Role of Egr3 in Regulation of DNA Repair

Egr3 is an immediate early gene transcription factor that shows genetic association with schizophrenia, and is found in decreased levels in the brains of schizophrenia patients. Schizophrenia patients also exhibit cognitive and memory deficits, both of which Egr3 has been shown to play a crucial role in. Additionally, high levels of DNA damage are found in the brains of schizophrenia patients. A recent study has shown that DNA damage occurs as a result of normal physiological activity in neurons and is required for induction of gene expression of a subset of early response genes. Also, failure to repair this damage can lead to gene expression in a constitutive switched on state. Egr3 knockout (Egr3-/-) mice show deficits in hippocampal synaptic plasticity and memory. We were interested in characterizing downstream targets of EGR3 in the hippocampus. To determine these targets, electroconvulsive seizure (ECS) was carried out in Egr3 -/- versus wild type (WT) mice, and a microarray study was first done in our lab. ECS maximally stimulates Egr3 expression and we hypothesized that there would be gene targets that are differentially expressed between Egr3 -/- and WT mice that had been subjected to ECS. Two separate analyses of the microarray yielded 65 common genes that were determined as being differentially expressed between WT and Egr3 -/- mice after ECS. Further Ingenuity Pathway Analysis of these 65 genes indicated the Gadd45 signaling pathway to be the top canonical pathway, with the top four pathways all being associated with DNA damage or DNA repair. A literature survey was conducted for these 65 genes and their associated pathways, and 12 of the 65 genes were found to be involved in DNA damage response and/or DNA repair. Validation of differential expression was then conducted for each of the 12 genes, in both the original male cohort used for microarray studies and an additional female cohort of mice. 7 of these genes validated through quantitative real time PCR (qRT-PCR) in the original male cohort used for the microarray study, and 4 validated in both the original male cohort and an independent female cohort. Bioinformatics analysis yielded predicted EGR3 binding sites in promoters of these 12 genes, validating their role as potential transcription targets of EGR3. These data reveal EGR3 to be a novel regulator of DNA repair. Further studies will be needed to characterize the role of Egr3 in repairing DNA damage.