, 2010 and Suto et al., 2005). In addition, some Semas can also function as receptors to elicit signals check details in reverse ( Yu et al., 2010), although how cis-binding can influence Plexin:Sema reverse signaling is still unclear. Thus, cis-interaction between receptors and ligands in axon guidance signaling is emerging as a mechanism complementary to trans-interactions allowing for an increased diversity and modulation of growth cone responses. In addition to their role in axon guidance, Ephs and ephrins have been implicated in a multitude of processes such as

glucose homeostasis, immune responses, angiogenesis, and cancer (Pasquale, 2008). Ephs and ephrins are coexpressed in β cells in the pancreas (Konstantinova et al., 2007), T- and B cells (Nakanishi et al., 2007 and Wu and Luo, 2005), and several types of cancer cells (Ireton and Chen, 2005, Noren and Pasquale, 2007 and Pasquale, 2010), but the significance of Eph/ephrin cis-interaction is still unclear. The imbalance of Eph/ephrin function may contribute to disease progression, for example, in melanoma cells coexpressing Ephs and ephrins, where diverse effects of bidirectional 5-Fluoracil ic50 trans-signaling on proliferation and/or metastasis have

been reported ( Noren et al., 2006 and Yang et al., 2006), with little understanding of the contribution of Eph/ephrin cis-interactions in this context. However, our insights into ephrin cis-attenuation of Eph signaling in motor axon guidance as well as studies in other

systems suggest that ligand mediated cis-attenuation of receptor function is a universal mechanism for not only augmenting the diversity of axon guidance responses but it also modulating other cell signaling responses. Fertilized chicken eggs (Couvoir Simetin) were incubated and staged according to standard protocols (Hamburger and Hamilton, 1951). Chick spinal cord electroporation of expression plasmids or siRNAs was performed at HH st. 18/19 as described (Kao et al., 2009, Luria et al., 2008 and Momose et al., 1999). SiRNA duplex oligonucleotides with 3′TT overhang were purified over MicroSpin G-25 columns (GE Healthcare) until in 10 mM Tris-Cl (Fisher Scientific), 1 mM EDTA (Invitrogen), and 20 mM NaCl (EMD Chemicals). GFP expression plasmid (1 μg/μl) was coelectroporated with the siRNA solution to label motor axons. SiRNA sequences (sense strand) are [ephrin-A5]siRNA, 1:1 mixture of GCCAGAAGAUAAGACCGAA and GCUAUGUUCUGUACAUGGU; [ephrin-B2]siRNA, 1:1 mixture of GGACAAGGAUUGGUACUAU and GCCUGGAAUUUCAGAAGAA; scrambled [ephrin-A5]siRNA, 1:1 mixture of GCCGAAAUAAGACCAGGAA and GCUUUGGUCCAUUAAUGGU; scrambled [ephrin-B2]siRNA, 1:1 mixture of GGAAGGAGGUUCAUACUAU and GCCUAAGACUUAAGGUGAA. Retrograde labeling of chick motor neurons using HRP (Roche) as tracers was performed as described (Kao et al., 2009).