Beyond the mammalian nucleolus—a comparative perspective on nucleolar dynamics in stress and through the life cycle

Ricardo Carvalho, Elizaveta Gubanova, Gautam Dey 

Classically the site of ribosomal RNA transcription, processing and early ribosome assembly, the nucleolus is increasingly understood as a dynamic multiphase condensate reshaped by cell state. Most reviews of this plasticity are mammal-centred. Here we set mammals alongside fungi, plants and animal germlines, following the nucleolus through the life cycle under environmental change and through the programmed transitions of mitosis and meiosis. Under stress it acts in protein quality control, sequestration and transcriptional regulation. In mitosis, fungi partition a persistent nucleolus, unlike the dissolve-and-rebuild strategy of animal open mitosis. In meiosis, nucleolar fate diverges between the sexes: lost during spermatogenesis in mammals and amphibians, cycling through prenucleolar bodies in arthropods, and persisting through oogenesis to predict meiotic competence. Across all three states the same tasks recur: reducing rRNA output, managing rDNA as a specialised chromosomal domain, coupling nucleolar material to division machinery, and controlling the granular component, met differently across lineages. We argue that nucleolar identity is defined by functional logic rather than fixed morphology, and outline open questions for extending this comparative approach across the breadth of eukaryotic diversity.