The mammalian brain is formed through a series of intricately orchestrated events whereby neurons born in germinal zones migrate for long distances to reach their final positions and form specific connections.The postmitotic neurons use the radial glial fibers as scaffold to migrate to their final destination during the brain development.It has been established that the Reelin signaling pathway is crucial for neuronal migration and positioning during corticogenesis.However, the mechanism of Reelin action on migrating neurons has remained unclear.The plasmid containing green fluorescence protein (GFP) sequence was injected into the lateral ventricles and transfected into the cells in ventricular zone of cerebral cortex in mouse embryos (E14.5-E17.5) by using in utero electroporation.The transfected brains were fixed with 4% PFA two or five days after the electroporation and used for immunocytochemisty against Reelin and different markers for radial glail cells.Our results showed that the transfected cells expressed strong GFP.Some GFP-positive cells showed the typical morphology of radial glial cells possessing a long and thin process that spans the whole developing cerebral cortex and gave rise to intensive branching in marginal zone where Reelin is expressed.The GFP-labeled cells located between ventricular zone and marginal zone showed the typical morphology of migrating neurons having a long and thick unbranched leading process and a short and thin trailing process.As soon as the tip of leading process of migrating neurons reach Reelin-abundant marginal zone, they generate intensive branches and anchor to the marginal zone of the cortex, which facilitates somal translocation to finish the migration process.In the present study, we first used in vivo research method-in utero electroporation to elaborate that Reelin induces branching of the leading process of migrating neurons, as well as the apical process of radial glial cells.