title: Lack of mGluR6-related cascade elements leads to retrograde trans-synaptic effects on rod photoreceptor synapses via matrix-associated proteins.
abstract: Heterotrimeric G-proteins couple metabotropic receptors to downstream effectors. In retinal ON bipolar cells, Go couples the metabotropic receptor mGluR6 to the TRPM1 channel and closes it in the dark, thus hyperpolarizing the cell. Light, via GTPase-activating proteins, deactivates Go , opens TRPM1 and depolarizes the cell. Go comprises Gαo1 , Gβ3 and Gγ13; all are necessary for efficient coupling. In addition, Gβ3 contributes to trafficking of certain cascade proteins and to maintaining the synaptic structure. The goal of this study was to determine the role of Gαo1 in maintaining the cascade and synaptic integrity. Using mice lacking Gαo1 , we quantified the immunostaining of certain mGluR6-related components. Deleting Gαo1 greatly reduced staining for Gβ3, Gγ13, Gβ5, RGS11, RGS7 and R9AP. Deletion of Gαo1 did not affect mGluR6, TRPM1 or PCP2. In addition, deleting Gαo1 reduced the number of rod bipolar dendrites that invaginate the rod terminal, similar to the effect seen in the absence of mGluR6, Gβ3 or the matrix-associated proteins, pikachurin, dystroglycan and dystrophin, which are localized presynaptically to the rod bipolar cell. We therefore tested mice lacking mGluR6, Gαo1 and Gβ3 for expression of these matrix-associated proteins. In all three genotypes, staining intensity for these proteins was lower than in wild type, suggesting a retrograde trans-synaptic effect. We propose that the mGluR6 macromolecular complex is connected to the presynaptic rod terminal via a protein chain that includes the matrix-associated proteins. When a component of the macromolecular chain is missing, the chain may fall apart and loosen the dendritic tip adherence within the invagination.
authors.affiliation: Department of Neuroscience, University of Pennsylvania, Philadelphia, PA, 19104, USA.
authors.forename: Shanti R
authors.initials: SR
authors.lastname: Tummala
authors.affiliation: Department of Neuroscience, University of Pennsylvania, Philadelphia, PA, 19104, USA.
authors.forename: Anuradha
authors.initials: A
authors.lastname: Dhingra
authors.affiliation: Department of Neuroscience, University of Pennsylvania, Philadelphia, PA, 19104, USA.
authors.forename: Marie E
authors.initials: ME
authors.lastname: Fina
authors.affiliation: Department of Neurology, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Jian J
authors.initials: JJ
authors.lastname: Li
authors.affiliation: Department of Neuroscience, University of Pennsylvania, Philadelphia, PA, 19104, USA.
authors.forename: Hariharasubramanian
authors.initials: H
authors.lastname: Ramakrishnan
authors.affiliation: Department of Neuroscience, University of Pennsylvania, Philadelphia, PA, 19104, USA.
authors.forename: Noga
authors.initials: N
authors.lastname: Vardi
mesh_terms: D000818:Animals; D003712:Dendrites / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000378:metabolism*; D005260:Female; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000235:genetics / Q000378:metabolism*; D044387:GTP-Binding Protein beta Subunits / Q000378:metabolism; D044388:GTP-Binding Protein gamma Subunits / Q000378:metabolism; D020690:GTPase-Activating Proteins / Q000378:metabolism; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D018094:Receptors, Metabotropic Glutamate / Q000378:metabolism*; D051245:Retinal Bipolar Cells / Q000378:metabolism / Q000648:ultrastructure; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism* / Q000648:ultrastructure; D015398:Signal Transduction; D013569:Synapses / Q000648:ultrastructure*; D050053:TRPM Cation Channels / Q000378:metabolism
chemical_list: D016326:Extracellular Matrix Proteins; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D020690:GTPase-Activating Proteins; D018094:Receptors, Metabotropic Glutamate; D050053:TRPM Cation Channels; C116297:Trpm1 protein, mouse; C113897:metabotropic glutamate receptor 6; C000594262:GNAO1 protein, mouse; D019206:GTP-Binding Protein alpha Subunits, Gi-Go
keywords: G-protein; dystrophin; mouse; pikachurin; β-dystroglycan