Dynamic equilibrium between insertion and excision of P elements in highly inbred lines from an M? strain of Drosophila melanogaster

Abstract

Six highly inbred lines of Drosophila melanogaster extracted from an M' strain (in the P/M system of hybrid dysgenesis) were studied for the evolution of the number and chromosomal location of complete and defective P elements through generations 52-200. These lines possessed full-sized P elements but differed in their cytotype (M or P). Three lines with P cytotype and full-sized P elements at site 1A had a constant P copy number over generations with low rates of insertion and excision. Three lines with M cytotype and at least one full-sized P element accumulated P copies over the generations and reached a plateau near generation 196, at which rates of transposition and excision were equal to 1.2 x 10(-3) to 3 x 10(-3) events per element per generation. At that time these three lines still presented an M cytotype, produced transposase, and were able to regulate P copy number. The similarity at equilibrium between insertion and excision rates was exactly what was expected from theoretical models for a self-regulated element. The large number of generations necessary to attain the equilibrium in copy number indicates, however, that caution may be de rigueur when testing theoretical models of copy-number containment based on transposition and excision-rate comparison.

Experimental evolution reveals hyperparasitic interactions among transposable elements

“…Here, we observed replicative transposition rates ranging from 0.3-0.5 per copy and per generation during the very early stages of the invasion and 0.01-0.03 for the 50 subsequent generations. These figures are of the same order of magnitude as for active P elements during hybrid-dysgenesis stages recorded in the laboratory (35), although dysgenic symptoms were never observed for mariner.…”

Abundance, distribution and dynamics of retrotransposable elements and transposons: similarities and differences

“…Several studies of D. melanogaster report transposition rates ranging from 10 -5 to 10 -3 events/copy/generation under normal conditions for retroelements (Charlesworth et al, 1992;Nuzhdin and Mackay, 1995;Suh et al, 1995;Maside et al, 2000), about 10 -2 after heat shocks (Vasilyeva et al, 1999) and up to 10 -1 in dysgenic crosses (Seleme et al, 1999). The same orders of magnitude are reported for Class II elements, in normal and dysgenic conditions (Eggleston et al, 1988;Biémont, 1994). Although they remain exceptional and hardly quantifiable events, excisions seem to occur more frequently for Class II elements.…”

Reexamining the P-Element Invasion of Drosophila melanogaster Through the Lens of piRNA Silencing

“…Thus, P-element insertions residing in cluster 20A could account for zygotic repression in some Q strains. However, P-element insertions in cytological position 20A, which harbors cluster 20A, are relatively rare in natural populations (Ronsseray et al 1989b;Biémont 1994), which is inconsistent with the reported prevalence of zygotic P-element repression (Jackson et al 1988).…”