Cell Biology Terms Starting With Q
Cell Biology Glossary: Q
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Quiescence
/ kwee-ES-ents / · Latin: quiescere (to rest)
Quiescence is a reversible, non-dividing state in which a cell remains metabolically active but has withdrawn from the cell cycle, retaining the ability to re-enter division when appropriate signals arrive.
Quiescent cells arrest in the G0 phase by reducing cyclin D1 levels and maintaining low CDK4 and CDK6 activity, keeping the retinoblastoma protein hypophosphorylated and the E2F transcription factors inactive. Growth factors such as fibroblast growth factor or serum components can reactivate quiescent cells, triggering cyclin D1 re-expression, CDK activation, and re-entry into G1 phase. Satellite cells, the muscle stem cells that reside in niches adjacent to muscle fibers, remain quiescent until injury releases hepatocyte growth factor and other signals that drive proliferation and differentiation.
Maintaining this reversible arrest conserves cellular resources and preserves a stem cell reserve capable of rapid mobilization during tissue repair.
Certain neurons in the adult human brain, long considered permanently post-mitotic, appear to enter a quiescence-like state rather than a terminally differentiated one; studies of the subventricular zone have identified neural stem cells that can remain dormant for months before reactivating, suggesting quiescence is more widespread in the nervous system than previously recognized.
Cell Cycle →Quiescent cells are dead or permanently inactive. Quiescent cells carry out normal metabolic functions, maintain ion gradients, and respond to extracellular signals; they differ from senescent cells, which have lost the capacity to divide even when stimulated.
Hematopoietic stem cells in adult mouse bone marrow spend the majority of their time in quiescence, dividing on average only about 5 times per year. When the bone marrow is depleted by irradiation, these dormant cells re-enter the cell cycle within hours and can reconstitute the entire blood cell population within weeks.