title: Reelin signaling is necessary for a specific step in the migration of hindbrain efferent neurons.
abstract: The cytoarchitecture of the hindbrain results from precise and co-ordinated sequences of neuronal migrations. Here, we show that reelin, an extracellular matrix protein involved in neuronal migration during CNS development, is necessary for an early, specific step in the migration of several hindbrain nuclei. We identified two cell populations not previously known to be affected in reeler mutants that show a common migratory defect: the olivocochlear efferent neurons and the facial visceral motor nucleus. In control embryos, these cells migrate first toward a lateral position within the neural tube, and then parallel to the glial cell processes, to a ventral position where they settle close to the pial surface. In reeler mutants, the first migration is not affected, but the neurons are unable to reach the pial surface and remain in an ectopic position. Indeed, this is the first evidence that the migration of specific hindbrain nuclei can be divided into two parts: a reelin-independent and a reelin-dependent migration. We also show that reelin is expressed at high levels at the final destination of the migratory process, while the reelin intracellular effector Dab1 was expressed by cell groups that included the two populations affected. Mice mutant at the Dab1 locus, called scrambler, exhibit the same phenotype, a failure of final migration. However, examination of mice lacking both reelin receptors, ApoER2 and VLDLR, did not reveal the same phenotype, suggesting involvement of an additional reelin-binding receptor. In the hindbrain, reelin signaling might alter the adhesive properties of efferent neurons and their ability to respond to directional cues, as has been suggested for the migration of olfactory bulb precursors.
authors.affiliation: EPHE Quantitative Cell Biology, INSERM EMI 343, IFR 122, University Montpellier 2, 34090 Montpellier, France. mrossel@univ-montp2.fr
authors.forename: Mireille
authors.initials: M
authors.lastname: Rossel
authors.forename: Karine
authors.initials: K
authors.lastname: Loulier
authors.forename: Christian
authors.initials: C
authors.lastname: Feuillet
authors.forename: Serge
authors.initials: S
authors.lastname: Alonso
authors.forename: Patrick
authors.initials: P
authors.lastname: Carroll
mesh_terms: D000818:Animals; D001934:Branchial Region / Q000502:physiology; D015816:Cell Adhesion Molecules, Neuronal / Q000378:metabolism*; D002465:Cell Movement / Q000502:physiology*; D016326:Extracellular Matrix Proteins / Q000378:metabolism*; D051379:Mice; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D009476:Neurons, Efferent / Q000378:metabolism*; D000091042:Reelin Protein; D012249:Rhombencephalon / Q000196:embryology / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D015816:Cell Adhesion Molecules, Neuronal; C103773:Dab1 protein, mouse; D016326:Extracellular Matrix Proteins; D009419:Nerve Tissue Proteins; D000091042:Reelin Protein; C000717128:Reln protein, mouse; D012697:Serine Endopeptidases