Evolution of alternative splicing in newly evolved genes of Drosophila.

New gene origination is a fundamental process underlying evolution of biological diversity. Although new genes usually evolve rapidly in sequences, structure and expression, the evolutionary pattern of alternative splicing (AS) in new genes and the molecular mechanisms involved in this alternation remain to be explored. Here, we used the new genes identified in the Drosophila melanogaster lineage to study alternation of AS and the possible functional consequences of these genes. We found that new genes tended to exhibit low degree of AS, though a few new genes were alternatively spliced. Interestingly loss of introns in retroposed new genes can only account for one third of the low-level AS in new genes, while partial gene duplication without AS exons and mutations in the duplicated AS exons/introns together have resulted in two-third AS losses in new genes, indicating that reducing the degree of AS is a general trend in all categories of new genes. Further investigations on tissue expression patterns of these new genes showed that those with AS alternation had a relatively lower expression level, were expressed in fewer tissues and tended to be more likely expressed in testis than their parental genes. All these observations imply that these new genes may have gained diverged structures and expression patterns from their parental genes after AS alternation.