Signal transduction mediated by heterotrimeric G-proteins occurs throughout nature and is best represented by phototransduction in retinal rods. However, how trimeric G-proteins subserve vertebrate vision outside photoreceptors is still poorly understood. This application will fill this gap by elucidating the roles of the fifth Gb subnit (Gb5) and its obligate partners R7 Regulators of G-protein Signaling (RGS6, RGS7, RGS9, RGS11) in mouse retina. The proposal is based on defects found in the visual system of Gb5-/-mice, which include: 1) infrequent spontaneous retinal waves~ 2) poorly refined retinogeniculate projections~ 3) abnormal ribbon synapses at outer plexiform layer (OPL) with unincorporated depolarizing bipolar cells (DBC) dendrites~ 4) lack of electroretinography (ERG) b-waves~ 5) reduction of starburst amacrine cell (SAC) dendritic field, 6) rhythmic oscillation SAC membrane potentials, and 7) prolonged phototransduction recovery. We demonstrate that Gb5 works exclusively through stabilizing R7 RGS proteins in retina and hence in its absence the signaling state of Gbo is hypothesized to be pathologically prolonged to cause these visual defects. Furthermore, we find that the requirement of Gb5 and R7 RGS for normal DBC function takes place during retinal development and that Gb5 may be very slowly turned over at dendritic tips of adult DBC. Solving the underlying mechanism(s) of the aforementioned defects will thus advance knowledge concerning the development and function of retina. We propose here to use an integrated approach combining molecular biology, biochemistry, histology, mouse genetics, ERG, and single cell electrophysiology to achieve the following goals.
Aim -1 will test whether prolonged Gbo signaling retards formation of OPL triadic ribbon synapses in Gb5-/- mice.
Aim -2 will define a critical period during which Gb5 and R7 RGS proteins are needed for visual system development. It will also measure the stability of OPL synapse and turnover rate of Gb5, Gbo, Gb13 and R7 RGS proteins in DBC.
Aim - 3 will examine which and how R7 RGS proteins are involved in stage II cholinergic retinal waves, whether prolonged Gbo activation underlies the reduction of SAC dendritic fields, and the synaptic origin and oscillatory mechanism of adult Gb5-/- SAC. By completing these aims we shall know which and how trimeric G-proteins are used in vision beyond phototransduction in different retinal neurons. Useful mouse lines will be made here and characterized to facilitate future inquiry of the applicability of newly gained knowledge in the retina to central visual system and/or other CNS circuits. Finally, knowing the normal visual mechanism is indispensable for efficient prevention, preservation, and restoration of vision in patients suffering from various debilitating blinding diseases.
Retinal neurons downstream of photoreceptors compute and relay visual information to brain. Many hereditary human blinding diseases affect not only photoreceptors but also downstream retinal neurons. The application seeks to advance knowledge on the roles of heterotrimeric G-proteins in retina beyond phototransduction of photoreceptors and to strengthen the knowledge base to provide novel treatment and therapeutic modalities to improve or preserve human vision.