Properties of transgenic strains ofDrosophila melanogastercontaining I transposable elements fromDrosophila teissieri

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Abstract
Summary: I factors are transposable elements ofDrosophila melanogaster similarto mammalian LINEs, that transpose by reverse transcription of an RNA intermediate and are responsible for the I–R system of hybrid dysgenesis. There are two categories of strains in this species: inducer, that contain about 15 I elements at the various sites on chromosomal arms, and reactive, that lack active I factors. I elements occur in variousDrosophilaspecies. Potentially functional I factors fromDrosophila teissierican transpose when introduced by P-element-mediated transformation in a reactive strain ofDrosophila melanogaster. We have studied the properties ofDrosophila melanogasterstrains into which such an I factor fromDrosophila teissieri, namedItei, was introduced. Typical hybrid dysgenesis is produced when males carryingIteiare crossed with reactive females. However, more than one copy of the element seems necessary to produce dysgenic traits, whereas only one I factor ofDrosophila melanogasterseems to be sufficient. The copy number ofIteiin transformed lines maintained by endogamous crosses increases rapidly and stabilizes at values similar to those observed in inducer strains. AsDrosophila teissiericontains much fewer copies than theDrosophila melanogasterstrains, this suggests that the copy number of I elements is not simply regulated by sequences present in the element itself.