“…Recent invertebrate studies have identified a number of cell-surface molecules that are required cell-autonomously for establishing non-overlapping dendrites or axons in a roughly two dimensional (2D) plane. They include the Down’s syndrome cell adhesion molecule (Dscam) (Hughes et al, 2007; Matthews et al, 2007; Soba et al, 2007), the secreted guidance molecule Netrin and its receptors (Smith et al, 2012), the cadherin member Flamingo (Fmi) (Matsubara et al, 2011), the Leukocyte Antigen Related (LAR) protein receptor tyrosine phosphatase (Baker and Macagno, 2000), the cell adhesion molecule integrin (Han et al, 2012; Kim et al, 2012), and the tripartite ligand-receptor complex involving SAX-7, MNR-1, and DMA-1 (Dong et al, 2013; Salzberg et al, 2013). In mammals, however, only a few molecules, including Dscam and the related DscamL1 (Fuerst et al, 2009), the transmembrane semaphorin 6A (Sema6A) (Matsuoka et al, 2012), and the gamma cluster of protocadherins (Pcdhgs) (Lefebvre et al, 2012), have been studied for their self-avoidance function in subpopulations of retinal cells and cerebellar Purkinje cells (PCs).…”