Different levels of alternative splicing among eukaryotes. Nucleic Acids Res

Alternative splicing increases transcriptome and proteome diversification. Previous analyses aiming at comparing the rate of alternative splicing between different organisms provided contradicting results. These contradicting results were attributed to the fact that both analyses were dependent on the ex-pressed sequence tag (EST) coverage, which varies greatly between the tested organisms. In this study we compare the level of alternative splicing among eight different organisms. By employing an EST independent approach we reveal that the percentage of genes and exons undergoing alternative splicing is higher in vertebrates compared with inverte-brates. We also find that alternative exons of the skipping type are flanked by longer introns com-pared to constitutive ones, whereas alternative 50 and 30 splice sites events are generally not. In addition, although the regulation of alternative spli-cing and sizes of introns and exons have changed during metazoan evolution, intron retention re-mained the rarest type of alternative splicing, where-as exon skipping is more prevalent and exhibits a slight increase, from invertebrates to vertebrates. The difference in the level of alternative splicing suggests that alternative splicing may contribute greatly to the mammal higher level of phenotypic complexity, and that accumulation of introns con-fers an evolutionary advantage as it allows increas-ing the number of alternative splicing forms