Gβ5 is required for normal light responses and morphology of retinal ON-bipolar cells

G beta 5 exists as two splice variants, G beta 5-S and G beta 5-L, which interact with and stabilize the R7 members of the regulators of G-protein signaling (RGSs): RGS6, RGS7, RGS9, and RGS11. Although the role of G beta 5-L and RGS9-1 is established in photoreceptors, the physiological functions of G beta 5-S and other R7 RGS proteins remain unclear. We found that the electroretinogram of G beta 5(-)/-mice lacks the b-wave component and that G beta 5-S and RGS11 colocalize with Go alpha at the tips of the ON-bipolar cell dendrites. Unexpectedly, we found a significant reduction in the number of synaptic triads in the outer plexiform layer (OPL) of the G beta 5(-)/(-) mice, which is evident at postnatal day 14. Transgenic expression of G beta 5-L in rods failed to rescue the b-wave or the OPL defects. These results indicate that G beta 5-S is indispensable for OPL integrity and normal light responses of the retina.