eukaryotic protist Lingulodinium polyedra TRPMs, TPPMLs and TRPPs have been identified [2,12,54]. In conclusion, TRPML, alongside TRPP, TRPV, and TRPM, seems to have been present in a common ancestor of Unikonts and Bikonts.…”

“…Numbers of TRP, TRPML, and TPC proteins of selected species of the Metazoa, Fungi, and Viridiplantae as well as selected ancestral species. The tree was constructed based on information included in the following resources[2,12,48,[50][51][52][53][54][55][56][57][58][59][60][61], and constructed manually based on this information. Branch color coding of the tree indicates a first (orange), second (bright green), and third (blue) gene duplication of TPRML.…”

Responses to transient receptor potential (TRP) channel agonists inChlamydomonas reinhardtii

“…The responses to capsaicin in protists are still poorly understood. To the best of our knowledge, there is only one report describing bioluminescence stimulation by capsaicin in the dinoflagellate Lingulodinium polyedra ( Lindström et al, 2017 ). Uncovering protist responses to pungent substances and identifying their receptors would promote our understanding of TRP channel evolution and its role in sensing pungent substances.…”

The Making of Infinity Cube, a Bioluminescence Art Exhibit

“…My own research over the past 35 yr has investigated the level of mechanical forces that stimulate bioluminescence, first using populations of cells experiencing fully characterized flow fields, and more recently by studying the mechanosensitivity of individual cells using microfluidics and atomic force microscopy (Latz et al ; Tesson and Latz ). In our investigation of the bioluminescence mechanotransduction signaling pathway, we have identified signaling proteins that have been conserved in the force sensing pathways of higher organisms including humans (Lindström et al ). So in a sense, we have a connection to dinoflagellates, whose bioluminescence can provide insights into the origins of mechanical sensing in eukaryotes.…”