title: Subcellular translocation of the eGFP-tagged TRPL channel in Drosophila photoreceptors requires activation of the phototransduction cascade.
abstract: Signal-mediated translocation of transient receptor potential (TRP) channels is a novel mechanism to fine tune a variety of signaling pathways including neuronal path finding and Drosophila photoreception. In Drosophila phototransduction the cation channels TRP and TRP-like (TRPL) are the targets of a prototypical G protein-coupled signaling pathway. We have recently found that the TRPL channel translocates between the rhabdomere and the cell body in a light-dependent manner. This translocation modifies the ion channel composition of the signaling membrane and induces long-term adaptation. However, the molecular mechanism underlying TRPL translocation remains unclear. Here we report that eGFP-tagged TRPL expressed in the photoreceptor cells formed functional ion channels with properties of the native channels, whereas TRPL-eGFP translocation could be directly visualized in intact eyes. TRPL-eGFP failed to translocate to the cell body in flies carrying severe mutations in essential phototransduction proteins, including rhodopsin, Galphaq, phospholipase Cbeta and the TRP ion channel, or in proteins required for TRP function. Our data, furthermore, show that the activation of a small fraction of rhodopsin and of residual amounts of the Gq protein is sufficient to trigger TRPL-eGFP internalization. In addition, we found that endocytosis of TRPL-eGFP occurs independently of dynamin, whereas a mutation of the unconventional myosin III, NINAC, hinders complete translocation of TRPL-eGFP to the cell body. Altogether, this study revealed that activation of the phototransduction cascade is mandatory for TRPL internalization, suggesting a critical role for the light induced conductance increase and the ensuing Ca2+ -influx in the translocation process. The critical role of Ca2+ influx was directly demonstrated when the light-induced TRPL-eGFP translocation was blocked by removing extracellular Ca2+.
authors.affiliation: Department of Biosensorics, Institute of Physiology, University of Hohenheim, 70599 Stuttgart, Germany.
authors.forename: Nina E
authors.initials: NE
authors.lastname: Meyer
authors.forename: Tamar
authors.initials: T
authors.lastname: Joel-Almagor
authors.forename: Shahar
authors.initials: S
authors.lastname: Frechter
authors.forename: Baruch
authors.initials: B
authors.lastname: Minke
authors.forename: Armin
authors.initials: A
authors.lastname: Huber
mesh_terms: D000818:Animals; D019390:Arrestins / Q000096:biosynthesis / Q000502:physiology; D002118:Calcium / Q000378:metabolism / Q000528:radiation effects; D029721:Drosophila Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000528:radiation effects; D004331:Drosophila melanogaster / Q000378:metabolism* / Q000528:radiation effects; D049452:Green Fluorescent Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000528:radiation effects; D008027:Light; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology* / Q000528:radiation effects; D021381:Protein Transport / Q000502:physiology / Q000528:radiation effects; D012243:Rhodopsin / Q000502:physiology; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D050051:Transient Receptor Potential Channels / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000528:radiation effects; D014785:Vision, Ocular / Q000502:physiology* / Q000528:radiation effects
chemical_list: D019390:Arrestins; D029721:Drosophila Proteins; D050051:Transient Receptor Potential Channels; C485184:enhanced green fluorescent protein; C074192:trpl protein, Drosophila; D049452:Green Fluorescent Proteins; D012243:Rhodopsin; D002118:Calcium