Regional analysis of developmental changes in the extent of GluR6 mRNA editing in rat brain.

The extent of mRNA editing of the kainate receptor subunit GluR6 was evaluated in the cortex, hippocampus and cerebellum of embryonic brains at days 14 and 19 of gestation, in brains of animals aged 4, 25 days, or 3 months, and in hippocampal neurons isolated from embryonic brains at day 19 of gestation and held in tissue culture for 2 or 8 days. Total RNA was isolated and reverse transcribed into cDNA, which was used as template for PCR across the edited base A in TMII of GluR6. The extent of editing was evaluated by restriction digest of PCR products with Bbv 1, gel electrophoresis and image analysis of bands. In all brain structures studied the extent of editing was significantly upregulated during development (P < 0.001). The most pronounced increase in the extent of editing was observed between embryonic days 14 and 19. Highest levels were reached 4 days (94 +/- 1.3%) or 3 months after birth (95 +/- 1.7%) in the cortex and hippocampus, respectively. Notably, in hippocampal neurons held in tissue culture editing was sharply reduced to 67 +/- 3.1% and 29 +/- 3.1% after 2 or 8 days in culture (P < 0.001 vs. the embryonic and adult state). The results illustrate that moderate but significant regional differences exist in the regulation of GluR6 mRNA editing during development (cortex vs. hippocampus and cerebellum). Comparing developmental changes in the extent of editing of AMPA/kainate receptor subunits in vivo and in vitro may help to elucidate the molecular mechanisms of the editing process.