The use of mature zebrafish (Danio rerio) as a model for human aging and disease

Age-related cone abnormalities in zebrafish with genetic lesions in sonic hedgehog

PURPOSE

Sonic hedgehog (Shh) signaling is essential for photoreceptor differentiation and retinal cell survival in embryonic zebrafish. The study was conducted to determine whether adult heterozygous carriers of mutant alleles for the shh gene display retinal abnormalities.

METHODS

Retinal cryosections from young, middle-aged, and senescent wild-type and sonic-you(+/-) (syu(+/-)) zebrafish were probed with retinal cell type-specific markers. Contralateral retinal flatmounts from these fish, and from adult albino zebrafish subjected to light-induced photoreceptor damage followed by regeneration, were hybridized with blue cone opsin cRNA for quantitative analysis of the blue cone pattern. Retinal expression of shh mRNA was measured by quantitative RT-PCR.

RESULTS

Regions of cone loss and abnormal cone morphology were observed in the oldest syu(+/-) zebrafish, although no other retinal cell type was affected. This phenotype was age-related and genotype-specific. Cone distribution in the oldest syu(+/-) zebrafish was predominantly random, as assessed by measuring the short-range pattern, whereas that of wild-type fish and the younger syu(+/-) zebrafish was statistically regular. A measure of long-range pattern revealed atypical cone aggregation in the oldest syu(+/-) zebrafish. The light-treated albino zebrafish displayed random cone patterns immediately after light toxicity, but showed cone aggregation on regeneration. Retinas from the syu(+/-) fish showed reduced expression of shh mRNA compared with those of wild-type siblings.

CONCLUSIONS

The syu(+/-) zebrafish presents a model for the study of hereditary age-related cone abnormalities. The syu(+/-) retinas most likely experience progressive cone photoreceptor loss, accompanied by cone regeneration. Shh signaling may be required to maintain cone viability throughout life.

Conditional transgene and gene targeting methodologies in zebrafish

The zebrafish has become a powerful tool for dissecting vertebrate gene function during embryogenesis. Numerous molecular systems have been developed to examine gene function in zebrafish, including transgenics for creating lineage-tracer lines of zebrafish that express a fluorescent protein as a marker for specific populations of cells, and antisense strategies, primarily morpholinos, for knocking down gene function. The focus of this review is to summarize the pros and cons of the currently available systems for functional genomics in zebrafish, and to discuss the need for future methodologies.

Heat stress-induced heat shock protein 70 expression is dependent on ERK activation in zebrafish (Danio rerio) cells

Heat shock response is a common event that occurs in many species. Despite its evolutionary conservation, comparative studies of heat shock response have been largely unexplored. In mammals, heat shock response decreases with age through unclear mechanisms. Understanding how the age-related decline in heat shock response occurs may provide information to understanding the biology of aging. We have previously shown that heat shock response similarly declines with age in zebrafish. However, signaling pathways that regulate the heat shock response in zebrafish are unknown. In mammals there is evidence that mitogen-activated protein kinases (MAPKs) of the ERK family alter Hsp70 transcription, serving as a potential regulator of the heat shock response. We explored if heat stress-induced Hsp70 expression is altered by activation of ERK in the zebrafish Pac2 fibroblast cell line as occurs in mammalian cells. Heat stress induced both Hsp70 mRNA expression and phosphorylation of both ERK1 and ERK2 (ERK1/2) in Pac2 cells. ERK inhibitors PD98059 and U0126 blocked both heat stress-induced and plated-derived growth factor (PDGF)-induced ERK1/2 phosphorylation, and also diminished heat-induced Hsp70 expression. Pac2 cell viability was not affected by either the ERK inhibitors or heat stress. These results demonstrate that induction of Hsp70 in response to heat stress is dependent on ERK activation in Pac2 cells. This suggests that the heat shock response in zebrafish utilizes a similar signaling pathway to that of mammals and that zebrafish are a good model for comparative studies of heat shock response.

How to create the vascular tree? (Latest) help from the zebrafish

The cardiovascular system provides oxygen, nutrients and hormones to organs, it directs traffic of metabolites and it maintains tissue homeostasis. It is one of the first organs assembled during vertebrate development and it is essential to life from early stages to adult. For these reasons, the process of vessel formation has being studied for more than a century, but it is only in the late eighties that there has been an explosion of research in the field with the employment of various in vitro and in vivo model systems. The zebrafish (Danio rerio) offers several advantages for in vivo studies; it played a fundamental role in new discoveries and helped to refine our knowledge of the vascular system. This review recapitulates the zebrafish data on vasculogenesis and angiogenesis, including the specification of the haemangioblasts from the mesoderm, their migration to form the vascular cord followed by axial vessels specification, the primary and secondary sprouting of intersomitic vessels, the formation of the lumen, the arterial versus venous specification and patterning. To emphasize the strengths of the zebrafish system in the vascular field, we summarize main tools, such as gene expression and mutagenesis screens, knock down technologies, transgenic lines and imaging, which played a major role in the development of the field and allowed significant discoveries, for instance the recent visualization of the lymphatic system in zebrafish. This information contributes to the prospective of drug discovery to cure human diseases linked to angiogenesis, not last tumours.

Comparative genomics for detecting human disease genes

Originally, comparative genomics was geared toward defining the synteny of genes between species. As the human genome project accelerated, there was an increase in the number of tools and means to make comparisons culminating in having the genomic sequence for a large number of organisms spanning the evolutionary tree. With this level of resolution and a long history of comparative biology and comparative genetics, it is now possible to use comparative genomics to build or select better animal models and to facilitate gene discovery. Comparative genomics takes advantage of the functional genetic information from other organisms, (vertebrates and invertebrates), to apply it to the study of human physiology and disease. It allows for the identification of genes and regulatory regions, and for acquiring knowledge about gene function. In this chapter, the current state of comparative genomics and the available tools are discussed in the context of developing animal model systems that reflect the clinical picture.

Aging of the circadian system in zebrafish and the effects of melatonin on sleep and cognitive performance

Aging is a complex process involving intracellular changes and, notably, modifications in intercellular communications, required for coordinated responses to internal and external events. One of the potential reasons for such changes is an age-dependent failure of the integrating systems, including the circadian clock. Here we demonstrate that aging in a diurnal vertebrate, zebrafish (Danio rerio), is associated with major but selective circadian alterations. By 3-5 years of age, zebrafish have reduced amplitude and increased fragmentation of entrained circadian rhythms of activity, with fast desynchronization of the rhythms in the absence of environmental time cues. Aging in zebrafish is also associated with a reduction in the overall duration of nighttime sleep, followed by lower activity levels and a higher arousal threshold during the day. The production of the principal circadian hormone, melatonin, progressively declines during zebrafish aging. However, the ability of melatonin to acutely promote sleep and entrain circadian rhythms of activity remains robust until at least 4-5 years of age, consistent with the preserved levels of mRNA expression for melatonin receptors. Aged zebrafish have altered expression of the circadian genes zBmal1 and zPer1 but not zClock1. A lack of circadian time cues alters cognitive performance in aged more than in young zebrafish and this can be partially attenuated by daily melatonin administration. The advantages of zebrafish as a diurnal, small, prolific and genetically well-characterized vertebrate model provide new opportunities to clarify the intrinsic circadian factors involved in human aging and promote the search for prophylactic and treatment strategies.

Differential effects of genotoxic stress on both concurrent body growth and gradual senescence in the adult zebrafish

Among vertebrates, fish and mammals show intriguing differences in their growth control properties with age. The potential for unlimited or indeterminate growth in a variety of fish species has prompted many questions regarding the senescent phenomena that appear during the aging process in these animals. Using zebrafish as our model system, we have attempted in our current study to examine the growth phenomena in fish in relation to the onset of senescence-associated symptoms, and to evaluate the effects of genotoxic stress on these processes. We observed in the course of these analyses that the zebrafish undergoes continuous growth, irrespective of age, past the point of sexual maturation with gradually decreasing growth rates at later stages. Animal population density, current body size and chronological age also play predominant roles in regulating zebrafish growth and all inversely influence the growth rate. Interestingly, the induction of genotoxic stress by exposure to ionizing radiation (IR) did not adversely affect this body growth ability in zebrafish. However, IR was found to chronically debilitate the regeneration of amputated caudal fins and thereby induce high levels of abnormal fin regeneration in the adult zebrafish. In addition, by resembling and mimicking the natural course of aging, IR treatments likewise enhanced several other symptoms of senescence, such as a decline in reproductive abilities, increased senescence-associated beta-galactosidase activity and a reduction in melatonin secretion. Our current data thus suggest that during the lifespan of zebrafish, the onset of senescence-associated symptoms occurs in parallel with continuous growth throughout mid-adulthood. Moreover, our present findings indicate that genotoxic DNA damage may play a role as a rate-limiting factor during the induction of senescence, but not in the inhibition of continuous, density-dependent growth in adult zebrafish.

The mutant guppy syndrome curveback as a model for human heritable spinal curvature

STUDY DESIGN

This study investigated the morphology, pathogenesis, and inheritance of idiopathic-like spinal curvature in the guppy syndrome, curveback.

OBJECTIVE

To determine whether curveback could be applied as a model for the primary factors that contribute to heritable spinal curvature in humans, specifically, the etiopathogenesis of human familial idiopathic scoliosis.

SUMMARY OF BACKGROUND DATA

Although a genetic basis is accepted, phenotypic complexity and the lack of an animal model with noninduced curvature have made identification of idiopathic scoliosis etiology difficult. It is well established that humans and fish share many genes with similar tissue and temporal expression characteristics, and comparisons between human and fish genomes have proven to be valuable for understanding the genetics of diseases affecting humans.

METHODS

The curveback lineage of guppies was constructed from a single curved male crossed to a normal female. Offspring (103) from the original cross were scored from birth until death for the presence and magnitude of spinal curvature. Genetic architecture was investigated through selective inbreeding, analysis of the distribution of curve magnitude in the mature population, and assessment of curve dynamics during development. Computed tomography assessed vertebral detail.

RESULTS

Computed tomography reveals that vertebral breakage or fusion is not associated with the curveback syndrome. Inbreeding demonstrates a strong genetic influence on curveback, and the distribution of curve magnitude among adult fish suggests polygenic inheritance. There is a female bias for curves of high magnitude and curves that resolve before maturity. There is developmental variability for the age of curve onset, curve progression, and final curve magnitude.

CONCLUSIONS

Observed parallels between the curveback syndrome and human idiopathic scoliosis suggest that the guppy model is an unexploited resource for the identification of primary etiological factors involved in curvature. As models for biomedical research, teleosts offer great potential regarding spinal stability and deformity.

Cognitive aging in zebrafish

Background

Age-related impairments in cognitive functions represent a growing clinical and social issue. Genetic and behavioral characterization of animal models can provide critical information on the intrinsic and environmental factors that determine the deterioration or preservation of cognitive abilities throughout life.

Methodology/Principal Findings

Behavior of wild-type, mutant and gamma-irradiated zebrafish (Danio rerio) was documented using image-analysis technique. Conditioned responses to spatial, visual and temporal cues were investigated in young, middle-aged and old animals. The results demonstrate that zebrafish aging is associated with changes in cognitive responses to emotionally positive and negative experiences, reduced generalization of adaptive associations, increased stereotypic and reduced exploratory behavior and altered temporal entrainment. Genetic upregulation of cholinergic transmission attenuates cognitive decline in middle-aged achesb55/+ mutants, compared to wild-type siblings. In contrast, the genotoxic stress of gamma-irradiation accelerates the onset of cognitive impairment in young zebrafish.

Conclusions/Significance

These findings would allow the use of powerful molecular biological resources accumulated in the zebrafish field to address the mechanisms of cognitive senescence, and promote the search for therapeutic strategies which may attenuate age-related cognitive decline.

Cloning, characterization, and heat stress-induced redistribution of a protein homologous to human hsp27 in the zebrafish Danio rerio

Hsp27 is a small heat shock protein (shsp) regulating stress tolerance and increasingly thought to play roles in tissue homeostasis and differentiation. The zebrafish Danio rerio is an important model for the study of developmental processes, but little is known regarding shsps in this animal. Here, we report the sequence, expression, regulation, and function of a zebrafish protein (zfHsp27) homologous to human Hsp27. zfHsp27 contains three conserved phosphorylatable serines and a cysteine important for regulation of apoptosis, but it lacks much of a C-terminal tail domain and shows low homology in two putative actin interacting domains that are features of mammalian Hsp27. zfHsp27 mRNA is most abundant in adult skeletal muscle and heart and is upregulated during early embryogenesis. zfHsp27 expressed in mammalian fibroblasts was phosphorylated in response to heat stress and anisomycin, and this phosphorylation was prevented by treatment with SB202190, an inhibitor of p38 MAPK. Expression of zfHsp27 and human Hsp27 in mammalian fibroblasts promoted a similar degree of tolerance to heat stress. zfHsp27 fusion proteins entered the nucleus and associated with the cytoskeleton of heat stressed cells in vitro and in zebrafish embryos. These results reveal conservation in regulation and function of mammalian and teleost Hsp27 proteins and define zebrafish as a new model for the study of Hsp27 function.