Characterization of telomeres and telomerase expression in Xiphophorus

Abstract

Research investigating telomere lengths and telomerase expression in vertebrates has progressively become important due to the association of these two biological endpoints with cellular aging and cancer in humans. Studies that rely upon the traditional use of laboratory mice have been faced with limitations largely due to inbred mice possessing large telomeres and ubiquitous expression of telomerase. Recently, a number of small fish species have been shown to provide potentially informative models for examining the role of telomeres and telomerase within intact vertebrate animals. Xiphophorus fishes represent a new world live-bearing genus that has not previously been assessed for telomere length or telomerase expression. To add to the knowledge base of telomere and telomerase biology in vertebrates we assessed telomere length and telomerase expression among several species of Xiphophorus. The telomere lengths in several organs (gill, brain, eyes, testis, ovary and liver) in three species (X. hellerii, X. maculatus, X. couchianus) and also in F1 interspecies hybrids were approximately 2–6 kb. This size was consistent within the same organs of the same species, as well as between species and F1 hybrids. Despite possessing relatively short telomere lengths compared to humans, the consistency of size among Xiphophorus species and organs may allow experimental detection of telomere shortening. The relative expression of telomerase reverse transcriptase (TERT) was determined by quantitative real-time PCR. Expression levels of TERT was measured in seven organs (ovary, testis, liver, gill, brain, heart, skin) from X. maculatus, X. hellerii and in control and ultraviolet light (UVB) exposed skin samples from X. maculatus, X. hellerii, and F1 interspecies hybrids. TERT gene expression was significantly higher in ovary and testis, while all other organs showed low relative TERT expression. Detectable increases in TERT expression were found in skin samples upon UVB exposure. Our findings suggest Xiphophorus may serve as a suitable model for future studies investigating the association of telomere length and telomerase expression in regard to aging and disease.

Does Reproductive Investment Decrease Telomere Length in Menidia menidia?

“…In Japanese medaka ( Oryzias latipes ), telomeres shorten during aging despite the considerable amount of telomerase activity and the telomere length is inversely correlated with the increase in body length. Similar to silversides, the platyfish ( Xiphophorus ) do show homogenous telomere lengths among tissues, which indicate a good model for telomere shortening research, but the age-dependency has not been investigated yet [ 18 ]. The actual mechanisms that regulate telomere length in silversides are as yet unknown.…”

“…In fishes, however, the age-dependence of telomere length is far less clear [ 12 – 24 ]. The majority of fish telomeres studied have been in freshwater species, primarily zebrafish ( Dano rerio , [ 12 – 14 ]), Japanese medaka ( Oryzias latipes , [ 15 , 16 ]), African killifish ( Nothobranchis furzeri , [ 17 ]), platyfish ( Xiphophorus , [ 18 ]) and eastern mosquito fish ( Gambusia holbrooki , [ 19 ]) and the results for fishes are apparently more complicated than those for other taxa. For instance, in zebrafish telomere length did not decline steadily over time [ 12 ] but then drastically declined in aged fish [ 13 ] while the telomerase activity remained high throughout the entire life [ 12 , 13 ].…”

Telomeres in Fishes

“…Rather short telomeres are observed in some of the sharks and rays (about 3 kb) [Rocco et al, 2001], in Nothobranchius furzeri (4.5-6.6 kb) [Hartman et al, 2009] and Xiphophorus fish species (2-6 kb) [Downs et al, 2012]. The Nile tilapia (Oreochromis niloticus) shows telomeric repeat tracts extending for 4-10 kb [Chew et al, 2002], while telomere length in medaka (Oryzias latipes) oscillates from 3 to 12 kb [Elmore et al, 2008].…”

“…The length of the telomeric DNA arrays in fish shows interspecies variation and ranges from 2 to 25 kb [Lund et al, 2009;Downs et al, 2012]. Rather short telomeres are observed in some of the sharks and rays (about 3 kb) [Rocco et al, 2001], in Nothobranchius furzeri (4.5-6.6 kb) [Hartman et al, 2009] and Xiphophorus fish species (2-6 kb) [Downs et al, 2012].…”

Preliminary Identification of Candidate Genes Related to Survival of Gynogenetic Rainbow Trout (Oncorhynchus mykiss) Based on Comparative Transcriptome Analysis

“…Contrary to mammals where TERT expression and telomerase activity are restricted to germ line cells, stem cells and tumor cells, fish including rainbow trout show a high activity of telomerase in somatic tissues regardless of the age of the studied specimens [29]. In Xiphophorus maculatus and X. helleri, the expression of TERT in ovary and testis was significantly higher than in other organs [30]. Moreover, in killifish (Fundulus heteroclitus) the TERT expression was confirmed in eggs [31].…”