Cell Cycle Regulation
In the cell cycle, transition from one phase to the next is regulated at checkpoints (see Fig 5-1). Important checkpoints occur at the following:
Checkpoints allow monitoring of the cell to verify the successful, error-free completion of the previous phase. At the G1 checkpoint, cell size and the availability of nutrients and growth factors are assessed, and the cell is checked for DNA damage. After completion of this checkpoint, the cell is committed to proceeding with cell division; otherwise, it enters the quiescent G0 phase. Before the cycle progresses to the M phase, further inspection of the DNA occurs at the G2 checkpoint. If damaged DNA is detected at either checkpoint, it may be repaired, or programmed cell death (see the section Apoptosis) may be initiated.
Checkpoint regulation occurs via a family of proteins known as cyclins and cyclindependent kinases (CDKs). At the G1 checkpoint, CDK phosphorylation of proteins of the retinoblastoma (Rb) family facilitates downstream transcription in preparation for S phase. Tumor suppressor genes like the Rb family often have a role in regulation of the cell cycle, dysregulation of which can lead to cancer (see the section “Tumor suppressor genes”).
Sun A, Bagella L, Tutton S, Romano G, Giordano A. From G0 to S phase: a view of the roles played by the retinoblastoma (Rb) family members in the Rb-E2F pathway. J Cell Biochem. 2007;102(6):1400–1404.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.