ABSTRACT
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.
Subject(s)
Cell Membrane/metabolism , Drosophila Proteins/metabolism , Drosophila melanogaster/enzymology , Endocytosis/radiation effects , Phospholipase D/metabolism , Photoreceptor Cells, Invertebrate/metabolism , ADP-Ribosylation Factor 1/genetics , ADP-Ribosylation Factor 1/metabolism , Animals , Cell Membrane/radiation effects , Cell Membrane/ultrastructure , Cytoplasmic Vesicles/metabolism , Drosophila Proteins/genetics , Drosophila melanogaster/cytology , Drosophila melanogaster/genetics , Drosophila melanogaster/radiation effects , Gene Expression , Genetic Complementation Test , Guanosine Triphosphate/metabolism , Light , Phosphatidic Acids/metabolism , Phospholipase D/genetics , Photic Stimulation , Photoreceptor Cells, Invertebrate/radiation effects , Photoreceptor Cells, Invertebrate/ultrastructure , Rhodopsin/genetics , Rhodopsin/metabolism , Vision, Ocular/physiology , rab GTP-Binding Proteins/genetics , rab GTP-Binding Proteins/metabolism , rab7 GTP-Binding ProteinsABSTRACT
Phosphatidic acid (PA) is postulated to have both structural and signaling functions during membrane dynamics in animal cells. In this study, we show that before a critical time period during rhabdomere biogenesis in Drosophila melanogaster photoreceptors, elevated levels of PA disrupt membrane transport to the apical domain. Lipidomic analysis shows that this effect is associated with an increase in the abundance of a single, relatively minor molecular species of PA. These transport defects are dependent on the activation state of Arf1. Transport defects via PA generated by phospholipase D require the activity of type I phosphatidylinositol (PI) 4 phosphate 5 kinase, are phenocopied by knockdown of PI 4 kinase, and are associated with normal endoplasmic reticulum to Golgi transport. We propose that PA levels are critical for apical membrane transport events required for rhabdomere biogenesis.
Subject(s)
Drosophila melanogaster/ultrastructure , Phosphatidic Acids/metabolism , Photoreceptor Cells/ultrastructure , 1-Phosphatidylinositol 4-Kinase/antagonists & inhibitors , 1-Phosphatidylinositol 4-Kinase/physiology , ADP-Ribosylation Factor 1/physiology , ADP-Ribosylation Factor 6 , ADP-Ribosylation Factors/physiology , Adaptor Protein Complex alpha Subunits/antagonists & inhibitors , Adaptor Protein Complex alpha Subunits/physiology , Animals , Cell Membrane/metabolism , Cell Membrane/ultrastructure , Diacylglycerol Cholinephosphotransferase/genetics , Drosophila Proteins/genetics , Drosophila Proteins/metabolism , Drosophila Proteins/physiology , Drosophila melanogaster/genetics , Drosophila melanogaster/growth & development , Dynamins/genetics , Dynamins/metabolism , Dynamins/physiology , Membrane Lipids/metabolism , Microscopy, Electron, Transmission , Phenotype , Phosphatidate Phosphatase/genetics , Phosphatidate Phosphatase/metabolism , Phospholipase D/metabolism , Phosphotransferases (Alcohol Group Acceptor)/genetics , Phosphotransferases (Alcohol Group Acceptor)/metabolism , Phosphotransferases (Alcohol Group Acceptor)/physiology , Photoreceptor Cells/metabolism , Photoreceptor Cells/physiology , RNA InterferenceABSTRACT
We identified the gene smooth (sm) in a screen for genes that are specifically expressed within the lineage that forms the adult chemosensory bristles. sm is expressed in most or all differentiating neurones during embryogenesis, but is specifically expressed in the neurones of the adult chemosensory organs on the wings and legs during metamorphosis. The inactivation of sm results in axonal defects in the chemosensory neurones, in the inability of mutant flies to feed and in their precocious death. As sm belongs to a family of heterogeneous nuclear ribonucleoprotein (hnRNP), we propose that the control of axonal navigation and connectivity is partly achieved at the level of mRNA splicing or exporting.
