Chromosome Research

, Volume 27, Issue 1–2, pp 141–152 | Cite as

The nucleolar transcriptome regulates Piwi shuttling between the nucleolus and the nucleoplasm

  • Elena A. Mikhaleva
  • Toomas A. Leinsoo
  • Hirotsugu Ishizu
  • Vladimir A. GvozdevEmail author
  • Mikhail S. KlenovEmail author
Original Article


The nucleolus contains a lot of proteins unrelated to ribosome biogenesis. Some of these proteins shuttle between the nucleolus and the nucleoplasm regulating the cell cycle and stress response. The piRNA binding protein Piwi is involved in silencing of transposable elements (TEs) in the Drosophila gonads. Here we used cultured ovarian somatic cells (OSC) to characterize Piwi as a visitor to the nucleolus. Dynamic Piwi localization was shown to vary from its uniform distribution between the nucleoplasm and the nucleolus to pronounced nucleolar immobilization. We were intrigued by this localization behavior and revealed that nascent nucleolar transcripts recruit Piwi for nucleolar retention. Piwi eviction from the nucleolus was observed upon RNase treatment and after RNA polymerase (Pol) I inhibition, but not after Pol II inactivation. On the contrary, heat shock caused drastic Piwi redistribution from the nucleoplasm to the nucleolus, which occurred only in the presence of Pol I-mediated transcription. These results allow us to hypothesize that specific stress-induced transcripts made by Pol I promote the nucleolar sequestration of proteins in Drosophila, similar to previous observations in mammalian cells. We also found that in OSC, Piwi partially restricts expression of the rDNA copies containing R1 and R2 retrotransposon insertions especially upon heat shock-induced activation of these copies. Therefore, we suggest that Piwi intranuclear shuttling may have a functional role in ensuring a balance between silencing of rDNA-specific TEs under stress and the canonical Piwi function in non-nucleolar TE repression.


Piwi Nucleolus rDNA Pol I Transposable elements Ovarian somatic cells 



Transposable elements


Ovarian somatic cells




5-Ethynyl uridine



We are grateful to Mikiko Siomi for providing OSC line, myc-Piwi vector and help in the implementation of this work; Artem Ilyin for assistance in performing Piwi knockdowns; Elena Fefelova for helpful advice on Piwi-GFP; Igor Kireev for assistance with EU incorporation assay; Konstantin Panov for providing 9-hydroxyellipticine inhibitor, and Michael Buszczak for Udd antibody. The work was carried out with the use of the equipment of the common use center “Center of Cell and Gene Technology”, Institute of Molecular Genetics, RAS.

Authors’ contribution statement

EM, VG, and MK conceived and designed the study; EM, TL, and HI performed research; EA, VG, and MK analyzed data; and VG and MK wrote the paper.

Funding information

The work was supported by the Russian Foundation for Basic Research (grant no. 18-54-50015 YaPh_a) and by the Presidium of the Russian Academy of Sciences program Molecular and Cell Biology for VAG.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Supplementary material

10577_2018_9595_MOESM1_ESM.pdf (46 kb)
Fig S1 H3-uridine incorporation in OCSs treated with different transcription inhibitors. Treatment with 9НЕ inhibitor of Pol I-mediated transcription causes more than 60% reduction of H3-uridine incorporation demonstrating a known significant contribution of rRNA to total RNA synthesis. Simultaneous 9HE and Pol II inhibitor DRB treatment reduces H3-uridine incorporation to the background level comparable with that in cells treated with actinomycin D (ActD), which inhibits both Pol I and Pol II. (PDF 46 kb)


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Copyright information

© Springer Nature B.V. 2018

Authors and Affiliations

  1. 1.Department of Molecular Genetics of the Cell, Institute of Molecular GeneticsRussian Academy of SciencesMoscowRussian Federation
  2. 2.Department of Biological Sciences, Graduate School of ScienceThe University of TokyoTokyoJapan

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