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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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Pld overexpression restores light responses in the rdgB9mutant. ERGs were performed on flies raised under continuous light conditions for 1 d: (A) rdgB9 and (B) rdgB9; P{UAS-Pld}/ Rh1. The abnormal ERG seen in the rdgB9 mutant was rescued by the overexpression of Pld, resulting in normal response amplitude with both on- and off-transients. Retinal tissue sections from flies raised under continuous light for 1 or 3 d were prepared and imaged using electron microscopy: (C and F) rdgB9, (D and G) P{UAS-Pld}/ Rh1, and (E and H) rdgB9; P{UAS-Pld}/ Rh1. (C) rdgB9 flies displayed some retinal degeneration 1 d after eclosion. (F) By 3 d after eclosion, more apparent retinal degeneration, with decreased rhabdomere size and increased vacuolation, had ensued. Flies overexpressing Pld had some degeneration 1 d after hatching (D) as described in Fig. 5; but, after 3 d, the flies had even more severe degeneration, with reduced rhabdomeres and degenerating photoreceptor cell bodies (G). In mutant flies overexpressing Pld (E and H), the degeneration caused by Pld expression was reduced. Note that photoreceptor cell R7 (7) appears relatively normal in G and H, which is consistent with the fact that the Rh1 promoter drives expression of Pld only in R1–6. Sections are representative of three experiments performed.
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fig6: Pld overexpression restores light responses in the rdgB9mutant. ERGs were performed on flies raised under continuous light conditions for 1 d: (A) rdgB9 and (B) rdgB9; P{UAS-Pld}/ Rh1. The abnormal ERG seen in the rdgB9 mutant was rescued by the overexpression of Pld, resulting in normal response amplitude with both on- and off-transients. Retinal tissue sections from flies raised under continuous light for 1 or 3 d were prepared and imaged using electron microscopy: (C and F) rdgB9, (D and G) P{UAS-Pld}/ Rh1, and (E and H) rdgB9; P{UAS-Pld}/ Rh1. (C) rdgB9 flies displayed some retinal degeneration 1 d after eclosion. (F) By 3 d after eclosion, more apparent retinal degeneration, with decreased rhabdomere size and increased vacuolation, had ensued. Flies overexpressing Pld had some degeneration 1 d after hatching (D) as described in Fig. 5; but, after 3 d, the flies had even more severe degeneration, with reduced rhabdomeres and degenerating photoreceptor cell bodies (G). In mutant flies overexpressing Pld (E and H), the degeneration caused by Pld expression was reduced. Note that photoreceptor cell R7 (7) appears relatively normal in G and H, which is consistent with the fact that the Rh1 promoter drives expression of Pld only in R1–6. Sections are representative of three experiments performed.

Mentions: 1 d after eclosion, rdgB9 mutants did not respond appropriately to a light stimulus (Fig. 6 A), even though retinal degeneration was not obvious (Fig. 6 C). Pld expression in these mutants rescued the light response, as evidenced by the presence of the slow depolarization and repolarization waves with both on- and off-transients, which signified intact connections that were downstream of the photoreceptor (Fig. 6 B). Because the conversion of the Pld-generated PA to DAG showed no evidence of being light regulated (Fig. 4 C), the functional rescue of the rdgB9 mutation by Pld overexpression suggests that Pld activity facilitates phototransduction via the maintenance of adequate PIP2 substrate levels for PLC hydrolysis. These results are consistent with the findings described in Fig. 2, in which the loss of Pld activity resulted in blunted phototransduction.


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)

Pld overexpression restores light responses in the rdgB9mutant. ERGs were performed on flies raised under continuous light conditions for 1 d: (A) rdgB9 and (B) rdgB9; P{UAS-Pld}/ Rh1. The abnormal ERG seen in the rdgB9 mutant was rescued by the overexpression of Pld, resulting in normal response amplitude with both on- and off-transients. Retinal tissue sections from flies raised under continuous light for 1 or 3 d were prepared and imaged using electron microscopy: (C and F) rdgB9, (D and G) P{UAS-Pld}/ Rh1, and (E and H) rdgB9; P{UAS-Pld}/ Rh1. (C) rdgB9 flies displayed some retinal degeneration 1 d after eclosion. (F) By 3 d after eclosion, more apparent retinal degeneration, with decreased rhabdomere size and increased vacuolation, had ensued. Flies overexpressing Pld had some degeneration 1 d after hatching (D) as described in Fig. 5; but, after 3 d, the flies had even more severe degeneration, with reduced rhabdomeres and degenerating photoreceptor cell bodies (G). In mutant flies overexpressing Pld (E and H), the degeneration caused by Pld expression was reduced. Note that photoreceptor cell R7 (7) appears relatively normal in G and H, which is consistent with the fact that the Rh1 promoter drives expression of Pld only in R1–6. Sections are representative of three experiments performed.
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Related In: Results  -  Collection

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fig6: Pld overexpression restores light responses in the rdgB9mutant. ERGs were performed on flies raised under continuous light conditions for 1 d: (A) rdgB9 and (B) rdgB9; P{UAS-Pld}/ Rh1. The abnormal ERG seen in the rdgB9 mutant was rescued by the overexpression of Pld, resulting in normal response amplitude with both on- and off-transients. Retinal tissue sections from flies raised under continuous light for 1 or 3 d were prepared and imaged using electron microscopy: (C and F) rdgB9, (D and G) P{UAS-Pld}/ Rh1, and (E and H) rdgB9; P{UAS-Pld}/ Rh1. (C) rdgB9 flies displayed some retinal degeneration 1 d after eclosion. (F) By 3 d after eclosion, more apparent retinal degeneration, with decreased rhabdomere size and increased vacuolation, had ensued. Flies overexpressing Pld had some degeneration 1 d after hatching (D) as described in Fig. 5; but, after 3 d, the flies had even more severe degeneration, with reduced rhabdomeres and degenerating photoreceptor cell bodies (G). In mutant flies overexpressing Pld (E and H), the degeneration caused by Pld expression was reduced. Note that photoreceptor cell R7 (7) appears relatively normal in G and H, which is consistent with the fact that the Rh1 promoter drives expression of Pld only in R1–6. Sections are representative of three experiments performed.
Mentions: 1 d after eclosion, rdgB9 mutants did not respond appropriately to a light stimulus (Fig. 6 A), even though retinal degeneration was not obvious (Fig. 6 C). Pld expression in these mutants rescued the light response, as evidenced by the presence of the slow depolarization and repolarization waves with both on- and off-transients, which signified intact connections that were downstream of the photoreceptor (Fig. 6 B). Because the conversion of the Pld-generated PA to DAG showed no evidence of being light regulated (Fig. 4 C), the functional rescue of the rdgB9 mutation by Pld overexpression suggests that Pld activity facilitates phototransduction via the maintenance of adequate PIP2 substrate levels for PLC hydrolysis. These results are consistent with the findings described in Fig. 2, in which the loss of Pld activity resulted in blunted phototransduction.

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