Fluorescent light exposure incites acute and prolonged immune responses in zebrafish (Danio rerio) skin

The Zebrafish model in dermatology: an update for clinicians

Recently, the zebrafish has been established as one of the most important model organisms for medical research. Several studies have proved that there is a high level of similarity between human and zebrafish genomes, which encourages the use of zebrafish as a model for understanding human genetic disorders, including cancer. Interestingly, zebrafish skin shows several similarities to human skin, suggesting that this model organism is particularly suitable for the study of neoplastic and inflammatory skin disorders. This paper appraises the specific characteristics of zebrafish skin and describes the major applications of the zebrafish model in dermatological research.

Review of inflammation in fish and value of the zebrafish model

Inflammation is a crucial step in the development of chronic diseases in humans. Understanding the inflammation environment and its intrinsic mechanisms when it is produced by harmful stimuli may be a key element in the development of human disease diagnosis. In recent decades, zebrafish (Danio rerio) have been widely used in research, due to their exceptional characteristics, as a model of various human diseases. Interestingly, the mediators released during the inflammatory response of both the immune system and nervous system, after its integration in the hypothalamus, could also facilitate the detection of injury through the register of behavioural changes in the fish. Although there are many studies that give well-defined information separately on such elements as the recruitment of cells, the release of pro- and anti-inflammatory mediators or the type of neurotransmitters released against different triggers, to the best of our knowledge there are no reviews that put all this knowledge together. In the present review, the main available information on inflammation in zebrafish is presented in order to facilitate knowledge about this important process of innate immunity, as well as the stress responses and behavioural changes derived from it.

Global assessment of organ specific basal gene expression over a diurnal cycle with analyses of gene copies exhibiting cyclic expression patterns

BACKGROUND

Studying functional divergences between paralogs that originated from genome duplication is a significant topic in investigating molecular evolution. Genes that exhibit basal level cyclic expression patterns including circadian and light responsive genes are important physiological regulators. Temporal shifts in basal gene expression patterns are important factors to be considered when studying genetic functions. However, adequate efforts have not been applied to studying basal gene expression variation on a global scale to establish transcriptional activity baselines for each organ. Furthermore, the investigation of cyclic expression pattern comparisons between genome duplication created paralogs, and potential functional divergence between them has been neglected. To address these questions, we utilized a teleost fish species, Xiphophorus maculatus, and profiled gene expression within 9 organs at 3-h intervals throughout a 24-h diurnal period.

RESULTS

Our results showed 1.3-21.9% of genes in different organs exhibited cyclic expression patterns, with eye showing the highest fraction of cycling genes while gonads yielded the lowest. A majority of the duplicated gene pairs exhibited divergences in their basal level expression patterns wherein only one paralog exhibited an oscillating expression pattern, or both paralogs exhibit oscillating expression patterns, but each gene duplicate showed a different peak expression time, and/or in different organs.

CONCLUSIONS

These observations suggest cyclic genes experienced significant sub-, neo-, or non-functionalization following the teleost genome duplication event. In addition, we developed a customized, web-accessible, gene expression browser to facilitate data mining and data visualization for the scientific community.

Deconvoluting Wavelengths Leading to Fluorescent Light Induced Inflammation and Cellular Stress in Zebrafish (Danio rerio)

Fluorescent light (FL) has been shown to induce a cellular immune and inflammatory response that is conserved over 450 MY of evolutionary divergence and among vertebrates having drastically different lifestyles such as Mus musculus, Danio rerio, Oryzias latipes and Xiphophorus maculatus. This surprising finding of an inflammation and immune response to FL not only holds for direct light receiving organs (skin) but is also observed within internal organs (brain and liver). Light responsive genetic circuitry initiated by the IL1B regulator induces a highly conserved acute phase response in each organ assessed for all of biological models surveyed to date; however, the specific light wavelengths triggering this response have yet to be determined so investigation of mechanisms and/or light specific molecule(s) leading to this response are difficult to assess. To understand how specific light wavelengths are received in both external and internal organs, zebrafish were exposed to specific 50 nm light wavebands spanning the visible spectrum from 300–600 nm and the genetic responses to each waveband exposure were assessed. Surprisingly, the induced cellular stress response previously observed following FL exposure is not triggered by the lower “damaging” wavelengths of light (UVB and UVA from 300–400 nm) but instead is maximally induced by higher wavelengths ranging from 450–500 nm in skin to 500–600 nm in both brain and liver).

Fluorescent Light Incites a Conserved Immune and Inflammatory Genetic Response within Vertebrate Organs (Danio Rerio, Oryzias Latipes and Mus Musculus)

Fluorescent light (FL) has been utilized for ≈60 years and has become a common artificial light source under which animals, including humans, spend increasing amounts of time. Although the solar spectrum is quite dissimilar in both wavelengths and intensities, the genetic consequences of FL exposure have not been investigated. Herein, we present comparative RNA-Seq results that establish expression patterns within skin, brain, and liver for Danio rerio, Oryzias latipes, and the hairless mouse (Mus musculus) after exposure to FL. These animals represent diurnal and nocturnal lifestyles, and ≈450 million years of evolutionary divergence. In all three organisms, FL induced transcriptional changes of the acute phase response signaling pathway and modulated inflammation and innate immune responses. Our pathway and gene clustering analyses suggest cellular perception of oxidative stress is promoting induction of primary up-stream regulators IL1B and TNF. The skin and brain of the three animals as well as the liver of both fish models all exhibit increased inflammation and immune responses; however, the mouse liver suppressed the same pathways. Overall, the conserved nature of the genetic responses observed after FL exposure, among fishes and a mammal, suggest the presence of light responsive genetic circuitry deeply embedded in the vertebrate genome.

Workshop Report: Zebrafish and Other Fish Models-Description of Extrinsic Environmental Factors for Rigorous Experiments and Reproducible Results

Current standards for husbandry and maintenance of zebrafish and other aquatic species in the laboratory are diverse, and are subject to laboratory performance, engineering, and practice standards (the Guide), institutional interpretation, national animal welfare laws, and cultural differences. Consequently, it is difficult, and probably not advantageous, to establish a single standard in view of the hardy nature of zebrafish and the diversity of research requirements it is used to address. Based on their natural habitat, zebrafish can thrive in a variety of environmental conditions, which is a specific advantage for working with this laboratory organism. However, it also makes reporting and reproducibility difficult, because variations in the husbandry and environmental conditions, including the environmental conditions before and during experiments, are often underreported in the scientific literature. This lack of consistency presents a potential problem for research reproducibility. To begin addressing this emerging scientific gap, the National Institutes of Health's (NIH) Office of Research Infrastructure Programs (ORIP), Division of Construction and Instruments (DCI), hosted a workshop in late 2017, entitled "Zebrafish and Other Aquatic Models: Reporting of Environmental Husbandry Conditions for Rigorous Experiments and Reproducible Results," that was attended by ∼60 participants. The objectives of the workshop were to bring together a diverse group of stakeholders-researchers, facility managers, veterinarians, journal editors, commercial vendors, and others to (1) review current husbandry and environmental management practices for the care of zebrafish and other aquatic organisms in the laboratory and to (2) propose a process for the development of a minimal set of environmental parameters that should be reported in publications to ensure rigor and robustness of experiments and reproducible outcomes. The participants also discussed how these recommendations, as an initial step, might be collected, disseminated, implemented, and improved upon after future iteration.