Figure 9. Model of aluRNA‐driven maintenance of the nucleolus.

The knockdown of aluRNA or treatment with α‐amanitin induces the segregation of nucleolar compartments into smaller domains (dispersion process) as observed (Figs 1A and 4A, and Appendix Fig S2). With regard to rRNA production, those “droplets,” which may vary in composition, are less efficient but some rRNAs are still produced albeit at low levels (Appendix Fig S1B and C and Fig 4C and D). Overexpression of aluRNA promotes assembly into larger nucleolar subcompartments, with enhanced Pol I activity (see Fig 5). This model is in excellent agreement with the previously reported liquid‐like model of the nucleolus (Brangwynne et al, 2011; Weber & Brangwynne, 2012) and suggests a RNA binding‐driven liquid‐like transition between dispersed nucleolar domains and intact and fully functional nucleoli.