Defective I elements introduced into Drosophila as transgenes can regulate reactivity and prevent I-R hybrid dysgenesis.
The I-R hybrid dysgenesis syndrome is characterized by a high level of sterility and I element transposition, occurring in the female offspring of crosses between males of inducer (I) strains, which contain full-length transposable I elements, and females of reactive (R) strains, devoid of functional I elements. The intensity of the syndrome in the dysgenic cross is essentially dependent on the reactivity level of the R females, which is ultimately controlled by still unresolved polygenic chromosomal determinants. In the work reported here, we have introduced a transposition-defective I element with a 2.6 kb deletion within its second open reading frame into a highly reactive R strain, by P-mediated transgenesis. We demonstrate that this defective I element gradually alters the level of reactivity in the three independent transgenic lines that were obtained, over several generations. After > 15 generations, the transgenic Drosophila show strongly reduced reactivity, and finally become refractory to hybrid dysgenesis, without, however, acquiring the inducer phenotype. Induction of a low reactivity level is reversible--reactivity again increases upon transgene removal--and is maternally inherited, as observed for the control of reactivity in natural R strains. These results demonstrate that defective I elements introduced as single-copy transgenes can act as regulators of reactivity, and suggest that some of the ancestral defective pericentromeric I elements that can be found in all reactive strains could be the molecular determinants of reactivity.
Jensen
S
S
Institut Gustave Roussy, CNRS URA147, Villejuif, France.
Cavarec
L
L
Gassama
M P
MP
Heidmann
T
T
D000818:Animals; D030801:Animals, Genetically Modified; D003433:Crosses, Genetic; D004251:DNA Transposable Elements; D004331:Drosophila melanogaster / Q000235:genetics*; D005260:Female; D005298:Fertility / Q000235:genetics; D017344:Genes, Insect; D008297:Male; D010641:Phenotype
D004251:DNA Transposable Elements