Telomere length varies substantially between blood cell types in a reptile.

Mats Olsson,Erik Wapstra,Nicholas J Geraghty,Mark Wilson

doi:10.1098/rsos.192136

Abstract

Telomeres are repeat sequences of non-coding DNA-protein molecules that cap or intersperse metazoan chromosomes. Interest in telomeres has increased exponentially in recent years, to now include their ongoing dynamics and evolution within natural populations where individuals vary in telomere attributes. Phylogenetic analyses show profound differences in telomere length across non-model taxa. However, telomeres may also differ in length within individuals and between tissues. The latter becomes a potential source of error when researchers use different tissues for extracting DNA for telomere analysis and scientific inference. A commonly used tissue type for assessing telomere length is blood, a tissue that itself varies in terms of nuclear content among taxa, in particular to what degree their thrombocytes and red blood cells (RBCs) contain nuclei or not. Specifically, when RBCs lack nuclei, leucocytes become the main source of telomeric DNA. RBCs and leucocytes differ in lifespan and how long they have been exposed to ‘senescence' and erosion effects. We report on a study in which cells in whole blood from individual Australian painted dragon lizards (Ctenophorus pictus) were identified using flow cytometry and their telomere length simultaneously measured. Lymphocyte telomeres were on average 270% longer than RBC telomeres, and in azurophils (a reptilian monocyte), telomeres were more than 388% longer than those in RBCs. If this variation in telomere length among different blood cell types is a widespread phenomenon, and DNA for comparative telomere analyses are sourced from whole blood, evolutionary inference of telomere traits among taxa may be seriously complicated by the blood cell type comprising the main source of DNA.

Highlights

The number of studies of telomeres, the non-coding protein-nuclelotide ‘caps’ primarily at the ends of chromosomes, has rapidly increased recently across a wide range of disciplines, from functional mechanisms and biochemistry to their ongoing evolution in the wild [1,2,3,4,5]
We used t-tests supported by Kruskal–Wallis tests to look for differences in telomere length between red blood cells (RBCs) and lymphocytes because this comparison is more generalized to other taxa, that is, we excluded azurophils as these only occur in reptiles
Azurophils had the longest telomeres, RBCs the shortest and lymphocyte telomeres were intermediate in length

Summary

Introduction

The number of studies of telomeres, the non-coding protein-nuclelotide ‘caps’ primarily at the ends of chromosomes, has rapidly increased recently across a wide range of disciplines, from functional mechanisms and biochemistry to their ongoing evolution in the wild [1,2,3,4,5]. The conserved, non-coding protein-(TTAGGG)n sequences in most metazoans [6] protect the chromosome ends from erosion and from the cell’s own DNA repair system but suffer from attrition during cell replication and onslaught by reactive molecules [1,2,3]. Telomere sequences interspersed within the chromosomes themselves (interstitial telomeres) are likely to be more stable over time but may have negative effects on chromosomal stability and risk of genetic disease, such as cancer [1,2,3,4,5]. Telomere heritability has been estimated as having widely different values, from zero to more than one (reviewed in [4]), which makes inferences of their ongoing evolution hard to depict

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