PXD021814-1

PXD021814 is an original dataset announced via ProteomeXchange.

Title	SON and SRRM2 form nuclear speckles in human cells
Description	The nucleus of higher eukaryotes is a highly compartmentalized and dynamic organelle consisting of several biological condensates that regulate gene expression at multiple levels. First reported more than 100 years ago by Ramón y Cajal, nuclear speckles (NS) are among the most prominent of such condensates, which were independently rediscovered multiple times and are also known as interchromatin granule clusters (ICGs), splicing speckles, or SC35 domains. 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. The monoclonal antibody SC35, which was raised against a spliceosomal extract, is a frequently used reagent to mark NS since its debut in 1990. Despite its prolific use, and the consensus regarding its primary target as SRSF2, clear inconsistencies between observations made with mAb SC35, and transgenic SRSF2 constructs in the same experiment are noted. Intrigued by these disparities, we carried out a systematic re-characterization of this monoclonal antibody and its cellular targets. Unexpectedly, we found no evidence for SC35 mAb recognizing SRSF2 in human cells. In contrast, our results show that the 35 kDa namesake protein recognized by SC35 mAb is SRSF7, a related but distinct SR protein. More importantly, using mass-spectrometry, CRISPR-mediated knock-ins, immunoblotting and fluorescence microscopy, we show that the main target of SC35 mAb is SRRM2, a large (300 kDa), spliceosome-associated protein with prominent intrinsically disordered regions (IDRs) that sharply localizes to NS. Analysis of protein length evolution among metazoa revealed a peculiar IDR extension specifically for SRRM2 and SON in vertebrates, a hallmark of condensate formation. Combining these results, we tested a long-standing question in the study of NS: whether NS are formed around a specific core, or various SR-proteins self-assemble into a phase-separated compartment without the need for a defined core. Here we show that, the elusive core of NS is formed by SON and SRRM2, since depletion of SON leads only to a partial disassembly of NS, while 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.
HostingRepository	PRIDE
AnnounceDate	2020-10-26
AnnouncementXML	Submission_2020-10-26_01:09:51.xml
DigitalObjectIdentifier
ReviewLevel	Peer-reviewed dataset
DatasetOrigin	Original dataset
RepositorySupport	Unsupported dataset by repository
PrimarySubmitter	David Meierhofer
SpeciesList	scientific name: Homo sapiens (Human); NCBI TaxID: 9606;
ModificationList	iodoacetamide derivatized residue
Instrument	Q Exactive HF

Revision	Datetime	Status	ChangeLog Entry
0	2020-10-05 03:50:05	ID requested
⏵ 1	2020-10-26 01:09:52	announced

Ilik İ A, Malszycki M, L, ü, bke AK, Schade C, Meierhofer D, Akta, ş T, SON and SRRM2 are essential for nuclear speckle formation. Elife, 9():(2020) [pubmed]

submitter keyword: SRRM2

nuclear speckles

Tugce, Aktas
contact affiliation	Max Planck Research Group Leader, Quantitative RNA Biology OWL, MPIMG Berlin, Germany
contact email	aktas@molgen.mpg.de
lab head
David Meierhofer
contact affiliation	Mass Spectrometry Facility MPIMG
contact email	meierhof@molgen.mpg.de
dataset submitter

Dataset FTP location NOTE: Most web browsers have now discontinued native support for FTP access within the browser window. But you can usually install another FTP app (we recommend FileZilla) and configure your browser to launch the external application when you click on this FTP link. Or otherwise, launch an app that supports FTP (like FileZilla) and use this address: ftp://ftp.pride.ebi.ac.uk/pride/data/archive/2020/10/PXD021814

PRIDE project URI

• PRIDE
  1. PXD021814
     1. Label: PRIDE project
     2. Name: SON and SRRM2 form nuclear speckles in human cells