Neuronal Migration and Survival in the Developing Chick Optic Tectum
University of Delaware
In the developing brain, neurons are born in the ventricular zone and migrate outward via radial glia scaffolds. There also supposedly is an early period of widespread programmed cell death in the brain, occurring while these neurons are still migrating from embryonic day 7.5 (E7.5) through E8. We hypothesize there is a relation between these two processes whereby the cells that die do so because of anoikis: loss of contact with the necessary extracellular matrix produced by radial glia. Specifically, we predict that fibronectin secreted by radial glia interacts with the α8β1; integrin receptors on the neuronal membrane, initiating an intracellular cascade which eventually increases expression of Bcl-2, an anti-apoptotic molecule. The developing chick optic tectum (OT) was used as a model. OT cells were immunostained at different ages and show a general trend that there is a period where pro-apoptotic signals are present when Bcl-2 is down-regulated. Propidium Iodide staining experiments support this data with more fragmented DNA appearing during this time period, which is a hallmark of apoptosis. Bcl-2 also was ectopically expressed in the OT using a retroviral vector in hopes of analyzing behavior of neurons kept alive artificially. Additionally, OT cells were plated at different densities on a culture dish to determine whether radial glia contact could suppress neuronal apoptosis and/or increase Bcl-2 levels.