title: Synaptic localization and function of Sidekick recognition molecules require MAGI scaffolding proteins.
abstract: Four transmembrane adhesion molecules-Sidekick-1, Sidekick-2, Down's syndrome cell adhesion molecule (Dscam), and Dscam-like-are determinants of lamina-specific synapse formation in the vertebrate retina. Their C termini are predicted to bind postsynaptic density (PSD)-95/Discs Large/ZO-1 (PDZ) domains, which are present in many synaptic scaffolding proteins. We identify members of the membrane-associated guanylate kinase with inverted orientation (MAGI) and PSD-95 subfamilies of multi-PDZ domain proteins as binding partners for Sidekicks and Dscams. Specific MAGI and PSD-95 family members are present in distinct subsets of retinal synapses, as are Sidekicks and Dscams. Using Sidekick-2 as an exemplar, we show that its PDZ-binding C terminus is required for both its synaptic localization in photoreceptors and its ability to promote lamina-specific arborization of presynaptic and postsynaptic processes in the inner plexiform layer. In photoreceptor synapses that contain both MAGI-1 and PSD-95, Sidekick-2 preferentially associates with MAGI-1. Depletion of MAGI-1 from photoreceptors by RNA interference blocks synaptic localization of Sidekick-2 in photoreceptors without affecting localization of PSD-95. Likewise, depletion of MAGI-2 from retinal ganglion cells and interneurons interferes with Sidekick-2-dependent laminar targeting of processes. These results demonstrate that localization and function of Sidekick-2 require its incorporation into a MAGI-containing synaptic scaffold.
authors.affiliation: Center for Brain Science and Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Masahito
authors.initials: M
authors.lastname: Yamagata
authors.forename: Joshua R
authors.initials: JR
authors.lastname: Sanes
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000032:analysis / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015815:Cell Adhesion Molecules; D002460:Cell Line; D002645:Chickens; D051528:Guanylate Kinases; D006801:Humans; D007074:Immunoglobulin G / Q000032:analysis / Q000378:metabolism* / Q000502:physiology; D008565:Membrane Proteins / Q000032:analysis / Q000378:metabolism* / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D034521:Nuclear Matrix-Associated Proteins / Q000032:analysis / Q000378:metabolism* / Q000502:physiology; D012165:Retinal Ganglion Cells / Q000737:chemistry / Q000502:physiology; D013569:Synapses / Q000378:metabolism* / Q000502:physiology
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D015815:Cell Adhesion Molecules; D007074:Immunoglobulin G; D008565:Membrane Proteins; D034521:Nuclear Matrix-Associated Proteins; C506156:Sdk2 protein, mouse; D051528:Guanylate Kinases; C493280:Magi1 protein, mouse