R9AP stabilizes RGS11-G beta5 and accelerates the early light response of ON-bipolar cells.
The rate-limiting step in the recovery of the photoreceptor light response is the hydrolysis of GTP by transducin, a reaction that is accelerated by the RGS9-Gbeta5 complex, and its membrane anchor, R9AP. Similar complexes, including RGS7, RGS11, and Gbeta5, are found in retinal ON-bipolar cell dendrites. Here, we present evidence that R9AP is also expressed in the dendritic tips of ON-bipolar cells. Immunofluorescent staining for R9AP revealed a punctate pattern of labeling in the outer plexiform layer, where it colocalized with mGluR6. In photoreceptors, R9AP is required for proteolytic stability of the entire regulator of G protein signaling complex, and we found that genetic deletion of R9AP also results in a marked reduction in the levels of RGS11 and Gbeta5 in the bipolar cell dendrites; the level of RGS7 was unaffected, suggesting the presence of another interaction partner to stabilize RGS7. To determine the effect of R9AP deletion on the response kinetics of ON-bipolar cells, we compared the electroretinogram (ERG) between wild-type and R9AP-deficient mice. The ERG b-wave, reflecting ON-bipolar cell activity, was delayed and larger in the R9AP-deficient mice. Our data indicate that R9AP is required for stable expression of RGS11-Gbeta5 in ON-bipolar cell dendrites. Furthermore, they suggest that the RGS11-Gbeta5-R9AP complex accelerates the initial ON-bipolar cell response to light.
Jeffrey
Brett G
BG
Oregon National Primate Research Center, Oregon Health & Science University, Beaverton, Oregon 97006, USA. jeffreyb@ohsu.edu
Morgans
Catherine W
CW
Puthussery
Theresa
T
Wensel
Theodore G
TG
Burke
Neal S
NS
Brown
R Lane
RL
Duvoisin
Robert M
RM
D000818:Animals; D002461:Cell Line, Transformed; D003712:Dendrites / Q000378:metabolism / Q000648:ultrastructure; D004596:Electroretinography / Q000379:methods; D005071:Evoked Potentials / Q000235:genetics; D044387:GTP-Binding Protein beta Subunits / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000235:genetics*; D006801:Humans; D008027:Light; D008565:Membrane Proteins / Q000172:deficiency / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D046529:Microscopy, Electron, Transmission / Q000379:methods; D011930:Reaction Time / Q000235:genetics; D012160:Retina / Q000166:cytology*; D051245:Retinal Bipolar Cells / Q000502:physiology* / Q000648:ultrastructure; D013569:Synapses / Q000378:metabolism / Q000648:ultrastructure; D014162:Transfection / Q000379:methods
D044387:GTP-Binding Protein beta Subunits; D008565:Membrane Proteins; C508769:R9AP protein, mouse