Molecular basis of amplification in Drosophila phototransduction: roles for G protein, phospholipase C, and diacylglycerol kinase.
In Drosophila photoreceptors, the amplification responsible for generating quantum bumps in response to photoisomerization of single rhodopsin molecules has been thought to be mediated downstream of phospholipase C (PLC), since bump amplitudes were reportedly unaffected in mutants with greatly reduced levels of either G protein or PLC. We now find that quantum bumps in such mutants are reduced approximately 3- to 5-fold but are restored to near wild-type values by mutations in the rdgA gene encoding diacylglycerol kinase (DGK) and also by depleting intracellular ATP. The results demonstrate that amplification requires activation of multiple G protein and PLC molecules, identify DGK as a key enzyme regulating amplification, and implicate diacylglycerol as a messenger of excitation in Drosophila phototransduction.
Hardie
R C
RC
Department of Anatomy, Cambridge University, Downing Street, Cambridge, United Kingdom.
Martin
F
F
Cochrane
G W
GW
Juusola
M
M
Georgiev
P
P
Raghu
P
P
D000255:Adenosine Triphosphate / Q000235:genetics / Q000378:metabolism; D000818:Animals; D003623:Dark Adaptation / Q000235:genetics; D019852:Diacylglycerol Kinase / Q000235:genetics*; D015536:Down-Regulation / Q000235:genetics; D004331:Drosophila melanogaster / Q000201:enzymology* / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D019204:GTP-Binding Proteins / Q000235:genetics*; D020962:Heterotrimeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D008564:Membrane Potentials / Q000235:genetics; D009154:Mutation / Q000235:genetics; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D017956:Photoreceptor Cells, Invertebrate / Q000166:cytology / Q000201:enzymology*; D012243:Rhodopsin / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D012684:Sensory Thresholds / Q000502:physiology; D014157:Transcription Factors / Q000172:deficiency / Q000235:genetics; D010738:Type C Phospholipases / Q000172:deficiency / Q000235:genetics*; D014785:Vision, Ocular / Q000235:genetics*
D005656:Fungal Proteins; C100530:PIP2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D000255:Adenosine Triphosphate; D012243:Rhodopsin; D019852:Diacylglycerol Kinase; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020962:Heterotrimeric GTP-Binding Proteins; D043265:Phosphatidylinositol Diacylglycerol-Lyase