A noncanonical ping-pong amplification cycle takes place in Drosophila testes. (A) Immunostaining of endogenous Aub and Ago3 in Drosophila testis of the indicated genotype. The asterisk denotes the anterior apex. Scale bars represent 50 µm. Insets show magnified cells from the GPC. In aub mutant testes, Aub and Ago3 expressions were significantly reduced. In ago3 mutant testes, Ago3 was lost but Aub was comparably expressed and localized to perinuclear nuage. (B) Bar graph showing the normalized numbers of transposon-mapping piRNAs in the indicated libraries. Black and gray bars represent those without a ping-pong signature and with a ping-pong signature, respectively. The pie charts represent the percentage of those piRNAs in the total population of transposon-mapping piRNAs. Transposon-mapping piRNAs with a ping-pong signature were totally lost in aub mutant testes, while a small fraction of them was still present in ago3 mutants. (C) Heat-map representing the ping-pong ratios of the transposon-mapping piRNAs (minimum in white, maximum in green) in the indicated libraries. In aub mutant testes, piRNAs containing ping-pong signatures are significantly reduced for almost all transposon families. Ago3 loss did not cause as severe a loss in ping-pong signatures for most transposon-mapping piRNAs as observed for that in aub mutants.
