Age dependence of the copia transposition rate is positively associated with copia transcript abundance in a Drosophila melanogaster isogenic line

In males of an inbred Drosophila melanogaster line (2b), a significant age dependence of the transposition rate of the retrotransposon copier was noted. Among males of seven different age groups, the lowest transposition rate was detected in 12- to 15-day-old males, and the highest transposition rates were observed in 1- to 3- and in 24- to 27-day-old males: rates of 0.36 +/- 0.07, 1.09 +/- 0.20 and 117 +/- 0.27 transpositions per generation per gamete, respectively, were measured. This type of age dependence of the transposition rate indicates that copia transpositions do not occur in stem cells. Clusters of copia transpositions were detected, which confirms that copia transpositions occur at premeiotic stages of spermatogenesis. A positive association between copier transposition rate and copia transcript abundance in the testes was demonstrated for 1- to 3-, 12- to 15- and 24- to 27-day-old males, as well as for 1- to 3-day-old males of two closely related sublines of the 2b line that differed in copia transposition rate. Thus, copier transposition rate in males is apparently regulated at the level of copia RNA abundance in testes. The age dependence of the copier transposition rate and copier transcript abundance within the 2b line demonstrates that the physiological stale of the host may affect expression and transposition of the retroelement.