We have reported that a variety of mRNAs are attached to post-synaptic density (PSD) purified from cerebral cortex of rat brain (Suzuki et al., Neurosci.Res. 57, 61–85). More than one hundred among thousands of PSD–mRNAs code not only synaptic proteins but also nuclear proteins. General transcription factor II–I (Gtf2i) is one of such PSD–mRNAs coding nuclear proteins. Gtf2i is one of responsible genes for human Williams–Beuren syndrome (WBS), an autism spectrum disorder (ASD) characterized by abnormal cognitive and social behavior, because a 1.5 Mb deletion of human chromosome 7q11.23 including human Gtf2i gene causes WBS. We are studying molecular mechanisms of dendritic localization and local-translation of Gtf2i mRNA, and nuclear translocation of Gtf2i protein and its function in long-term synaptic plasticity.
In this study, we investigated promoter region of rat Gtf2i gene and predicted alternative transcription start points of Gtf2i mRNA based on cap analysis gene expression (CAGE) database of mouse. Using these information we identified seven novel transcripts of Gtf2i with different 5´UTRs in rat brain by RT–PCR method. We examined expression of these novel Gtf2i mRNAs with alternative 5´UTRs in rat brain by in situ hybridization. Gtf2i mRNAs with different 5´UTRs showed differential expression patterns in rat brain and some of them were detected in dendritic processes of neuronal cells, suggesting that Gtf2i mRNA with these 5´UTRs exist in neuronal dendrite/PSD. We identified four novel splicing variants of the coding sequence of Gtf2i in addition to two known variants in rat brain. We also found that some 5´UTR have a preference for specific variants of the coding region.
These results suggest 5´UTRs of Gtf2i mRNA play important roles in expression of Gtf2i gene in the brain: differential cellular expression via alternative promoter usage, selective usage of unique splice variants in coding region, mRNA localization to and spatiotemporally specific translation in neural dendrites.