RESUMEN
PURPOSE: The Down syndrome cell adhesion molecule (Dscam) gene is required for normal dendrite arborization and lamination in the mouse retina. In this study, we characterized the developmental localization of the DSCAM protein to better understand the postnatal stages of retinal development during which laminar disorganization occur in the absence of the protein. METHODS: Immunohistochemistry and colocalization analysis software were used to assay the localization of the DSCAM protein during development of the retina. RESULTS: We found that DSCAM was initially localized diffusely throughout mouse retinal neurites but then adopted a punctate distribution. DSCAM colocalized with catenins in the adult retina but was not detected at the active zone of chemical synapses, electrical synapses, and tight junctions. Further analysis identified a wave of colocalization between DSCAM and numerous synaptic and junction proteins coinciding with synaptogenesis between bipolar and retinal ganglion cells. CONCLUSIONS: Research presented in this study expands our understanding of DSCAM function by characterizing its location during the development of the retina and identifies temporally regulated localization patterns as an important consideration in understanding the function of adhesion molecules in neural development.
Asunto(s)
Envejecimiento/metabolismo , Cateninas/genética , Moléculas de Adhesión Celular/genética , Neurogénesis/genética , Células Bipolares de la Retina/metabolismo , Células Ganglionares de la Retina/metabolismo , Envejecimiento/genética , Animales , Animales Recién Nacidos , Cateninas/metabolismo , Moléculas de Adhesión Celular/metabolismo , Dendritas/metabolismo , Dendritas/ultraestructura , Perfilación de la Expresión Génica , Regulación del Desarrollo de la Expresión Génica , Ratones , Ratones Transgénicos , Mutación , Neuritas/metabolismo , Neuritas/ultraestructura , Células Bipolares de la Retina/ultraestructura , Células Ganglionares de la Retina/ultraestructura , Sinapsis/metabolismo , Sinapsis/ultraestructura , Uniones Estrechas/metabolismo , Uniones Estrechas/ultraestructuraRESUMEN
The Down syndrome cell adhesion molecule (DSCAM) is required for regulation of cell number, soma spacing, and cell type-specific dendrite avoidance in many types of retinal ganglion and amacrine cells. In this study we assay the organization of cells making up the outer plexiform layer of the retina in the absence of Dscam. Some types of OFF bipolar cells, type 3b and type 4 bipolar cells, had defects in dendrite arborization in the Dscam mutant retina, whereas other cell types appeared similar to wild type. The cone synapses that these cells project their dendrites to were intact, as visualized by electron microscopy, and had a distribution and density that was not significantly different from that of wild type. The spacing of type 3b bipolar cell dendrites was further analyzed by Voronoi domain analysis, density recovery profiling (DRP) analysis, and nearest neighbor analysis. Spacing was found to be significantly different when wild-type and mutant type 3b bipolar cell dendrites were compared. Defects in arborization of these bipolar cells could not be attributed to the disorganization of inner plexiform layer cells that occurs in the Dscam mutant retina or an increase in cell number, as they arborized when Dscam was targeted in retinal ganglion cells only or in the bax null retina. Localization of DSCAM was assayed and the protein was localized near to cone synapses in mouse, macaque, and ground squirrel retinas. DSCAM protein was detected in several types of bipolar cells, including type 3b and type 4 bipolar cells.