Why do cells enter G0?

Cells enter the G0 phase when they no longer need to divide as part of their differentiation process. For example, cells stop dividing after they undergo mitosis and thus, enter the G0 phase. Neurons and muscle cells have specific functions to carry out and do not need to continually divide. Cells may also enter the G0 phase when they do not have the necessary energy and nutrients to divide. Additionally, cells may enter the G0 phase when irreparable DNA damage has occurred; this is done as a protective measure to prevent damaged or cancerous cells from dividing uncontrollably. It is important to note that cells in the G0 phase may re-enter the growth cycle in response to stimulation by mitogens (induced by injury or normal cell turnover). The entering of cells to the G0 phase may also be part of their normal progression in the cell cycle; after a certain number of divisions, certain cells enter a rest phase in G0 before they re-enter the cell cycle.