A SEPTUM-DERIVED CHEMOREPULSIVE FACTOR FOR MIGRATING OLFACTORY INTERNEURON PRECURSORS

During mammalian brain development, immature neurons often migrate con siderable distances. A dramatic example is the rostral migration of ol factory interneuron precursors from near the septum to the olfactory b ulb via a subventricular pathway. Heterotopic transplantations establi sh that this migration is unidirectional and that guidance cues operat e over a considerable distance. The guidance cues for this translocati on have not been identified, and the present studies provide evidence that a diffusible chemorepulsive factor, secreted by caudal septum but not by other tissue regions surrounding the pathway, may be involved. This activity is functionally distinct from that produced by factors that influence vertebrate axon outgrowth, such as netrin-1, netrin-2, and collapsin-1/semaphorin-III. The presence of this activity in the f loor plate/ventral spinal cord as well as the septum suggests that it may influence other types of cell migration.