Glutamate Receptor Trafficking in Visual Development

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DESCRIPTION (provided by applicant): Abnormal activity-mediated developmental regulation of glutamatergic neurotransmission is implicated in amblyopia, disruption of stereopsis and changes in retinal function. Thus, an understanding of molecular bases of synaptic plasticity during visual development is central to the mission of the National Eye Institute. Data suggest that myosin VA (myo VA) moves membrane vesicles on actin and delivers glutamate receptors (GRs) to synapses. Our recent data indicate that this process is rapidly regulated by light-driven synaptic activity following eye-opening. We hope to establish the mouse mutant strain flailer as a model for mechanistic studies of myo VA in synaptogenesis and for visual activity-dependent trafficking of the NMDA receptor and its mature scaffolding complex, the postsynaptic density proteins PSD-95 and GKAP-95. Flailer mice express a fusion gene containing the promoter and first two exons of a brain-specific G protein plus the C-terminal of myo VA (Jones et al. 2000). The flailer protein appears to act as a dominant-negative myo VA in the central nervous system. Flailer mice have neural abnormalities similar to those of myo VA null mutants, but unlike the null mice homozygous flailer mice survive and breed normally. Functional changes caused by the flailer mutation have not yet been explored at synaptic levels. We propose to determine (l) if flailer protein and normal myo VA are present in retina, superficial visual, layers of the superior colliculus (sSC), and visual cortex (VC) of homozygous flailer mice, and (II) if flailer mice show activity-dependent transport of the PSD-95/GKAP NR scaffolding complex to visual synapses within 6 hours of eye-opening. We will perform quantitative immunoblotting of homogenates of these regions and of fractions enriched for dendritic or whole-lysate protein from VC and sSC using antibodies that distinguish normal and flailer myo VA, PSD-95, GKAP-130 and GKAP-95. If flailer protein is present in retina, we will (Ill) determine whether flailer and WT retina are similar in the distribution of PSD-95 after eye-opening and in ganglion cell responses to light. Retinal function will be analyzed by our collaborator Dr. Niang Tian at Yale University. He will use ERG, mutielectrode arrays, and whole-cell patch clamping to study retinal ganglion cell responses to light. We will perform quantitative confocal analyses of retinas processed for PSD-95 immunocytochemistry before and after eye-opening. Finally, (IV) we will determine, central visual pathway glutamate receptor function is normal in flailer mouse brain using whole-cell voltage recordings of glutamate receptor currents in slice preparations of the sSC.