Biopolym. Cell. 2019; 35(3):231-232.
Chronicle and Information
The topological relationship between ribogenesis, mRNA transcription/splicing and the tension of actin cytoskeleton
- Latvian Biomedical Research and Study Centre
- Institute of Technology, University of Tartu
To study the topological relationship between the nucleolar fibrillar centres, perinucleolar heterochromatin, nuclear speckles (splicesomes) and the lamin- associated heterochromatin after RNA transcription inhibition. Methods: MCF7 breast cancer cells were treated in 3D preserving conditions by increasing concentration/time of Actinomycin D (AcD). Immunofluorescent staining, confocal microscopy, and image analysis were performed. Results: In control cells with active rRNA and mRNA synthesis, the perinucleolar repressive heterochromatin labelled by H3K9Me3/cen forms extended structures bent around nucleoli, speckles located more externally are also extended, lamin B1 ideally outlines the nuclear envelope (NE), while actin filaments form fibrils both circular around NE and perpendicular or at angles to it, attached to the cellular membrane. When the nucleolar synthesis is initially suppressed by low AcD, the remnant Pol I cofactor RPA194 forms a few large granules at the nucleolar margin, H3K9Me3 heterochromatin condenses in round clumps between them, while speckles also condense as regular circular structures around the latter вЂ“ all together revealing a radial-concentric order. The lamin B1-positive nuclear contour becomes irregular and lamin forms folds in nuclear interior reaching the nucleoli. Actin ring around the nucleus becomes thicker, while its extending cytoplasmic fibers less tense. Full suppression of both syntheses by high dosage/prolong AcD or a-amanitin brings to disorganization of the radial-concentric nuclear order. Conclusions: The links of the perinucleolar and lamin-associated heterochromatin with inner nuclear compartments are involved in topological coordination between the ribogenesis and mRNA maturation, where the radial tension of the actin cytoskeleton exerted via concentric elasticity of the nuclear lamin is part of this regulation.