Abstract
The piRNA pathway is a highly conserved mechanism to repress transposon activation in the germline in Drosophila and mammals. This pathway starts from transcribing piRNA clusters to generate long piRNA precursors. The majority of piRNA clusters lack conventional promoters, and utilize heterochromatin- and HP1D/Rhino-dependent noncanonical mechanisms for transcription. However, information regarding the transcriptional regulation of piRNA clusters is limited. Here, we report that the Drosophila acetyltransferase Enok, which can activate transcription by acetylating H3K23, is critical for piRNA production from 54% of piRNA clusters including 42AB, the major piRNA source. Surprisingly, we found that Enok not only promotes rhino expression by acetylating H3K23, but also directly enhances transcription of piRNA clusters by facilitating Rhino recruitment. Taken together, our study provides novel insights into the regulation of noncanonical transcription at piRNA clusters and transposon silencing.
Highlights
In a wide range of organisms, repressing the activation of transposon insertions is essential for maintenance of genome stability [1]
The PIWI-interacting RNA pathway, which is highly conserved between mammals and flies, is a key mechanism to suppress transposon activation in the germline
We found that Enok can promote the expression of three genes involved in PIWI-interacting RNA (piRNA) production by acetylating histone H3 lysine 23 (H3K23)
Summary
Fly strains and cultureDrosophila melanogaster was crossed and grown on standard media at 25 ̊C unless stated otherwise. MTD-Gal driven RNAi and overexpression of transgenes were carried out at 29 ̊C for 2–3 days. Females were conditioned with wet yeast for 1–2 days before ovary dissection. The following fly lines were obtained from the Bloomington Drosophila Stock Center with their stock numbers in parentheses: UAS-Luciferase (35788), UAS-enok RNAi-1 (40917), UASenok RNAi-2 (41664), UAS-enok RNAi-3 (29518), UAS-EGFP RNAi-1 (41556), UAS-Dcr; nosGAL4 (25751) and MTD-GAL4 (31777). The fly lines containing the MTD-GAL4 driver and a GFP-rhi or GFP-del transgene were obtained from the JB-STOCK Library in the Vienna Drosophila Resource Center (stock number 313667 and 313672) [14]. The fly line containing the nos-Gal4-VP16 driver and a UASp-rhi:GFP transgene was kindly provided by William E.
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