45: RNA-dependent mechanics of nucleolar subcompartments

Cheng HH et al., Proceedings of the National Academy of Sciences (PNAS) - Using micropipette aspiration in Xenopus laevis oocyte nuclei, authors show the nucleolar granular component behaves as a liquid while the dense fibrillar component and fibrillar center exhibit RNA-dependent viscoelastic, partially solid-like properties; RNase A fluidizes the DFC and alters interfacial tensions. Key terms: nucleolus, micropipette aspiration, viscoelasticity, RNA, Xenopus laevis. Study Highlights:The study adapts micropipette aspiration (MPA) to measure viscoelasticity and interfacial tensions of nucleoli in isolated Xenopus laevis germinal vesicles. The outer granular component (GC) behaves as a Newtonian, liquid-like material, whereas the inner dense fibrillar component (DFC) and fibrillar center (FC) show signatures of a viscoelastic, partially solid-like material. Degrading RNA with RNase A fluidizes the DFC, speeds fusion, and increases apparent DFC–GC interfacial tension. These results link RNA content and processing to spatially varying nucleolar material properties relevant to ribosome maturation. Conclusion:Nascent rRNA confers partially solid-like viscoelastic properties to the DFC/FC and modulates interfacial tensions, coupling nucleolar material state to ribosome biogenesis; MPA provides direct in vivo rheological measurements of condensates. Music:Enjoy the music based on this article at the end of the episode. Article title:Micropipette aspiration reveals differential RNA-dependent viscoelasticity of nucleolar subcompartments First author:Cheng HH Journal:Proceedings of the National Academy of Sciences (PNAS) DOI:10.1073/pnas.2407423122 Reference:Cheng HH, Roggeveen JV, Wang H, Stone HA, Shi Z, Brangwynne CP. Micropipette aspiration reveals differential RNA-dependent viscoelasticity of nucleolar subcompartments. Proc Natl Acad Sci U S A. 2025;122(22):e2407423122. doi:10.1073/pnas.2407423122 License:This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/ Support:Base by Base – Stripe donations: https://donate.stripe.com/7sY4gz71B2sN3RWac5gEg00 Official website https://basebybase.com On PaperCast Base by Base you'll discover the latest in genomics, functional genomics, structural genomics, and proteomics. Episode link: https://basebybase.com/episodes/nucleolus-rna-viscoelasticity-ep45 QC:This episode was checked against the original article PDF and publication metadata for the episode release published on 2025-06-12. QC Scope:- article metadata and core scientific claims from the narration- excludes analogies, intro/outro, and music- transcript coverage: Audited the spoken content describing nucleolar architecture, MPA methodology, material-property distinctions between GC and DFC/FC, RNA's role in solid-like DFC behavior, RNase A effects, and the implications for ribosome biogenesis, including measured viscosities, interfacial tensions, and fusion dynamics.- transcript topics: Nucleolus architecture and subcompartments (GC vs DFC/FC); Micropipette aspiration methodology and nonwetting conditions; Material-property division: GC as Newtonian liquid; DFC/FC as viscoelastic solid; RNA dependence of DFC/FC properties; RNase A experiments fluidizing DFC and changing fusion dynamics; Interfacial tensions and inverse capillary velocity measurements QC Summary:- factual score: 10/10- metadata score: 10/10- supported core claims: 6- claims flagged for review: 1- metadata checks passed: 4- metadata issues found: 0 Metadata Audited:- article_doi- article_title- article_journal- license Factual Items Audited:- GC is a New...