Changes in splice junctions did not always change neighboring exon expression levels (Figure 7). A known junction at exons 20-21 and a novel splice junction at exon 23 changed without affecting surrounding exon expression levels. Exons 20 and 21 were the third and fourth left end exons in Figure 4, respectively. Between the two exons, many unknown novel splice junctions were identified from our RNA-seq junction data which possibly diminished expression changes despite the fact that their splice junctions increased in alcoholic brains. A novel splice junction spliced out 108bp at the 3’ UTR and showed decreased expression in alcoholic brains. This novel splice junction was not as abundant as other known junctions (27, 30), and its length was much shorter than the 1,489bp exon 23. Therefore, this splice junction could not change the expression level of exon 23. However, a miRBase search (http://www.mirbase.org/) showed that this splice junction is a possible target of two miRNAs (hsa-miR- 3916 and hsa-miR-769-5p) suggesting that noncoding RNAs may decrease the population of normal GABAB1 transcripts and thereby decrease signal transduction.
