The differentiation of a small number of cells in the developing embryo into the hundreds of cell and tissue types present in a human adult is associated with a multitude of changes in gene expression. In addition to many differences between tissues in transcriptional and translational regulation of genes, alternative pre-mRNA splicing (AS) is also frequently used to regulate gene expression and to generate tissue-specific mRNA and protein isoforms [1-5]. Between one-third and two-thirds of human genes are estimated to undergo AS [6-11] and the disruption of specific AS events has been implicated in several human genetic diseases [12]. The diverse and important biological roles of alternative splicing have led to significant interest in understanding its regulation.
