Characterization of RNA editing of the glutamate-receptor subunits GluR5 and GluR6 in granule cells during cerebellar development.

The non-NMDA class of ionotropic glutamate receptors are subject to RNA editing resulting in single amino acid changes within individual subunits that make up these oligomeric receptors. These amino acid changes result in significant alterations of important channel properties. Both edited and unedited versions of the kainate-receptor subunits GluR5 and GluR6 are present in brain, but whether this reflects the expression of both versions in individual types of neurons or differences in editing between different cell types is unclear. To characterize editing in a single identified type of central neuron, we have determined the extent to which GluR5 and GluR6 mRNAs are edited in acutely isolated cerebellar granule cells. RT-PCR analysis revealed that editing at each site in GluR5 and GluR6 increased during early postnatal development. The Q/R site was predominantly unedited in GluR5, whereas GluR6 was mostly edited. The Q/R and Y/C sites of GluR6 were edited to similar extents, whereas a smaller percentage of transcripts were edited at the I/V site. The expression of two double-stranded RNA adenosine deaminases implicated in GluR editing (DRADA and RED1) increased in granule cells between postnatal days 1 and 15. Finally, cerebellar granule cells express a previously unreported variant of RED1 which appears to arise from developmentally regulated alternative splicing.