G0 phase

Many mammal cells, such as this 9x Hneuron, remain permanently or semipermanently in G₀.

The G₀ phase, G zero phase, or 'resting phase' is a period in the cell cycle in which cells exist in a quiescent state. G₀ phase is viewed as either an extended G₁ phase, where the cell is neither dividing nor preparing to divide, or a distinct quiescent stage that occurs outside of the cell cycle.^[1] Some types of cells, such as nerve and heart muscle cells, become quiescent when they reach maturity (i.e., when they are terminally differentiated) but continue to perform their main functions for the rest of the organism's life. Multinucleated muscle cells that do not undergo cytokinesis are also often considered to be in the G₀ stage.^[1] On occasion, a distinction in terms is made between a G₀ cell and a 'quiescent' cell (e.g., heart muscle cells and neurons), which will never enter the G₁ phase, whereas other G₀ cells may.

Distinction from senescent cells

Cellular senescence is distinct from quiescence because it is a state that occurs in response to DNA damage or degradation that would make a cell's progeny nonviable. Senescence then, unlike quiescence, is often a biochemical alternative to the self-destruction of such a damaged cell by apoptosis. Furthermore, quiescence is reversible whereas senescence isn't.

References

1. Re: Are the cells in the G0 (g zero) phase of mitosis really suspended? Erin Cram, Grad student, Molecular and Cellular Biology, University of California, Berkeley. 1999. MadScience Network. Question ID 942142089.Cb.

See also