Transposition of mobile genetic elements in interspecific hybrids of Drosophila

In situ hybridization of labeled DNA of four mobile dispersed genetic elements (mdg), isolated from D. melanogaster and C. virilis genomes, with polytene chromosomes of the larvae of several Drosophila species has been carried out. The data show that the mdg elements exhibit a high degree of species specificity. The same conclusions are derived from filter hybridization using 32P-labeled D. melanogaster and D. virilis DNA and cloned mdg sequences immobilized on nitrocellulose filters. We attempted to induce transpositions ("jumping") of mdg elements specific for D. virilis chromosomes to the chromosomes of related species (e.g. D. littoralis Meigen) originally lacking the representatives of this family of repeats. For this purpose we produced hybrid stocks with "synthetic" karyotoypes characterized by different combinations of D. virilis homologous chromosomes and "hybrid" chromosomes. In one of such stocks we did find by in situ hybridization the insertion of a D. virilis mdg element into the fifth chromosome of D. littoralis Meigen. The transposition ("jumping") took place in the only region where somatic pairing between the fifth chromosomes of D. virilis and D. littoralis occurs more or less regularly in the hybrids. Since crossing-over in hybrid chromosomes of males is excluded in such "synthetic" stocks, gene conversion may be responsible for this transposition. The possible bearing of the phenomenon observed on the problem of hybrid dysgenesis is discussed.