Nucleolus

The nucleolus is a dense, membrane-free region inside a cell nucleus where ribosomal RNA is produced and ribosome subunits are assembled.

Ribosomal RNA: RNA molecules that form the structural and catalytic core of ribosomes. The nucleolus transcribes and processes much of the ribosomal RNA used in ribosome assembly.
Cell nucleus: A membrane-enclosed organelle that contains most of a eukaryotic cell’s genetic material. The nucleolus forms within the nucleus and lacks a surrounding membrane of its own.
Felice Fontana: An Italian naturalist whose eighteenth-century observations included descriptions of structures within cell nuclei. His observations are among the early descriptions associated with the nucleolus.
Nucleolar stress: A cellular state caused by impaired ribosome production that can trigger signaling responses. Disrupted nucleolar activity can activate stress pathways, including regulation of p53.
Nucleolar phase separation: The organization of nucleolar components into coexisting phases through biomolecular interactions. Its layered structure offers a test case for how phase separation shapes cellular compartments.
Ribosome biogenesis: The cellular production of ribosomes from ribosomal RNA, proteins, and assembly factors. This broader process includes the nucleolar production and assembly of ribosome subunits.
Nucleolar organizer region: A chromosome region containing ribosomal RNA genes that can organize nucleolus formation. Ribosomal RNA gene clusters provide the transcription sites around which nucleoli form.
Cell theory: The biological framework that identifies cells as the basic structural and functional units of living organisms. Microscopic study of structures such as the nucleolus grew alongside the development of cell theory.
p53: A tumor-suppressing protein that regulates cell-cycle arrest, DNA repair, senescence, and cell death. Nucleolar stress can stabilize p53 by disrupting proteins that normally restrain it.
Ribosome stress response: Signaling pathways that detect defects in ribosome production or function and alter cell behavior. How nucleolar disruptions are sensed and converted into distinct cellular responses remains under study.

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