Migration And Layer Positioning Of Early Generated Neurons In Chicken Embryonic Optic Tectum

The optic tectum is important visual central nervous system with highly laminatedstructure in mature chicken brain. Both neurons and glial cells are the main cell componentsof the nervous system. Neuronal migration and layer formation are crucial for development ofchicken optic tectum. Glial cells provide nutritional and mechanical support for neuronalmigration, survival, proliferation and differentiation. Reelin plays a key role in regulatingneuronal migration during the development. Recently, the studies on Reelin have beenfocused on mouse cerebral cortex, but few studies on chicken embryos. Reelin is a largeextracellular protein involved in neuronal positioning, dendritic growth, synaptic plasticity,learning and memory and implicated as a susceptibility factor in psychoses. We used chickenembryo as animal model, performed in ovo electroporation, immunofluorescence, westernblot to elucidate the migration mode of neurons and lamination in the chicken optic tectumduring embryonic development. We compared the expression difference of four differentmarkers for radial glial cells: Brain Lipid Binding Protein (BLBP), Radial Glial Cell Marker-2(RC2), Nestin and Glial Fibrillary Acidic Protein (GFAP) in chicken embryonic optic tectumat different developmental stages. Ectopic overexpression of mouse Reelin affected neuronalmigration and layer formation. The Results were as follows:1. From embryonic day8(E8) to E12the optic tectum of chick embryo can bedivided into six layers from the inside to outside, most of the neurons migrated radially, andsome neurons migrated tangentially, the neurons in different layers showed differentmorphological features. Neurons in optic tectum used different migration modes, radialmigration and tangential migration.2. BLBP, RC2, Nestin and GFAP began to express from E8. GCs could be labeledby BLBP and GFAP from E8to E18. The cells labeled by BLBP began to change from E14,showing the morphological characteristics of migrating neurons. The cells labeled by GFAPbegan to change in E18, showing morphological characteristics of astrocytes. RGCs werelabeled by RC2and Nestin from E8to E16. Expression of RC2and Nestin in RGCsdisappeared at E18.3. The embryonic optic tectum was transfected with Reelin and GFP plasmids at E4.5and harvested at E12. Exogenous mouse Reelin induced aggregates in deeper laminae, gbecame sparser and i became thinner which were above aggregates. Branching neuronstransfected by Reelin in g and i gave rise to lots of branches.The results showed that most of the neurons migrated radially from E8to E12;some neurons migrated tangentially from E8to E10. BLBP labeled RGC better as a RGCmarker. Nestin and RC2mainly labeled neuronal precursors. The cells labeled by GFAP wereastrocytes. Exogenous Reelin induced aggregations, disturbed the layer formation andpromoted neuronal branching. This indicates that Reelin is very important for optic tectumdevelopment.