Piwi-piRNA complexes induce stepwise changes in nuclear architecture at target loci.

Area of Science:

• Epigenetics
• Molecular Biology
• Genomics

Background:

• PIWI-interacting RNAs (piRNAs) are crucial for germline genomic integrity.
• They repress transposable elements (TEs) by forming Piwi-piRNA complexes.
• Drosophila Piwi utilizes heterochromatin formation and histone modifications for silencing.

Purpose of the Study:

• To investigate the role of Piwi/Nxf2 in nuclear architecture and chromatin changes during piRNA-mediated silencing.
• To understand the functional consequences of recruiting piRNA targets to the nuclear periphery.

Main Methods:

• Chromatin enrichment followed by sequencing (ChEP) and DamID-seq.
• Hi-C analysis in Piwi or Nxf2-depleted cells.
• Forced tethering system to study recruitment to the nuclear periphery.

Main Results:

• Piwi/Nxf2 mediates target association with nuclear lamins.
• Piwi or Nxf2 depletion alters intra- and inter-TAD interactions at TE loci.
• Recruitment to the nuclear periphery induces transcriptional silencing, chromatin changes, and histone modifications.

Conclusions:

• The Piwi-piRNA pathway induces stepwise changes in nuclear architecture and chromatin state.
• These changes facilitate transcriptional silencing of target loci.
• Nxf2 acts as a co-factor in Piwi-mediated transcriptional silencing and nuclear organization.