An efficient negative selection marker for -mediated single-copy integration in .

-mediated single-copy integration (MosSCI) in relies on the introduction of plasmid constructs into the germ line. Such plasmids form extrachromosomal arrays containing multiple copies of the transgene. Presently, one positive-selection and four negative-selection reporters are used to identify animals that carry the integrated transgene but not the array. Even with four reporters, the negative selection is inefficient. Here, we show that the expression of the toxic protein PEEL-1 from a transgene containing the endogenous introns kills all array-carrying animals, which facilitates efficient selection of animals carrying the integrated transgene.