Recent studies suggest that the fly uses the inositol lipid signaling system for visual excitation and that the Drosophila transient receptor potential (trp) mutation disrupts this process subsequent to the production of IP3. trp is shown to encode a novel 1275 amino acid protein with eight putative transmembrane segments. Immunolocalization indicates that the Trp protein is expressed predominantly in the rhabdomeric membranes of the photoreceptor cells (Montell, 1989).
Invertebrate phototransduction is an important model system for studying the ubiquitous inositol-lipid signaling system. In the transient receptor potential (trp) mutant, one of the most intensively studied transduction mutants of Drosophila, the light response quickly declines to baseline during prolonged intense light. Using whole-cell recordings from Drosophila photoreceptors, the wild-type response is shown to be mediated by at least two functionally distinct classes of light-sensitive channels and both the trp mutation and a Ca2+ channel blocker (La3+) selectively abolish one class of channel with high Ca2+ permeability. Evidence is also presented that Ca2+ is necessary for excitation and that Ca2+ depletion mimics the trp phenotype. It is concluded that the recently sequenced Trp protein represents a class of light-sensitive channels required for inositide-mediated Ca2+ entry, and it is suggested that this process is necessary for maintained excitation during intense illumination in fly photoreceptors (Hardie, 1992).
Phototransduction in Drosophila is mediated by the ubiquitous phosphoinositide cascade, leading to opening of the TRP and TRPL channels, which are prototypical members of a novel class of membrane proteins. Drosophila mutants lacking the TRP protein display a response to light that declines to the dark level during illumination. It has recently been suggested that this response inactivation results from a negative feedback by calcium-calmodulin, leading to closure of the TRPL channels. It is also suggested that in contrast to other phosphoinositide-mediated systems, Ca2+ release from internal stores is neither involved in channel activation nor in phototransduction in general. This study shows that inactivation of the light response in Trp photoreceptors is enhanced upon reduction of the intracellular Ca2+ concentration. Furthermore, in Ca(2+)-free medium, when there is no Ca2+ influx into the photoreceptors, a significant elevation of intracellular Ca2+ is seen upon illumination. This elevation correlates with ability of the cells to respond to light. Accordingly, malfunctioning of Ca2+ stores, either by Ca2+ deprivation or by application of the Ca2+ pump inhibitor, thapsigargin, confers a trp phenotype on wild type flies. The results indicate that the response inactivation in trp cells results from Ca2+ deficiency rather than from Ca(2+)-dependent negative feedback. The results also indicate that there is light-induced release of Ca2+ from intracellular stores. Furthermore, the response to light is correlated to Ca2+ release, and normal function of the stores is required for prolonged excitation. It is suggested that phototransduction in Drosophila depends on Ca(2+)-release mediated signalling and that TRP is essential for the normal function of this process (Cook, 1999).
The Drosophila trp gene encodes a light-activated Ca(2+) channel subunit that 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. A new mutant, Trp(P365), is described 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. 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 transmembrane segment region of the mutant channel protein. Whole-cell recordings clarified the mechanism underlying the retinal degeneration by showing that the TRP channels of Trp(P365) are constitutively active. Although several genes, when mutated, have been shown to cause retinal degeneration in Drosophila, the underlying mechanism has not been identified for any of them. The present studies provide evidence for a specific mechanism for massive degeneration of photoreceptors in Drosophila. Insofar as some human homologs of TRP are highly expressed in the brain, a similar mechanism could be a major contributor to degenerative disorders of the brain (Yoon, 2000).
The trp gene encodes subunits of a highly Ca(2+)-permeable class of light-activated channels of Drosophila photoreceptors. The recently characterized mutation in this gene, Trp(P365), is semidominant and causes massive degeneration of photoreceptors by making the TRP channel constitutively active. A single amino acid change, Phe-550 to Ile, near the beginning of the fifth transmembrane domain of TRP channel subunits is necessary to induce, and sufficient to closely mimic, the original mutant phenotypes of Trp(P365). Hypotheses are presented as to why the amino acid residues at position 550 and its immediate vicinity might be important in influencing the regulation of the TRP channel and why the substitution of Phe for Ile at this position, in particular, could result in constitutive activity of the channel. The following are some tentative conclusions from this study: (1) Trp(P365) is important for the regulation of TRP channel opening; (2) The particular amino acid residue preferred for this position appears to be different for different species (Phe for Drosophila and Leu for mammals) perhaps because of slightly different channel environments; (3) Ile appears to be particularly poorly tolerated at this position. It is concluded that the residues at positions 550 or in its immediate vicinity may be in a position to critically affect channel gating (Hong, 2002).
To identify new alleles of the trp locus, a screen was performed for the recently isolated collection of chemically induced third chromosome mutations, which display defects in the electroretinogram (ERG) recording (for details see T. Wang, 2005a). Exposure of wild-type flies to light results in two discriminable components in the ERG. These include a sustained corneal negative maintained component arising from responses of all retinal cells (photoreceptor cells and pigment cells) and on- and off-transients emanating from activity in the second-order neurons in the optic lobes. The classic trp phenotype is characterized by a transient response to light, resulting from rapid light-dependent inactivation of the remaining Trpl cation channel (T. Wang, 2005b).
Each of the third chromosome mutations was crossed to the strong trpP343 allele and five were identified that failed to complement the recessive Trp phenotype: therefore, they represented new trp alleles. Four of the new trp alleles exhibited a transient ERG phenotype indistinguishable from trpP343, whereas the phenotype of the fifth (trp14) was distinct in that the decline in the light response was much slower than in trpP343 or other alleles isolated in this or previous studies. The trp14 phenotype was due to an autonomous defect in the photoreceptor cells, rather than the pigment cells, since the slower decline in the receptor potential was evident in single photoreceptor cells assayed by performing intracellular recordings (T. Wang, 2005b).
Currently, all of the existing loss-of-function mutations cause large reductions in protein levels, although the molecular lesions have not been defined. Among the extant trp alleles, the one with the strongest phenotype is trpP343. The trpP343 genomic region was sequenced and it was found that the Trp protein coding region was identical to wild type. Rather, there was a mutation in a conserved 5' splice site that was essential for mRNA splicing. The mutation presumably results in instability of the mRNA, since no trpP343 mRNA is detected (Montell, 1989). Given the strong phenotype and lack of mRNA or Trp protein expressed in trpP343 (Montell, 1989), this allele would appear to represent a null (T. Wang, 2005b).
To examine the levels of Trp protein expressed in the new alleles described in this study, Western blots were performed. Among those alleles that displayed a phenotype typical of trpP343, three did not express any detectable Trp protein (trp38, trp74, and trp92), whereas a fourth expressed very low levels of Trp (trp47). This was in contrast to trp14 flies in which Trp was expressed at ~60% the level as in wild type. Other rhabdomeral proteins including INAD, INAC, NORPA, and Rh1 (rhodopsin 1) were expressed at comparable levels in trp14, trpP343, and wild-type flies (T. Wang, 2005b).
To determine the molecular defects associated with the five new trp alleles, the genomic DNA was sequenced and the sequences were compared to that of the original isogenized stock used to conduct the mutagenesis. Among the four alleles that expressed very low or no detectable Trp, one had a frameshift mutation resulting in premature translation termination (trp92), two had missense mutations (trp47 and trp74), and one had no mutation in the transcribed region and therefore may contain a mutation affecting the trp promoter. The allele (trp14) expressing Trp at 60% wild-type levels, and which exhibited a phenotype distinct from other trp alleles, had two missense mutations. One of these mutations changed an amino acid in the pore loop between transmembrane domains five and six (residue 612; leucine to phenylalanine), whereas the other was situated between the sixth transmembrane segment and a highly conserved sequence referred to as Trp box 1 (residue 671; arginine to glutamine) (T. Wang, 2005b).
Given that Trp has dual functions as a molecular anchor and as a cation channel (Li, 2000; Tsunoda, 2001), whether the Trp phenotype in trp14 was a consequence of perturbation of the anchoring role was considered. Drosophila compound eyes consist of ~800 repetitive units, referred to as ommatidia, each of which includes six outer photoreceptor cells (R1-6) and a central R7 or R8 cell in the distal region of the retina. Each photoreceptor cell contains a microvillar segment, the rhabdomere, where most of the proteins that function in phototransduction, such as the core members of the signalplex, are concentrated. These include Trp, protein kinase C (INAC), phospholipase C (NORPA), and INAD. Mutations that eliminate or disrupt the anchoring role of Trp result in mislocalization of these core members such that they are present in both the rhabdomeres and cell bodies (Chevesich, 1997; Tsunoda, 1997; Li, 2000; Tsunoda, 2001). However, other INAD binding partners, such as Rh1, do not depend on Trp for normal localization (Li, 2000). In trp14 photoreceptor cells, each of the core and other rhabdomeral proteins examined displayed a rhabdomere localization pattern indistinguishable from wild type. Consistent with these data, it was found that INAD coimmunoprecipitated effectively with the Trp14 protein. These data indicate that the Trp phenotype in trp14 flies is not due to an alteration in the Trp anchoring function. Rather, they raise the possibility that the phenotype is due to a defect in Trp channel function (T. Wang, 2005b).
In trp flies such as trpP343 the transient potential ERG phenotype is a consequence of inactivation of the Trpl channel during constant light stimulation. However, in Trpl mutant flies, which express Trp but not Trpl, the ERG response is maintained during a typical 5-10-s light pulse. To examine Trp14 channel function independent of Trpl, the trp14 allele was introduced into a Trpl-null mutant (Trpl302) background. As previously shown, Trpl302;trpP343 flies are blind, since they do not express Trpl or Trp (Niemeyer, 1996; Reuss, 1997). Flies harboring just the Trpl302 mutation show a response to 10 s of light similar to wild type, because these flies express wild-type Trp. In contrast, Trpl302;trp14 flies displayed a Trp phenotype similar to trp14. These data indicate that the transient light response in trp14 flies is due to disruption of Trp channel function (T. Wang, 2005b).
To exclude the possibility that the trp14 phenotype is a consequence of mislocalization of Trp14, the mutant protein was spatially localized. Immunostaining experiments were performed and it was found that Trp14 was detected exclusively in the rhabdomeres, as is the case for wild-type Trp. Therefore, the transient light response in trp14 is not due to mislocalization of the Trp protein (T. Wang, 2005b).
Given that trp14 flies express a 40% lower concentration of Trp, whether a transient light response could be induced by expression of low levels of Trp was tested. Therefore, transgenic flies that expressed varying levels of wild-type Trp under the control of the heat-shock promoter (hs-trp) were generated and the transgene was placed in a Trpl302;trpP343 genetic background. Even though use of the heat shock protein 70 (hsp70) promoter typically results in widespread expression, the Trp protein expressed under the control of the hsp70 promoter was found exclusively in the retina and not in the optic lobes or elsewhere in the adult head. To induce different low levels of Trp, the hs-trp flies were exposed to 30, 60, and 120 min heat-shock treatments, which resulted in the production of ~4%, 7%, and 10% of the wild-type levels of Trp, respectively. Expression of only ~10% the normal concentration of Trp restored an ERG in Trpl302;trpP343 flies, which was not transient. Even 4% the normal levels of Trp did not cause a transient light response similar to trp14, although the amplitude of the ERG was reduced. These data indicate that the trp14 mutant phenotype was due to the mutation of the Trp14 protein, rather than simply due to expression of low levels or mislocalized Trp protein (T. Wang, 2005b).
Strong loss-of-function mutations in trp, such as in trpP343, result in light dependent retinal degeneration. Considering Trp has dual channel and nonchannel roles, disruption of either function could potentially cause retinal degeneration. To address which of these two roles is more critical to prevent retinal cell death, the morphology was examined of trpDelta1272 (Li, 2000: and trp14 ommatidia, which display specific defects in the scaffold and Trp channel functions, respectively. Wild-type ommatidia contain eight photoreceptor cell rhabdomeres, seven of which are present in any given plane regardless of their age or whether the flies were maintained in the dark or under a light-dark cycle (T. Wang, 2005b).
The retinal degeneration in trp14 and trpP343 was much more severe than that in trpDelta1272 flies. In both trpP343 and trp14 flies, the rhabdomeres began to disappear between 7 and 10 d after eclosion and almost no rhabdomeres remained after 14 d of exposure to a 12-h light-12-h dark cycle. By contrast most trpDelta1272 flies maintain a full complement of seven rhabdomeres after 14 d of a light-dark cycle. Nevertheless, the size of the rhabdomeres was typically smaller than in similarly aged wild-type and large intracellular vacuoles were present inside the cell bodies indicating that retinal degeneration had initiated. By 30 d after eclosion, most of the rhabdomeres in these flies had degenerated. Thus, the retinal degeneration is much more severe in trpP343 and trp14 than trpDelta1272, indicating that the Trp channel function rather than the scaffold function is more critical to prevent the retinal cell death (T. Wang, 2005b).
The retinal degeneration resulting from defects in Trp function was suppressed by maintaining the flies in the dark; this keeps the Trp channels in an inactive state. To assess the extent of suppression, the flies were maintained in the dark for 30 d, which was more than twice as long the 14-d light-dark cycle that caused elimination of almost all rhabdomeres in trp14 or trpP343 flies. In dark-maintained trpDelta1272 flies, seven rhabdomeres were present in ommatidia, although the size of the rhabdomeres was reduced. Indistinguishable results were obtained with trpP343. The suppression of retinal degeneration was even more complete with trp14, as all ommatidia contained a full set of seven rhabdomeres of normal size. This result was striking since the retinal degeneration occurring under a light-dark cycle is significantly more rapid in trp14 than in trpDelta1272 (T. Wang, 2005b).
To explore the mechanism underlying the retinal degeneration in trp mutants, a genetic approach was used. The combination of results described above indicates that a defect in Trp channel function underlies the retinal degeneration in trp flies. If the basis of the retinal degeneration in the trp mutant was due to diminished Ca2+ influx during light stimulation, then the cell death might be reduced by mutations in the Na+/Ca2+ exchanger, CalX, which functions in Ca2+ extrusion in photoreceptor cells (T. Wang, 2005b).
To test whether calx can suppress the retinal degeneration in trpP343 and trp14, the morphology of calxB,trpP343, and calxB,trp14 compound eyes was examined. trp14 or trpP343 flies maintained under a light-dark cycle for 14 d displayed nearly complete loss of the rhabdomeres. The retinal degeneration in calxB flies was even more severe; there were few rhabdomeres left after a 7 d light-dark cycle and almost no rhabdomeres left after a 14-d light-dark cycle. In contrast, most ommatidia from either calxB,trpP343 or calxB,trp14 double mutant flies contained all the rhabdomeres after 14 d under a light-dark cycle. Moreover, the core signalplex proteins, NORPA, INAC, and INAD were mislocalized in calxB,trpP343 flies, indicating that introducing the calx mutation does not prevent loss of the Trp scaffold function in trpP343. The effect of calx on trp was specific because the calxB mutation did not suppress the cell death resulting from mutations in other phototransduction genes such as inaC, which encodes an eye-enriched PKC. These results indicated that the retinal degeneration in trp14 or trpP343 is a consequence of decreased intracellular Ca2+ levels, whereas the photoreceptor cell death in the calx mutant results from Ca2+ overload (T. Wang, 2005b).
To explore further the mechanism of the retinal degeneration in trp14 and trpP343, tests were made to see whether it could be suppressed by mutations in the gene encoding the major arrestin (arrestin2 -- arr2). Elimination of Arr2 reduces the retinal degeneration associated with certain mutations, such as norpA (disrupts phospholipase C), which prevents light-dependent activation of Trp channels. The retinal degeneration in norpA results from formation of stable rhodopsin-arrestin complexes and subsequent endocytosis of rhodopsin (T. Wang, 2005b). It was found that strong mutations in arr2 partially suppress the retinal degeneration in trp14 and trpP343 flies. Whereas a 14-d exposure to a light-dark cycle results in extensive loss of rhabdomeres in arr25,trpP343 or trp14 eyes, most ommatidia in arr25,trpP343 or arr25,trp14 double mutants contained seven rhabdomeres. However, the sizes of the rhabdomeres were significantly reduced (T. Wang, 2005b).
The two mutations in trp14 alter residues in the pore loop or immediately NH2 terminal to Trp box 1 (residues 612 and 671, respectively). Given the potential effects of a pore-loop mutation on ion selectivity and the highly conserved nature of the region between the sixth transmembrane segment (TM6) and the Trp domain (Montell, 2005b), both of these mutations were in intriguing positions that could potentially be responsible for the trp14 phenotype (T. Wang, 2005b).
To determine whether one or both mutations were responsible for the transient light response phenotype in trp14, transgenic flies expressing Trp isoforms with just the L612F or R671Q amino acid substitution (trp612F and trp671Q, respectively) were generated and tested. The wild-type or mutant trp cDNAs were fused to the ninaE (neither inactivation nor afterpotential E [encodes Rh1]) promoter and introduced into the Trpl302;trpP343 double mutant background. Subsequently Western blots were performed on the transgenic flies demonstrating that wild-type Trp, Trp612F, and Trp671Q were all expressed at similar levels (T. Wang, 2005b).
It was found that the missense mutation juxtaposed to the Trp domain was responsible for the phenotype in trp14. The Trpl;ninaE-trp612F,trpP343 flies displayed a wild-type ERG response indistinguishable from Trpl;ninaE-trpwt,trpP343. Conversely, the Trpl;ninaE-trp671Q,trpP343 flies showed a transient ERG phenotype. Moreover, the trp671Q flies exhibited an ERG phenotype with a more rapid decline typical of trpP343, suggesting that the 612F mutation resulted in a slight suppression of the Trp phenotype. These data demonstrate that the missense mutation at residue 671 situated between the sixth transmembrane domain and Trp box 1 (Montell, 2005b) was the key mutation responsible for the trp14 phenotype (T. Wang, 2005b).
The residues in Trpl and Trpgamma, corresponding to the required arginine 671 in Trp, are also basic amino acids (histidine 678 and arginine 662, respectively) suggesting that a basic residue at this position flanking the Trp domain is essential in the Drosophila TrpC channels. Therefore, transgenic flies were generated expressing derivatives of Trpl in which histidine 678 was replaced either with a conservative arginine substitution (Trpl678R) or with an uncharged glutamine (Trpl678Q). The mutant and wild-type Trpl cDNAs were fused to the ninaE promoter and introduced into a Trpl302;trpP343 background. The transgenic Trpl proteins were all expressed at similar levels, though at an approximate sevenfold higher level than in wild-type due to the strong ninaE promoter (T. Wang, 2005b).
To determine the consequences of the mutations in Trpl, ERGs were performed after introducing the transgenes in a Trpl302;trpP343 background. Whereas the double Trpl302;trpP343 mutant was blind, overexpression of the wild-type Trpl in this genetic background (Trplwt) restored a transient response to light indistinguishable from trpP343. Furthermore, introduction of the Trpl678R transgene into the genome of Trpl302;trpP343 flies resulted in an ERG response similar to Trplwt. Thus, replacing histidine 678 with an arginine did not disrupt Trpl function. However, the amplitude of the ERG was significantly reduced in Trpl302;trpP343 flies expressing the Trpl678Q transgene with the histidine to glutamine substitution in residue 678. The combination of these results demonstrates a critical role of a basic residue at the corresponding positions in Trp and Trpl, flanking the highly conserved Trp box 1 (T. Wang, 2005b).
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. 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. This study reports that eGFP-tagged TRPL expressed in the photoreceptor cells formed functional ion channels with properties of the native channels, allowing TRPL-eGFP translocation to 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, Gαq, phospholipase Cß and the TRP ion channel, or in proteins required for TRP function. These 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, it was 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+ (Meyer, 2006; full text of article).
Besides TRPL, at least two other proteins mediating Drosophila phototransduction, Arrestin 2 and the visual Gαq, undergo light-dependent translocation between the rhabdomere and the cell body. Likewise, in vertebrate photoreceptors arrestin and the visual G protein transducin translocate between the inner and outer segment in a light-dependent way. In both visual systems, arrestin and G protein movements occur in opposite directions, that is, in the light arrestin accumulates whereas the G protein is depleted in the photoreceptive membrane and vice versa in the dark. Accordingly, these light-dependent relocations of visual signaling proteins make the photoreceptor more sensitive in the dark and less sensitive in the light and mediate long-term adaptation of the Drosophila and vertebrate visual systems. A third protein that translocates in vertebrate photoreceptors is the Ca2+ binding protein recoverin (Meyer, 2006).
The mechanisms underlying these protein translocations have been elucidated in part for Drosophila arrestin, the Gαq subunit and for vertebrate transducin. Translocation of Drosophila arrestin from the cell body to the rhabdomere has been reported to require the ninaC-encoded myosin III which may actively transport arrestin along the actin cytoskeleton of the photoreceptor microvilli through PIP3-enriched vesicles, to which arrestin binds. However, the requirement of the myosin III NINAC for arrestin translocation has been challenged in a more recent publication. Removal of arrestin from the rhabdomeral membranes in the dark does not require cytoskeletal elements and may thus occur passively. Likewise, Gαq translocation into the rhabdomere, but not its removal, is facilitated by the myosin III NINAC. Translocation of vertebrate transducin is aided by phosducin, an abundant photoreceptor-specific protein that binds to the ßγ subunits of transducin. Phosducin increases the solubility of the G protein subunits and may thereby facilitate transducin translocation (Meyer, 2006).
These mechanisms are markedly different from the mechanism underlying TRPL translocation because TRPL is a transmembrane protein that cannot enter the soluble fraction and needs to be removed from the rhabdomere by an endocytotic pathway, whereas arrestin and the visual G protein change from a membrane attached state to a soluble state. Therefore, elucidating the triggering mechanism of TRPL translocation reported in the present study is the first step for unraveling the mechanism underlying an important cellular process (Meyer, 2006).
Reference names in red indicate recommended papers.
Aarts, M., et al. (2003). A key role for TRPM7 channels in anoxic neuronal death. Cell 115: 863-877. 14697204
Agam, K., et al. (2000). Metabolic stress reversibly activates the Drosophila light-sensitive channels TRP and TRPL in vivo. J. Neurosci. 20: 5748-5755. 14697204
Bandyopadhyay, B. C. and Payne, R. (2004). Variants of TRP ion channel mRNA present in horseshoe crab ventral eye and brain. J. Neurochem. 91(4): 825-35. 15525336
Bandyopadhyay, B. C., et al. (2005). Apical localization of a functional TRPC3/TRPC6-Ca2+-signaling complex in polarized epithelial cells. Role in apical Ca2+ influx. J. Biol. Chem. 280(13): 12908-16. 15623527
Bähner, M., et al. (2002). Light-regulated subcellular translocation of Drosophila Trpl channels induces long-term adaptation and modifies the light-induced current. Neuron 34: 83-93. 11931743
Chevesich, J., Kreuz, A. J. and Montell, C. (1997). Requirement for the PDZ domain protein, INAD, for localization of the Trp store-operated channel to a signaling complex. Neuron. 18: 95-105.
Chorna-Ornan, I., et al. (2005). Light-regulated interaction of Dmoesin with Trp and Trpl channels is required for maintenance of photoreceptors. J. Cell Biol. 171(1): 143-52. 16216927
Chyb, S., Raghu, P. and Hardie, R. C. (1999). Polyunsaturated fatty acids activate the Drosophila light-sensitive channels TRP and TRPL. Nature 397(6716): 255-9.
Cook, B. and Minke, B. (1999). TRP and calcium stores in Drosophila phototransduction. Cell Calcium 25(2): 161-71. 10326683
Cosens, D. and Perry, M. M. (1972). The fine structure of the eye of a visual mutant, A-type, of Drosophila melanogaster. J. Insect Physiol. 18: 1773-1786. 4626550
Dietrich, A., et al. (2005). Increased vascular smooth muscle contractility in TRPC6-/- mice. Mol. Cell Biol. 25(16): 6980-9. 16055711
Flemming, P. K., et al. (2006). Sensing of lysophospholipids by TRPC5 calcium channel. J. Biol. Chem. 281(8): 4977-82. 16368680
Georgiev, P., Garcia-Murillas, I., Ulahannan, D., Hardie, R. C. and Raghu, P. (2005). Functional INAD complexes are required to mediate degeneration in photoreceptors of the Drosophila rdgA mutant. J. Cell Sci. 118(Pt 7): 1373-84. 15755798
Goel, M., et al. (2005). Proteomic analysis of TRPC5- and TRPC6-binding partners reveals interaction with the plasmalemmal Na(+)/K(+)-ATPase. Pflugers Arch. 451(1): 87-98. 16025302
Graziani, A., et al. (2006). Cellular cholesterol controls TRPC3 function: evidence from a novel dominant-negative knockdown strategy. Biochem. J. 396(1): 147-55. 16448384
Gu, Y., Oberwinkler, J., Postma, M. and Hardie, R. C. (2005). Mechanisms of light adaptation in Drosophila photoreceptors. Curr. Biol. 15(13): 1228-34. 16005297
Hara, Y., et al. (2002). LTRPC2 Ca2+-permeable channel activated by changes in redox status confers susceptibility to cell death. Mol. Cell. 9: 163-173. 11804595
Hardie, R. C. and Minke, B. (1992). The trp gene is essential for a light-activated Ca2+ channel in Drosophila photoreceptors. Neuron 8: 643-651. 1314617
Hardie, R. C. and Minke, B. (1994a). Spontaneous activation of light-sensitive channels in Drosophila photoreceptors. J. Gen. Physiol. 103: 389-407. 8195780
Hardie, R. C. and Minke, B. (1994b). Calcium-dependent inactivation of light-sensitive channels in Drosophila photoreceptors, J. Gen. Physiol. 103: 409-427. 8195781
Hardie, R.C., et al. (2001). Calcium influx via TRP channels is required to maintain PIP2 levels in Drosophila photoreceptors, Neuron 30: 149-159. 11343651
Hong, Y. S., et al. (2002). Single amino acid change in the fifth transmembrane segment of the TRP Ca2+ channel causes massive degeneration of photoreceptors. J. Biol. Chem. 277(37): 33884-9. 12107168
Huber, A., Sander, P., Bahner, M. and Paulsen, R. (1998). The TRP Ca2+ channel assembled in a signaling complex by the PDZ domain protein INAD is phosphorylated through the interaction with protein kinase C (ePKC). FEBS Lett. 425(2): 317-22. 9559672
Hui, H., et al. (2006). Calcium-sensing mechanism in TRPC5 channels contributing to retardation of neurite outgrowth. J. Physiol. 572(Pt 1): 165-72. 16469785
Jors, S., Kazanski, V., Foik, A., Krautwurst, D. and Harteneck, C. (2006). Receptor-induced activation of Drosophila TRP gamma by polyunsaturated fatty acids. J. Biol. Chem. 281(40): 29693-702. Medline abstract: 16901908
Kawasaki, B. T., Liao, Y. and Birnbaumer, L. (2006). Role of Src in C3 transient receptor potential channel function and evidence for a heterogeneous makeup of receptor- and store-operated Ca2+ entry channels. Proc. Natl. Acad. Sci. 103(2): 335-40. 16407161
Kurahashi, T. and Menini, A. (1997). Mechanism of odorant adaptation in the olfactory receptor cell. Nature 385: 725-729. 9034189
Lee, E. H., Cherednichenko, G., Pessah, I. N. and Allen, P. D. (2006). Functional coupling between TRPC3 and RyR1 regulates the expressions of key triadic proteins. J. Biol. Chem. 281(15):10042-8. 16484216
Leung, H. T., Geng, C. and Pak, W. L. (2000). Phenotypes of trpl mutants and interactions between the transient receptor potential (TRP) and TRP-like channels in Drosophila. J. Neurosci. 20(18): 6797-803. 10995823
Li, C., et al. (1999), INAF, a protein required for transient receptor potential Ca(2+) channel function. Proc. Natl. Acad. Sci. 96(23): 13474-9. 10557345
Li, H.-S. and Montell, C. (2000). TRP and the PDZ Protein, INAD, form the core complex required for retention of the signalplex in Drosophila photoreceptor cells. J. Cell Bio. 150: 1411-1422. 10995445
Li Y., et al. (2005). Essential role of TRPC channels in the guidance of nerve growth cones by brain-derived neurotrophic factor. Nature 434(7035): 894-8. 15758952
Lockwich, T., Singh, B.B., Liu, X. and Ambudkar, I.S. (2001). Stabilization of cortical actin induces internalization of transient receptor potential 3 (Trp3)-associated caveolar Ca2+ signaling complex and loss of Ca2+ influx without disruption of Trp3-inositol trisphosphate receptor association. J. Biol. Chem. 276: 42401-42408. 11524429
Lussier, M. P., et al. (2005), MxA, a member of the dynamin superfamily, interacts with the ankyrin-like repeat domain of TRPC. J. Biol. Chem. 280(19): 19393-400. 15757897
Mery, L., et al. (2002). The PDZ-interacting domain of TrpC4 controls its localization and surface expression in HEK293 cells. J. Cell Sci. 115: 3497-3508. 12154080
Meyer, N. E., Joel-Almagor, T., Frechter, S., Minke, B. and Huber, A. (2006). Subcellular translocation of the eGFP-tagged TRPL channel in Drosophila photoreceptors requires activation of the phototransduction cascade. J. Cell Sci. 119(Pt 12): 2592-603. Medline abstract: 16735439
Montell, C., and Rubin. G. M. (1989). Molecular characterization of the Drosophila trp locus: a putative integral membrane protein required for phototransduction. Neuron. 2:1313-1323. 2516726
Montell, C., et al. (2002). A unified nomenclature for the superfamily of TRP cation channels. Mol. Cell 9: 229-231. 11864597
Montell, C. (2005a). Trp channels in Drosophila photoreceptor cells. J. Physiol. 567.1: 45-51. 15961416
Montell, C. (2005b). The Trp superfamily of cation channels. Sci. STKE. 2005:re3. 15728426
Nadler, M. J., et al (2001). LTRPC7 is a Mg.ATP-regulated divalent cation channel required for cell viability. Nature. 411: 590-595. 11385574
Niemeyer, B.A., et al. (1996). The Drosophila light-activated conductance is composed of the two channels Trp and Trpl. Cell. 85: 651-659. 8646774
Obukhov, A. G. and Nowycky, M. C. (2004). TrpC5 activation kinetics are modulated by the scaffolding protein ezrin/radixin/moesin-binding phosphoprotein-50 (EBP50). J. Cell. Physiol. 201: 227-235. 15334657
Obukhov, A. G. and Nowycky, M. C. (2005). A cytosolic residue mediates Mg2+ block and regulates inward current amplitude of a transient receptor potential channel. J. Neurosci. 25(5): 1234-9. 15689561
Odell, A. F., Scott, J. L., Van Helden, D. F. (2005). Epidermal growth factor induces tyrosine phosphorylation, membrane insertion, and activation of transient receptor potential channel 4. J. Biol. Chem. 280(45): 37974-87. 16144838
Ordaz B., et al. (2005). Calmodulin and calcium interplay in the modulation of TRPC5 channel activity. Identification of a novel C-terminal domain for calcium/calmodulin-mediated facilitation. J. Biol. Chem. 280(35): 30788-96. 15987684
Polesello, C., Delon, I., Valenti, P., Ferrer, P. and Payre F. (2002). Dmoesin controls actin-based cell shape and polarity during Drosophila melanogaster oogenesis. Nat. Cell Biol. 4(10): 782-9. 12360288
Popescu, D. C., Ham, A. J. and Shieh, B. H. (2005). Scaffolding protein INAD regulates deactivation of vision by promoting phosphorylation of transient receptor potential by eye protein kinase C in Drosophila. J. Neurosci. 26(33): 8570-7. Medline abstract: 16914683
Poteser, M., et al. (2006). TRPC3 and TRPC4 associate to form a redox-sensitive cation channel: Evidence for expression of native TRPC3-TRPC4 heteromeric channels in endothelial cells. J. Biol. Chem. 281(19): 13588-95. 16537542
Raghu, P., et al. (2000). Constitutive activity of the light-sensitive channels TRP and TRPL in the Drosophila diacylglycerol kinase mutant, rdgA. Neuron 26(1): 169-79. 10798401
Reiser J., et al. (2005). TRPC6 is a glomerular slit diaphragm-associated channel required for normal renal function. Nat. Genet. 37(7): 739-44. 15924139
Reuss, H., et al. (1997). In vivo analysis of the Drosophila light-sensitive channels, Trp and Trpl. Neuron 19:1249-1259. 9427248
Scott, K. Sun, Y. M. Beckingham, K. and Zuker, S. Z. (1997). Calmodulin regulation of Drosophila light-activated channels and receptor function mediates termination of the light response in vivo. Cell 91: 375-383. 9363946
Shieh, B. H. and Zhu, M. Y. (1996). Regulation of the TRP Ca2+ channel by INAD in Drosophila photoreceptors. Neuron 16(5): 991-8.
Shimizu, S., et al. (2006). Ca2+-calmodulin-dependent myosin light chain kinase is essential for activation of TRPC5 channels expressed in HEK293 cells. J. Physiol. 570(Pt 2): 219-35. 16284075
Sinkins, W. G., Vaca, L., Hu, Y., Kunze, D. L. and Schilling, W. P. (1996). The COOH-terminal domain of Drosophila TRP channels confers thapsigargin sensitivity. J. Biol. Chem. 271(6): 2955-60. 8621686
Soboloff, J., et al. (2005). Role of endogenous TRPC6 channels in Ca2+ signal generation in A7r5 smooth muscle cells. J. Biol. Chem. 280(48): 39786-94. 16204251
Speck, O., Hughes, S. C., Noren, N. K., Kulikauskas, R. M. and Fehon, R. G. (2003). Moesin functions antagonistically to the Rho pathway to maintain epithelial integrity. Nature 421(6918): 83-7. 12511959
Stamboulian, S., et al. (2005). Junctate, an inositol 1,4,5-triphosphate receptor associated protein, is present in rodent sperm and binds TRPC2 and TRPC5 but not TRPC1 channels. Dev. Biol. 286(1): 326-37. 16153633
Tang, Y., et al. (2000). Association of mammalian trp4 and phospholipase C isozymes with a PDZ domain-containing protein, NHERF. J. Biol. Chem. 275: 37559-37564. 10980202
Tsunoda, S., et al. (2001). Independent anchoring and assembly mechanisms of INAD signaling complexes in Drosophila photoreceptors. J. Neurosci. 21(1): 150-158. 11150331
van Rossum, D. B., et al. (2005). Phospholipase Cgamma1 controls surface expression of TRPC3 through an intermolecular PH domain. Nature 434(7029): 99-104. 15744307
Wang, G. X. and Poo, M. M. (2005). Requirement of TRPC channels in netrin-1-induced chemotropic turning of nerve growth cones. Nature 434(7035): 898-904. 15758951
Wang, T., Xu, H., Oberwinkler, J., Gu, Y., Hardie, R. C. and Montell, C. (2005a). Light activation, adaptation, and cell survival functions of the Na+/Ca2+ exchanger CalX. Neuron. 45: 367-378. 15694324
Wang, T., Jiao, Y. and Montell, C. (2005b). Dissecting independent channel and scaffolding roles of the Drosophila transient receptor potential channel. J. Cell Biol. 171(4): 685-94. 16301334
Wehage, E., et al. (2002). Activation of the cation channel long transient receptor potential channel 2 (LTRPC2) by hydrogen peroxide. A splice variant reveals a mode of activation independent of ADP-ribose. J. Biol. Chem. 277: 23150-23156. 11960981
Winn, M. P., et al. (2005). A mutation in the TRPC6 cation channel causes familial focal segmental glomerulosclerosis. Science 308(5729): 1801-4. 15879175
Xu, X.-Z. S., Li, H.-S., Guggino, W. B. and Montell, C. (1997). Coassembly of TRP and TRPL produces a distinct store-operated conductance. Cell 89: 1155-1164. 9215637
Xu, X.-Z. S., Choudhury, A., Li, X. and Montell, C. (1998). Coordination of an array of signaling proteins through homo- and heteromeric interactions between PDZ domains and target proteins. J. Cell Biol. 142: 545-555. 9679151
Xu, X. Z., Chien, F., Butler, A., Salkoff, L. and Montell, C. (2000). TRPgamma, a Drosophila TRP-related subunit, forms a regulated cation channel with TRPL. Neuron 26(3): 647-57. 10896160
Yang H., et al. (2005). TRPC4 knockdown suppresses epidermal growth factor-induced store-operated channel activation and growth in human corneal epithelial cells. J. Biol. Chem. 280(37): 32230-7. 16033767
Yildirim, E., Kawasaki, B. T., Birnbaumer, L. (2005). Molecular cloning of TRPC3a, an N-terminally extended, store-operated variant of the human C3 transient receptor potential channel. Proc. Natl. Acad. Sci. 102(9): 3307-11. 15728370
Yoon, J., et al. (2000). Novel mechanism of massive photoreceptor degeneration caused by mutations in the trp gene of Drosophila. J. Neurosci. 20(2): 649-59. 10632594
Zagranichnaya, T. K., Wu, X. and Villereal, M. L. (2005). Endogenous TRPC1, TRPC3, and TRPC7 proteins combine to form native store-operated channels in HEK-293 cells. J. Biol. Chem. 280(33): 29559-69. 15972814
date revised: 15 August 2007
Home page: The Interactive Fly © 2006 Thomas Brody, Ph.D.
The Interactive Fly resides on the
Society for Developmental Biology's Web server.