What is G0 (quiescent phase) of cell cycle?

G0 phase, also known as the quiescent phase or resting phase, is a stage of the cell cycle in which cells exit the active cell cycle and enter a non-dividing state. Cells in G0 phase are metabolically active but are not actively proliferating. Instead, they may carry out specialized functions, undergo differentiation, or remain in a dormant state until signaled to re-enter the cell cycle.

The transition of cells from the active cell cycle (G1, S, G2, M phases) to G0 phase can be triggered by various factors, including:

1. Cellular Differentiation: Cells may exit the cell cycle to undergo differentiation into specialized cell types with specific functions. Once differentiated, these cells may remain in G0 phase indefinitely or resume proliferation in response to signals.

2. Cellular Senescence: Aging or damaged cells may enter G0 phase as a protective mechanism to prevent the propagation of DNA damage or mutations. Senescent cells remain metabolically active but do not divide further.

3. External Signals: External signals from the cellular microenvironment, such as growth factors, nutrient availability, or contact inhibition, can induce cells to enter G0 phase. These signals may promote cell growth and proliferation or trigger cell cycle arrest and entry into G0 phase, depending on the cellular context.

Cells in G0 phase can remain in this state temporarily or indefinitely, depending on the specific cell type and environmental conditions. Importantly, cells in G0 phase retain the ability to re-enter the active cell cycle and proliferate in response to appropriate signals. This flexibility allows cells to adapt to changing physiological demands and maintain tissue homeostasis.