ONCOVIRAL DNAS INDUCE TRANSPOSITION OF ENDOGENOUS MOBILE ELEMENTS IN THE GENOME OF DROSOPHILA-MELANOGASTER

Previously, we have shown that particles of Rous sarcoma virus or clon ed fragments of RSV cDNA as well as DNA of oncogenic simian adenovirus Sa7, injected into the polar plasm of early Drosophila melanogaster e mbryos, were able to induce, with high frequency, unstable visible mut ations in different groups of genetic loci. The genetic instability of the recovered mutations, i.e., their ability to revert to normal stat e or to generate new mutant alleles at the affected locus, was manifes t in mutant lines through several generations. The molecular analysis undertaken in this study of the yellow-scute loci region which is high ly sensitive to the microinjected Sa7 DNA, and of the white locus, tha t frequently mutates under the influence of RSV cDNA, clearly shows th at the induced mutations and reversions are accompanied by insertion/e xcision of endogenous mobile elements. This conclusion is confirmed by in situ hybridization experiments which demonstrate that the adenovir us DNA is able to change, though with different efficiency, the chromo somal localization of certain Drosophila retrotransposons. These resul ts partially elucidate the molecular mechanism of the genetic instabil ity in D. melanogaster induced by microinjection of oncoviruses into e arly embryos, implying that it results from mobilization of endogenous transposons which play the role of insertional elements directly caus ing unstable mutations. (C) 1998 Elsevier Science B.V. All rights rese rved.