Abstract
Luteinizing hormone-releasing hormone (LHRH) neurons migrate from the vomeronasal organ (VNO) to the forebrain in all mammals studied. In mice, most LHRH neuron migration is dependent on axons that originate in the VNO but bypass the olfactory bulb and project into the basal forebrain. Thus, cues that regulate the trajectories of these vomeronasal axons are candidates for determining the destination of LHRH neurons. Using in situ hybridization techniques, we examined the expression of Deleted in colorectal cancer (DCC), a vertebrate receptor for the guidance molecule netrin-1, during development of the olfactory system. DCC is expressed by cells in the olfactory epithelium (OE) and VNO, and in cells migrating from the OE and VNO from embryonic day 11 (E11) to E14. Some DCC(+) cells on vomeronasal axons in the nose also express LHRH. However, DCC expression is downregulated beginning at E12, so few if any LHRH neurons in the forebrain also express DCC. In rat, DCC is expressed on TAG-1(+) axons that guide migrating LHRH neurons. We therefore examined LHRH neuron migration in DCC(-/-) mice and found that trajectories of the caudal vomeronasal nerve and positions of LHRH neurons are abnormal. Fewer than the normal number of LHRH neurons are found in the basal forebrain, and many LHRH neurons are displaced into the cerebral cortex of DCC(-/-) mice. These results are consistent with the idea that DCC regulates the trajectories of a subset of vomeronasal axons that guide the migration of LHRH neurons. Loss of DCC function results in the migration of many LHRH neurons to inappropriate destinations.