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Telomerase is a reverse transcriptase enzyme that carries its own RNA molecule (e.g., with the sequence 3′-CCCAAUCCC-5′ in Trypanosoma brucei) [3] which is used as a template when it elongates telomeres. Telomerase is active in gametes and most cancer cells, but is normally absent in most somatic cells.
In most multicellular eukaryotic organisms, telomerase is active only in germ cells, some types of stem cells such as embryonic stem cells, and certain white blood cells. [9] Telomerase can be reactivated and telomeres restored to the embryonic state by somatic cell nuclear transfer. [18]
Telomerase levels were measured at baseline, and again after three months, when researchers discovered that, in the 24 participants with sufficient data for analysis, telomerase in the blood had increased by 29 percent. The authors commented that "The implications of this study are not limited to men with prostate cancer.
Two concerns with applying telomerase inhibitors in cancer treatment are that effective treatment requires continuous, long-term drug application and that off-target effects are common. [30] For example, the telomerase inhibitor imetelstat, first proposed in 2003, [31] [32] has been held up in clinical trials due to hematological toxicity. [30]
Human chromosomes (grey) capped by telomeres (white). A telomere (/ ˈ t ɛ l ə m ɪər, ˈ t iː l ə-/; from Ancient Greek τέλος (télos) 'end' and μέρος (méros) 'part') is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes (see Sequences).
An enzyme called telomerase elongates telomeres in gametes and stem cells. [12] Telomerase deficiency in humans has been linked to several aging-related diseases related to loss of regenerative capacity of tissues. [13] It has also been shown that premature aging in telomerase-deficient mice is reverted when telomerase is reactivated. [14]
Alternative Lengthening of Telomeres (also known as "ALT") is a telomerase-independent mechanism by which cancer cells avoid the degradation of telomeres.. At each end of the chromosomes of most eukaryotic cells, there is a telomere: a region of repetitive nucleotide sequences which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes.
Thus the age correlation is close to its maximum possible correlation value of 1. Other biological clocks are based on a) telomere length, b) p16INK4a expression levels (also known as INK4a/ARF locus), [38] and c) microsatellite mutations. [39] The correlation between chronological age and telomere length is r = −0.51 in women and r = −0.55 ...