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. 2015 Dec 8;9(2):86–90. doi: 10.1080/19336934.2015.1128599

Figure 1.

Figure 1.

piRNA pathways in the Drosophila ovary. In germline cells, antisense piRNAs are produced and loaded onto Aub by the de novo primary pathway or through maternal deposition. Aub then triggers the ping-pong pathway to produce sense piRNAs bound to AGO3 and own antisense piRNAs by consuming transposon transcripts (post-transcriptional gene silencing; PTGS). AGO3 initiates the phased primary pathway to produce antisense piRNAs bound to Piwi. Very few Piwi-bound piRNAs are maternally deposited. Piwi translocates to the nucleus, where it provokes transcriptional gene silencing (TGS). In soma, only Piwi is expressed, and the de novo primary and phased primary pathways operate to produce antisense piRNAs bound to Piwi. Krimp promotes the Aub-AGO3 heterotypic ping-pong pathway and blocks de novo primary piRNA loading onto AGO3. Qin inhibits the Aub-Aub homotypic ping-pong pathway and the production of Piwi-bound phased primary piRNAs triggered by Aub. Sense and antisense piRNAs are indicated in blue and red, respectively.