Environmental stresses and mobilization of transposable elements in inbred lines of Drosophila melanogaster.

Drastic changes in insertion patterns of the mobile elements copia and mdg-1 (a copia-like element) were checked in highly inbred lines of Drosophila melanogaster subjected to various stresses. Flies were treated by factors known for their ability to increase mutation rates of classical genes, and for their action on transcription or transposition of mobile elements: heat shocks at 37 degrees C, dichlorvos, hydrogen peroxide and ecdysterone. The insertion patterns were analyzed in progenies of the treated flies, either on larvae by in situ hybridization of giant salivary gland chromosomes, or on adult flies by Southern blotting interpreted by densitometric analysis. The techniques used made it possible to detect only changes with frequencies of more than 10% of the insertion sites. We show that the copia and mdg-1 elements cannot be radically mobilized in our inbred lines under the stressful conditions used. This absence of 'explosion' of mobilization of transposable elements after the action of external factors suggests that the genomes of our highly inbred lines are relatively protected against environmental stresses.