This Df screen had two problems. First, homozygotes for many Dfs in the kit had severe CNS defects that preclude screening. To alleviate this, we replaced Dfs for which development failed with smaller Dfs that allow better development, creating a “phenotype Df kit” with which >80% of the genome can be screened for ligands (http://fly.bio.indiana.edu/Browse/df/zinn.php). This kit can also be used for systematic genome screening for any embryonic phenotype, and such a screen requires analysis VE-822 order of less than 400 lines (Wright

et al., 2010). Second, if multiple RPTP ligands are expressed in overlapping patterns, deletion of a gene encoding one ligand might not produce a decrease in staining that can be unambiguously scored. For Lar-AP, deletion of Sdc only slightly reduces axonal staining. A Lar-AP mutant that cannot bind

to HSPGs stained CNS axons with equal intensity in wild-type and Sdc embryos, indicating that Lar has non-HSPG axonal binding partners ( Fox and Zinn, 2005). In this paper, we describe a screen that addresses the second problem. GAL4-dependent expression of Sdc on muscles conferred bright staining with Lar-AP (Fox and Zinn, 2005). This suggested that if we ectopically expressed many cell-surface and secreted (CSS) proteins, potential ligands could be identified by ectopic staining with RPTP-AP probes. We had assembled a collection of lines bearing P element insertions with GAL4 binding sites upstream of 410 CSS protein genes in order to screen for genes involved in targeting of motor axons to muscle fibers (Kurusu et al., 2008). These lines were later used to find genes affecting axonal and dendritic targeting

Sirolimus in the antennal lobe (Hong et al., 2009, 2012). Screening the CSS insertion lines for ectopic staining with Ptp10D-AP (10D-AP) identified a binding partner for Ptp10D, Stranded at second (Sas). The sas gene encodes two large cell-surface proteins of unknown function that are expressed on the apical surfaces of epithelially derived cells ( Schonbaum et al., 1992). Ptp10D is a type III RPTP. It is orthologous to a group of four mammalian RPTPs that negatively regulate receptor TKs (RTKs) by direct dephosphorylation (reviewed by Matozaki et al., 2010). PTPRJ (DEP-1/CD148), which corresponds to the Suppressor of colon cancer 1 (Scc1) gene ( Ruivenkamp et al., 2002) dephosphorylates Methisazone the epidermal growth factor receptor (EGFR), vascular endothelial growth factor receptor (VEGFR), and CSF1R/Met growth factor RTKs ( Chabot et al., 2009; Palka et al., 2003; Tarcic et al., 2009). PTPRB (VE-PTP) regulates Tie-2 ( Winderlich et al., 2009), and PTPRO regulates TrkC and Eph RTKs ( Hower et al., 2009; Shintani et al., 2006). Type III RPTPs can be tyrosine-phosphorylated on a C-terminal YxNΦ (Φ = hydrophobic) motif, and this causes activation of Src-family tyrosine kinases (SFKs) ( Murata et al., 2010). Ptp10D is expressed on CNS axons (Tian et al., 1991; Yang et al.