, 1998). Numb is an inhibitor of Notch signaling, and both elevation and loss of Notch signaling AZD5363 chemical structure affect longitudinal glia (Griffiths et al., 2007; Griffiths and Hidalgo, 2004; Kato et al., 2011; Thomas and van Meyel, 2007). We suggest that when Sas is overexpressed in glia and is not restrained by Ptp10D binding, it might sequester Numb, thereby increasing Notch signaling. Binding of Sas to Ptp10D on longitudinal axons facilitates Ptp10D’s

functions in regulation of CNS axon guidance. In glia, overexpressed Sas produces a signal that is suppressed by interactions with neuronal Ptp10D (Figure 8). Other receptors involved in axon guidance exhibit interactions with ligands that produce different signaling outcomes depending on whether the ligands and receptors are expressed on the same or on different cells. In retinal ganglion cells and spinal motor neurons, Eph RTKs interact with Ephrin ligands both on other cells (in trans) and on the same cells (in cis), and cis interactions attenuate the responses of the RTKs to ligand presented in trans ( Carvalho et al., 2006; for review, see Dudanova and Klein, 2011). Gefitinib order Like Sas, Ephrins and type III neuregulin 1, a ligand for ErbB RTKs, also generate “reverse” signals in the cells that express them that are important for axon pathfinding (Hancock et al., 2011). However, Ephrin and

neuregulin signals are produced upon engagement of the ligands with their receptors, not blocked by receptor engagement as in the case of Sas and Ptp10D. FasII-GAL4Mz507 was from Hermann Aberle. Ptp10D is on the X, and is examined as a hemizygote. Ptp10D1, which is a P element excision mutation that deletes N-terminal coding sequence, eliminates all detectable protein expression ( Jeon and Zinn, 2009; Sun et al., 2000). For Ptp69D, transheterozygotes between 5′ (Ptp69D1) and 3′ (Df(3L)8ex25) excision mutations, both of which remove coding sequence, are used in order to generate a null phenotype affecting only Ptp69D ( Desai et al., 1996).

Crosses and embryo collections were performed at room temperature. For the screen, embryos were shifted to 29°C for 60 min prior to dissection. For Sas overexpression experiments, embryos were shifted to 29°C for 90 min prior to fixation and staining. To express Sas and Ptp10D together on glia in a Ptp10D background ( Figure S6), we used the Ptp10DEP1172 allele, which 3-mercaptopyruvate sulfurtransferase reduces Ptp10D expression and produces a phenotype when combined with Ptp69D ( Sun et al., 2000), but also confers GAL4-dependent Ptp10D expression. Procedures for live dissection and RPTP-AP staining were described previously (Fox and Zinn, 2005; Lee et al., 2009). For whole-mount antibody staining of embryo collections, we modified procedures described by Patel (1994). The following antibodies were used: mAb 1D4 (Vactor et al., 1993; used at 1:3), mAb BP102 (Seeger et al., 1993; used at 1:20), mAb 8B2 against Ptp10D (Kurusu and Zinn, 2008; used at 1:5); rabbit-anti-Sas (Schonbaum et al.