Identifying splicing targets of CLAMP by mRNA-sequencing

CLAMP is a GA-repeat motif binding transcription factor that regulates gene expression. We hypothesized that CLAMP also regulates RNA processing, specifically alternative splicing that occurs co-transcriptionally because CLAMP is bound to intronic regions that are rich in polypyrimidine tracts which contain GA-rich sequences. Furthermore, GA-rich repeat sequences are thought to have evolved from polypyrimidine tracts that regulate splicing. Also, MALDI-mass spectrometry data identifying putative CLAMP interactors found association with 33 RNA binding proteins, including 6 that regulate alternative splicing. Thus, to test our hypothesis that CLAMP shapes transcriptome diversity by regulating RNA transcript splicing, we performed mRNA-sequencing in the presence and absence of CLAMP in Kc (female) and S2 (male) cell lines and used a SUPPA based pipeline called time2splice (https://github.com/ashleymaeconard/time2splice) to analyze the sequencing data. Using both cell lines helped us to identify female (Kc) and male (S2) specific splicing events. We identified 452 genes differentially spliced beetween Kc and S2 cells. There are 46 and 113 CLAMP-dependent splicing events in Kc and S2 cells, respectively. Interestingly, 45 CLAMP-dependent events (belonging to 42 genes) are specific to Kc cells, i.e female-specific, whereas 112 CLAMP dependent events (belonging to 100 genes) in S2 cells are specific to S2 cells, i.e male-specific. Therefore, we identified a new role for the transcription factor CLAMP in regulated sex-specific splicing events in Kc and S2 cells. dsRNA for CLAMP was used to deplete CLAMP from cell lines (Kc and S2), validated using qRT-PCR for CLAMP mRNA transcript. Total RNA was extracted from control (GFPRNAi) and experimental (CLAMPRNAi) Kc and S2 cell lines to make cDNA libraries and sequenced. Sequencing data was analyzed for changes in splicing events between control and experimental groups. Three replicates for each categories was performed.