Arrestin migrates in photoreceptors in response to light: a study of arrestin localization using an arrestin-GFP fusion protein in transgenic frogs.
Subcellular translocation of phototransduction proteins in response to light has previously been detected by immunocytochemistry. This movement is consistent with the hypothesis that migration is part of a basic cellular mechanism regulating photoreceptor sensitivity. In order to monitor the putative migration of arrestin in response to light, we expressed a functional fusion between the signal transduction protein arrestin and green fluorescent protein (GFP) in rod photoreceptors of transgenic Xenopus laevis. In addition to confirming reports that arrestin is translocated, this alternative approach generated unique observations, raising new questions regarding the nature and time scale of migration. Confocal fluorescence microscopy was performed on fixed frozen retinal sections from tadpoles exposed to three different lighting conditions. A consistent pattern of localization emerged in each case. During early light exposure, arrestin-GFP levels diminished in the inner segments (ISs) and simultaneously increased in the outer segments (OSs), initially at the base and eventually at the distal tips as time progressed. Arrestin-GFP reached the distal tips of the photoreceptors by 45-75 min at which time the ratio of arrestin-GFP fluorescence in the OSs compared to the ISs was maximal. When dark-adaptation was initiated after 45 min of light exposure, arrestin-GFP rapidly re-localized to the ISs and axoneme within 30 min. Curiously, prolonged periods of light exposure also resulted in re-localization of arrestin-GFP. Between 150 and 240 min of light adaptation the arrestin-GFP in the ROS gradually declined until the pattern of arrestin-GFP localization was indistinguishable from that of dark-adapted photoreceptors. This distribution pattern was observed over a wide range of lighting intensity (25-2700 lux). Immunocytochemical analysis of arrestin in wild-type Xenopus retinas gave similar results.
Peterson
James J
JJ
Department of Ophthalmology, University of Florida, 1600 SW Archer Road, D4-32, Gainesville, FL 32610-0284, USA.
Tam
Beatrice M
BM
Moritz
Orson L
OL
Shelamer
Charles L
CL
Dugger
Donald R
DR
McDowell
J Hugh
JH
Hargrave
Paul A
PA
Papermaster
David S
DS
Smith
W Clay
WC
D000221:Adaptation, Ocular / Q000502:physiology*; D000818:Animals; D030801:Animals, Genetically Modified; D019393:Arrestin / Q000378:metabolism*; D003623:Dark Adaptation / Q000502:physiology; D049452:Green Fluorescent Proteins; D008027:Light; D008164:Luminescent Proteins; D018613:Microscopy, Confocal; D010775:Photic Stimulation; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000378:metabolism; D014982:Xenopus laevis
D019393:Arrestin; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins