Phospholipase D activity couples plasma membrane endocytosis with retromer dependent recycling

• Published in: eLife Vol. 5
• Main Authors: Thakur, Rajan, Panda, Aniruddha, Coessens, Elise, Raj, Nikita, Yadav, Shweta, Balakrishnan, Sruthi, Zhang, Qifeng, Georgiev, Plamen, Basak, Bishal, Pasricha, Renu, Wakelam, Michael JO, Ktistakis, Nicholas T, Raghu, Padinjat
• Format: Journal Article
• Language: English
• Published: England eLife Science Publications, Ltd 16.11.2016; eLife Sciences Publications Ltd; eLife Sciences Publications, Ltd
• Subjects: ADP-Ribosylation Factor 1 - genetics; ADP-Ribosylation Factor 1 - metabolism; Animals; Arf1; Biochemistry; Cell Biology; Cell body; Cell Membrane - metabolism; Cell Membrane - radiation effects; Cell Membrane - ultrastructure; Cell membranes; Cytoplasmic Vesicles - metabolism; Drosophila; Drosophila melanogaster - cytology; Drosophila melanogaster - enzymology; Drosophila melanogaster - genetics; Drosophila melanogaster - radiation effects; Drosophila Proteins - genetics; Drosophila Proteins - metabolism; Endocytosis; Endocytosis - radiation effects; Gene Expression; Genetic Complementation Test; Guanosine triphosphate; Guanosine Triphosphate - metabolism; Illumination; Insects; Light; lipid signalling; Lipids; Observations; Phosphatidic acid; Phosphatidic Acids - metabolism; Phospholipase D; Phospholipase D - genetics; Phospholipase D - metabolism; Phospholipases; Photic Stimulation; Photoreceptor Cells, Invertebrate - metabolism; Photoreceptor Cells, Invertebrate - radiation effects; Photoreceptor Cells, Invertebrate - ultrastructure; Photoreceptors; Physiological aspects; Protein turnover; rab GTP-Binding Proteins - genetics; rab GTP-Binding Proteins - metabolism; rab7 GTP-Binding Proteins; retromer; Rhodopsin; Rhodopsin - genetics; Rhodopsin - metabolism; Software; Vision, Ocular - physiology; rhodopsin; phospholipase D; Arf1; cell biology; retromer; biochemistry; lipid signalling; phosphatidic acid; D. melanogaster
• ISSN: 2050-084X; 2050-084X
• DOI: 10.7554/eLife.18515

During illumination, the light-sensitive plasma membrane (rhabdomere) of Drosophila photoreceptors undergoes turnover with consequent changes in size and composition. However, the mechanism by which illumination is coupled to rhabdomere turnover remains unclear. We find that photoreceptors contain a light-dependent phospholipase D (PLD) activity. During illumination, loss of PLD resulted in an enhanced reduction in rhabdomere size, accumulation of Rab7 positive, rhodopsin1-containing vesicles (RLVs) in the cell body and reduced rhodopsin protein. These phenotypes were associated with reduced levels of phosphatidic acid, the product of PLD activity and were rescued by reconstitution with catalytically active PLD. In wild-type photoreceptors, during illumination, enhanced PLD activity was sufficient to clear RLVs from the cell body by a process dependent on Arf1-GTP levels and retromer complex function. Thus, during illumination, PLD activity couples endocytosis of RLVs with their recycling to the plasma membrane thus maintaining plasma membrane size and composition. Certain cells in the eye contain a receptor protein known as rhodopsin that enables them to detect light. Rhodopsin is found in distinct patches on the membrane surrounding each of these “photoreceptor” cells and the number of rhodopsin molecules present controls how sensitive the cell is to light. In humans, vitamin A deficiency or genetic defects can decrease the number of rhodopsin molecules on the membrane, leading to difficulty in seeing in dim light. Fruit fly eyes also contain rhodopsin. Exposure to normal levels of light triggers parts of the membranes of fly photoreceptor cells to detach and move into the interior of the cell. These internalized pieces of membrane have two possible fates: they can either be destroyed or recycled back to the cell surface. This membrane turnover adjusts the size of the membrane surrounding the cell and the number of rhodopsin molecules in it to regulate the cell’s sensitivity to light. It is crucial that turnover is tightly regulated in order to maintain the integrity of the cell membrane. However, it is not clear how the process is regulated during light exposure. Thakur et al. set out to address this question in fruit flies. The experiments show that an enzyme called phospholipase D is activated when photoreceptors are exposed to light. Active phospholipase D – which generates a molecule called phosphatidic acid – coordinates the internalization of pieces of membrane with the recycling of rhodopsin back to the cell surface. Thakur et al. generated fly mutants that lacked phospholipase D and in these animals the internalized rhodopsin was not transported back to the cell membrane. This caused the membrane to shrink in size and decreased the number of rhodopsin molecules in it. As a result, the photoreceptor cells became less sensitive to light. The findings of Thakur et al. show that in response to normal levels of light, phospholipase D balances membrane internalization and recycling to maintain the size and rhodopsin composition of the membrane. Future challenges will be to work out exactly how phospholipase D is activated and how phosphatidic acid tunes membrane internalization and recycling.