Telomere length varies substantially between blood cell types in a reptile

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.

Decline in telomere length with increasing age across nonhuman vertebrates: A meta‐analysis

“…At the within‐tissue level, tissues are composed of various cell types that can have their own telomere dynamics. In the Australian Painted Dragon ( Ctenophorus pictus ), white blood cell (WBC) populations (lymphocytes and azurophils) have different TL, and TL is also much longer in WBC than in red blood cells (RBC) (Olsson et al, 2020). Given the lack of a nucleus in their erythrocytes, telomeres in mammals are mostly measured in WBC, which equates to measuring the average TL in a heterogeneous population of cells, each with potentially different sized telomeres.…”

Morphological and cytochemical characteristics ofVaranus niloticus(Squamata, Varanidae) blood cells

“…The platelets of mammals are relatively short‐lived as the life spans range between 10 days in humans and 5 days in mice (Johnson et al, 2018; Lebois & Josefsson, 2016). Taking in our consideration the mean erythrocyte lifespan in reptiles ranges between 600 to 800 days while in humans it is only 120 days, thrombocytes have a longer lifespan of thrombocytes in reptiles (Louis et al, 2020; Olsson et al, 2020). It is assumed that the slow metabolic rate of reptiles is closely related to the exceedingly slow turnover of erythrocytes comparing to other vertebrates (Khalaf et al, 2020; Stacy et al, 2011).…”

Inbreeding is associated with shorter early-life telomere length in a wild passerine

“…We measured TL in blood, thus it is possible that inbreeding or heterosis only affected telomeres in erythrocytes (Manning et al, 2002;Olsson, Geraghty, Wapstra, & Wilson, 2020). However, this is unlikely because TLs often correlate well across tissues within the organism (Daniali et al, 2013;Demanelis et al, 2020;Reichert, Criscuolo, Verinaud, Zahn, & Massemin, 2013), especially in early-life (Prowse & Greider, 1995).…”