A Pandas complex adapted for piRNA-guided transposon silencing (RNA-seq)

The repression of transposons by the Piwi-interacting RNA (piRNA) pathway is essential to protect animal germ cells. In Drosophila ovaries, Panoramix (Panx) enforces transcriptional silencing by binding to the target-engaged Piwi-piRNA complex, although the precise mechanisms by which this occur remain elusive. Here, we show that Panx functions together with a germline specific paralogue of a nuclear export factor, dNxf2, and its cofactor dNxt1 (p15) as a ternary complex to suppress transposon expression. Structural and functional analysis demonstrate that dNxf2 binds Panx via its UBA domain and play an important role in transposon silencing through binding to transposon transcripts directly. Unexpectedly, dNxf2 interacts directly with dNxf1 (TAP), which is also essential for transposon silencing. Transient tethering of dNxf2 to nascent transcripts leads to their nuclear retention. Therefore, we propose that dNxf2 may function as a Pandas (Panoramix dNxf2 dependent TAP/p15 silencing) complex, which counteracts the canonical RNA exporting machinery (TAP/p15) and restricts transposons to nuclear peripheries. Our finding may have broader implications for understanding how RNA metabolism modulates epigenetic gene silencing and heterochromatin formation. Examination of transcriptome from dNxf2 mutant comparing to dNxf2 heterogygous with panx tethered to FL10B tethered, and Panx mutant comparing to Panx heterogygous with dNxf2 tethered to FL10B from Drosophila ovaries.