SciCombinator

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Concept: Zebrafish

170

BACKGROUND: Successful delivery of compounds to the brain and retina is a challenge in the development of therapeutic drugs and imaging agents. This challenge arises because internalization of compounds into the brain and retina is restricted by the blood–brain barrier (BBB) and blood-retinal barrier (BRB), respectively. Simple and reliable in vivo assays are necessary to identify compounds that can easily cross the BBB and BRB. METHODS: We developed six fluorescent indoline derivatives (IDs) and examined their ability to cross the BBB and BRB in zebrafish by in vivo fluorescence imaging. These fluorescent IDs were administered to live zebrafish by immersing the zebrafish larvae at 7–8 days post fertilization in medium containing the ID, or by intracardiac injection. We also examined the effect of multidrug resistance proteins (MRPs) on the permeability of the BBB and BRB to the ID using MK571, a selective inhibitor of MRPs. RESULTS: The permeability of these barriers to fluorescent IDs administered by simple immersion was comparable to when administered by intracardiac injection. Thus, this finding supports the validity of drug administration by simple immersion for the assessment of BBB and BRB permeability to fluorescent IDs. Using this zebrafish model, we demonstrated that the length of the methylene chain in these fluorescent IDs significantly affected their ability to cross the BBB and BRB via MRPs. CONCLUSIONS: We demonstrated that in vivo assessment of the permeability of the BBB and BRB to fluorescent IDs could be simply and reliably performed using zebrafish. The structure of fluorescent IDs can be flexibly modified and, thus, the permeability of the BBB and BRB to a large number of IDs can be assessed using this zebrafish-based assay. The large amount of data acquired might be useful for in silico analysis to elucidate the precise mechanisms underlying the interactions between chemical structure and the efflux transporters at the BBB and BRB. In turn, understanding these mechanisms may lead to the efficient design of compounds targeting the brain and retina.

Concepts: Fluorescence, Brain, In vivo, Retina, Chemical compound, Zebrafish, Injection, Intracardiac injection

165

Anxiety and depression are major chronic mood disorders, and the etiopathology for each appears to be repeated exposure to diverse unpredictable stress factors. Most of the studies on anxiety and related mood disorders are performed in rodents, and a good model is chronic unpredictable stress (CUS). In this study, we have attempted to understand the molecular basis of the neuroglial and behavioral changes underlying CUS-induced mood disorders in the simplest vertebrate model, the zebrafish, Danio rerio. Zebrafish were subjected to a CUS paradigm in which two different stressors were used daily for 15 days, and thorough behavioral analyses were performed to assess anxiety and related mood disorder phenotypes using the novel tank test, shoal cohesion and scototaxis. Fifteen days of exposure to chronic stressors appears to induce an anxiety and related mood disorder phenotype. Decreased neurogenesis, another hallmark of anxiety and related disorders in rodents, was also observed in this zebrafish model. The common molecular markers of rodent anxiety and related disorders, corticotropin-releasing factor (CRF), calcineurin (ppp3r1a) and phospho cyclic AMP response element binding protein (pCREB), were also replicated in the fish model. Finally, using 2DE FTMS/ITMSMS proteomics analyses, 18 proteins were found to be deregulated in zebrafish anxiety and related disorders. The most affected process was mitochondrial function, 4 of the 18 differentially regulated proteins were mitochondrial proteins: PHB2, SLC25A5, VDAC3 and IDH2, as reported in rodent and clinical samples. Thus, the zebrafish CUS model and proteomics can facilitate not only uncovering new molecular targets of anxiety and related mood disorders but also the routine screening of compounds for drug development.

Concepts: Protein, Oxygen, Mitochondrion, Antidepressant, Mood disorder, Zebrafish

150

Early retinal progenitor cells (RPCs) in vertebrates produce lineages that vary greatly both in terms of cell number and fate composition, yet how this variability is achieved remains unknown. One possibility is that these RPCs are individually distinct and that each gives rise to a unique lineage. Another is that stochastic mechanisms play upon the determinative machinery of equipotent early RPCs to drive clonal variability. Here we show that a simple model, based on the independent firing of key fate-influencing transcription factors, can quantitatively account for the intrinsic clonal variance in the zebrafish retina and predict the distributions of neuronal cell types in clones where one or more of these fates are made unavailable.

Concepts: DNA, Neuron, Genetics, Cell nucleus, Gene expression, Developmental biology, Retina, Zebrafish

59

Current efforts to repair damaged or diseased mammalian retinas are inefficient and largely incapable of fully restoring vision. Conversely, the zebrafish retina is capable of spontaneous regeneration upon damage using Müller glia (MG)-derived progenitors. Understanding how zebrafish MG initiate regeneration may help develop new treatments that prompt mammalian retinas to regenerate. We show that inhibition of γ-aminobutyric acid (GABA) signaling facilitates initiation of MG proliferation. GABA levels decrease following damage, and MG are positioned to detect decreased ambient levels and undergo dedifferentiation. Using pharmacological and genetic approaches, we demonstrate that GABAA receptor inhibition stimulates regeneration in undamaged retinas while activation inhibits regeneration in damaged retinas.

Concepts: Neuron, Retina, Enzyme inhibitor, Zebrafish, Benzodiazepine, GABAA receptor, Ligand-gated ion channel, GABA receptor

46

Vomocytosis, or nonlytic extrusion, is a poorly understood process through which macrophages release live pathogens that they have failed to kill back into the extracellular environment. Vomocytosis is conserved across vertebrates and occurs with a diverse range of pathogens, but to date, the host signaling events that underpin expulsion remain entirely unknown. We use a targeted inhibitor screen to identify the MAP kinase ERK5 as a critical suppressor of vomocytosis. Pharmacological inhibition or genetic manipulation of ERK5 activity significantly raises vomocytosis rates in human macrophages, whereas stimulation of the ERK5 signaling pathway inhibits vomocytosis. Lastly, using a zebrafish model of cryptococcal disease, we show that reducing ERK5 activity in vivo stimulates vomocytosis and results in reduced dissemination of infection. ERK5 therefore represents the first host signaling regulator of vomocytosis to be identified and a potential target for the future development of vomocytosis-modulating therapies.

Concepts: Immune system, Disease, Signal transduction, Enzyme, Model organism, Enzyme inhibitor, Inhibitor, Zebrafish

28

Hyperargininemia is an inborn error of metabolism (IEM) characterized by tissue accumulation of arginine (Arg). Mental retardation and other neurological features are common symptoms in hyperargininemic patients. Considering purinergic signaling has a crucial role from the early stages of development and underlying mechanisms of this disease are poorly established, we investigated the effect of Arg administration on locomotor activity, morphological alterations, and extracellular nucleotide hydrolysis in larvae and adult zebrafish. We showed that 0.1 mM Arg was unable to promote changes in locomotor activity. In addition, 7-day-post-fertilization (dpf) larvae treated with Arg demonstrated a decreased body size. Arg exposure (0.1 mM) promoted an increase in ATP, ADP, and AMP hydrolysis when compared to control group. These findings demonstrated that Arg might affect morphological parameters and ectonucleotidase activities in zebrafish larvae, suggesting that purinergic system is a target for neurotoxic effects induced by Arg.

Concepts: Adenosine triphosphate, Effect, Fish, Affect, Zebrafish, Danio kyathit, Inborn error of metabolism, Danios

26

Demyelinating diseases consist of a variety of autoimmune conditions in which the myelin sheath is damaged due to genetic and/or environmental factors. During clinical treatment, some patients undergo partial remyelination, especially during the early disease stages. However, the mechanisms that regulate demyelination remain unclear. The myelin structure, myelin formation and myelin-related gene expression are highly conserved between mammals and zebrafish. Therefore, the zebrafish is an ideal model organism to study myelination. In this study, we generated a transgenic zebrafish Tg(mbp:nfsB-egfp) expressing a fusion protein composed of enhanced green fluorescent protein (EGFP) and NTR from the myelin basic protein (mbp) promoter. Tg(mbp:nfsB-egfp) expressed NTR-EGFP reproducibly and hereditarily in oligodendrocytes along the spinal cord. Treatment of zebrafish larvae Tg(mbp:nfsB-egfp) with metronidazole (Mtz) resulted in the selective ablation of oligodendrocytes and led to demyelination, accompanied by behavioral changes, including decreased total movement distance, velocity, total movement time and fast movement time. After withdrawal of Mtz for a seven day recovery period, the expression of EGFP and MBP protein was observed again which indicates remyelination. Additionally, locomotor capacity was restored. Collectively, Tg(mbp:nfsB-egfp), a heritable and stable transgenic line, provides a novel, powerful tool to study the mechanisms of demyelination and remyelination.

Concepts: Protein, Gene, Gene expression, Green fluorescent protein, Multiple sclerosis, Myelin, Zebrafish, Myelin basic protein

20

The proliferative and functional heterogeneity among seemingly uniform cells is a universal phenomenon. Identifying the underlying factors requires single-cell analysis of function and proliferation. Here we show that the pancreatic beta-cells in zebrafish exhibit different growth-promoting and functional properties, which in part reflect differences in the time elapsed since birth of the cells. Calcium imaging shows that the beta-cells in the embryonic islet become functional during early zebrafish development. At later stages, younger beta-cells join the islet following differentiation from post-embryonic progenitors. Notably, the older and younger beta-cells occupy different regions within the islet, which generates topological asymmetries in glucose responsiveness and proliferation. Specifically, the older beta-cells exhibit robust glucose responsiveness, whereas younger beta-cells are more proliferative but less functional. As the islet approaches its mature state, heterogeneity diminishes and beta-cells synchronize function and proliferation. Our work illustrates a dynamic model of heterogeneity based on evolving proliferative and functional beta-cell states.Βeta-cells have recently been shown to be heterogeneous with regard to morphology and function. Here, the authors show that β-cells in zebrafish switch from proliferative to functional states with increasing time since β-cell birth, leading to functional and proliferative heterogeneity.

Concepts: Enzyme, Insulin, Islets of Langerhans, Pancreas, Beta cell, Category theory, Zebrafish

20

are the anaesthetics used for fish aversive? Despite years of routine general use of many agents, within both scientific research and aquaculture, there is a paucity of information regarding their tolerance and associated behavioural responses by fish. This study examined nine of the most commonly used fish anaesthetic agents, and performed preference tests using adult mixed sex zebrafish (Danio rerio), the most commonly held laboratory fish. Video tracking software quantified swimming behaviour related to aversion for each anaesthetic at 50% of its standard recommended dose compared with clean water in a flow-through chemotaxic choice chamber. Results suggest that several commonly used anaesthetics were aversive, including two of the most commonly recommended and used: MS222 (ethyl 3-aminobenzoate methanesulphate) and benzocaine. For ethical best practice, it is recommended that compounds that are aversive, even at low concentration, should no longer be used routinely for anaesthesia or indeed the first step of humane euthanasia of adult zebrafish. Two agents were found not to induce aversive behavioural responses: etomidate and 2,2,2 tribromoethanol. For the millions of adult zebrafish used in laboratories and breeding worldwide, etomidate appears best suited for future routine humane use.

Concepts: Psychology, Fish, Anesthesia, Motivation, Zebrafish, Danio kyathit, Local anesthetic, Danios

19

Microplastics have become an emerging contaminant and caused widespread concern about its potential toxic effects. In this study, the uptake and tissue accumulation of polystyrene microplastics (PS-MPs) in zebrafish were detected, as well as the toxic effects in liver were investigated. The results showed that after 7 days of exposure, 5-μm diameter MPs accumulated in fish gill, liver, and gut, while 20-μm diameter MPs only accumulated in fish gill and gut. Histopathological analysis showed that both sizes of 5-μm and 70-nm PS-MPs caused inflammation and lipid accumulation in fish liver. PS-MPs also induced significantly increased activities of SOD and CAT, indicating oxidative stress was induced after MPs treatment. In addition, metabolomic analysis suggested that MPs exposure induced alterations of metabolic profiles in fish liver and disturbed the lipid and energy metabolism. These findings provide new insights into the toxic effects of MPs on fish.

Concepts: Carbon dioxide, Metabolism, Adenosine triphosphate, Fish, Oxidative phosphorylation, Cellular respiration, Zebrafish, Danio kyathit