Fig. 9. Schematic diagram of Pax6/ephrin A5-dependent mechanisms for alignment of olfactory cortex neurons at PSB. (A) Olfactory cortex neurons are generated in the dorsal part of the rat telencephalon at around E11.75 (corresponding to E9.75 in mouse embryos). These neurons migrate ventrally and align at the PSB through ephrin A5 repulsive activity. In the Pax6 mutant, reduced ephrin A5 expression allows these neurons to invade the ventral part of the telencephalon. (B) The ventrally migrating neurons include several distinct subtypes such as lot cells and olfactory cortex neurons. They migrate ventrally, probably owing to some attractant distributed in the dorsal part of the telencephalon and/or secreted from the ventral part of the telencephalon. Netrin 1 acts as an attractant for lot cells (Kawasaki et al., 2006). Ephrin A5 and other factors act as contact-dependent repellents for these neurons.