In this report , we analyzed the RISE of the nuclear RNA - Seq data together with those from cytoplasmic or whole cell RNA to identify the delayed pairing patterns of splice sites in depolarization - regulated splicing . Their splice site - specific accumulation within genes or around exons and their regulation by depolarization/5 - azaC support the pre - mRNA origin of the reads rather than genomic DNA , where in the latter case , random distribution of reads and non - regulation is expected . The analysis has led to the first - time observation of not only delayed 3 splice site usage of the endogenous STREX and other exons we have studied ( Figure 2 ) but also globally delayed , or depolarization - regulated , across intron - or exon - pairing of splice sites in the pituitary cells .