Function Of Cis-element LCR In Mutually Exclusive Splicing Of Drosophila Dscam Exon6Cluster

Alternative splicing is an important means to generate protein diversity. Mutually exclusive alternative splicing is a special form of alternative splicing. In this splicing means, only one exon is chosen out of two or more variable exons which arrange in a tandem array. As one of the most outstanding cases, Down syndrome cell adhesion molecule (Dscam) can potentially encode38,016distinct axon guidance receptors through the mutually exclusive splicing of95variable exons in Drosophila melanogaster. The hypothesis of docking site-selector sequence interactions can explain the mutually exclusive splicing mechanism in Dscam exon6cluster and this hypothesis has been confirmed by experiments. But the specific mechanisms how the selected variable exon is activated are poorly understood.In this study, we identified an RNA architectural locus control region (LCR) upstream the docking site in Dscam exon6cluster by using comparative genomics and deletion experiments. This element plays an important role in splicing of the mutually exclusive exons. Mutations and complementary mutations experiments show that LCR has its functions in a form of six adjacent tandem RNA secondary structures.Previous studies demonstrated that hrp36is a repressor protein combined exon6cluster. Removal of hrp36by RNA interference, there will be numbers of variable exon6spliced together. However, our results show that LCR is required even in Ahrp36variable exon. These results reveal that the LCR is essential in Dscam exon6cluster splicing. Further research indicates that the LCR can activate the selected variable exon by enhancing the signal strength of the weak splice sites.This study illustrates an LCR-dependent mutually exclusive splicing mechanism. LCR can activate the specifical variable exon6. together with docking site-selector sequence interactions. It is significant for deeply understanding the mutually exclusive splicing of Dscam.