The Role of EphA4 in Glial Scar Formation Following Injury

Although many areas of the brain lose their regenerative capacity with age, stem cell niches have been identified in both the subventricular zone (SVZ) along the lateral walls of the lateral ventricles and the subgranular zone (SGZ) of the dentate gyrus (Gage, 2000; Alvarez-Buylla et al., 2001; Alvarez-Buylla and Lim, 2004). The SVZ niche utilizes many mechanisms to determine the migration patterns of neuroblasts along the RMS into the olfactory bulb, one being Eph/ephrin signaling (Conover et al., 2000; Holmberg et al., 2005). EphA4-mediated signaling is necessary for axon guidance during development, and its continued expression in the SVZ niche suggests a regulatory role throughout adulthood. Previous studies have suggested that EphA4 plays a role in the regulation of astrocytic gliosis and glial scar formation, which inhibits axonal regeneration in these areas following spinal cord injury (Goldshmit et al., 2004). Blood vessels may also play an important role in SVZ cell proliferation and neuroblast migration following injury (Tavazoie et al., 2008; Yamashita et al., 2006). The goal of this project is to examine glial scar formation as well as the relationship between SVZ vasculature, neuroblasts, and neural stem cells in EphA4 +/+, EphA4 +/-, and EphA4 -/- mice following a needle stick injury in the cortex or striatum. The outcome of these experiments will determine whether invasive procedures such as injections will affect neuroblast migration and/or the organization of the SVZ.

Investigating the Diversity of Radial Glia Fates in the Rat Neocortex

Radial Glia (RG) are a mitotically active population of cells which reside within the ventricular zone at the lateral ventricle and give rise to the pyramidal neurons and astrocytes of the neocortex. Through cellular divisions, RG produce two daughter cells, one which resides in the ventricular zone and becomes another RG while the other is an immature progenitor which migrates away from the ventricle and populates the growing cortex. RG have been found to be a heterogeneous population of cells which express different surface antigens and genetic promoters which may influence the cellular fate of their progeny. In this study we have investigated the progenitor profiles of two promoters, nestin (a neural intermediate filament) and GLAST (astrocyte specific glutamate transporter) within the RG. In-utero electroporation was used to transfect reporter plasmids under the control of promoter driven Cre-Recombinase into the RG lining the lateral ventricle during mid-neurogensesis (E14). It was found that there was a large amount of overlap between the nestin and GLAST expressing populations of RG, however, there was still a small subset of cells which exclusively expressed GLAST. This prompted us to investigate the lineage of these two promoters using the PiggyBac transposon system which uses promoter driven episomal plasmids to incorporate a reporter gene into the genome of the transfected cells, allowing use to trace their full progeny. Our data shows that nestin expressing RG generate mostly neurons and few astrocytes while the GLAST expressing RG generate a greater proportion of astrocytes to neurons.