Drosophila Photoreceptors and Signaling Mechanisms

The Journal of neuroscience : the official journal of the Society for Neuroscience, 2000

The Drosophila trp gene encodes a light-activated Ca(2+) channel subunit, which is a prototypical member of a novel class of channel proteins. Previously identified trp mutants are all recessive, loss-of-function mutants characterized by a transient receptor potential and the total or near-total loss of functional TRP protein. Although retinal degeneration does occur in these mutants, it is relatively mild and slow in onset. We report herein a new mutant, Trp(P365), that does not display the transient receptor potential phenotype and is characterized by a substantial level of the TRP protein and rapid, semi-dominant degeneration of photoreceptors. We show that, in spite of its unusual phenotypes, Trp(P365) is a trp allele because a Trp(P365) transgene induces the mutant phenotype in a wild-type background, and a wild-type trp transgene in a Trp(P365) background suppresses the mutant phenotype. Moreover, amino acid alterations that could cause the Trp(P365) phenotype are found in the...

Biomedical Research

In fruit fly, Drosophi/a me/anogasrer, three eye proteins are known to be phosphorylated by light stimulation (8, 9). Among them, 49K protein is most abundant. Matsumoto er af. (8, 9) suggested their possible involvement in the visual processes. In this paper, we describe its cellular localization revealed by immunohistological methods. The protein is localized in all the visual receptor cells including retinular

The Journal of general physiology, 1994

In Drosophila photoreceptors light induces phosphoinositide hydrolysis and activation of Ca(2+)-permeable plasma membrane channels, one class of which is believed to be encoded by the trp gene. We have investigated the properties of the light-sensitive channels under conditions where they are activated independently of the transduction cascade. Whole-cell voltage clamp recordings were made from photoreceptors in a preparation of dissociated Drosophila ommatidia. Within a few minutes of establishing the whole-cell configuration, there is a massive spontaneous activation of cation-permeable channels. When clamped near resting potential, this "rundown current" (RDC) accelerates over several seconds, peaks, and then relaxes to a steady-state which lasts indefinitely (many minutes). The RDC is invariably associated with a reduction in sensitivity to light by at least 100-fold. The RDC has a similar absolute magnitude, reversal potential, and voltage dependence to the light-indu...

The Journal of Neuroscience, 2017

Drosophila photoreceptors respond to oscillating light of high frequency (ϳ100 Hz), while the detected maximal frequency is modulated by the light rearing conditions, thus enabling high sensitivity to light and high temporal resolution. However, the molecular basis for this adaptive process is unclear. Here, we report that dephosphorylation of the light-activated transient receptor potential (TRP) ion channel at S936 is a fast, graded, light-dependent, and Ca 2ϩ -dependent process that is partially modulated by the rhodopsin phosphatase retinal degeneration C (RDGC). Electroretinogram measurements of the frequency response to oscillating lights in vivo revealed that darkreared flies expressing wild-type TRP exhibited a detection limit of oscillating light at relatively low frequencies, which was shifted to higher frequencies upon light adaptation. Strikingly, preventing phosphorylation of the S936-TRP site by alanine substitution in transgenic Drosophila (trp S936A ) abolished the difference in frequency response between dark-adapted and light-adapted flies, resulting in high-frequency response also in dark-adapted flies. In contrast, inserting a phosphomimetic mutation by substituting the S936-TRP site to aspartic acid (trp S936D ) set the frequency response of light-adapted flies to low frequencies typical of dark-adapted flies. Light-adapted rdgC mutant flies showed relatively high S936-TRP phosphorylation levels and light-dark phosphorylation dynamics. These findings suggest that RDGC is one but not the only phosphatase involved in pS936-TRP dephosphorylation. Together, this study indicates that TRP channel dephosphorylation is a regulatory process that affects the detection limit of oscillating light according to the light rearing condition, thus adjusting dynamic processing of visual information under varying light conditions.

Cell, 1996

During sensory transduction, Drosophila photoreceptors experience substantial increases in intracellular Ca 2 ϩ levels ([Ca 2 ϩ ] i ). Nevertheless in a number of mutants associated with excessive Ca 2 ϩ infl ux through transient receptor potential (TRP) channels, Drosophila photoreceptors undergo loss of normal cellular structure manifest as a retinal degeneration. However, the molecular mechanisms that underpin this degeneration process remain unclear. The authors previously isolated a mutant, su , that is able to suppress the retinal degeneration seen in photoreceptors from loss-of-function alleles of rdgA that are known to have constitutively active TRP channels. Here the authors report the genetic mapping of su(40) as well the isolation of additional alleles of su(40) . Studies of su(40) as well as these new alleles should facilitate the understanding of the mechanisms by which excessive Ca 2 ϩ infl ux results in retinal degeneration.

Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids, 2012

Drosophila photoreceptors are sensory neurons whose primary function is the transduction of photons into an electrical signal for forward transmission to the brain. Photoreceptors are polarized cells whose apical domain is organized into finger like projections of plasma membrane, microvilli that contain the molecular machinery required for sensory transduction. The development of this apical domain requires intense polarized membrane transport during development and it is maintained by post developmental membrane turnover. Sensory transduction in these cells involves a high rate of G-protein coupled phosphatidylinositol 4,5 bisphosphate [PI(4,5)P 2 ] hydrolysis ending with the activation of ion channels that are members of the TRP superfamily. Defects in this lipid-signaling cascade often result in retinal degeneration, which is a consequence of the loss of apical membrane homeostasis. In this review we discuss the various membrane transport challenges of photoreceptors and their regulation by ongoing lipid signaling cascades in these cells. This article is part of a Special Issue entitled Lipids and Vesicular Transport. j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / b b a l i p 50 μm thick. Thus during development, the precursor cells of the Drosophila eye undergo a substantial increase in size which requires generating new membrane [4]. Indeed during the last 30% of pupal development, photoreceptors show an approximately fourfold increase in plasma membrane surface area [6] a process that requires a massive surge in polarized membrane transport capacity starting at ca. 70% p.d (pupal development).

Journal of Physiology-Paris, 2006

Illumination of Drosophila photoreceptor cells induces multi-facet responses, which include generation of the photoreceptor potential, screening pigment migration and translocation of signaling proteins which is the focus of recent extensive research. Translocation of three signaling molecules is covered in this review: (1) Light-dependent translocation of arrestin from the cytosol to the signaling membrane, the rhabdomere, determines the lifetime of activated rhodopsin. Arrestin translocates in PIP 3 and NINAC myosin III dependent manner, and specific mutations which disrupt the interaction between arrestin and PIP 3 or NINAC also impair the light-dependant translocation of arrestin and the termination of the response to light. (2) Activation of Drosophila visual G protein, DGq, causes a massive and reversible, translocation of the α subunit from the signaling membrane to the cytosol, accompanied by activity-dependent architectural changes. Analysis of the translocation and the recovery kinetics of DGq α in wild-type flies and specific visual mutants indicated that DGq α is necessary but not sufficient for the architectural changes. (3) The TRP-like (TRPL) but not TRP channels translocate in a light-dependent manner between the rhabdomere and the cell body. As a physiological consequence of this light-dependent modulation of the TRP/TRPL ratio, the photoreceptors of dark-adapted flies operate at a wider dynamic range, which allows the photoreceptors enriched with TRPL to function better in darkness and dim background illumination. Altogether, signal-dependent movement of signaling proteins plays a major role in the maintenance and function of photoreceptor cells.

Neuron, 2000

only incompletely known. Despite differences in the Downing Street transduction cascades of vertebrates and invertebrates, Cambridge CB2 3DY mutations in homologous genes, including rhodopsin, † Department of Biochemistry arrestin, and PLC, result in degeneration in both cases Tennis Court Road (Stark et al., 1989; Dryja et al., 1990; Leonard et al., 1992; Cambridge CB2 1GA Dolph et al., 1993; Fuchs et al., 1995; Rao et al., 1995). United Kingdom Probably the most severe Drosophila retinal degener- ‡ Sechenov Institute of Evolutionary ation mutant is the retinal degeneration A (rdgA) mutant. Physiology and Biochemistry Unlike most other such mutants, degeneration in rdgA Russian Academy of Sciences is light independent and, in severe alleles, already ad-44 Prospekt Thoreza vanced at the time of eclosion (Hotta and Benzer, 1970; 194223 St. Petersburg Harris and Stark, 1977; Johnson et al., 1982; Matsumoto Russia et al., 1988). There is also virtually no response to light. The rdgA gene encodes an eye-specific diacylglycerol kinase (DGK) (Masai et al., 1993), which controls cellular Summary levels of diacylglycerol (DAG) and its metabolic fate by phosphorylating DAG to phosphatidic acid (PA) (re-

Molecular and Cellular Neuroscience, 2000

The Drosophila light-sensitive channels TRP and TRPL are prototypical members of an ion channel family responsible for a variety of receptor-mediated Ca 2؉ influx phenomena, including store-operated calcium influx. While phospholipase C␤ is essential, downstream events leading to TRP and TRPL activation remain unclear. We investigated the role of the InsP 3 receptor (InsP 3 R) by generating mosaic eyes homozygous for a deficiency of the only known InsP 3 R gene in Drosophila. Absence of gene product was confirmed by RT-PCR, Western analysis, and immunocytochemistry. Mutant photoreceptors underwent late onset retinal degeneration; however, whole-cell recordings from young flies demonstrated that phototransduction was unaffected, quantum bumps, macroscopic responses in the presence and absence of external Ca 2؉ , light adaptation, and Ca 2؉ release from internal stores all being normal. Using the specific TRP channel blocker La 3؉ we demonstrated that both TRP and TRPL channel functions were unaffected. These results indicate that InsP 3 R-mediated store depletion does not underlie TRP and TRPL activation in Drosophila photoreceptors.

Nature, 2001

The brain's capacity to analyse and interpret information is limited ultimately by the input it receives. This sets a premium on information capacity of sensory receptors, which can be maximized by optimizing sensitivity, speed and reliability of response. Nowhere is selection pressure for information capacity stronger than in the visual system, where speed and sensitivity can mean the difference between life and death. Phototransduction in flies represents the fastest G-protein-signalling cascade known. Analysis in Drosophila has revealed many of the underlying molecular strategies, leading to the discovery and characterization of signalling molecules of widespread importance.

Current Biology, 2010

Background: Phototransduction in microvillar photoreceptors is mediated via G protein-coupled phospholipase C (PLC), but how PLC activation leads to the opening of the light-sensitive TRPC channels (TRP and TRPL) remains unresolved. In Drosophila, InsP 3 appears not to be involved, and recent studies have implicated lipid products of PLC activity, e.g., diacylglycerol, its metabolites, or the reduction in PIP 2 . The fact that hydrolysis of the phosphodiester bond in PIP 2 by PLC also releases a proton is seldom recognized and has neither been measured in vivo nor implicated previously in a signaling context. Results: Following depletion of PIP 2 and other phosphoinositides by a variety of experimental manipulations, the lightsensitive channels in Drosophila photoreceptors become remarkably sensitive to rapid and reversible activation by the lipophilic protonophore 2-4 dinitrophenol in a pH-dependent manner. We further show that light induces a rapid (<10 ms) acidification originating in the microvilli, which is eliminated in mutants of PLC, and that heterologously expressed TRPL channels are activated by acidification of the cytosolic surface of inside-out patches. Conclusions: Our results indicate that a combination of phosphoinositide depletion and acidification of the membrane/ boundary layer is sufficient to activate the light-sensitive channels. Together with the demonstration of light-induced, PLCdependent acidification, this suggests that excitation in Drosophila photoreceptors may be mediated by PLC's dual action of phosphoinositide depletion and proton release.

Journal of Neurogenetics, 2010

Transient Receptor Potential (TRP) channels are polymodal cellular sensors involved in a wide variety of cellular processes, mainly by changing membrane voltage and increasing cellular Ca 2+ . This review outlines in detail the history of the founding member of the TRP family, the Drosophila TRP channel. The field began with a spontaneous mutation in the trp gene that led to a blind mutant during prolonged intense light. It was this mutant that allowed for the discovery of the first TRP channels. A combination of electrophysiological, biochemical, Ca 2+ measurements, and genetic studies in flies and in other invertebrates pointed to TRP as a novel phosphoinositideregulated, and Ca 2+ permeable channel. The cloning and sequencing of the trp gene provided its molecular identity. These seminal findings led to the isolation of the first mammalian homologues of the Drosophila TRP channels. We now know that TRP channel proteins are conserved through evolution and are found in most organisms, tissues, and cell-types. The TRP channel superfamily is classified into seven related subfamilies: TRPC, TRPM, TRPV, TRPA, TRPP, TRPML and TRPN. A great deal is known today about participation of TRP channels in many biological processes including initiation of pain, thermoregulation, salivary fluid secretion, inflammation, cardiovascular regulation, smooth muscle tone, pressure regulation, Ca 2+ and Mg 2+ homeostasis and lysosomal function. The native Drosophila photoreceptor cells, where the founding member of the TRP channels superfamily was found is still a useful preparation to study basic features of this remarkable channel.

Cell Calcium, 2004

The Transient Receptor Potential (TRP) proteins constitute a large and diverse family of channel proteins, which is conserved through evolution. TRP channel proteins have critical functions in many tissues and cell types, but their gating mechanism is an enigma. In the present study patch-clamp whole-cell recordings was applied to measure the TRP-and TRP-like (TRPL)-dependent currents in isolated Drosophila ommatidia. Also, voltage responses to light and to metabolic stress were recorded from the eye in vivo. We report new insight into the gating of the Drosophila light-sensitive TRP and TRPL channels, by which both Ca 2+ and protein dephosphorylation are required for channel activation. ATP depletion or inhibition of protein kinase C activated the TRP channels, while photo-release of caged ATP or application of phorbol ester antagonized channels openings in the dark. Furthermore, Mg 2+ -dependent stable phosphorylation event by ATP␥S or protein phosphatase inhibition by calyculin A abolished activation of the TRP and TRPL channels. While a high reduction of cellular Ca 2+ abolished channel activation, subsequent application of Ca 2+ combined with ATP depletion induced a robust dark current that was reminiscent of light responses. The results suggest that the combined action of Ca 2+ and protein dephosphorylation activate the TRP and TRPL channels, while protein phosphorylation by PKC antagonized channels openings.

Biomolecules, 2022

Transient Receptor Potential (TRP) channels constitute a large superfamily of polymodal channel proteins with diverse roles in many physiological and sensory systems that function both as ionotropic and metabotropic receptors. From the early days of TRP channel discovery, membrane lipids were suggested to play a fundamental role in channel activation and regulation. A prominent example is the Drosophila TRP and TRP-like (TRPL) channels, which are predominantly expressed in the visual system of Drosophila. Light activation of the TRP and TRPL channels, the founding members of the TRP channel superfamily, requires activation of phospholipase Cβ (PLC), which hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) into Diacylglycerol (DAG) and Inositol 1, 4,5-trisphosphate (IP3). However, the events required for channel gating downstream of PLC activation are still under debate and led to several hypotheses regarding the mechanisms by which lipids gate the channels. Despite many efforts...