Sequence specificity of human telomerase Biology Diagrams In organisms with linear chromosomes, incomplete replication of telomere ends may lead to the loss of genetic information (1, 2).This so-called end replication problem can be further compounded by telomere attrition and cell cycle arrest as a result of nucleolytic degradation and DNA damage repair reactions ().The telomerase, a ribonucleoprotein with reverse transcriptase activity, synthesizes
Telomerase activity and RNA levels change as cells enter and exit the cell cycle. Gradual telomere shortening in the absence of telomerase does not immediately affect cell cycling; however, "critically" short telomeres are hypothesised to play a role in senescence and the triggering of DNA damage checkpoints.
Telomeres, telomerase, and the cell cycle Biology Diagrams
Some adult human somatic cells have detectable telomerase activity, Cusanelli E, Ouenzar F, Querido E, et al. Live cell imaging of telomerase RNA dynamics reveals cell cycle-dependent clustering of telomerase at elongating telomeres. Mol Cell. 2011;44:819-27. doi: 10.1016/j.molcel.2011.09.020. [Google Scholar] 110. Bajon E, Laterreur N In roughly 85% of cancer cells, telomerase is reactivated. This reactivation allows cancer cells to bypass normal aging mechanisms and continue proliferating without limit. The persistence of telomerase activity in tumors is linked to cancer progression, making it an attractive target for therapeutic interventions. Regulation of the Cell Cycle The TCAB1-hTR association is lost in mitotic cells, suggesting that some elements of the telomerase enzyme are assembled in a cell cycle-regulated manner 136.This observation fits with the
Telomerase activity and cell cycle checkpoints 3.1. Genetic lesions that disable key regulators of G1 phase progression in mammalian cells are present in most human cancers and such cells are mostly positive for telomerase activity. Mitogen-dependent cdk4 and cdk6 phosphorylate retinoblastoma (Rb) protein, that helps to cancel Rb's growth
Telomerase Mechanism of Telomere Synthesis Biology Diagrams
In nonactivated CD4+ T cells telomerase activity is detected only in cytoplasm. However, in activated T cells, the TERT protein is present in both, cytoplasm and nucleus. assembly of the telomerase enzyme complex may be regulated during cell cycle. Telomerase assembly could take place during S phase and it is disassembled probably during M This study reported, for the first time, the telomere-telomerase dance in single living cells during different phases of the cell cycle (Figure 2a). Gratifyingly, the results obtained with this technology are consistent with previous findings that predicted there are only a few telomere elongation events on a per cell and per S-phase basis [28] .
