Mos1 Mariner Transposon Based Transgenesis of the Human Blood Fluke, Schistosoma mansoni

Genome sequences for Schistosoma mansoni are now available. The schistosome genome includes ∼13,000 protein encoding genes for which the function of only a minority is understood well. There is a valuable role for transgenesis in functional genomic investigations of these new schistosome gene sequences. In gain-of-function approaches, transgenesis could lead to integration of transgenes into the schistosome genome, which could facilitate insertional mutagenesis screens. By contrast, transgene driven, vector-based RNA interference offers powerful loss-of-function manipulations. Exogenous transposons have been shown to be powerful transgenesis tools in other target species in forward genetics approaches. Therefore, our laboratory has focused on the development of tools to facilitate schistosome transgenesis. The utility of transposons to transduce schistosomes was investigated. The Mos1 mariner transposon, originally isolated from the fruit fly, Drosophila mauritiana, has been widely used for transgenesis and for genetic analysis in other species. Given its activity in a number of unrelated taxa, and given that a related transposon called piggyBac is active in schistosomes, the ability of the Mos1 mariner transposon to mobilize in schistosomes was investigated and its performance compared to piggyBac. At the outset of this investigation, a binary transposon system for Mos1 mariner was established. The binary components included (1) a donor component, which is the plasmid construct that included a promoter from an endogenous schistosome protein-encoding gene driving the reporter gene encoding firefly luciferase, flanked at the left and right termini by the inverted terminal repeat elements of the Mos1 mariner transposon, and (2) the helper partner which was here represented by a plasmid that encoded the Mos1 transposase. I hypothesized that help provided in the form the transposase translated within schistosome tissues transfected with mRNA transcribed in vitro from this helper construct would recognize the inverted terminal repeats of Mos1, and in turn 'cut-and-paste' the donor cassette from the donor helper and insert it into the chromosomes of schistosome cells. In addition, I hypothesized that the transposable element Mos1 mariner could mediate expression of transgenes in schistosomes. To test these hypothesis, the Mos1 mariner transposition activity in schistosomes was investigated. The binary transposon system was assembled by ligating the schistosome actin promoter and the reporter firefly luciferase gene, between the Mos1 inverted terminal repeats in the donor plasmid. Subsequently, transposition activity of Mos1 was examined in S. mansoni by identifying the excision and integration of the transposon. Moreover, somatic transgenesis of the transgene was examined in S. mansoni and whether the Mos1 transposon could deliver functional reporter transgenes into the genome of S. mansoni parasites. The findings from these analyses indicated, for the first time, the mobilization of Mos1 mariner in schistosome tissues culminating in the apparent integration of transposon transgenes into the genome of S. mansoni and somatic transgenesis of this important human pathogen. These findings extended the range of target species in which Mos1 mariner has been shown to transpose, and they demonstrated the utility of this Tc1-mariner like transposon as a functional genomics tool for investigation of the genome of S. mansoni and for transgenesis studies of this important neglected tropical diseases pathogen.