A Pandas complex adapted for piRNA-guided transposon silencing (RNA-seq). 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. Overall design: 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.

Piwi互作RNA（Piwi-interacting RNA，piRNA）通路对转座子的抑制作用对于保护动物生殖细胞至关重要。在果蝇卵巢中，Panoramix（Panx）通过结合靶结合的Piwi-piRNA复合物实现转录沉默，但其具体作用机制仍不明确。本研究发现，Panx可与核输出因子的生殖系特异性旁系同源物dNxf2及其辅助因子dNxt1（p15）形成三元复合物，进而抑制转座子的表达。结构与功能分析表明，dNxf2通过其UBA结构域结合Panx，并可直接结合转座子转录本，在转座子沉默过程中发挥重要作用。出乎意料的是，dNxf2可直接与同样对转座子沉默至关重要的dNxf1（TAP）相互作用。将dNxf2瞬时锚定至新生转录本会导致其在细胞核内滞留。据此，我们提出dNxf2可作为Pandas（由Panoramix与dNxf2介导的TAP/p15沉默复合物）发挥功能，该复合物可拮抗经典RNA输出机器（TAP/p15），并将转座子限制在核周区域。本研究结果对于理解RNA代谢如何调控表观遗传基因沉默与异染色质形成具有更广泛的参考价值。整体实验设计：对果蝇卵巢来源的转录组进行分析，比较dNxf2突变体与dNxf2杂合样本（其中Panx被锚定至FL10B），以及Panx突变体与Panx杂合样本（其中dNxf2被锚定至FL10B）的转录组差异。