Inducible transgenic expression in the short‐lived fish Nothobranchius furzeri

This study demonstrates inducible transgenic expression in the exceptionally short‐lived turquoise killifish Nothobranchius furzeri, which is a useful vertebrate model for ageing research. Transgenic N. furzeri bearing a green fluorescent protein (Gfp) containing construct under the control of a heat shock protein 70 promoter were generated, heat shock‐induced and reversible Gfp expression was demonstrated and germline transmission of the transgene to the F1 and F2 generations was achieved. The availability of this inducible transgenic expression system will make the study of ageing‐related antagonistically pleiotropic genes possible using this unique vertebrate model organism.     

Cytoskeletal dynamics of the teleostean fin ray during fin epimorphic regeneration

Teleost fishes can regenerate their fins by epimorphic regeneration, a process that involves the transition of the formerly quiescent tissues of the stump to an active, growing state. This involves dynamic modifications of cell phenotype and behavior that must rely on alterations of the cytoskeleton. We have studied the spatial and temporal distribution of three main components of the cytoskeleton (actin, keratin and vimentin) in the regenerating fin, in order to establish putative relationships between cell cytoskeleton and cell behavior. According to our results, the massive rearrangement undergone by the epidermis right after injury, which takes place by cell migration, correlates with a transient down-regulation of keratin and a strong up-regulation of actin in the epidermal cells. During the subsequent epidermal growth, based on cell proliferation, keratin normal pattern is recovered while actin is down-regulated, although not to normal (quiescent) levels. The epidermal basal layer in contact with the blastema displays a particular cytoskeletal profile, different to that of the rest of the epidermal cells, which reflects its special features. In the connective tissue compartment, somatic cells do not contain vimentin, but keratin, as intermediate filament. Proliferative and migrative activation of these cells after injury correlates with actin up-regulation. Although this initial activation does not involve keratin down-regulation, blastemal cells were later observed to lack keratin, suggesting that such cytoskeletal modification might be needed for connective tissue cells to dedifferentiate and form the blastema. Cell differentiation in the newly formed, regenerated ray is accompanied by actin down-regulation and keratin up-regulation.     

Quantification of noradrenergic‐, dopaminergic‐, and tectal‐neurons during aging in the short‐lived killifish Nothobranchius furzeri

Parkinson''s disease (PD) is characterized by phosphorylation and aggregation of the protein α‐Synuclein and ensuing neuronal death progressing from the noradrenergic locus coeruleus to midbrain dopaminergic neurons. In 2019, Matsui and colleagues reported a spontaneous age‐dependent degeneration of dopaminergic neurons and an even greater neurodegeneration of the noradrenergic neurons in the short‐lived killifish Nothobranchius furzeri. Given the great possible relevance of a spontaneous model for PD, we assessed neurodegeneration of noradrenergic and dopaminergic neurons in two further laboratory strains of N. furzeri. We implemented, for the first time in N. furzeri, a whole‐brain clarification technique and proceeded to entire 3D nuclei reconstruction to quantify total cell numbers in two different stains of N. furzeri. In both strains, we observed that age‐dependent neurodegeneration is limited to the locus coeruleus and does not involve the posterior tuberculum. We also applied 3D counting to the optic tectum, an area of active adult neurogenesis, and detected an increase of neurons with age. Our results confirm age‐dependent neurodegeneration of noradrenergic neurons, a condition reminiscent of the presymptomatic stage of PD indicating that N. furzeri could be used in the future to identify modifying factors for age‐dependent neurodegeneration and open the intriguing possibility that natural genetic variation may influence the susceptibility of dopaminergic neurons.     

The age factor in optic nerve regeneration: Intrinsic and extrinsic barriers hinder successful recovery in the short‐living killifish

As the mammalian central nervous system matures, its regenerative ability decreases, leading to incomplete or non‐recovery from the neurodegenerative diseases and central nervous system insults that we are increasingly facing in our aging world population. Current neuroregenerative research is largely directed toward identifying the molecular and cellular players that underlie central nervous system repair, yet it repeatedly ignores the aging context in which many of these diseases appear. Using an optic nerve crush model in a novel biogerontology model, that is, the short‐living African turquoise killifish, the impact of aging on injury‐induced optic nerve repair was investigated. This work reveals an age‐related decline in axonal regeneration in female killifish, with different phases of the repair process being affected depending on the age. Interestingly, as in mammals, both a reduced intrinsic growth potential and a non‐supportive cellular environment seem to lie at the basis of this impairment. Overall, we introduce the killifish visual system and its age‐dependent regenerative ability as a model to identify new targets for neurorepair in non‐regenerating individuals, thereby also considering the effects of aging on neurorepair.     

Temperature affects longevity and age-related locomotor and cognitive decay in the short-lived fish Nothobranchius furzeri

Temperature variations are known to modulate aging and life-history traits in poikilotherms as different as worms, flies and fish. In invertebrates, temperature affects lifespan by modulating the slope of age-dependent acceleration in death rate, which is thought to reflect the rate of age-related damage accumulation. Here, we studied the effects of temperature on aging kinetics, aging-related behavioural deficits, and age-associated histological markers of senescence in the short-lived fish Nothobranchius furzeri. This species shows a maximum captive lifespan of only 3 months, which is tied with acceleration in growth and expression of aging biomarkers. These biological peculiarities make it a very convenient animal model for testing the effects of experimental manipulations on life-history traits in vertebrates. Here, we show that (i) lowering temperature from 25 degrees C to 22 degrees C increases both median and maximum lifespan; (ii) life extension is due to reduction in the slope of the age-dependent acceleration in death rate; (iii) lowering temperature from 25 degrees C to 22 degrees C retards the onset of age-related locomotor and learning deficits; and (iv) lowering temperature from 25 degrees C to 22 degrees C reduces the accumulation of the age-related marker lipofuscin. We conclude that lowering water temperature is a simple experimental manipulation which retards the rate of age-related damage accumulation in this short-lived species.     

Retracted: Evolution and development of the homocercal caudal fin in teleosts

The vertebrate caudal skeleton is one of the most innovative structures in vertebrate evolution and has been regarded as an excellent model for functional morphology, a discipline that relates a structure to its function. Teleosts have an internally‐asymmetrical caudal fin, called the homocercal caudal fin, formed by the upward bending of the caudal‐most portion of the body axis, the ural region. This homocercal type of the caudal fin ensures powerful and complex locomotion and is thought to be one of the most important evolutionary innovations for teleosts during adaptive radiation in an aquatic environment. In this review, we summarize the past and present research of fish caudal skeletons, especially focusing on the homocercal caudal fin seen in teleosts. A series of studies with a medaka spontaneous mutant have provided important insight into the evolution and development of the homocercal caudal skeleton. By comparing developmental processes in various vertebrates, we propose a scenario for acquisition and morphogenesis of the homocercal caudal skeleton during vertebrate evolution.     

Age‐related decline in BubR1 impairs adult hippocampal neurogenesis

Aging causes significant declines in adult hippocampal neurogenesis and leads to cognitive disability. Emerging evidence demonstrates that decline in the mitotic checkpoint kinase BubR1 level occurs with natural aging and induces progeroid features in both mice and children with mosaic variegated aneuploidy syndrome. Whether BubR1 contributes to age‐related deficits in hippocampal neurogenesis is yet to be determined. Here we report that BubR1 expression is significantly reduced with natural aging in the mouse brain. Using established progeroid mice expressing low amounts of BubR1, we demonstrate these mice exhibit deficits in neural progenitor proliferation and maturation, leading to reduction in new neuron production. Collectively, our identification of BubR1 as a new and critical factor controlling sequential steps across neurogenesis raises the possibility that BubR1 may be a key mediator regulating aging‐related hippocampal pathology. Targeting BubR1 may represent a novel therapeutic strategy for age‐related cognitive deficits.     

The median‐fin skeleton of the Eastern Atlantic and Mediterranean clingfishes Lepadogaster lepadogaster (Bonnaterre) and Gouania wildenowi (Risso) (Teleostei: Gobiesocidae)

Previous research on the osteology of the Gobiesocidae focused mostly on the neurocranium and the thoracic sucking disc (formed by the paired‐fin girdles). Little attention has been paid to the skeleton of the median fins. The dorsal‐ and anal‐fin skeleton of Lepadogaster lepadogaster and other gobiesocids (excluding Alabes, which lacks these fins) are characterized by the absence of spines, branched fin‐rays, and middle radials. In gobiesocids, the distal radials never ossify and consist of elastic hyaline‐cell cartilage. Gouania wildenowi is unique among gobiesocids in having further reductions of the dorsal‐ and anal‐fin skeleton, including a notable decrease in the size of the proximal‐middle radials in an anterior–posterior direction. Unlike L. lepadogaster, which exhibits a one‐to‐one relationship between the dorsal‐ and anal‐fin rays and proximal‐middle radials, G. wildenowi has a higher number of proximal‐middle radials than distal radial cartilages and fin rays in the dorsal and anal fins. In G. wildenowi, the dorsal‐ and anal‐fin rays do not articulate with the distal tip of the proximal‐middle radials but are instead positioned between proximal‐middle radials, which is unusual for teleosts. Previously unrecognized dorsal and ventral pads of elastic hyaline‐cell cartilage are also present in the caudal skeleton of L. lepadogaster, G. wildenowi, and all other gobiesocids examined. J. Morphol., 2010. © 2009 Wiley‐Liss, Inc.     

Geographical variation in reproductive ageing patterns and life‐history strategy of a short‐lived passerine bird

We investigated differences in ageing patterns in three measures of breeding performance in populations of barn swallows Hirundo rustica L. from Spain and Denmark differing in breeding latitude and hence migration distance and duration of the breeding season. We found differences in ageing patterns between populations. Generally, young (i.e. yearling) and old females (i.e. ≥ 5 years of age) laid their first eggs later and produced smaller clutches than middle‐aged females (i.e. 2–4 years of age) in both populations. The southernmost population (i.e. Spanish) showing the shorter migratory distance experienced a greater within‐individual increase in timing of breeding and clutch size in early life and a greater within‐individual decrease in laying date but not in clutch size during senescence compared with the northernmost population (i.e. Danish). We also found that the number of fledglings produced annually was related to the age of the two members of the breeding pairs with pairs composed of young and old females performing less well than breeding pairs composed of middle‐aged females. We did not find reproductive senescence for the age of the male while controlling for the age of the female on the number of fledglings produced annually by the breeding pair. Differential survival between individuals did not explain age effects on laying date or annual clutch size in neither population. However, the increase in the number of fledglings produced annually with age was partly explained by the disappearance of poor‐quality members of the pairs, mainly poor‐quality males. Age‐related breeding success (i.e. number of fledglings) was similar for barn swallows from Spain and Denmark. Therefore, the study of ageing patterns and life‐history strategies in free‐ranging animals from more than a single population can throw new light on life‐history theory, population dynamics and evolutionary studies of senescence.     

Age‐dependent mutational effects curtail the evolution of senescence by antagonistic pleiotropy

One of the two main hypotheses to account for ageing is antagonistic pleiotropy (AP). This model requires alleles that increase vital rates (reproduction or survival) at early age at the expense of vital rates at late age. An important focus of evolutionary studies has been to assess the relative abundance of AP‐type aging alleles that arise through mutation. Here, we develop theory that predicts that senescence per se reduces the probability that these alleles arise by mutation. A direct result is that these mutations should arise with extremely low frequencies in already senescing populations. This has profound implications for the evolution of life histories because it implies that the adaptive evolution of aging via AP will experience negative feedback. This theory also clarifies the previously inexplicable epistatic patterns of genetic covariance across age‐specific vital rates that are observed in mutation accumulation experiments. We show that this epistasis is an emergent property of aging.     

Age‐related changes in stem cell dynamics,neurogenesis, apoptosis,and gliosis in the adult brain: A novel teleost fish model of negligible senescence

Adult neurogenesis, the generation of new neurons in the adult central nervous system, is a reported feature of all examined vertebrate species. However, a dramatic decline in the rates of cell proliferation and neuronal differentiation occurs in mammals, typically starting near the onset of sexual maturation. In the present study, we examined possible age‐related changes associated with adult neurogenesis in the brain of brown ghost knifefish (Apteronotus leptorhynchus), a teleost fish distinguished by its enormous neurogenic potential. Contrary to the well‐established alterations in the mammalian brain during aging, in the brain of this teleostean species we could not find evidence for any significant age‐related decline in the absolute levels of stem/progenitor cell proliferation, neuronal and glial differentiation, or long‐term survival of newly generated cells. Moreover, there was no indication that the amount of glial fibrillary acidic protein or the number of apoptotic cells in the brain was altered significantly over the course of adult life. We hypothesize that this first demonstration of negligible cellular senescence in the vertebrate brain is related to the continued growth of this species and to the lack of reproductive senescence during adulthood. The establishment of the adult brain of this species as a novel model of negligible senescence provides new opportunities for the advancement of our understanding of the biology of aging and the fundamental mechanisms that underlie senescence in the brain. © 2013 Wiley Periodicals, Inc. Develop Neurobiol 74: 514–530, 2014     

Age‐dependent racemization of serine residues in a human chaperone protein

Racemization is one of the most abundant modifications in long‐lived proteins. It has been proposed that the accumulation of such modifications over time could lead to changes in tissues and ultimately human age‐related diseases. Serine is one of the main amino acids involved in racemization; however, the site of D‐Ser in any aged protein has yet to be reported. In this study, racemization of two residues, Ser 59 and Ser 62, has been demonstrated in an unstructured region of the small heat shock protein, αA‐crystallin. αA‐crystallin is also the most abundant structural protein in the human lens. D‐Ser increased linearly with age in normal lenses, until it accounted for approximately 35% of the Ser at both sites by the age of 75 years. In agreement with a possible role in human age‐related disease, levels were significantly higher in cataract lenses. It is likely that such prevalent age‐related changes contribute to the denaturation of α‐crystallin, and therefore its ability to act as a chaperone. Racemization of amino acids, such as serine, in flexible regions of long‐lived proteins, could be associated with the development of human age‐related conditions such as cataract.     

Age‐dependent DNA methylation patterns on the Y chromosome in elderly males

The Y chromosome, a sex chromosome that only exists in males, has been ignored in traditional epigenetic association studies for multiple reasons. However, sex differences in aging‐related phenotypes and mortality could suggest a critical role of the sex chromosomes in the aging process. We obtained blood‐based DNA methylation data on the Y chromosome for 624 men from four cohorts and performed a chromosome‐wide epigenetic association analysis to detect Y‐linked CpGs differentially methylated over age and cross‐validated the significant CpGs in the four cohorts. We identified 40–219 significant CpG sites (false discovery rate <0.05) with >82% of them hypermethylated with increasing age, which is in strong contrast to the patterns reported on the autosomal chromosomes. Comparing the rate of change in the Y‐linked DNA methylation across cohorts that represent different age intervals revealed a trend of acceleration in DNA methylation with increasing age. The age‐dependent DNA methylation patterns on the Y chromosome were further examined for their association with all‐cause mortality with results suggesting that the predominant pattern of age‐related hypermethylation on the Y chromosome is associated with reduced risk of death.