Regional differences in the extent of RNA editing of the glutamate receptor subunits GluR2 and GluR6 in rat brain.

The extent of RNA editing of the glutamate receptor subunits GluR2 and GluR6 was studied by using a newly developed method based on the restriction analysis of the subunit-specific polymerase chain reaction (PCR) product with the enzyme Bbv 1. Total RNA was isolated from following brain regions: cortex, striatum, hippocampus, thalamus, hypothalamus, cerebellum, pons/medulla oblongata and white matter. RNA was transcribed into cDNA, which was used as template for PCR. PCR was run with GluR2- and GluR6-specific primers to amplify a product across the edited region. The PCR products were analysed with the restriction enzyme Bbv 1 and gel electrophoresis of the restriction digest. Bbv 1 recognizes the sequence GCAGC which is identical with the sequence of the PCR product originating from unedited GluR2 or GluR6 mRNA. Thus, this enzyme splits the non-edited PCR product into two fragments while leaving the edited PCR product intact. After electrophoresis of the restriction digest and photographing gels, optical density of bands was quantified with image analysis. For quantification calibration curves were made with PCR products from constructs originating from edited and non-edited GluR6 mRNA. GluR2 mRNA was completely edited in all brain structures studied. Editing of GluR6 mRNA, in contrast, was high in gray matter structures (above 90%) but considerably lower in the pons/medulla oblongata (66%) and white matter (55%). It is, therefore, suggested that editing of GluR2 and GluR6 mRNA is performed by different enzymatic activities. Studying RNA editing of glutamate receptor subunits will extend knowledge about the role of calcium fluxes through non-NMDA glutamate receptor ion channels.