The cerebellum is a well-defined region of the brain where active neurogenesis continues perinatally. During cerebellar development, granule cell precursors (GCPs) proliferate superficially in the external granule cell layer (EGL), migrate in a tangential manner parallel to the brain surface, and extend axonal processes before undergoing radial migration to the inner granule cell layer (IGL) along Bergmann glia (Bglia) processes. Proliferation of GCPs continues in the EGL after birth for several weeks in mice, and for up to two years after birth in humans. Little is known about what cues regulate GCP tangential migration and axon extension, but misregulation of these processes could lead to dysfunctional integration of GCPs into cerebellar circuitry and conditions such as ataxia or autism. Previous findings have shown glutamate and kainate receptors play a role in cell development, migration, and axon extension (Tashiro et al., 2003;Ibarretxe et al., 2007;Manent and Represa, 2007). Our preliminary data suggest that within the EGL Bglia can tightly control extracellular glutamate concentrations. Evidence also demonstrates that GCPs of the EGL express functional GluK6-containing kainate receptors. Importantly, the human gene for GluK6 (GRIK2) has been linked to autism (Jamain et al., 2002;Shuang et al., 2004;Kim et al., 2007). We therefore hypothesize that GCP tangential migration and axonal extension necessary for proper cerebellar circuitry is regulated by glutamate signaling through GluK6 receptors. In order to test this hypothesis, we will first use a combination of immunostaining, RT-PCR, calcium imaging and electrophysiology to determine whether GCPs in the EGL express functional kainate receptors, with a particular focus on GluK6. We will then determine whether GluK6 receptors orchestrate proper migration and axon extension of GCPs in the EGL. Pharmacology, in vivo electroporation of shRNA, and transgenic mouse models will be employed to perturb GluK6 function, and imaging studies will be performed to assess the role of GluK6 in GCP tangential migration and axon extension. Since GluK6 dysfunction may play a role in the etiology of autism spectrum disorders, understanding the role of GluK6 in cerebellum circuitry development is paramount.
|Kubera, C; Hernandez, A L; Heng, V et al. (2012) Transient mGlu5R inhibition enhances the survival of granule cell precursors in the neonatal cerebellum. Neuroscience 219:271-9|