| Popis: |
In the developing central nervous system, many neurons migrate tangentially, parallel to the pial surface and independently of radial glia processes. Tangential migration has been first described in the embryonic hindbrain where neurons of the precerebellar nuclei (PCN) and of the facial branchiomotor nucleus (FBM) follow complex migratory routes along the anterior–posterior and dorsoventral axis. We are reviewing here the cellular and molecular mechanisms which control the tangential migration of PCN and FBM neurons. To a large extent these models are based on the phenotypic analysis of multiple mouse and fish mutants. Although mounting evidence suggests that various diffusible molecules, such as slits and netrin1, influence the ventral migration of PCN neurons and their behavior at the midline, the mechanisms controlling their anterior–posterior distribution are still largely unknown. By contrast, the caudal migration of FBM neurons has been extensively studied and shown to be controlled by wnt, growth factors, and components of the PCP pathways, even though chemotropic attractive and repulsive molecules might also be involved. Interestingly, various secreted molecules such as CXCL12 and retinoic acid seem responsible of the preferential subpial position of both PCN and FBM migrating neurons. For the two types of neurons, the final switch from a tangential mode of migration to a radial one also seems to obey to some common rules. |
