Targeting of RGS7/Gβ5 to the Dendritic Tips of ON-Bipolar Cells Is Independent of Its Association with Membrane Anchor R7BP

Complexes of regulator of G-protein signaling (RGS) proteins with G-protein beta 5 (G beta 5) subunits are essential components of signaling pathways that regulate the temporal characteristics of light-evoked responses in vertebrate retinal photoreceptors and ON-bipolar cells. Recent studies have found that RGS/G beta 5 complexes bind to a new family of adapter proteins, R9AP (RGS9 anchor protein) and R7 family binding protein (R7BP), that in case of the RGS9/G beta 5 complex were shown to determine its precise subcellular targeting to either the outer segment of photoreceptors or postsynaptic structures of striatal neurons, respectively. In this study, we establish that another trimeric complex consisting of RGS7, G beta 5, and R7BP subunits is specifically targeted to the dendritic tips of retinal bipolar cells. However, examination of the mechanisms of complex targeting in vivo surprisingly revealed that the delivery of RGS7/G beta 5 to the dendrites of ON-bipolar cells occurs independently of its association with R7BP. These findings provide a new mechanism for adapter-independent targeting of RGS/G beta 5 complexes.