Son maintains accurate splicing for a subset of human pre-mRNAs

Serine-arginine-rich (SR) proteins play a key role in alternative pre-mRNA splicing in eukaryotes. We recently showed that a large SR protein called Son has unique repeat motifs that are essential for maintaining the subnuclear organization of pre-mRNA processing factors in nuclear speckles. Motif analysis of Son highlights putative RNA interaction domains that suggest a direct role for Son in pre-mRNA splicing. Here, we used in situ approaches to show that Son localizes to a reporter minigene transcription site, and that RNAi-mediated Son depletion causes exon skipping on reporter transcripts at this transcription site. A genome-wide exon microarray analysis was performed to identify human transcription and splicing targets of Son. Our data show that Son-regulated splicing encompasses all known types of alternative splicing, the most common being alternative splicing of cassette exons. We confirmed that knockdown of Son leads to exon skipping in pre-mRNAs for chromatin-modifying enzymes, including ADA, HDAC6 and SetD8. This study reports a comprehensive view of human transcription and splicing targets for Son in fundamental cellular pathways such as integrin-mediated cell adhesion, cell cycle regulation, cholesterol biosynthesis, apoptosis and epigenetic regulation of gene expression.