Panoramix SUMOylation at chromatin recruits the heterochromatin machinery to piRNA target loci [RNA-seq]

Nuclear Argonaute proteins, guided by small RNAs, mediate sequence-specific heterochromatin formation. The molecular principles that link Argonaute–small RNA complexes, once bound to a nascent target RNA, to general heterochromatin effectors are poorly understood. Here, we uncover the mechanistic basis of how the PIWI interacting RNA (piRNA) pathway engages the heterochromatin machinery in Drosophila. Piwi-mediated recruitment of the corepressor complex SFiNX to chromatin leads to SUMOylation of its Panoramix subunit. SUMOylation, together with a hydrophobic LxxLL motif in the intrinsically disordered repressor domain of Panoramix, are necessary and sufficient to recruit Small ovary (Sov), a multi-zinc finger protein essential for general heterochromatin formation and viability. Structure-guided mutations that abrogate the Panoramix-Sov interaction or that prevent Panoramix SUMOylation uncouple Sov from the piRNA pathway, resulting in viable but sterile flies that exhibit de-repression of Piwi-targeted transposons. Thus, coupling the piRNA-guided recruitment of a corepressor to chromatin with its SUMOylation underlies sequence-specific heterochromatin formation. RNA-seq of Piwi KD, Panx KD, Sov KD, HP1 KD or Control KD OSCs.

由小RNA引导的核Argonaute（Argonaute）蛋白介导序列特异性异染色质的形成。目前，针对结合新生靶RNA后的Argonaute-小RNA复合物与通用异染色质效应因子之间的关联分子机制，人们尚不明晰。本研究阐明了果蝇体内PIWI互作RNA（piRNA）通路招募异染色质功能复合体的分子机制基础。Piwi蛋白介导共抑制因子复合物SFiNX招募至染色质，可使其Panoramix亚基发生类泛素化修饰（SUMOylation）。类泛素化修饰与Panoramix内在无序阻遏结构域中的疏水LxxLL基序协同作用，既必要且足以招募小卵巢蛋白（Sov）——一种对通用异染色质形成和个体存活至关重要的多锌指蛋白。通过结构设计的突变可破坏Panoramix与Sov的相互作用，或阻止Panoramix发生类泛素化修饰，从而使Sov脱离piRNA通路，最终导致果蝇可存活但不育，并出现Piwi靶向转座子去阻遏的表型。由此可见，将piRNA引导的共抑制因子染色质招募与其类泛素化修饰相偶联，是序列特异性异染色质形成的核心调控机制。本研究的数据集涵盖经Piwi敲低（KD）、Panx敲低、Sov敲低、HP1敲低或对照敲低的卵巢干细胞（OSCs）的RNA测序（RNA-seq）数据。