Post-transcriptional regulation of gene expression in hippocampal neurons by glutamate receptor activation.

Previous work from this laboratory has documented that glutamate receptor activation and extracellular calcium entry into hippocampal neurons caused a long-lasting down-regulation of ligatin mRNA and protein. Here, we investigated whether glutamate reduced ligatin mRNA levels by decreasing the transcriptional activity of the gene and/or by regulating post-transcriptional RNA processing steps including mRNA stability. Using nuclear run-on assays, it was demonstrated that transcriptional activity of the ligatin gene was not significantly decreased after glutamate receptor activation. Further, Northern analysis of RNA from neurons maintained in the presence of the transcription inhibitor, alpha-amanitin, showed that glutamate shortened the half life of the ligatin message from 10 h to 58 min. This post-transcriptional destabilization of ligatin mRNA was mimicked by NMDA, dependent on Ca2+, blocked by MK801, and not affected by AMPA and kainic acid, indicating that message stability was governed by changes in intracellular calcium. Moreover, using in situ hybridization and confocal microscopy, we showed that glutamate and NMDA decreased ligatin message within dendritic and somal regions without increasing nuclear levels. These findings demonstrated that glutamate receptor activation altered neuronal gene expression posttranscriptionally by destabilizing mRNA. Our data suggest that post-transcriptional regulation of gene expression may be part of the normal receptor mediated regulatory program of plasticity and provides the first description of a glutamate receptor-modulated, calcium-dependent mechanism which rapidly destabilizes mRNA in neurons.