Light-dependent redistribution of visual arrestins and transducin subunits in mice with defective phototransduction.
OBJECTIVE
The light-dependent redistribution of phototransduction components in photoreceptor cells plays a role in light adaptation. Upon illumination, rod and cone arrestins (Arr and cArr) translocate from the inner to the outer segments while transducin subunits (Talpha, Tbetagamma) translocate in the opposite direction. The underlying translocation mechanisms are unclear. This study examines these previously demonstrated translocation in mice with defective phototransduction.


METHODS
The distribution of Arr, cArr, Talpha, and Tbetagamma was examined using immunoblotting and immunocytochemistry in dark- and light-adapted single knockout mice lacking G-protein coupled receptor kinase 1 (Grk1-/-) and double knockout mice lacking GRK1 and transducin alpha subunit (Grk1-/-/Gnat1-/-), or lacking GRK1 and arrestin (Grk1-/-/Arr-/-).


RESULTS
Arr redistributed in the light to the outer segments in Grk1-/- mice as well as in Grk1-/-/Gnat1-/- double knockout retinas. Immunoblotting revealed that approximately 25-50% of Arr associated with the membrane in light-adapted wild-type, Grk1-/- and Gnat1-/-/Grk1-/- mouse retinas. In contrast, cArr did not stably associate with light-adapted membranes in either wild-type or Grk1-/- retinas under our experimental conditions, but redistributed to the cone outer segments in a light-dependent manner. The redistribution of transducin subunits to the inner segments in light occurred in both wild-type and Grk1-/-/Arr-/- double knockout photoreceptors. However, Tbetagamma subunits did not redistribute in the absence of Talpha, suggesting that transducin only translocates as an intact heterotrimer.


CONCLUSIONS
We conclude that in rods, Arr redistribution requires neither rhodopsin phosphorylation nor phototransduction, suggesting the presence of another light-dependent pathway to trigger translocation. In cones, the light-dependent movement of cArr appears to be independent of stable association with the cone pigments. The light-dependent translocations of Arr and transducin subunits in opposite directions appear to be based on independent mechanisms.
Zhang
Houbin
H
Department of Neurobiology and Anatomy, University of Utah, Salt Lake City, USA.
Huang
Wei
W
Zhang
Haikun
H
Zhu
Xuemei
X
Craft
Cheryl M
CM
Baehr
Wolfgang
W
Chen
Ching-Kang
CK
D000818:Animals; D019390:Arrestins / Q000235:genetics / Q000378:metabolism*; D001693:Biological Transport, Active / Q000528:radiation effects; D003623:Dark Adaptation; D005136:Eye Proteins; D019084:Fluorescent Antibody Technique, Indirect; D051606:G-Protein-Coupled Receptor Kinase 1; D015151:Immunoblotting; D008027:Light; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D010766:Phosphorylation; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism* / Q000528:radiation effects; D011494:Protein Kinases / Q000235:genetics; D021122:Protein Subunits; D021381:Protein Transport / Q000528:radiation effects; D012243:Rhodopsin / Q000378:metabolism; D015293:Transducin / Q000235:genetics / Q000378:metabolism*; D014785:Vision, Ocular / Q000502:physiology*
D019390:Arrestins; D005136:Eye Proteins; D021122:Protein Subunits; D012243:Rhodopsin; D011494:Protein Kinases; D051606:G-Protein-Coupled Receptor Kinase 1; C496762:Grk1 protein, mouse; D015293:Transducin