Hippocampal gene expression analysis using the ORESTES methodology shows that homer 1a mRNA is upregulated in the acute period of the pilocarpine epilepsy model

Abstract

In the study of temporal lobe epilepsy (TLE) the characterization of genes expressed in the hippocampus is of central importance for understanding their roles in epileptogenic mechanisms. Although several large-scale studies on TLE gene expression have been reported, precise assignment of individual genes associated with this syndrome is still debatable. Here we investigated differentially expressed genes by comparison of mRNAs from normal and epileptic rat hippocampus in the pilocarpine model of epilepsy. For this we used a powerful EST sequencing methodology, ORESTES (Open Reading frame Expressed Sequence Tags), which generates sequence datasets enriched for mRNAs open reading frames (ORFs) rather than simple 5' and 3' ends of mRNAs. Analysis of our sequences shows that ORESTES readily enables the identification of epilepsy associated ORFs. PFAM analysis of protein motifs present in our ORESTES epilepsy database revealed diverse important protein family domains, such as cytoskeletal, cell signaling and protein kinase domains, which could be involved in processes underlying epileptogenesis. More importantly, we show that the expression of homer 1a, known to be coupled to mGluR and NMDA synaptic transmission, is associated with pilocarpine induced status epilepticus (SE). The combined use of the pilocarpine model of epilepsy with the ORESTES technique can significantly contribute to the identification of specific genes and proteins related to TLE. This is the first study applying a large-scale method for rapid shotgun sequencing directed to ORFs in epilepsy research.