RESUMEN
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.
Asunto(s)
Membrana Celular/metabolismo , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/enzimología , Endocitosis/efectos de la radiación , Fosfolipasa D/metabolismo , Células Fotorreceptoras de Invertebrados/metabolismo , Factor 1 de Ribosilacion-ADP/genética , Factor 1 de Ribosilacion-ADP/metabolismo , Animales , Membrana Celular/efectos de la radiación , Membrana Celular/ultraestructura , Vesículas Citoplasmáticas/metabolismo , Proteínas de Drosophila/genética , Drosophila melanogaster/citología , Drosophila melanogaster/genética , Drosophila melanogaster/efectos de la radiación , Expresión Génica , Prueba de Complementación Genética , Guanosina Trifosfato/metabolismo , Luz , Ácidos Fosfatidicos/metabolismo , Fosfolipasa D/genética , Estimulación Luminosa , Células Fotorreceptoras de Invertebrados/efectos de la radiación , Células Fotorreceptoras de Invertebrados/ultraestructura , Rodopsina/genética , Rodopsina/metabolismo , Visión Ocular/fisiología , Proteínas de Unión al GTP rab/genética , Proteínas de Unión al GTP rab/metabolismo , Proteínas de Unión a GTP rab7RESUMEN
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.
Asunto(s)
Drosophila melanogaster/ultraestructura , Ácidos Fosfatidicos/metabolismo , Células Fotorreceptoras/ultraestructura , 1-Fosfatidilinositol 4-Quinasa/antagonistas & inhibidores , 1-Fosfatidilinositol 4-Quinasa/fisiología , Factor 1 de Ribosilacion-ADP/fisiología , Factor 6 de Ribosilación del ADP , Factores de Ribosilacion-ADP/fisiología , Subunidades alfa de Complejo de Proteína Adaptadora/antagonistas & inhibidores , Subunidades alfa de Complejo de Proteína Adaptadora/fisiología , Animales , Membrana Celular/metabolismo , Membrana Celular/ultraestructura , Diacilglicerol Colinafosfotransferasa/genética , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Proteínas de Drosophila/fisiología , Drosophila melanogaster/genética , Drosophila melanogaster/crecimiento & desarrollo , Dinaminas/genética , Dinaminas/metabolismo , Dinaminas/fisiología , Lípidos de la Membrana/metabolismo , Microscopía Electrónica de Transmisión , Fenotipo , Fosfatidato Fosfatasa/genética , Fosfatidato Fosfatasa/metabolismo , Fosfolipasa D/metabolismo , Fosfotransferasas (Aceptor de Grupo Alcohol)/genética , Fosfotransferasas (Aceptor de Grupo Alcohol)/metabolismo , Fosfotransferasas (Aceptor de Grupo Alcohol)/fisiología , Células Fotorreceptoras/metabolismo , Células Fotorreceptoras/fisiología , Interferencia de ARNRESUMEN
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.
