We have used Drosophila as a model to test the role of the piRNA pathway in transcriptional control and chromatin biology. We have shown, that unlike the cytoplasmic piwi proteins, which require their endonucleolytic activity for cleaving and destroying targets, the nuclear piwi protein, Piwi, does not need its catalytic activity for silencing transposable elements. We found that the Drosophila Piwi protein is recruited to chromatin at distinct genomic loci. Together, these findings are consistent with a role of Piwi in transcriptional control of targets.
Piwi induces transcriptional silencing and establishment of repressive chromatin over TE targets: Using RNAi, we tested the effect of Piwi on transcription and chromatin state of the targets, transposable elements. We found that based on Pol II ChIP-seqtranscription rate is repressed by Piwi and that this repression correlates with the establishment of a repressive chromatin on targets.
Piwi-associated piRNAs are required for recruiting Piwi to genomic targets: Based on the correspondence of targets transcriptionally silenced by Piwi and the Piwi-associated piRNAs we hypothesized that piRNAs are required for targeting Piwi to the genomic sites. We used reporter-based assays to confirm the role of piRNAs in recruiting Piwi to its genomic targets. We have also used this reporter system to identify additional chromatin changes that resulted from Piwi recruitment such as changes in some chromatin marks and recruitment of additional factors such as Rhino and Cuff.
