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Regulation of phototransduction responsiveness and retinal degeneration by a phospholipase D-generated signaling lipid.

LaLonde MM, Janssens H, Rosenbaum E, Choi SY, Gergen JP, Colley NJ, Stark WS, Frohman MA - J. Cell Biol. (2005)

Bottom Line: Drosophila melanogaster phototransduction proceeds via a phospholipase C (PLC)-triggered cascade of phosphatidylinositol (PI) lipid modifications, many steps of which remain undefined.We describe the involvement of the lipid phosphatidic acid and the enzyme that generates it, phospholipase D (Pld), in this process.Pld() flies exhibit decreased light sensitivity as well as a heightened susceptibility to retinal degeneration.

View Article: PubMed Central - PubMed

Affiliation: Program in Molecular and Cellular Biology, Center for Developmental Genetics, Stony Brook University, Stony Brook, NY 11794, USA.

ABSTRACT
Drosophila melanogaster phototransduction proceeds via a phospholipase C (PLC)-triggered cascade of phosphatidylinositol (PI) lipid modifications, many steps of which remain undefined. We describe the involvement of the lipid phosphatidic acid and the enzyme that generates it, phospholipase D (Pld), in this process. Pld() flies exhibit decreased light sensitivity as well as a heightened susceptibility to retinal degeneration. Pld overexpression rescues flies lacking PLC from light-induced, metarhodopsin-mediated degeneration and restores visual signaling in flies lacking the PI transfer protein, which is a key player in the replenishment of the PI 4,5-bisphosphate (PIP2) substrate used by PLC to transduce light stimuli into neurological signals. Altogether, these findings suggest that Pld facilitates phototransduction by maintaining adequate levels of PIP2 and by protecting the visual system from metarhodopsin-induced, low light degeneration.

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Pldmutant flies display decreased light sensitivity. ERGs were recorded from heterozygous Pld/CyO (A) and homozygous Pld (B) adult flies 7 d after eclosion. An intensity–response series to 570-nm stimuli is shown for each fly with intensities of 13.99, 13.38, 12.73, 12.07, and 11.41 log quanta/cm2/s for the control (A) and 15.91, 15.3, 14.65, 13.99, and 13.38 log quant/cm2/s for the Pld mutant (B). A significant response was not observed for the Pld mutant at the three lower intensities at which a response was obtained for control flies. Stimulation at 570 nm was chosen because the effects of differences in eye color pigmentation are lower, and on- and off-transients are larger at longer wavelengths (Stark and Wasserman, 1972). Potential was recorded in millivolts as indicated. Three flies were examined for each strain, with similar results observed. (C) The wild-type response was superimposed on the two Pld mutant ERGs that were conducted within the range examined for the control flies. Light-induced plateau amplitudes were estimated and plotted (D) as a function of the log of the light stimulation intensities to enable a comparison of the wild-type with the Pld mutant responses. Similar results were obtained when Canton-S was used as the wild-type control.
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fig2: Pldmutant flies display decreased light sensitivity. ERGs were recorded from heterozygous Pld/CyO (A) and homozygous Pld (B) adult flies 7 d after eclosion. An intensity–response series to 570-nm stimuli is shown for each fly with intensities of 13.99, 13.38, 12.73, 12.07, and 11.41 log quanta/cm2/s for the control (A) and 15.91, 15.3, 14.65, 13.99, and 13.38 log quant/cm2/s for the Pld mutant (B). A significant response was not observed for the Pld mutant at the three lower intensities at which a response was obtained for control flies. Stimulation at 570 nm was chosen because the effects of differences in eye color pigmentation are lower, and on- and off-transients are larger at longer wavelengths (Stark and Wasserman, 1972). Potential was recorded in millivolts as indicated. Three flies were examined for each strain, with similar results observed. (C) The wild-type response was superimposed on the two Pld mutant ERGs that were conducted within the range examined for the control flies. Light-induced plateau amplitudes were estimated and plotted (D) as a function of the log of the light stimulation intensities to enable a comparison of the wild-type with the Pld mutant responses. Similar results were obtained when Canton-S was used as the wild-type control.

Mentions: Potential roles for Pld in phototransduction were explored by examining the effects of Pld deficiency on the generation of a light-induced signal in the retina. Pld flies, which exhibit reduced viability during cellularization but, as adults, are overtly normal (unpublished data), were examined using electroretinograms (ERGs). ERGs measure the change over time in membrane potential (depolarization and repolarization) in retinal photoreceptors in response to light and, as such, constitute a summary of the light-triggered signals that are generated within an ommatidium. A typical recording for a control heterozygous (Pld/CyO) eye is shown in Fig. 2 A. A relatively high membrane potential is observed under resting (dark) conditions. Upon stimulation of the retina by light, the rhodopsin→metarhodopsin→PLC activation→DAG generation→TRP activation cascade results in an influx of Ca2+ that causes a rapid depolarization (net negative change in current potential). The membrane then remains depolarized until light stimulation ceases, because the TRP channels remain open as long as the light-induced signal continues. With return to dark conditions, the TRP channels close, Ca2+ is pumped out, the membrane repolarizes, and the slow steady wave (receptor wave) returns to its resting potential. Positive on- and negative off-transients are also observed after stimulus onset and offset, respectively. The presence of these postsynaptic responses indicates functional connections from the photoreceptor cells R1–6 to the first optic neuropil, the lamina ganglionaris.


Regulation of phototransduction responsiveness and retinal degeneration by a phospholipase D-generated signaling lipid.

LaLonde MM, Janssens H, Rosenbaum E, Choi SY, Gergen JP, Colley NJ, Stark WS, Frohman MA - J. Cell Biol. (2005)

Pldmutant flies display decreased light sensitivity. ERGs were recorded from heterozygous Pld/CyO (A) and homozygous Pld (B) adult flies 7 d after eclosion. An intensity–response series to 570-nm stimuli is shown for each fly with intensities of 13.99, 13.38, 12.73, 12.07, and 11.41 log quanta/cm2/s for the control (A) and 15.91, 15.3, 14.65, 13.99, and 13.38 log quant/cm2/s for the Pld mutant (B). A significant response was not observed for the Pld mutant at the three lower intensities at which a response was obtained for control flies. Stimulation at 570 nm was chosen because the effects of differences in eye color pigmentation are lower, and on- and off-transients are larger at longer wavelengths (Stark and Wasserman, 1972). Potential was recorded in millivolts as indicated. Three flies were examined for each strain, with similar results observed. (C) The wild-type response was superimposed on the two Pld mutant ERGs that were conducted within the range examined for the control flies. Light-induced plateau amplitudes were estimated and plotted (D) as a function of the log of the light stimulation intensities to enable a comparison of the wild-type with the Pld mutant responses. Similar results were obtained when Canton-S was used as the wild-type control.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2171926&req=5

fig2: Pldmutant flies display decreased light sensitivity. ERGs were recorded from heterozygous Pld/CyO (A) and homozygous Pld (B) adult flies 7 d after eclosion. An intensity–response series to 570-nm stimuli is shown for each fly with intensities of 13.99, 13.38, 12.73, 12.07, and 11.41 log quanta/cm2/s for the control (A) and 15.91, 15.3, 14.65, 13.99, and 13.38 log quant/cm2/s for the Pld mutant (B). A significant response was not observed for the Pld mutant at the three lower intensities at which a response was obtained for control flies. Stimulation at 570 nm was chosen because the effects of differences in eye color pigmentation are lower, and on- and off-transients are larger at longer wavelengths (Stark and Wasserman, 1972). Potential was recorded in millivolts as indicated. Three flies were examined for each strain, with similar results observed. (C) The wild-type response was superimposed on the two Pld mutant ERGs that were conducted within the range examined for the control flies. Light-induced plateau amplitudes were estimated and plotted (D) as a function of the log of the light stimulation intensities to enable a comparison of the wild-type with the Pld mutant responses. Similar results were obtained when Canton-S was used as the wild-type control.
Mentions: Potential roles for Pld in phototransduction were explored by examining the effects of Pld deficiency on the generation of a light-induced signal in the retina. Pld flies, which exhibit reduced viability during cellularization but, as adults, are overtly normal (unpublished data), were examined using electroretinograms (ERGs). ERGs measure the change over time in membrane potential (depolarization and repolarization) in retinal photoreceptors in response to light and, as such, constitute a summary of the light-triggered signals that are generated within an ommatidium. A typical recording for a control heterozygous (Pld/CyO) eye is shown in Fig. 2 A. A relatively high membrane potential is observed under resting (dark) conditions. Upon stimulation of the retina by light, the rhodopsin→metarhodopsin→PLC activation→DAG generation→TRP activation cascade results in an influx of Ca2+ that causes a rapid depolarization (net negative change in current potential). The membrane then remains depolarized until light stimulation ceases, because the TRP channels remain open as long as the light-induced signal continues. With return to dark conditions, the TRP channels close, Ca2+ is pumped out, the membrane repolarizes, and the slow steady wave (receptor wave) returns to its resting potential. Positive on- and negative off-transients are also observed after stimulus onset and offset, respectively. The presence of these postsynaptic responses indicates functional connections from the photoreceptor cells R1–6 to the first optic neuropil, the lamina ganglionaris.

Bottom Line: Drosophila melanogaster phototransduction proceeds via a phospholipase C (PLC)-triggered cascade of phosphatidylinositol (PI) lipid modifications, many steps of which remain undefined.We describe the involvement of the lipid phosphatidic acid and the enzyme that generates it, phospholipase D (Pld), in this process.Pld() flies exhibit decreased light sensitivity as well as a heightened susceptibility to retinal degeneration.

View Article: PubMed Central - PubMed

Affiliation: Program in Molecular and Cellular Biology, Center for Developmental Genetics, Stony Brook University, Stony Brook, NY 11794, USA.

ABSTRACT
Drosophila melanogaster phototransduction proceeds via a phospholipase C (PLC)-triggered cascade of phosphatidylinositol (PI) lipid modifications, many steps of which remain undefined. We describe the involvement of the lipid phosphatidic acid and the enzyme that generates it, phospholipase D (Pld), in this process. Pld() flies exhibit decreased light sensitivity as well as a heightened susceptibility to retinal degeneration. Pld overexpression rescues flies lacking PLC from light-induced, metarhodopsin-mediated degeneration and restores visual signaling in flies lacking the PI transfer protein, which is a key player in the replenishment of the PI 4,5-bisphosphate (PIP2) substrate used by PLC to transduce light stimuli into neurological signals. Altogether, these findings suggest that Pld facilitates phototransduction by maintaining adequate levels of PIP2 and by protecting the visual system from metarhodopsin-induced, low light degeneration.

Show MeSH
Related in: MedlinePlus