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Zebra fish: an uncharted behavior genetic model.
The zebra fish has been a preferred subject of genetic analysis. It produces a large number of offspring that can be kept in small aquaria, it can be easily mutagenized using chemical mutagens (e.g., ethyl nitrosourea [ENU]), and high-resolution genetic maps exist that aid identification of novel genes. Libraries containing large numbers of mutant fish have been generated, and the genetic mechanisms of the development of zebra fish, whose embryo is transparent, have been extensively studied. Given the extensive homology of its genome with that of other vertebrate species including our own and given the available genetic tools, zebra fish has become a popular model organism. Despite this popularity, however, surprisingly little is known about its behavior. It is argued that behavioral analysis is a powerful tool with which the function of the brain may be studied, and the zebra fish will represent an excellent subject of such analysis. The present paper is a proof of concept study that uses pharmacological manipulation (exposure to alcohol) to show that the zebra fish is amenable to the behavioral genetic analysis of aggression and thus may allow us to reveal molecular mechanisms of this behavioral phenomenon relevant to vertebrates.
Aggression↗
DNA methylation and control of gene expression in vertebrate development.
MeCpGs act as ligands for nuclear factors (repressors) that are components of chromatin modification and remodelling activities. The DNA-methylation-mediated repression system (Dnmt1s, MeCPs and MBDs) is highly conserved in vertebrates. DNA methylation is essential for normal vertebrate development. It is possible (but remains unproven) that the role of DNA methylation in regulating development is highly conserved in vertebrates. In mammals, DNA methylation has an additional role in regulating the expression of imprinted genes and in controlling X-inactivation.
Animals↗
Dual function of polysialic acid during zebrafish central nervous system development.
Polysialic acid (PSA), a carbohydrate epitope attached to the neural cell adhesion molecule, serves as a modulator of axonal interactions during vertebrate nervous system development. We have used PSA-specific antibodies and whole-mount immunocytochemistry to describe the spatiotemporal expression pattern of PSA during zebrafish central nervous system development. PSA is transiently expressed on all cell bodies and, except for the posterior commissure, it is not found on axons. Floorplate cells in the spinal cord and hindbrain strongly express PSA throughout development. Enzymatic removal of PSA leads to a defasciculated growth pattern of the posterior commissure and also affects distinct subsets of commissural axons in the hindbrain, which fail to cross the midline. Whereas the disordered growth pattern of hindbrain commissures produced by PSA-removal could be mimicked by injections of soluble PSA, the growth of axons in the posterior commissure was unaffected by such treatment. These results suggest that there are distinct mechanisms for PSA action during axon growth and pathfinding in the developing zebrafish CNS.
Animals↗
Mutagenesis by environmental pollutants and bio-monitoring of environmental mutagens.
There is serious concern about the adverse effects of environmental pollutants on human health. Various mutagens, which pollute air, water, and food, possibly induce mutations in humans, and are suspected of causing cancer. Environmental mutagens, such as polycyclic aromatic hydrocarbons (PAH) and heterocyclic amines are known to bind to nucleotides, resulting in the formation of DNA adducts. Some DNA adducts are fixed as mutations through replication of DNA. Reactive oxygen species generated by pollutants also induce the formation of DNA adducts. DNA adducts have been detected as a marker for the exposure of humans and wild life to mutagens. Because of its high sensitivity the 32P-postlabel-thin layer chromatography (TLC) method is widely used for the analysis of DNA adducts formed by PAH and related bulky compounds. However, new systems are required for detecting mutations induced in genomic DNA in vivo to monitor environmental mutagens. Recently, transgenic animals, in which a target gene for detecting mutations is integrated, have been developed. With these transgenic animals, not only mutant frequency but mutation spectra can be determined. We review here recent advances in the detection of DNA adducts formed by environmental pollutants and their application for biological monitoring of environmental mutagens. We also discuss transgenic animals as important tools for evaluating the total mutagenic potential of environmental chemicals.
Animals↗
The Zebrafish Information Network (ZFIN): a resource for genetic, genomic and developmental research.
The Zebrafish Information Network, ZFIN, is a WWW community resource of zebrafish genetic, genomic and developmental research information (http://zfin.org). ZFIN provides an anatomical atlas and dictionary, developmental staging criteria, research methods, pathology information and a link to the ZFIN relational database (http://zfin. org/ZFIN/). The database, built on a relational, object-oriented model, provides integrated information about mutants, genes, genetic markers, mapping panels, publications and contact information for the zebrafish research community. The database is populated with curated published data, user submitted data and large dataset uploads. A broad range of data types including text, images, graphical representations and genetic maps supports the data. ZFIN incorporates links to other genomic resources that provide sequence and ortholog data. Zebrafish nomenclature guidelines and an automated registration mechanism for new names are provided. Extensive usability testing has resulted in an easy to learn and use forms interface with complex searching capabilities.
Animals↗
Developmental biology of zebrafish.
The biology and genetics of zebrafish has become a very popular system in developmental biology especially because of their suitability for genetics and the transparent embryo of this small tropical fish. Studies reported briefly here demonstrate that one can use gene expression in the zebrafish embryo to find new components of important and well-studied developmental mechanisms and signal transduction pathways. The study of zebrafish developmental genetics has proven invaluable in determining many aspects of vertebrate development. Further use of this model organism promises to generate many interesting and useful data.
Animals↗
Melatonin stimulates cell proliferation in zebrafish embryo and accelerates its development.
All vertebrates show a dramatic circadian rhythm in circulating melatonin with high levels at night and very low levels during daytime. In adults, melatonin is thought to synchronize other circadian rhythms and regulate seasonal rhythms in photoperiodic animals by acting on specific G-protein coupled receptors. The role of melatonin in development is unknown, even though melatonin receptors appear to be more highly expressed in developing embryos and neonates than in adults. In this study on zebrafish embryos, we describe a role for melatonin in increasing cell proliferation and accelerating development. We propose that melatonin has a role in extending the safe limit of proliferation rate at night to allow more rapid development when potentially damaging ultraviolet light is absent.
Animals↗
Morphometric study of the regeneration of individual rays in teleost tail fins.
The results obtained using morphometric variables which describe fin ray regeneration patterns are reported for individual fin ray amputations in the goldfish (Carassius auratus) and zebrafish (Brachydanio rerio). Classical and updated experiments are compared to verify previous morphogenetic models of cell tractions (Oster et al. 1983) or epidermis-mesenchyme induction (Saunders et al. 1959) applied to the limb of other vertebrates. Position-dependent patterns within the fin of Carassius auratus are analysed under a comparative protocol using morphometric methods. Conditions in which the apical epidermis is separated from blastema may differentiate small fin rays, thus suggesting this epidermis is involved in blastemal formation. Blastemal cells differentiating as lepidotrichia forming cells (LFCs) may also be related to morphological changes in covering epidermis. Long-range interactions from neighbouring fin ray blastemas or short-range interactions within the blastema, may be postulated through the analysis of segmentation.
Animals↗
Investigations into the environmental fate and effects of iopromide (ultravist), a widely used iodinated X-ray contrast medium.
lodinated X-ray contrast media are pharmaceuticals which are biologically inert and metabolically stable during their passage through the body and are excreted almost completely within a day into waste water. They are not readily biodegradable. However, in a test system simulating sewage treatment, we were able to show that the model compound iopromide (N,N'-bis(2,3-dihydroxypropyl)-2,4,6-triiodo-5-methoxyacetylamino-N-methyliso-phthalamide) was amenable to primary degradation. The resulting degradation product (5-amino-N'N'-bis(2,3-dihydroxypropyl)-2,4,6-triiodo-N-methyliso-phthalamide) showed a faster photolysis than the parent compound. Additionally this product was further degraded in a test system simulating surface water conditions. Short-term toxicity of the primary degradation product was low, i.e. no effects on any of various aquatic species could be found even at concentrations of 1 gl(-1). Additionally no chronic toxicity of the degradation product was observed in an early-life stage test with zebrafish at the highest tested concentration of 100mgl(-1). Based on the results from model systems a degradation pathway for iopromide is postulated. Though further work showing the transferability of the laboratory results to environmental conditions is necessary the presently available information on the environmental fate and effects of iopromide and its degradation products do not provide evidence of a risk for aquatic life caused by the introduction of this contrast medium into waste water.
Animals↗
Mechanosensation: swimming round in circles.
Studies of inherited deafness disorders in mice and humans are providing new insights into the basis of hair-cell mechanosensitivity; this enterprise has been joined by large-scale genetic screening in the zebrafish, where a number of intriguing mutants defective in mechanosensation have recently been described.
Animals↗
Neurochemical and behavioural changes in zebrafish Danio rerio after systemic administration of 6-hydroxydopamine and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine.
Dopaminergic deficiency in the brain of zebrafish was produced by systemic administration of two catecholaminergic neurotoxins, 6-hydroxydopamine (6-OHDA) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and the neurochemical and behavioural changes were characterized. The levels of dopamine and noradrenaline decreased significantly after the injection of MPTP and 6-OHDA. Corresponding to these changes, fish exhibited characteristic changes in locomotor behaviour, i.e. the total distance moved and velocity decreased after both neurotoxins. Tyrosine hydroxylase and caspase 3 protein levels were not altered after MPTP or 6-OHDA injections, as studied by immunohistochemistry and western blotting. The catecholaminergic cell clusters suggested to correspond to the mammalian nigrostriatal cell group displayed normal tyrosine hydroxylase immunoreactivity after the toxin treatment and did not show signs of DNA fragmentation that would indicate activation of cascades that lead to cell death. The results show that single systemic injections of MPTP and 6-OHDA induce both biochemical and behavioural changes in zebrafish, albeit failing to produce any significant morphological alteration in catecholaminergic cell clusters at the tested doses. This approach may be used for the screening of chemicals affecting the dopaminergic system. The model may be especially useful for evaluation of the role of novel genes in neurotoxicity, as a large number of zebrafish mutants are becoming available.
1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
A nonsense mutation in the gene encoding a zebrafish myosin VI isoform causes defects in hair-cell mechanotransduction.
In a three-generation screen of chemically mutagenized zebrafish, we identified a group of mutations that affect the development and function of hair cells, the mechanically sensitive cells of the inner ear and lateral-line organ. One mutant line, ru920, was discovered in a behavioral screen for defects in the acoustically evoked escape response. Despite apparently normal numbers of hair cells, mutants lack an inner-ear microphonic potential and exhibit reduced labeling of hair cells by a fluorophore that traverses transduction channels. This hair-cell-specific phenotype suggested a defect in the mechanoelectrical transduction apparatus. Positional cloning revealed that the recessive mutation introduces a premature stop codon in the ORF of myosin6b (myo6b), one of the two zebrafish orthologs of the human gene myosin VI. The ru920 line therefore provides an animal model with which to study the role of class VI myosin proteins in mechanotransduction.
Animals↗
Is the somitogenesis clock really cell-autonomous? A coupled-oscillator model of segmentation.
A striking pattern of oscillatory gene expression, related to the segmentation process (somitogenesis), has been identified in chick, mouse, and zebrafish embryos. Somitogenesis displays great autonomy, and it is generally assumed in the literature that somitogenesis-related oscillations are cell-autonomous in chick and mouse. We point out in this article that there would be many biological reasons to expect some mechanism of coupling between cellular oscillators, and we present a model with such coupling, but which also has autonomous properties. Previous experiments can be re-interpreted in light of this model, showing that it is possible to reconcile both autonomous and non-autonomous aspects. We also show that experimental data, previously interpreted as supporting a purely negative-feedback model for the mechanism of the oscillations, is in fact more compatible with this new model, which relies essentially on positive feedback.
Animals↗
Spot pattern of leopard Danio is caused by mutation in the zebrafish connexin41.8 gene.
Leopard, a well-known zebrafish mutant that has a spotted skin pattern instead of stripes, is a model for the study of pigment patterning. To understand the mechanisms underlying stripe formation, as well as the spot variation observed in leopard, we sought to identify the gene responsible for this phenotype. Using positional cloning, we identified the leopard gene as an orthologue of the mammalian connexin 40 gene. A variety of different leopard alleles, such as leo(t1), leo(tq270) and leo(tw28), show different skin-pattern phenotypes. In this manuscript we show that the mutation in allele leo(t1) is a nonsense mutation, whereas alleles leo(tq270) and leo(tw28) contain the missense mutations I202F and I31F, respectively. Patch-clamp experiments of connexin hemichannels demonstrated that the I202F substitution in allele leo(tq270) disrupted the channel function of connexin41.8. These results demonstrate that mutations in this gene lead to a variety of leopard spot patterns.
Alleles↗
Ruffed cells identified in the adult zebrafish olfactory bulb.
The morphology and distribution of ruffed cells was examined in the olfactory bulb of adult zebrafish, Danio rerio, using retrograde tract tracing and Golgi-Kopsch techniques. The neurons had variable-shaped soma that ranged in size from 7 to 15 microm in diameter. There was an obvious protrusion of the membrane, a ruff, near the initial portion of the axon, and the cells appeared to be distributed primarily in the glomerular layer and superficial internal cell layer. This cell type has been described for a number of teleosts, but not for other animal groups. While the presence of ruffed cells in all teleosts has been suggested, the existence of this cell type in zebrafish was uncertain until now. This new evidence may provide additional insight into olfactory coding and processing in this key model system.
Animals↗
Cone contributions to the photopic spectral sensitivity of the zebrafish ERG.
Microspectrophotometry studies show that zebrafish (Danio rerio) possess four cone photopigments. The purpose of this study was to determine the cone contributions to the zebrafish photopic increment threshold spectral-sensitivity function. Electroretinogram (ERG) b-wave responses to monochromatic lights presented on a broadband or chromatic background were obtained. It was found that under the broadband background condition, the zebrafish spectral-sensitivity function showed several peaks that were narrower in sensitivity compared to the cone spectra. The spectral-sensitivity function was modeled with L - M and M - S opponent interactions and nonopponent S- and U-cone mechanisms. Using chromatic adaptation designed to suppress the contribution of the S-cones, a strong U-cone contribution to the spectral-sensitivity function was revealed, and the contributions of the S-cones to the M - S mechanism were reduced. These results show that the b-wave component of the ERG receives input from all four cone types and appears to reflect color opponent mechanisms. Thus, zebrafish may possess the fundamental properties necessary for color vision.
Adaptation, Physiological↗
Spontaneous activity-independent intracellular calcium signals in the developing spinal cord of the zebrafish embryo.
Calcium signals play an important role in a variety of processes necessary for neuronal development. Whilst the characteristics and function of calcium signals have been comprehensively examined in vitro, the significance of these signals during development in an intact embryo remains unclear. In this study, we have examined the spatial and temporal patterns of intracellular calcium signals in precursor cells (cells without processes) within the spinal cord of the intact zebrafish embryo aged between 17 and 27 h. In total, approximately one-third of cells displayed spontaneous intracellular calcium transients. The calcium transients had an average peak amplitude of 33.3 (+/-2.8%) above baseline, a duration of 52.2 (+/-6.3 s) and occurred with an average frequency of 4.6 (+/-0.4 per hour). Calcium transients were observed in precursor cells located throughout the spinal cord, with the highest percentage of active cells (35.1+/-8%) occurring at a developmental time of 21-22 h. Furthermore these intracellular calcium signals were observed in the presence of tricaine, indicating that they are not generated via sodium-dependent action potentials. In precursor cells loaded with the calcium buffer BAPTA both the frequency and the amplitude of the calcium transients was significantly reduced. The intracellular calcium transients may represent a common activity-independent calcium-mediated mechanism that contributes to the regulation of neuronal development in the spinal cord of the zebrafish embryo during the segmentation and early pharyngula period.
Action Potentials↗