Telomere Biology—Insights into an Intriguing Phenomenon

Abstract

Bacteria and viruses possess circular DNA, whereas eukaryotes with typically very large DNA molecules have had to evolve into linear chromosomes to circumvent the problem of supercoiling circular DNA of that size. Consequently, such organisms possess telomeres to cap chromosome ends. Telomeres are essentially tandem repeats of any DNA sequence that are present at the ends of chromosomes. Their biology has been an enigmatic one, involving various molecules interacting dynamically in an evolutionarily well-trimmed fashion. Telomeres range from canonical hexameric repeats in most eukaryotes to unimaginably random retrotransposons, which attach to chromosome ends and reverse-transcribe to DNA in some plants and insects. Telomeres invariably associate with specialised protein complexes that envelop it, also regulating access of the ends to legitimate enzymes involved in telomere metabolism. They also transcribe into repetitive RNA which also seems to be playing significant roles in telomere maintenance. Telomeres thus form the intersection of DNA, protein, and RNA molecules acting in concert to maintain chromosome integrity. Telomere biology is emerging to appear ever more complex than previously envisaged, with the continual discovery of more molecules and interplays at the telomeres. This review also includes a section dedicated to the history of telomere biology, and intends to target the scientific audience new to the field by rendering an understanding of the phenomenon of chromosome end protection at large, with more emphasis on the biology of human telomeres. The review provides an update on the field and mentions the questions that need to be addressed.

Telomeres, Trauma, and Training

“…This led her to conclude that the tips of chromosomes must normally be protected by some sort of cap to maintain stability and prevent them from fusing together. This confirmed earlier work that the ends of chromosomes were not susceptible to genetic alterations (deletions and insertions) and so must be sheltered (2).…”

Mechanisms of ovarian aging

“…Telomeres, present at chromosome ends in eukaryotes, consist of tandem DNA repeat sequences. They act in concert with proteins and RNA molecules to preserve chromosome integrity (Venkatesan et al 2017). In most cell types in the human body, DNA is lost with each cycle of DNA replication as a result of telomere shortening.…”

“…Some cells, including oocytes, possess the enzyme telomerase to help extend telomeric DNA (Keefe et al 2015). Telomerase is an RNA-dependent DNA polymerase (also known as reverse transcriptase) that ensures the proper DNA replication of the highly repetitive sequences of telomeres (Venkatesan et al 2017). Telomere length is known to directly correlate with both reproductive life span and life expectancy ( Keefe et al 2007, Kalmbach et al 2013.…”

Distinct Responses of Arabidopsis Telomeres and Transposable Elements to Zebularine Exposure

“…At the DNA level, they are formed by conserved minisatellite repetitive sequences, for example, TTTAGGG in most plants [ 1 ] and TTAGGG in vertebrates [ 2 ]. Telomeres distinguish natural chromosomal ends from double-strand DNA breaks, protect them against fusion and activities of repair complexes, and act as buffer zones against the replicative loss of DNA coding sequences (reviewed in [ 3 ]).…”