Figure 13.

Model of Netrin-Frazzled synaptogenic mechanism in the GFS. We identified two roles for Netrin-Frazzled signaling in assembly of the giant fiber system. First, we showed that Netrin (blue squares) acts as a cue to direct the GF to select a target. Netrin-Frazzled signaling was also a local guidance cue for the GF and the medial dendrite of TTMn. The TTMn medial dendrite grows toward the midline glia (orange cells), which we showed was a source of Netrin. Second, we hypothesize that Netrin bound on the postsynaptic Frazzled receptors served as a synaptogenic cue for presynaptic Frazzled located on the GF. We propose that the bound Frazzled receptors directed presynaptic synaptogenesis and Innexin localization in the presynaptic terminal.