Role Of Reelin Signal Molecules On Neuronal Migration

The brain is the responsible for higher cognitive functions, and neuronal migration isimportant for brain development. The neuronal migration is controled by the differentsignaling pathways, and the Reelin signaling cascade is one of the most typical signal pathway.Although many signal transduction and molecular interaction in the Reelin signaling pathwaywere studied in some detail, the accurate role of Reelin in migration and cortex layering isstill barely understood.To study the role of different Reelin signal molecules on neuronal migration. Weestablished the in utero electroportion first, and found out the timing of operation andsampling to observe the neuronal migration and morphology of migrating neurons. We tried totransfect the radial glial cells with specific promoter using in utero electroporation. Aftertransfection of different mutant mice, such as reeler, vldlr-/-, apoer-/-and dab1-/-, weobserved the neuronal migration and morphology of migrating neurons and radial glial cells.The results were as follows:1. We established the in utero electroporation system. Transfection of GFP plasmid intothe ventribular cells could describe the morphology of neurons. The neurons which weretransfected at different time point located at different position in cortical plate. Moreover, wefound the neurons born at E15.5migrated into cortical plate after3days of transfection andlocated at their final destination at the boundary between cortial plate and marginal zone after5days of transfection. The pCAG-EGFP plasmid had a long-term expression in the micecortex, which could apply to study the dendritic spine of neurons.2. With the fluorescent immunohistochemical staining, it’s hard to identify the intactmorphology of the radial glial cell. After transfection the pCAG-EGFP plasmid into theventricular zone with in utero electroporation, both of the neurons and the radial glial cellswere labeled that influence the observation of radial glial cells. Transfection with specificexpression plasmid pBLBP-EGFP into the ventricular zone, the pBLBP-EGFP was morespecifically expressed in the radial glial cells. With this plasmid, we could label an intactradial glial cell. Subsequently we transfected the pBLBP-EGFP in the radial glial cells atdifferent embryonic days, and found that the length of radial glial fibre was changed with thedifferent phase of migrating neurons in the cortex. The branches of radial glial cells had more significant morphological changes. As the neurons migrated from ventribular zone throughintermediate zone to cortical plate, the branches of radial glial cells had significant changes,such as longer branch, more branches and smaller angle between branches.3. Transfection of different mutant or knockout mice with in utero electroporation, suchas reeler，vldlr-/-apoer2-/-and dab1-/-was to study the role of different Reelin signalmolecules on neuronal migration. The resultes showed that, reeler，vldlr-/-apoer2-/-anddab1-/-had similar phenotype during neuronal migration: neurons could not migrate into thesuperfical layer of cortical plate to contact with marginal zone, and the polarity of migratingneurons changed significantly, moreover, the migrating neurons branched in the cortical plate.However, there were different morphological changes of radial glial cells between thesemutant mice: compared with wildtype, the number of branches, the branch length and thebranch angle of radial glial cells decreased in reeler and vldlr-/-apoer2-/-. In dab1-/-, thenumber of branches of radial glial cells was decreased significantly compared with wildtype,but still more than reeler and vldlr-/-apoer2-/-. The length of branches of radial glial cells indab1-/-was similar with wildtype, and the branch angle was obviously bigger than wildtype.4. The results of transfection indicated that more neuons migrated into the marginal zone,and the primary point of radial glial cells entered into the depth of marginal zone in vldlr-/-. Inapoer2-/-, late-born neurons could not migrate regularly, and migrating neurons had a longerleading process than wildtype. Besides, in apoer2-/-the length of branch of radial glial cellswas also longer than wildtype. Because of the migration defects of late-born neurons, thethickness of marginal zone of apoer2-/-became wider. This made the primary point of radialgilal cells located in the depth of marginal zone.In summary, the morphological changes of radial glial cells are closely related to theneuronal migration. Reelin binding to VLDLR and ApoER2receptors induces other adptorproteins to activate the downstream cascades to maintain the morphology of radial glial cells.Different receptor of Reelin have different effects on the morphology of neuronal migrationand radial glial cells. VLDLR is responsible for the stop signal of neuronal migration, andApoER2promotes the migration of late-born neurons.