(L) S5-laminating RGCs labeled in retina are stained with anti-Spp1 (osteopontin) which marks -RGCs and M2 RGCs (arrowhead). methods to assess functions of Sdk1. In adult retina, 3 neuronal types express but not at detectable levels, 5 express but not and 3 express both. Patterns of gene expression and protein localization at or near synapses are established during the first postnatal week. Dendrites of amacrine cells and RGCs that express but not arborize in the same thin Rabbit Polyclonal to p50 Dynamitin stratum in the center of the IPL. In the absence of Sdk1, this laminar restriction is usually degraded. Overexpression of in developing cells that normally express reorients their dendrites to resemble those of endogenously Sdk1-positive cells, indicating that Sdk1 plays an instructive role in patterning the IPL. Sdk1 fails to Chitosamine hydrochloride impact arbors when launched after they are mature, Chitosamine hydrochloride suggesting that it is required to form but not maintain laminar restrictions. The effect of ectopically expressed sdk1 requires the presence of endogenous Sdk1, suggesting that the effect requires homophilic interactions among Sdk1-positive neurites. Together with previous results on Sdk2, Dscam, DscamL1, as well as the related Contactins, our results support the idea that an sophisticated immunoglobulin superfamily code plays a prominent role in establishing neural circuits in the retina by means of tightly regulated cell type-specific expression and homophilically restricted intercellular interactions. gene in Drosophila, which was identified in a screen for genes that affect patterning of the travel vision (Nguyen et al., 1997) and was recently shown to be required for synaptic targeting of photoreceptors (Astigarraga et al., 2018). The Sdks are large (~250 kD), proteins, with six immunoglobulin domains, thirteen fibronectin repeats, a single transmembrane domain name, and a cytoplasmic domain name ending in a PDZ domain-binding motif. They are homophilic adhesion molecules (Yamagata et al., 2002; Hayashi et al., 2005; Yamagata and Sanes, 2008). Structural studies have shown that Chitosamine hydrochloride this immunoglobulin domains mediate homophilic adhesion, and defined critical residues required for adhesion and for homophilic specificity (Goodman et al., 2016; Tang et al., 2018). Their PDZ-binding motif binds scaffolding proteins of the MAGI family, an conversation that contributes to their concentration at synaptic sites (Yamagata and Sanes, 2010). In chick retina, the Sdks are expressed by non-overlapping subsets of retinal neurons, and required for restriction of neuronal processes to specific strata within the IPL (Yamagata et al., 2002; Yamagata and Sanes, 2008). Their closest relatives, two ((is usually expressed by restricted subsets of retinal neurons, including an unusual glutamatergic amacrine Chitosamine hydrochloride interneuron called VGlut3-positive amacrine cells (VG3-ACs) (Haverkamp and W?ssle, 2004; Johnson et al., 2004; Grimes et al., 2011) and an RGC type called W3B, which has the unusual house of responding when the Chitosamine hydrochloride timing of the movement of a small object differs from that of the background, but not when they coincide (Kim et al., 2010, 2015; Zhang et al., 2012; Lee et al., 2014; Krishnaswamy et al., 2015). We showed that VG3-ACs synapse on W3B-RGCs, that VG3 input is essential for W3B-RGC function, that Sdk2 is required for restriction of VG3-AC and W3B-RGC processes to appropriate strata, and that the number and strength of functional connections between VG3-ACs and W3B-RGCs are dramatically reduced in the absence of Sdk2 (Krishnaswamy et al., 2015). Here, we have analyzed expression and functions of Sdk1 in mouse retina. Confirming initial observations (Krishnaswamy et al., 2015), we show that and are largely non-overlapping, but we also found three types that express both in chick, is usually expressed by interneurons and RGCs that arborize in the same strata, and neurites of these cells exhibit decreased laminar restriction in the absence of Sdk1. Finally, we use ectopic overexpression of in cells that normally express to demonstrate that it plays an instructive role in laminar targeting and that it does so by a homophilic mechanism. Materials and Methods.