N-Cadherin and Ng-CAM/8D9 are involved serially in the migration of newly generated neurons into the adult songbird brain

In the adult avian forebrain, neurons continue to be produced in the subependymal zone (SZ), from which they migrate upon radial fibers. To identify ligands regulating this process, we studied N-cadherin and Ng- CAM/8D9 expression in HVC, a neurogenic region of the canary neostriatum. N- cadherin was relatively restricted to the SZ and was expressed by dividing, [³H]thymidine-labeled precursor cells. However, cellular N-cadherin was down-regulated prior to neuronal migration from the SZ. Addition of anti-N- cadherin Fab hastened neuronal migration from adult SZ explants, without influencing neuronal number. Unlike N-cadherin, Ng-CAM/8D9 was expressed by migrating neurons. Anti-8D9 Fab inhibited neuronal migration upon cultured ependymoglia, which did not express Ng-CAM/8D9. Thus, the departure of new neurons from the adult SZ may require their suppression of N-cadherin, whereas their subsequent migration and survival may depend upon neuronal expression of Ng-CAM/8D9 and its interaction with a heterophilic radial cell receptor.