Telomeres and genomic evolution

Abstract

The terminal regions of eukaryotic chromosomes, composed of telomere repeat sequences and sub-telomeric sequences, represent some of the most variable and rapidly evolving regions of the genome. The sub-telomeric regions are characterized by segmentally duplicated repetitive DNA elements, interstitial telomere repeat sequences and families of variable genes. Sub-telomeric repeat sequence families are shared among multiple chromosome ends, often rendering detailed sequence characterization difficult. These regions are composed of constitutive heterochromatin and are subjected to high levels of meiotic recombination. Dysfunction within telomere repeat arrays, either due to disruption in the chromatin structure or because of telomere shortening, can lead to chromosomal fusion and the generation of large-scale genomic rearrangements across the genome. The dynamic nature of telomeric regions, therefore, provides functionally useful variation to create genetic diversity, but also provides a mechanism for rapid genomic evolution that can lead to reproductive isolation and speciation. This article is part of the theme issue 'Understanding diversity in telomere dynamics'.This article is part of the theme issue 'Understanding diversity in telomere dynamics'.

Telomeres and Telomere Length: A General Overview

“…Human telomeres typically range between 10 to 15 kb [7,11,12]. Telomeres include proximal double-stranded and distal single-stranded regions ( Figure 1A) with subtelomeres and interstitial sections separating repeats from the rest of the chromosome [13,14]. Telomeres, intrinsically unstable fragile sites, are stabilized through binding with so-called shelterin complex proteins [12,15,16].…”

Repair and Reconstruction of Telomeric and Subtelomeric Regions and Genesis of New Telomeres: Implications for Chromosome Evolution

“…The major difference is that replication stress can cause stochastic telomere deletions, which causes large blocks of telomeric repeats to be lost at once (Figure 1A). [ 17 ] Due to the various telomere roadblocks mentioned above, stochastic telomere deletions may be caused by a truncated T‐loop or DSB in a stalled replication fork. Damage inside telomeres is generally repaired by telomerase.…”

“…DDR then triggers repair pathways including homologous recombination (HR) and non‐homologous end joining (NHEJ), [ 16 ] and these repair events can induce substantial rearrangements and chromosome fusions while restoring their ends. [ 17,18 ]…”

An Evolutionary View of Trypanosoma Cruzi Telomeres

“…Subtelomeres are often described as regions of genomic instability (Baird, 2018), and this observation is supported by the abundance of retrotransposon fragments and pseudogenes in T. cruzi telomeric clones, but they also represent a buffer region to minimize chromosome damage when telomere attrition occurs. However, despite this unstable environment, complete gene copies of DGF-1, TS, and RHDEAD/H-RNA helicase and N-acetyltransferase in T. cruzi subtelomeres are expressed, indicating that a positive selection is preserving the integrity of these genes at these locations (Moraes Barros et al, 2012).…”