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Intronless mRNAs transit through nuclear speckles to gain export competence
Ke Wang1, Lantian Wang1, Jianshu Wang1
1State Key Laboratory of Molecular Biology, Shanghai Key Laboratory of Molecular Andrology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai, China.
The Journal of Cell Biology
|September 9, 2018
Summary
Intronless mRNAs unexpectedly localize to nuclear speckles (NSs) via SR proteins, not splicing. This speckle targeting promotes their nuclear export through the TREX complex, acting as a quality control step.
Area of Science:
- Molecular Biology
- Cell Biology
- RNA Biology
Background:
- Nuclear speckles (NSs) are known storage sites for splicing factors.
- Intronless mRNAs, which do not undergo splicing, were not previously known to associate with NSs.
Purpose of the Study:
- To investigate the mechanisms of intronless mRNA localization to nuclear speckles.
- To determine the role of NSs in the nuclear export of intronless mRNAs.
Main Methods:
- Analysis of endogenous intronless mRNA association with NSs.
- Investigating the role of exonic splicing enhancers and SR proteins.
- Studying the involvement of the TREX complex and export factors (NXF1, UAP56).
Main Results:
- Intronless mRNAs associate with NSs independently of transcription and polyadenylation.
- Exonic splicing enhancers and SR proteins mediate intronless mRNA localization to NSs.
- Speckle targeting facilitates TREX complex recruitment and nuclear export; TREX, not NXF1, is crucial for releasing RNAs from NSs.
Conclusions:
- Nuclear speckles serve as sites for messenger RNP assembly and quality control for intronless mRNA export.
- The TREX complex plays a key role in releasing intronless mRNAs from NSs for export.
- NSs act as a critical checkpoint for ensuring the export competence of intronless mRNAs.
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