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. 2015 Apr 8;9:79. doi: 10.3389/fnbeh.2015.00079

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Copyright © 2015 Blaze, Asok and Roth.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution and reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Telomeres are regulated by telomeric-specific proteins and are subject to epigenetic regulation. (A) Telomeres are TTAGGG nucleotide repeats that (A1) contain a subtelomeric region and telomeric region that surrounds chromatin, in addition to (A2) a 50–300 bp overhang on the 3’ strand of DNA. (A2) Stress can induce shortening of telomeres whereas telomerase promotes elongation. (B) Telomere length is regulated by proteins within the (B1) shelterin and telomerase complexes. Shelterin proteins have a crucial role in recruiting and positioning (B2) telomerase RNA (TR) and telomerase reverse transcriptase (TERT) on the ends of telomeres during maintenance and repair. (C) In their native state, (C1) telomeres are in a hypermethylated state that is regulated and maintained by key DNA methyltransferases including DNMT1, DNA methyltransferase 3a (DNMT3a), and DNMT3b. However, (C2) telomere shortening induces a shift to a euchromatic state involving increased acetylation and decreased methylation which (C3) facilitates the recruitment of telomerase to telomere ends. Abbreviations: TTAGGG-repeat binding factor 1 (TRF1), TTAGGG-repeat binding factor 2 (TRF2), collective acronym of previous labels TINT1, PTOP, and PIP1 (TPP1), TRF-1 interacting nuclear protein/factor 2 (TIN2), (RAP1), protection of telomeres 1 (POT1), telomerase reverse transcriptase (TERT), TR, methyl group (pentagonal M), acetyl group (pentagonal A).