Validation of activity-dependent EGR1 overexpression using a novel virus

Immediate early genes (IEGs) are the first set of genes to be transcribed in a cell in response to stimuli; their expression is quick and is not protein synthesis dependent. Neurons are activated in response to external stimuli, causing a rapid increase in IEG expression in the brain. IEG proteins go on to affect fundamental neurobiological processes that are known to be dysfunctional in patients with psychiatric disorders, and therefore IEGs have been connected to the pathogenesis of schizophrenia. Early growth response (Egr) genes are immediate early gene transcription factors (IEG-TFs) that are expressed in response to an altered environment. The IEG-TFs, early growth response 1 (EGR1) and early growth response 3 (EGR3) are necessary for processes such as memory and synaptic plasticity; lack of function in these genes causes dysfunction or disruption of these processes. We wanted to observe if increasing the function of Egrs by overexpressing them will lead to improved memory. To help further understand how behavior is affected by the overexpression (O/E) of Egr1 in response to stimuli, the AAV-ESARE-Egr1 virus was developed to be injected in the hippocampus of mice. In the hippocampus of wild-type (WT) mice, cells that are active endogenously express Egr1. The virus was created using the synaptic activity-response element (SARE), an element discovered on the promoter of the IEG activity-regulated cytoskeleton-associated (Arc) gene by our collaborators in Japan. Using an “enhanced” form of SARE (ESARE), our newly created virus acts to overexpress Egr1 only in response to activity in the hippocampus; we can then observe if the behavioral processes associated with Egr1 will improve. First, this project aims to validate that the AAV-ESARE-Egr1 virus is increasing Egr1 expression in the active hippocampal dentate gyrus (DG) granule cells of WT mice, and only in response to activity. The activity is in the form of a physiological stimulus, environmental enrichment (EE) and a non-physiological stimulus, electroconvulsive seizures (ECS). After confirming these characteristics of AAV-ESARE-Egr1 we can then use it to observe if EGR1 O/E improves the memory of mice.