CLIP tags and clusters were analyzed with BED or WIG formatted custom tracks using the UCSC Genome Browser and Genome Graph tools (genome.ucsc.edu). Composite maps were generated by determining the distance between tags and closest splice sites within the alternative exon local region and converted to coordinates in a BED format custom track, with tags from each gene assigned different colors. MEME sequence analysis was done using tools available at meme.sdsc.edu. ASPIRE2 was based on ASPIRE20 (link).