UC Riverside

Mutator–like transposable elements (MULEs) are widespread across fungi, plants and animals. Most of the research of MULEs has focused on plant where they are discovered and have significant impact on genome structure. Despite being widespread, only a few active MULEs have been identified, meanwhile, the transposition mechanism of the MULEs is previously unknown. Pack-MULEs are able to capture and amplify genes or gene fragments on a large scale, and a subset of plant Pack-MULEs have been shown to be likely playing functional roles in regulating gene expression and providing novel coding capacities. However, the presence of Pack-MULEs in non-plant species has not been reported.

In this study we report that Muta1 identified from the mosquito Aedes aegypti is capable of excision and reinsertion in a yeast transposition assay, element reinsertion generated either 8 bp or 9 bp target site duplications (TSDs) with no apparent sequence preference. Mutagenesis analysis revealed the importance of several conserved amino acids, including the DDE triad in transposase function; donor site TSD also impacts the transposition of Muta1. Via in vitro assays, we have dissected the process of DNA breakage and end joining of Muta1. The transposition reactions involve double strand break with hairpin formation on the flanking DNA, and 3’ OH joining to the target DNA, which is also observed in the hAT transposons and the V(D)J recombination system. Mutagenesis analysis indicated the involvement of the DDE triad and a conserved W residue in transposition. The terminal motif and subterminal repeats also impact Muta1 transposition. We also report the identification 1136 Pack-MULEs in the mosquito Aedes Aegypti, genome. Pack-MULEs preferentially acquire genic fragments, they contain fragments from 410 parental genes, but 96.70% of acquired gene fragments are from intron or UTR sequences and their GC content is not significantly different to non-Pack-MULEs or parental genes. Among the Pack-MULEs acquired gene fragments. Only 10.91% of Pack-MULEs are expressed, and in less tissues and lower expression level compare to parental genes, and 15.49% of Pack-MULEs are directly involved in sRNAs production, indicating the presence and activity of Pack-MULEs are neutral to the Ae. Aegypti genome.