Extent and variability of interstitial telomeric sequences and their effects on estimates of telomere length

Abstract

Telomeres often shorten with time, although this varies between tissues, individuals and species, and their length and/or rate of change may reflect fitness and rate of senescence. Measurement of telomeres is increasingly important to ecologists, yet the relative merits of different methods for estimating telomere length are not clear. In particular the extent to which interstitial telomere sequences (ITSs), telomere repeats located away from chromosomes ends, confound estimates of telomere length is unknown. Here we present a method to estimate the extent of ITS within a species and variation among individuals. We estimated the extent of ITS by comparing the amount of label hybridized to in-gel telomere restriction fragments (TRF) before and after the TRFs were denatured. This protocol produced robust and repeatable estimates of the extent of ITS in birds. In five species, the amount of ITS was substantial, ranging from 15% to 40% of total telomeric sequence DNA. In addition, the amount of ITS can vary significantly among individuals within a species. Including ITSs in telomere length calculations always underestimated telomere length because most ITSs are shorter than most telomeres. The magnitude of that error varies with telomere length and is larger for longer telomeres. Estimating telomere length using methods that incorporate ITSs, such as Southern blot TRF and quantitative PCR analyses reduces an investigator's power to detect difference in telomere dynamics between individuals or over time within an individual.

Age, Sex, and Telomere Dynamics in a Long-Lived Seabird with Male-Biased Parental Care

“…Its output was correlated with both TRF and TOE, but its detection of sex effects in conjunction with age may have been diluted by the presence of interstitial repeats [26]. This may also be responsible for the lower correlation between the Southern blot-derived measures, which do not measure interstitial repeats, and qPCR, which does, than have been reported elsewhere (e.g.…”

Gender and telomere length: Systematic review and meta-analysis

“…In birds, the amount of interstitial telomeric sequence was substantial as compared to the actual telomeres and highly variable between species. Most importantly, it was also highly variable between individuals (Foote et al, 2013). It is not known whether frequencies of any of these polymorphisms might be gender-specific in humans.…”

Heritability of telomere length in the Zebra Finch

“…For example, interstitial repeats are infrequent in humans, and in this respect, the measurement technique should have little effect on telomere length heritability estimates in humans. In avian species, however, the frequency of interstitial repeats is frequently high (Foote et al 2013), and it remains to be investigated to what extent published heritability estimates (Table 1) can be attributed to variance in interstitial repeats versus terminal telomeres. To resolve this issue, additional studies in which the heritability can specifically be assigned to either interstitial telomeric repeats and/or terminal telomeres are required.…”

“…In contrast to humans, many avian species have numerous interstitial telomeric repeats, which are in addition to 'terminal' telomeric repeats (Delany et al 2000;Foote et al 2013). Terminal telomeres are susceptible to ageing and environmental factors and are involved in the protection and stabilization of the chromosomes.…”