Abstract

The nucleus of higher eukaryotes is a highly compartmentalized and dynamic organelle consisting of several biomolecular condensates that regulate gene expression at multiple levels (Banani et al., 2017; Shin and Brangwynne, 2017). First reported more than 100 years ago by Ramón y Cajal, nuclear speckles (NS) are among the most prominent of such condensates (Spector and Lamond, 2011). Despite their prevalence, research on the function of NS is virtually restricted to colocalization analyses, since an organizing core, without which NS cannot form, remains unidentified (Chen and Belmont, 2019; Galganski et al., 2017). The monoclonal antibody SC35, which was raised against a spliceosomal extract, is a frequently used reagent to mark NS since its debut in 1990 (Fu and Maniatis, 1990). Unexpectedly, we found that this antibody has been misidentified and the main target of SC35 mAb is SRRM2, a large (~300 kDa), spliceosome-associated (Jia and Sun, 2018) protein with prominent intrinsically disordered regions (IDRs) that sharply localizes to NS (Blencowe et al., 1994). Here we show that, the core of NS is likely formed by SON and SRRM2, since depletion of SON leads only to a partial disassembly of NS as reported previously (Ahn et al., 2011; Fei et al., 2017; Sharma et al., 2010), in contrast, combined depletion of SON together with SRRM2, but not other NS associated factors, or depletion of SON in a cell line where IDRs of SRRM2 are genetically deleted, leads to a near-complete dissolution of NS. This work, therefore, paves the way to study the role of NS under diverse physiological and stress conditions.

Data availability

All data generated or analysed during this study are included in the manuscript and Supplementary files and source data files.Mass Spectrometry results shown in Figure 1 and Figure1- figure supplement 1 are provided in Supplementary File 2.Furthermore, on ProteomeXchange with identifier PXD021814.Source data files have been provided for Figure 4, Figure 4 - figure supplement1 and 2; and Figures 5, Figure 5 - figure supplement 3 and 4 .These zipped files contain ilastik models, CellProfiler pipelines, results and Jupyter notebooks.

The following data sets were generated

Article and author information

Author details

  1. İbrahim Avşar Ilik

    Otto Warburg Laboratories, Max Planck Institute for Molecular Genetics, Berlin, Germany
    Competing interests
    The authors declare that no competing interests exist.
  2. Michal Malszycki

    Otto Warburg Laboratories, Max Planck Institute for Molecular Genetics, Berlin, Germany
    Competing interests
    The authors declare that no competing interests exist.
  3. Anna Katharina Lübke

    Otto Warburg Laboratories, Max Planck Institute for Molecular Genetics, Berlin, Germany
    Competing interests
    The authors declare that no competing interests exist.
  4. Claudia Schade

    Otto Warburg Laboratories, Max Planck Institute for Molecular Genetics, Berlin, Germany
    Competing interests
    The authors declare that no competing interests exist.
  5. David Meierhofer

    Mass Spectrometry, Max Planck Institute for Molecular Genetics, Berlin, Germany
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-0170-868X
  6. Tuğçe Aktaş

    Otto Warburg Laboratories, Max Planck Institute for Molecular Genetics, Berlin, Germany
    For correspondence
    aktas@molgen.mpg.de
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-1599-9454

Funding

Max Planck Research Group Leader Program

  • Tuğçe Aktaş

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Reviewing Editor

  1. Jonathan P Staley, University of Chicago, United States

Version history

  1. Received: June 30, 2020
  2. Accepted: October 20, 2020
  3. Accepted Manuscript published: October 23, 2020 (version 1)
  4. Version of Record published: November 17, 2020 (version 2)

Copyright

© 2020, Ilik et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

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  1. İbrahim Avşar Ilik
  2. Michal Malszycki
  3. Anna Katharina Lübke
  4. Claudia Schade
  5. David Meierhofer
  6. Tuğçe Aktaş
(2020)
SON and SRRM2 are essential for nuclear speckle formation
eLife 9:e60579.
https://doi.org/10.7554/eLife.60579

Share this article

https://doi.org/10.7554/eLife.60579

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