Skip to main contentJournal ClubPublished: 26 August 2026Nuclear organizationKatherine Alexander1 Nature Reviews Molecular Cell Biology (2026) Cite this articleSave articleView saved researchAlthough it is best known as the cell’s DNA container, the cell nucleus also contains non-DNA structures such as nuclear speckles that occupy a substantial portion of its volume. Also known as SC35 domains, interchromatin granule clusters or splicing speckles, speckles are heavily enriched in factors involved in RNA biogenesis, particularly in SR-protein components of the spliceosome. Hence, speckle research has centred on splicing. By investigating intronless mRNAs that localize at speckles, an article by Wang et al. in 2018 questioned the assumption that nuclear speckles are just for splicing.Using RNA microinjection, the authors found that intronless mRNAs do not require transcription or polyadenylation to be localized at speckles. Instead, they contain cis-regulatory elements that facilitate speckle localization. These speckle-targeting elements are defined by exon splicing element (ESE) sequences — purine-rich sequences known to recruit SR proteins. ESEs were sufficient to direct speckle localization when added to mature β-globin mRNA, which does not normally localize to speckles. Speckle localization also required SR proteins, indicating that intronless mRNAs co-localize with nuclear speckles using ESE RNA elements and their associated SR proteins.This is a preview of subscription content, access via your institutionAccess options Access through your institutionAccess Nature and 54 other Nature Portfolio journalsGet Nature+, our best-value online-access subscription27,99 € / 30 dayscancel any timeLearn moreSubscribe to this journalReceive 12 print issues and online access269,00 € per yearonly 22,42 € per issueLearn moreBuy this articlePurchase on SpringerLinkInstant access to the full article PDF.39,95 €Prices may be subject to local taxes which are calculated during checkoutSubjectsNuclear specklesRNA transportReferencesOriginal articleWang, K. et al. Intronless mRNAs transit through nuclear speckles to gain export competence. J. Cell Biol. 217, 3912–3929 (2018)Article CAS PubMed PubMed Central Google Scholar Download referencesAuthor informationAuthors and AffiliationsCold Spring Harbor Laboratory, Cold Spring Harbor, NY, USAKatherine AlexanderAuthorsKatherine AlexanderView author publicationsSearch author on:PubMed Google ScholarCorresponding authorCorrespondence to Katherine Alexander.Ethics declarationsRights and permissionsReprints and permissionsAbout this article