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Many mammal cells, such as this neuron, remain permanently or semipermanently in G₀.

The G₀ phase (G sub 0) is a period in the cell cycle where cells exist in a quiescent state. G₀ is sometimes referred to as a "post-mitotic" state since cells in G₀ are in a non-dividing phase outside of the cell cycle. Cells enter the G₀ phase from a cell cycle checkpoint in the G₁ phase, such as the restriction point (animal cells) or the start point (yeast). This usually occurs in response to a lack of growth factors or nutrients. During the G₀ phase, the cell cycle machinery is dismantled and cyclins and cyclin-dependent kinases disappear. Cells then remain in the G₀ phase until there is a reason for them to divide. Some cell types in mature organisms, such as parenchymal cells of the liver and kidney, enter the G₀ phase semi-permanently and can only be induced to begin dividing again under very specific circumstances; other types, such as epithelial cells, continue to divide throughout an organism's life.

Although many cells in the G₀ phase may die along with the organism, this does not mean that cells that enter the G₀ phase are destined to die; this is often simply a consequence of the cell lacking any stimulation to re-enter in the cell cycle.

However, the term "post-mitotic" is sometimes used to refer not only to quiescent cells but also to senescent cells. Cellular senescence is a state that occurs in response to DNA damage or degradation that would make a cell's progeny nonviable; it is often a biochemical alternative to the self-destruction of such a damaged cell by apoptosis.

See also

• Cell Cycle

v • d • e Cell cycle Interphase G1 phase - S phase - G2 phase M phase Mitosis (Prophase, Prometaphase, Metaphase, Anaphase, Telophase) - Cytokinesis Cell cycle checkpoints Restriction point - Postreplication checkpoint Other cellular phases G0 phase - Apoptosis

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