Light response of retinal ON bipolar cells requires a specific splice variant of Galpha(o).
Glutamate released onto retinal ON bipolar neurons binds to a metabotropic receptor to activate a heterotrimeric G-protein (G(o)) that ultimately closes a nonspecific cation channel. Signaling requires the alpha subunit (Galpha(o)), but its effector is unknown. Because Galpha(o) is transcribed into two splice variants (alpha(o1) and alpha(o2)) that differ in the key GTPase domain, the next step in elucidating this pathway was to determine which splice variant carries the signal. Here we show by reverse transcription-PCR and Western blots that retina expresses both splice variants. Furthermore, in situ hybridization and immunostaining on mouse retina deficient in one splice variant or the other show that both alpha(o1) and alpha(o2) are expressed by ON bipolar cells but that alpha(o1) is much more abundant. Finally, electroretinography performed on mice deficient for one splice variant or the other shows that the positive b-wave (response of ON bipolar cells to rod and cone input) requires alpha(o1) but not alpha(o2). Thus, the light response of the ON bipolar cell is probably carried by its strongly expressed splice variant, Galpha(o1).
Dhingra
Anuradha
A
Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA. annu@retina.anatomy.upenn.edu
Jiang
Meisheng
M
Wang
Tian-Li
TL
Lyubarsky
Arkady
A
Savchenko
Andrey
A
Bar-Yehuda
Tehilla
T
Sterling
Peter
P
Birnbaumer
Lutz
L
Vardi
Noga
N
D017398:Alternative Splicing; D025042:Amacrine Cells / Q000378:metabolism; D000818:Animals; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D020962:Heterotrimeric GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D007700:Kinetics; D008027:Light; D051379:Mice; D018345:Mice, Knockout; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D018092:Kainic Acid Receptors / Q000378:metabolism; D012160:Retina / Q000378:metabolism; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism; D014785:Vision, Ocular; D000097806:GluK2 Kainate Receptor
D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D020962:Heterotrimeric GTP-Binding Proteins; D012333:RNA, Messenger; D018092:Kainic Acid Receptors; D000097806:GluK2 Kainate Receptor