Modulation of telomerase activity in fish muscle by biological and environmental factors

Acclimation during Embryogenesis Remodulates Telomerase Activity and Gene Expression in Baikal Whitefish Larvae, Mitigating the Effects of Acute Temperature Stress

Acclimation through the hormesis effect increases the plasticity of organisms, which has been shown for many ectothermic animals, including fish. We investigated the effect of temperature acclimation in Baikal whitefish Coregonus baicalensis (Dybowski, 1874). Telomere length, telomerase activity, and the expression of genes, whose products are involved in the regulation of telomere length and defense against reactive oxygen species, were selected to assess the state of the larvae. Acclimation and acute temperature stress (+12 °C) had no effect on telomere length, but altered telomerase activity (acclimation decreased it; stress increased it) and the levels of genes expression. Under stress, the expression of superoxide dismutase genes was increased in acclimated larvae and that of glutathione peroxidases in non-acclimated larvae, which may indicate lower reactive oxygen species formation and slower antioxidant responses in acclimated fish. The expression of some telomere-related genes was reduced under temperature stress, but the expression of the tzap and smg genes, whose products improve the control of telomere length by preventing them from lengthening or shortening, was increased in acclimated individuals. The data obtained indicate a positive effect of acclimation on the state of the Baikal whitefish larvae by remodulation of their telomerase activity and the transcriptional profile.

Influence of EE2 exposure, age and sex on telomere length in European long-snouted seahorse (Hippocampus guttulatus)

After a Telomere Lengthening in juvenile stage, a progressive telomere shortening occurs with age despite higher telomerase level. Telomere Length (TL) may also reflect past physiological state such as a chronic chemical stress. Several studies have revealed a correlation between TL, ageing and/or sex in vertebrates, including teleosts; however, the patterns of telomere dynamics with telomerase mRNA expression, sex, lifespan or chemical stress in teleosts are unclear. The first aim of this study is to verify if telomere length is age and sex-dependent. The second aim is to consider if TL is a useful indicator of stress response in European long-snouted seahorse, Hippocampus guttulatus, an ectothermic and non-model system. We showed that after telomere lengthening during the juvenile stage, a telomeric attrition became significant in sexually mature individuals (p = 0.042). TL decreased in older seahorses despite the presence of somatic telomerase mRNA expression at all life stages studied. There was no difference in TL between males and females, but telomerase mRNA expression was consistently higher in females than males. Exposure to EE2 had no effect on TL in young seahorses, but was correlated with a significant increase in telomerase mRNA expression and various physiological disruptions. Here, a growth retardation of -10 % for body length (p = 0.016) and approximately -45 % for mass (p = 0.001) compared to healthy juvenile seahorses was observed. Our data suggest that telomere dynamics alone should not be used as a marker of EE2 exposure in juvenile seahorses.

The use of telomeric length as authenticity marker in fish and seafood - a new perspective in the detection of adulteration

In this review we propose the use of telomeric length (TL) as an authenticity marker that could provide an alternative method for differentiating fish and seafood samples or detecting fraud. Considering the ever-growing number of incidents of economically motivated fish and seafood adulteration using even more sophisticated methods to overcome current authenticity markers, the need to identify novel authenticity markers becomes essential. The TL of fish and seafood depends on individual characteristics (e.g., sex, age) and the environmental stimuli (e.g., temperature, water quality) to which these are exposed. Hence, both wild marine and freshwater populations occupying different geographical origin habitats might differ substantially because of the environmental cues affecting them. Moreover, the implementation of various rearing practices in aquaculture, such as different levels of fish and seafood density and increased ambient noise combined with site-specific environmental cues could affect TL, providing regulatory authorities with valuable information by distinguishing wild from reared populations and organic from conventional ones. In the present review the effects of both the environmental conditions and individual characteristics on the telomeric stability of fish and seafood telomeres are discussed, suggesting TL as a potential prospect authenticity marker that could be used to prevent fish and seafood adulteration.

Telomerase Activity in Somatic Tissues and Ovaries of Diploid and Triploid Rainbow Trout (Oncorhynchus mykiss) Females

Telomerase activity has been found in the somatic tissues of rainbow trout. The enzyme is essential for maintaining telomere length but also assures homeostasis of the fish organs, playing an important role during tissue regeneration. The unique morphological and physiological characteristics of triploid rainbow trout, when compared to diploid specimens, make them a promising model for studies concerning telomerase activity. Thus, in this study, we examined the expression of the Tert gene in various organs of subadult and adult diploid and triploid rainbow trout females. Upregulated Tert mRNA transcription was observed in all the examined somatic tissues sampled from the triploid fish when compared to diploid individuals. Contrastingly, Tert expression in the ovaries was significantly decreased in the triploid specimens. Within the diploids, the highest expression of Tert was observed in the liver and in the ovaries of the subadult individuals. In the triploids, Tert expression was increased in the somatic tissues, while the ovaries exhibited lower activity of telomerase compared to other organs and decreased compared to the ovaries in the diploids. The ovaries of triploid individuals were underdeveloped, consisting of only a few oocytes. The lack of germ cells, which are usually characterized by high Tert expression, might be responsible for the decrease in telomerase activity in the triploid ovaries. The increase in Tert expression in triploid somatic tissues suggests that they require higher telomerase activity to cope with environmental stress and maintain internal homeostasis.

Does pre-spawning catch and release angling affect offspring telomere dynamics in Atlantic salmon?

The practice of 'catch and release' (C&R) angling confers a balance between animal welfare, conservation efforts and preserving the socio-economic interests of recreational angling. However, C&R angling can still cause exhaustion and physical injury, and often exposes the captured fish to the stress of air exposure. Therefore, the true conservation success of C&R angling depends on whether the angled individuals then survive to reproduction and whether there are any persisting effects on subsequent generations. Here we tested the hypothesis that the stress of C&R angling is then passed on to offspring. We experimentally manipulated the C&R experience of wild adult salmon prior to the spawning season. These parental fish either underwent a C&R simulation (which involved exercise with/without air exposure) or were left as control individuals. We then measured the telomere length of the arising offspring (at the larval stage of development) since previous studies have linked a shorter telomere length with reduced fitness/longevity and the rate of telomere loss is thought to be influenced by stress. Family-level telomere length was positively related to rate of growth. However, the telomere lengths of the salmon offspring were unrelated to the C&R experience of their parents. This may be due to there being no intergenerational effect of parental stress exposure on offspring telomeres, or to any potential effects being buffered by the significant telomere elongation mechanisms that are thought to occur during the embryonic and larval stages of development. While this may suggest that C&R angling has a minimal intergenerational effect on offspring fitness, there have been numerous other reports of negative C&R effects, therefore we should still be aiming to mitigate and refine such practices, in order to minimize their impacts on fish populations.

Habitat restoration weakens negative environmental effects on telomere dynamics

Habitat quality can have far-reaching effects on organismal fitness, an issue of concern given the current scale of habitat degradation. Many temperate upland streams have reduced nutrient levels due to human activity. Nutrient restoration confers benefits in terms of invertebrate food availability and subsequent fish growth rates. Here we test whether these mitigation measures also affect the rate of cellular ageing of the fish, measured in terms of the telomeres that cap the ends of eukaryotic chromosomes. We equally distributed Atlantic salmon eggs from the same 30 focal families into 10 human-impacted oligotrophic streams in northern Scotland. Nutrient levels in five of the streams were restored by simulating the deposition of a small number of adult Atlantic salmon Salmo salar carcasses at the end of the spawning period, while five reference streams were left as controls. Telomere lengths and expression of the telomerase reverse transcriptase (TERT) gene that may act to lengthen telomeres were then measured in the young fish when 15 months old. While TERT expression was unrelated to any of the measured variables, telomere lengths were shorter in salmon living at higher densities and in areas with a lower availability of the preferred substrate (cobbles and boulders). However, the adverse effects of these habitat features were much reduced in the streams receiving nutrients. These results suggest that adverse environmental pressures are weakened when nutrients are restored, presumably because the resulting increase in food supply reduces levels of both competition and stress.

Telomerase Activity in Androgenetic Rainbow Trout with Growth Deficiency and in Normally Developed Individuals

Role of telomerase in specimens with retarded growth (dwarfs) has not been thoroughly examined to date. Considering that some of the fish species show correlation between somatic growth and activity of telomerase, it has been tempting to assume that pattern of telomerase activity in specimens with retarded growth and these with normal growth rate may vary. In the present research, telomerase activity has been examined in liver, skin, and muscles in the androgenetic rainbow trout (Oncorhynchus mykiss) with growth deficiency and their normally developed siblings. Among the examined organs, the liver showed the highest telomerase activity in all studied fish, what may be linked to the enormous regeneration capacity of the liver tissue. Although dwarf specimens examined here displayed significantly lower body size and weight they did not exhibit any significant differences in the telomerase activity measured in liver and muscle when compared to the rainbow trout without growth deficiency. In turn, telomerase activity in skin was significantly upregulated in the normally developed androgenotes. The present study indicates that dwarfism in the androgenetic rainbow trout is neither associated with ceased telomerase activity nor its decrease throughout the ontogenetic development.

Genome-Wide Identification, Characterization and Expression Profiling of myosin Family Genes in Sebastes schlegelii

Myosins are important eukaryotic motor proteins that bind actin and utilize the energy of ATP hydrolysis to perform a broad range of functions such as muscle contraction, cell migration, cytokinesis, and intracellular trafficking. However, the characterization and function of myosin is poorly studied in teleost fish. In this study, we identified 60 myosin family genes in a marine teleost, black rockfish (Sebastes schlegelii), and further characterized their expression patterns. myosin showed divergent expression patterns in adult tissues, indicating they are involved in different types and compositions of muscle fibers. Among 12 subfamilies, S. schlegelii myo2 subfamily was significantly expanded, which was driven by tandem duplication events. The up-regulation of five representative genes of myo2 in the skeletal muscle during fast-growth stages of juvenile and adult S. schlegelii revealed their active role in skeletal muscle fiber synthesis. Moreover, the expression regulation of myosin during the process of myoblast differentiation in vitro suggested that they contribute to skeletal muscle growth by involvement of both myoblast proliferation and differentiation. Taken together, our work characterized myosin genes systemically and demonstrated their diverse functions in a marine teleost species. This lays foundation for the further studies of muscle growth regulation and molecular mechanisms of indeterminate skeletal muscle growth of large teleost fishes.

Telomere dynamic in humans and animals: Review and perspectives in environmental toxicology

Telomeres (TLs) play major roles in stabilizing the genome and are usually shortened with ageing. The maintenance of TLs is ensured by two mechanisms involving telomerase (TA) enzyme and alternative lengthening telomeres (ALT). TL shortening and/or TA inhibition have been related to health effects on organisms (leading to reduced reproductive lifespan and survival), suggesting that they could be key processes in toxicity mechanisms (at molecular and cellular levels) and relevant as an early warning of exposure and effect of chemicals on human health and animal population dynamics. Consequently, a critical analysis of knowledge about relationships between TL dynamic and environmental pollution is essential to highlight the relevance of TL measurement in environmental toxicology. The first objective of this review is to provide a survey on the basic knowledge about TL structure, roles, maintenance mechanisms and causes of shortening in both vertebrates (including humans) and invertebrates. Overall, TL length decreases with ageing but some unexpected exceptions are reported (e.g., in species with different lifespans, such as the nematode Caenorhabditis elegans or the crustacean Homarus americanus). Inconsistent results reported in various biological groups or even between species of the same genus (e.g., the microcrustacean Daphnia sp.) indicate that the relation usually proposed between TL shortening and a decrease in TA activity cannot be generalized and depends on the species, stage of development or lifespan. Although the scientific literature provides evidence of the effect of ageing on TL shortening, much less information on the relationships between shortening, maintenance of TLs, influence of other endogenous and environmental drivers, including exposure to chemical pollutants, is available, especially in invertebrates. The second objective of this review is to connect knowledge on TL dynamic and exposure to contaminants. Most of the studies published on humans rely on correlative epidemiological approaches and few in vitro experiments. They have shown TL attrition when exposed to contaminants, such as polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), pesticides and metallic elements (ME). In other vertebrates, the studies we found deals mainly with birds and, overall, report a disturbance of TL dynamic consecutively to exposure to chemicals, including metals and organic compounds. In invertebrates, no data are available and the potential of TL dynamic in environmental risk assessment remains to be explored. On the basis of the main gaps identified some research perspectives (e.g., impact of endogenous and environmental drivers, dose response effects, link between TL length, TA activity, longevity and ageing) are proposed to better understand the potential of TL and TA measurements in humans and animals in environmental toxicology.

Distinct telomere differences within a reproductively bimodal common lizard population

Different strategies of reproductive mode, either oviparity (egg-laying) or viviparity (live-bearing), will be associated with a range of other life-history differences that are expected to affect patterns of ageing and longevity. It is usually difficult to compare the effects of alternative reproductive modes because of evolutionary and ecological divergence. However, the very rare exemplars of reproductive bimodality, in which different modes exist within a single species, offer an opportunity for robust and controlled comparisons.One trait of interest that could be associated with life history, ageing and longevity is the length of the telomeres, which form protective caps at the chromosome ends and are generally considered a good indicator of cellular health. The shortening of these telomeres has been linked to stressful conditions; therefore, it is possible that differing reproductive costs will influence patterns of telomere loss. This is important because a number of studies have linked a shorter telomere length to reduced survival.Here, we have studied maternal and offspring telomere dynamics in the common lizard (Zootoca vivipara). Our study has focused on a population where oviparous and viviparous individuals co-occur in the same habitat and occasionally interbreed to form admixed individuals.While viviparity confers many advantages for offspring, it might also incur substantial costs for the mother, for example require more energy. Therefore, we predicted that viviparous mothers would have relatively shorter telomeres than oviparous mothers, with admixed mothers having intermediate telomere lengths. There is thought to be a heritable component to telomere length; therefore, we also hypothesized that offspring would follow the same pattern as the mothers.Contrary to our predictions, the viviparous mothers and offspring had the longest telomeres, and the oviparous mothers and offspring had the shortest telomeres. The differing telomere lengths may have evolved as an effect of the life-history divergence between the reproductive modes, for example due to the increased growth rate that viviparous individuals may undergo to reach a similar size at reproduction. A free http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13408/suppinfo can be found within the Supporting Information of this article.

Hypoxia Causes Transgenerational Impairment of Ovarian Development and Hatching Success in Fish

Hypoxia is a pressing environmental problem in both marine and freshwater ecosystems globally, and this problem will be further exacerbated by global warming in the coming decades. Recently, we reported that hypoxia can cause transgenerational impairment of sperm quality and quantity in fish (in F0, F1, and F2 generations) through DNA methylome modifications. Here, we provide evidence that female fish ( Oryzias melastigma) exposed to hypoxia exhibit reproductive impairments (follicle atresia and retarded oocyte development), leading to a drastic reduction in hatching success in the F2 generation of the transgenerational group, although they have never been exposed to hypoxia. Further analyses show that the observed transgenerational impairments in ovarian functions are related to changes in the DNA methylation and expression pattern of two gene clusters that are closely associated with stress-induced cell cycle arrest and cell apoptosis. The observed epigenetic and transgenerational alterations suggest that hypoxia may pose a significant threat to the sustainability of natural fish populations.

Telomere elongation during early development is independent of environmental temperatures in Atlantic salmon

There is increasing evidence from endothermic vertebrates that telomeres, which cap the ends of chromosomes and play an important role in chromosome protection, decline in length during postnatal life and are a useful indicator of physiological state and expected lifespan. However, much less is currently known about telomere dynamics in ectothermic vertebrates, which are likely to differ from that of endotherms, at least in part due to the sensitivity of ectotherm physiology to environmental temperature. We report here on an experiment in which Atlantic salmon (Salmo salar) were reared through the embryonic and larval stages of development, and under differing temperatures, in order to examine the effects of environmental temperature during early life on telomere dynamics, oxidative DNA damage and cellular proliferation. Telomere length significantly increased between the embryonic and larval stages of development. Contrary to our expectations, variation in telomere length at the end of the larval stage was unrelated to either cell proliferation rate or the relative level of oxidative DNA damage, and did not vary between the temperature treatments. This study suggests that salmon are able to restore the length of their telomeres during early development, which may possibly help to buffer potentially harmful environmental effects experienced in early life.

Summary: The authors show that, in salmon, telomeres significantly lengthen between the embryonic and larval stages of development, and that this is not influenced by environmental temperature.

Age at maturation has sex- and temperature-specific effects on telomere length in a fish

Telomeres are highly conserved nucleoprotein structures which protect genome integrity. The length of telomeres is influenced by both genetic and environmental factors, but relatively little is known about how different hereditary and environmental factors interact in determining telomere length. We manipulated growth rates and timing of maturation by exposing full-sib nine-spined sticklebacks (Pungitius pungitius) to two different temperature treatments and quantified the effects of temperature treatments, sex, timing of maturation, growth rate and family (genetic influences) on telomere length. We did not find the overall effect of temperature treatment on the relative telomere length. However, we found that variation in telomere length was related to timing of maturation in a sex- and temperature-dependent manner. Telomere length was negatively related to age at maturation in elevated temperature and early maturing males and females differed in telomere length. Variation in growth rate did not explain any variation in telomere length. The broad sense heritability (h ²) of telomere length was estimated at h ² = 0.31 - 0.47, suggesting predominance of environmental over genetic determinants of telomere length variability. This study provides the first evidence that age at maturation together with factors associated with it are influencing telomere length in an ectotherm. Future studies are encouraged to identify the extent to which these results can be replicated in other ectotherms.

Telomerase Expression in Medaka ( Oryzias melastigma) Pharyngeal Teeth

Nonmammalian vertebrates have the capacity of lifelong tooth replacement. In all vertebrates, tooth formation requires contact and interaction between the oral or pharyngeal epithelium and the underlying mesenchyme. To secure lifelong replacement, the presence of odontogenic stem cells has been postulated, particularly in the epithelial compartment. This study uses an advanced teleost fish species, the marine medaka Oryzias melastigma, a close relative to Oryzias latipes, to examine the expression and distribution of telomerase reverse transcriptase (Tert), the catalytic unit of telomerase, in developing pharyngeal teeth and to relate these data to the proliferative activity of the cells. The data are complemented by expression analysis of the pluripotency marker oct4 and bona fide stem cell marker lgr5. Tert distribution and tert expression in developing tooth germs show a dynamic spatiotemporal pattern. Tert is present first in the mesenchyme but is downregulated as the odontoblasts differentiate. In contrast, in the epithelial enamel organ, Tert is absent during early stages of tooth formation and upregulated first in ameloblasts. Later, Tert is expressed and immunolocalized throughout the entire inner enamel epithelium. The pattern of Tert distribution is largely mutually exclusive with that of proliferating cell nuclear antigen (PCNA) immunoreactivity: highly proliferative cells, as revealed by PCNA staining, are negative for Tert; conversely, PCNA-negative cells are Tert-positive. Only the early condensed mesenchyme is both Tert- and PCNA-positive. The absence of tert-positive cells in the epithelial compartment of early tooth germs is underscored by the absence of oct4- and lgr5-positive cells, suggesting ways other than stem cell involvement to secure continuous renewal.

Interactions between parental traits, environmental harshness and growth rate in determining telomere length in wild juvenile salmon

A larger body size confers many benefits, such as increased reproductive success, ability to evade predators and increased competitive ability and social status. However, individuals rarely maximize their growth rates, suggesting that this carries costs. One such cost could be faster attrition of the telomeres that cap the ends of eukaryotic chromosomes and play an important role in chromosome protection. A relatively short telomere length is indicative of poor biological state, including poorer tissue and organ performance, reduced potential longevity and increased disease susceptibility. Telomere loss during growth may also be accelerated by environmental factors, but these have rarely been subjected to experimental manipulation in the natural environment. Using a wild system involving experimental manipulations of juvenile Atlantic salmon Salmo salar in Scottish streams, we found that telomere length in juvenile fish was influenced by parental traits and by direct environmental effects. We found that faster‐growing fish had shorter telomeres and there was a greater cost (in terms of reduced telomere length) if the growth occurred in a harsher environment. We also found a positive association between offspring telomere length and the growth history of their fathers (but not mothers), represented by the number of years fathers had spent at sea. This suggests that there may be long‐term consequences of growth conditions and parental life history for individual longevity.

A synopsis on aging-Theories, mechanisms and future prospects

Answering the question as to why we age is tantamount to answering the question of what is life itself. There are countless theories as to why and how we age, but, until recently, the very definition of aging - senescence - was still uncertain. Here, we summarize the main views of the different models of senescence, with a special emphasis on the biochemical processes that accompany aging. Though inherently complex, aging is characterized by numerous changes that take place at different levels of the biological hierarchy. We therefore explore some of the most relevant changes that take place during aging and, finally, we overview the current status of emergent aging therapies and what the future holds for this field of research. From this multi-dimensional approach, it becomes clear that an integrative approach that couples aging research with systems biology, capable of providing novel insights into how and why we age, is necessary.

Genome-Wide Mapping of Growth-Related Quantitative Trait Loci in Orange-Spotted Grouper (Epinephelus coioides) Using Double Digest Restriction-Site Associated DNA Sequencing (ddRADseq)

Mapping of quantitative trait loci (QTL) is essential for the discovery of genetic structures that related to complex quantitative traits. In this study, we identified 264,072 raw SNPs (single-nucleotide polymorphisms) by double digest restriction site associated DNA sequencing (ddRADseq), and utilized 3029 of these SNPs to construct a genetic linkage map in orange-spotted grouper (Epinephelus coioides) using a regression mapping algorithm. The genetic map contained 24 linkage groups (LGs) spanning a total genetic distance of 1231.98 cM. Twenty-seven significant growth-related QTLs were identified. Furthermore, we identified 17 genes (fez2, alg3, ece2, arvcf, sla27a4, sgk223, camk2, prrc2b, mchr1, sardh, pappa, syk, tert, wdrcp91, ftz-f1, mate1 and notch1) including three (tert, ftz-f1 and notch1) that have been reported to be involved in fish growth. To summarize, we mapped growth-related QTLs in the orange-spotted grouper. These QTLs will be useful in marker-assisted selection (MAS) efforts to improve growth-related traits in this economically important fish.