Fig. 8. The role of Dephrin/DEph signalling during CNS development in Drosophila embryos. (A,B) In stage 12 of embryogenesis, the first interneuronal axons project away from the midline (dotted line) and extend up to the lateral border (line) of the CNS (arrow labels growth cone in A). After reaching the border, the axons turn and continue to extend in parallel to the midline (B). At this stage anti-Futsch (brown) labels the axons of both MP2 neurones and anti-Odd (black) labels the nucleus of dMP2 and the MP1 neurones. (C,D) Anti-Dephrin staining at stage 13 shows that the MP2 axons (arrow labels growth cone) extend along a thin Dephrin-free channel (C, MP2 neurones are labelled by the expression of tau-GFP driven by the GAL4 driver CY27). D shows Dephrin expression only. (E) We propose that primary neurones project away from the ventral midline (pink) owing to the secretion of the long range repellent Slit (orange). When the growth cones reach the lateral border they are repelled by Dephrin (green). This repulsion induces growth cones, which carry the receptor DEph (blue), to turn and confines axon extension to within the CNS. Horizontal views, anterior to the left