Investigation On Evolution And Regulation Of RNA Mutually Exclusive Splicing

Alternative splicing is a widespread mechanism for gene regulation and for generating proteomic diversity in eukaryotes. There are several types of alternative splicing, including the mutually exclusive splicing in which only one exon is chosen out of a cluster of alternative exons arranged in a tandem array in mature mRNAs.In the current study, the expression data of more than13000genes from Drosophila melanogaster was analysed, and78sets of mutually exclusive exons from58genes were discovered. Using the58genes as query sequences, the orthologous genes from other20arthropod species were obtained by BLAST methods. We undertook comparative genomic analyses of mutually exclusive splicing to reveal a much more divergent and more rapidly evolving splice variant repertoire in immune genes than other functional gene categories. Notably, the majority of these splice variants represent species-and lineage-specific expansions. Unexpectedly, this bursting expansion in splice isoforms is positively correlated with rapid gene duplication in Dipteran species, particularly in mosquitoes and flies. Finally, comparative analysis revealed dynamic splices originating from several new and unexpected mechanisms. These include species-specific non-allelic homologous recombination, the intronization of exon, and replication slippage-based mechanism.A lot of examples of mutually exclusive splicing have been found, but the underlying mechanisms are poorly understood. In this study, evolutionary dynamics of the cluster of mutually exclusive exons in insect14-3-3ξ; reveals a clue for classifying the determinants for mutually exclusive splicing. Moreover, comparative genomic analysis of73arthropod species was carried out, and two kinds of intronic elements:"docking site" and "selector sequence" were found. These elements are species-or clade-specific, but evolutionarily conserved at the secondary structure level. Importantly, as only one selector sequence can interact with the docking site at a time, the docking site-selector sequence interactions likely play an important role in the mutually exclusive splicing. Disrupting, compensatory, and deletion mutagenesis revealed these inter-intronic RNA pairings to ensure mutually exclusive splicing via physical competition. It also revealed that the strength of inter-intronic RNA pairing correlates with the frequency of variant selection. At last, we provided a new model which suggests an applicable mechanism to assure mutually exclusive splicing.