Two tyrosine hydroxylase genes in vertebrates New dopaminergic territories revealed in the zebrafish brain

Medaka fish Parkinson's disease model

The teleost fish has been widely used in creating neurodegenerative models. Here we describe the teleost medaka fish Parkinson's disease (PD) models we developed using toxin treatment and genetic engineering. 1-Methyl-4-phenyl-1,2,3,4-tetrahydropyridine (MPTP), 6-hydroxydopamine (6-OHDA), proteasome inhibitors, lysosome inhibitors and tunicamycin treatment in our model fish replicated some salient features of PD: selective dopamine cell loss and reduced spontaneous movement with the last three toxins producing inclusion bodies ubiquitously in the brain. Despite the ubiquitous distribution of the inclusion bodies, the middle diencephalic dopaminergic neurons were particularly vulnerable to these toxins, supporting the idea that this dopamine cluster is similar to the human substantia nigra. PTEN-induced putative kinase 1 (PINK1) homozygous mutants also showed reduced spontaneous swimming movements. These data indicate that medaka fish can serve as a new model animal of PD. In this review we summarize our previous data and discuss future prospects.

Sulpiride, but not SCH23390, modifies cocaine-induced conditioned place preference and expression of tyrosine hydroxylase and elongation factor 1α in zebrafish

Finding genetic polymorphisms and mutations linked to addictive behavior can provide important targets for pharmaceutical and therapeutic interventions. Forward genetic approaches in model organisms such as zebrafish provide a potentially powerful avenue for finding new target genes. In order to validate this use of zebrafish, the molecular nature of its reward system must be characterized. We have previously reported the use of cocaine-induced conditioned place preference (CPP) as a reliable method for screening mutagenized fish for defects in the reward pathway. Here we test if CPP in zebrafish involves the dopaminergic system by co-treating fish with cocaine and dopaminergic antagonists. Sulpiride, a potent D2 receptor (DR2) antagonist, blocked cocaine-induced CPP, while the D1 receptor (DR1) antagonist SCH23390 had no effect. Acute cocaine exposure also induced a rise in the expression of tyrosine hydroxylase (TH), an important enzyme in dopamine synthesis, and a significant decrease in the expression of elongation factor 1α (EF1α), a housekeeping gene that regulates protein synthesis. Cocaine selectively increased the ratio of TH/EF1α in the telencephalon, but not in other brain regions. The cocaine-induced change in TH/EF1α was blocked by co-treatment with sulpiride, but not SCH23390, correlating closely with the action of these drugs on the CPP behavioral response. Immunohistochemical analysis revealed that the drop in EF1α was selective for the dorsal nucleus of the ventral telencephalic area (Vd), a region believed to be the teleost equivalent of the striatum. Examination of TH mRNA and EF1α transcripts suggests that regulation of expression is post-transcriptional, but this requires further examination. These results highlight important similarities and differences between zebrafish and more traditional mammalian model organisms.

MANF regulates dopaminergic neuron development in larval zebrafish

Mesencephalic astrocyte derived neurotrophic factor (MANF) is recognized as a dopaminergic neurotrophic factor, which can protect dopaminergic neurons from neurotoxic damage. However, little is known about the function of MANF during the vertebrate development. Here, we report that MANF expression is widespread during embryonic development and in adult organs analyzed by qPCR and in situ hybridization in zebrafish. Knockdown of MANF expression with antisense splice-blocking morpholino oligonucleotides resulted in no apparent abnormal phenotype. Nevertheless, the dopamine level of MANF morphants was lower than that of the wild type larvae, the expression levels of the two tyrosine hydroxylase gene transcripts were decreased and a decrease in neuron number in certain groups of th1 and th2 cells in the diencephalon region in MANF morphants was observed. These defects were rescued by injection of exogenous manf mRNA. Strikingly, manf mRNA could partly restore the decrease of th1 positive cells in Nr4a2-deficient larvae. These results suggest that MANF is involved in the regulation of the development of dopaminergic system in zebrafish.

Transient knockdown of tyrosine hydroxylase during development has persistent effects on behaviour in adult zebrafish (Danio rerio)

Abnormal dopamine (DA) signaling is often suggested as causative in schizophrenia. The other prominent hypothesis for this disorder, largely driven by epidemiological data, is that certain adverse events during the early stages of brain development increase an individual's risk of developing schizophrenia later in life. However, the clinical and preclinical literature consistently implicates behavioural, cognitive, and pharmacological abnormalities, implying that DA signaling is abnormal in the adult brain. How can we reconcile these two major hypotheses underlying much of the clinical and basic research into schizophrenia? In this study we have transiently knocked down tyrosine hydroxylase (TH, the rate limiting enzyme in DA synthesis) gene expression in the early stages of brain development in zebrafish using morpholinos. We show that by adulthood, TH and DA levels have returned to normal and basic DA-mediated behaviours, such as locomotion, are also normal. However, when they were exposed to a novel environment the levels of freezing and immediate positioning in deeper zones were significantly reduced in these adult fish. The neurochemistry underlying these behaviours is complex, and the exact mechanisms for these abnormal behaviours remains unknown. This study demonstrates that early transient alterations in DA ontogeny can produce persistent alterations in adult brain function and suggests that the zebrafish may be a promising model animal for future studies directed at clarifying the basic neurodevelopmental mechanisms behind complex psychiatric disease.

Analysis of transcriptional codes for zebrafish dopaminergic neurons reveals essential functions of Arx and Isl1 in prethalamic dopaminergic neuron development

Distinct groups of dopaminergic neurons develop at defined anatomical sites in the brain to modulate function of a large diversity of local and far-ranging circuits. However, the molecular identity as judged from transcription factor expression has not been determined for all dopaminergic groups. Here, we analyze regional expression of transcription factors in the larval zebrafish brain to determine co-expression with the Tyrosine hydroxylase marker in dopaminergic neurons. We define sets of transcription factors that clearly identify each dopaminergic group. These data confirm postulated relations to dopaminergic groups defined for mammalian systems. We focus our functional analysis on prethalamic dopaminergic neurons, which co-express the transcription factors Arx and Isl1. Morpholino-based knockdown reveals that both Arx and Isl1 are strictly required for prethalamic dopaminergic neuron development and appear to act in parallel. We further show that Arx contributes to patterning in the prethalamic region, while Isl1 is required for differentiation of prethalamic dopaminergic neurons.

Sex differences in the expression of vasotocin/isotocin, gonadotropin-releasing hormone, and tyrosine and tryptophan hydroxylase family genes in the medaka brain

In teleost fish, sex differences in several behavioral and physiological traits have been assumed to reflect underlying sex differences in the central expression of neurotransmitter/neuromodulator-related molecules, including vasotocin (VT)/isotocin (IT), gonadotropin-releasing hormone (GnRH), and tyrosine and tryptophan hydroxylases (TH and TPH). However, the sex-dependent expression patterns of these molecules have not been fully characterized in the teleost brain. In the present study, we therefore systematically evaluated sex differences in their expression in the medaka (Oryzias latipes) brain. The most prominent sex difference was observed in vt expression in the nucleus posterior tuberis (NPT) and the posterior part of the nucleus ventral tuberis (NVT) in the hypothalamus, where the expression was completely male-specific. Male-biased expression of gnrh1, tph1, and tph2 was also evident in the supracommissural and posterior nuclei of the ventral telencephalic area (Vs/Vp), medial nucleus of the dorsal telencephalic area (Dm), and thalamic dorsal posterior nucleus (DP), respectively. In contrast, the overall expression levels of it and gnrh3 were higher in the female brain than in the male brain. Equally importantly, no conspicuous sex differences were observed in the expression of gnrh2, th1, and th2, despite several previous reports of their sex-biased expression in the brains of other teleost species. Taken together, these data have uncovered previously unidentified sex differences in the expression of VT/IT, GnRH, and TPH in the teleost brain, which may possibly be relevant to sexual dimorphism in some behavioral and/or physiological traits, and have simultaneously highlighted potential species differences in the roles of these molecules.

Transgenic zebrafish expressing green fluorescent protein in dopaminergic neurons of the ventral diencephalon

We have generated a line of transgenic zebrafish, Tg(dat:EGFP), in which the green fluorescent protein (GFP) is expressed under the control of cis-regulatory elements of the dopamine transporter (dat) gene. In Tg(dat:EGFP) fish, dopamine (DA) neurons are labeled with GFP, including those in ventral diencephalon (vDC) clusters, amacrine cells in the retina, in the olfactory bulb, in the pretectum, and in the caudal hypothalamus. In the vDC, DA neurons of groups 2-6 are correctly labeled with GFP, based on colocalization analyses. MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) treatments induced a modest but significant loss of DA neurons in groups 2-6 of the vDC. This transgenic line will be useful for the study of DA neuron development and in models of DA neuron loss.

Epigenetic, transcriptional and posttranscriptional regulation of the tyrosine hydroxylase gene

The activity of tyrosine hydroxylase (TH, EC 1.14.16.2) gene and protein determines the catecholamine level, which, in turn, is crucial for the organism homeostasis. The TH gene expression is regulated by near all possible regulatory mechanisms on epigenetic, transcriptional and posttranscriptional levels. Ongoing molecular characteristic of the TH gene reveals some of the cis and trans elements necessary for its proper expression but most of them especially these responsible for tissue specific expression remain still obscure. This review will focus on some aspects of TH regulation including spatial chromatin organization of the TH locus and TH gene, regulatory elements mediating basal, induced and cell-specific activity, transcriptional elongation, alternative TH RNA processing, and the regulation of TH RNA stability in the cell.

Identification of a dopaminergic enhancer indicates complexity in vertebrate dopamine neuron phenotype specification

The dopaminergic neurons of the basal ganglia play critical roles in CNS function and human disease, but specification of dopamine neuron phenotype is poorly understood in vertebrates. We performed an in vivo screen in zebrafish to identify dopaminergic neuron enhancers, in order to facilitate studies on the specification of neuronal identity, connectivity, and function in the basal ganglia. Based primarily on identification of conserved non-coding elements, we tested 54 DNA elements from four species (zebrafish, pufferfish, mouse, and rat), that included 21 genes with known or putative roles in dopaminergic neuron specification or function. Most elements failed to drive CNS expression or did not express specifically in dopaminergic neurons. However, we did isolate a discrete enhancer from the otpb gene that drove specific expression in diencephalic dopaminergic neurons, although it did not share sequence conservation with regulatory regions of otpa or other dopamine-specific genes. For the otpb enhancer, regulation of expression in dopamine neurons requires multiple elements spread across a large genomic area. In addition, we compared our in vivo testing with in silico analysis of genomic regions for genes involved in dopamine neuron function, but failed to find conserved regions that functioned as enhancers. We conclude that regulation of dopaminergic neuron phenotype in vertebrates is regulated by dispersed regulatory elements.

Differential expression of dopaminergic cell markers in the adult zebrafish forebrain

Although the simultaneous presence of tyrosine hydroxylase (TH), aromatic amino acid decarboxylase (AADC), dopamine transporter (DAT), and vesicular monoamine transporter 2 (VMAT2) is considered as a phenotypic signature of dopamine (DA) neurons, it has been suggested that they are not uniformly expressed in all dopaminergic brain nuclei. Moreover, in nonmammalian vertebrates, two tyrosine hydroxylase genes (TH1 and TH2) are found, and they exhibit different expression patterns in zebrafish brains. Here we present a detailed description of the distribution of TH1, TH2, AADC, DAT, and VMAT2 transcripts, in relation to TH and DA immunoreactivity to better characterize dopaminergic nuclei in the adult zebrafish forebrain. TH2-positive cells in the hypothalamus are strongly DA immunoreactive (DAir), providing direct evidence that they are dopaminergic. DAir cells are also found in most TH1-positive or TH-immunoreactive (THir) nuclei. However, the DAir signal was weaker than THir in the olfactory bulb, telencephalon, ventral thalamus, pretectum, and some posterior tubercular and preoptic nuclei. These cell populations also exhibited low levels of VMAT2 transcripts, suggesting that low DA is due to a lower vesicular DA accumulation. In contrast, cell populations with low levels of AADC did not always have low levels of DA. DAT transcripts were abundantly expressed in most of the TH1- or TH2-positive territories. In addition, DAT and/or VMAT2 transcripts were found in some periventricular cell populations such as in the telencephalon without TH1 or TH2 expression. Thus, expression patterns of dopaminergic cell markers are not homogeneous, suggesting that the gene regulatory logic determining the dopaminergic phenotype is unexpectedly complex.

Unpredictable chronic stress model in zebrafish (Danio rerio): behavioral and physiological responses

Zebrafish (Danio rerio) have emerged as a promising model organism to study development, toxicology, pharmacology, and neuroscience, among other areas. Despite the increasing number of studies using zebrafish, behavioral studies with this species are still elementary when compared to rodents. The aim of this study was to develop a model of unpredictable chronic stress (UCS) in zebrafish. We evaluated the effects of UCS protocol during 7 or 14 days on behavioral and physiological parameters. The effects of stress were evaluated in relation to anxiety and exploratory behavior, memory, expression of corticotrophin-releasing factor (CRF) and glucocorticoid receptor (GR), and cortisol levels. As expected, UCS protocol increased the anxiety levels, impaired cognitive function, and increased CRF while decreased GR expression. Moreover, zebrafish submitted to 7 or 14 days of UCS protocol presented increased cortisol levels. The protocol developed here is a complementary model for studying the neurobiology and the effects of chronic stress in behavioral and physiological parameters. In addition, this protocol is less time consuming than standard rodent models commonly used to study chronic stress. These results confirm UCS in zebrafish as an adequate model to preclinical studies of stress, although further studies are warranted to determine its predictive validity.

The evolution of dopamine systems in chordates

Dopamine (DA) neurotransmission in the central nervous system (CNS) is found throughout chordates, and its emergence predates the divergence of chordates. Many of the molecular components of DA systems, such as biosynthetic enzymes, transporters, and receptors, are shared with those of other monoamine systems, suggesting the common origin of these systems. In the mammalian CNS, the DA neurotransmitter systems are diversified and serve for visual and olfactory perception, sensory–motor programming, motivation, memory, emotion, and endocrine regulations. Some of the functions are conserved among different vertebrate groups, while others are not, and this is reflected in the anatomical aspects of DA systems in the forebrain and midbrain. Recent findings concerning a second tyrosine hydroxylase gene (TH2) revealed new populations of DA-synthesizing cells, as evidenced in the periventricular hypothalamic zones of teleost fish. It is likely that the ancestor of vertebrates possessed TH2 DA-synthesizing cells, and the TH2 gene has been lost secondarily in placental mammals. All the vertebrates possess DA cells in the olfactory bulb, retina, and in the diencephalon. Midbrain DA cells are abundant in amniotes while absent in some groups, e.g., teleosts. Studies of protochordate DA cells suggest that the diencephalic DA cells were present before the divergence of the chordate lineage. In contrast, the midbrain cell populations have probably emerged in the vertebrate lineage following the development of the midbrain–hindbrain boundary. The functional flexibility of the DA systems, and the evolvability provided by duplication of the corresponding genes permitted a large diversification of these systems. These features were instrumental in the adaptation of brain functions to the very variable way of life of vertebrates.

Zebrafish for the study of the biological effects of nicotine

INTRODUCTION

Zebrafish are emerging as a powerful animal model for studying the molecular and physiological effects of nicotine exposure. The zebrafish have many advantageous physical characteristics, including small size, high fecundity rates, and externally developing transparent embryos. When combined with a battery of molecular-genetic tools and behavioral assays, these attributes enable studies to be conducted that are not practical using traditional animal models.

METHODS

We reviewed the literature on the application of the zebrafish model as a preclinical model to study the biological effects of nicotine exposure.

RESULTS

The identified studies used zebrafish to examine the effects of nicotine exposure on early development, addiction, anxiety, and learning. The methods used included green fluorescent protein-labeled proteins to track in vivo nicotine-altered neuron development, nicotine-conditioned place preference, and locomotive sensitization linked with high-throughput molecular and genetic screens and behavioral models of learning and stress response to nicotine. Data are presented on the complete homology of all known human neural nicotinic acetylcholine receptors in zebrafish and on the biological similarity of human and zebrafish dopaminergic signaling.

CONCLUSIONS

Tobacco dependence remains a major health problem worldwide. Further understanding of the molecular effects of nicotine exposure and genetic contributions to dependence may lead to improvement in patient treatment strategies. While there are limitations to the use of zebrafish as a preclinical model, it should provide a valuable tool to complement existing model systems. The reviewed studies demonstrate the enormous opportunity zebrafish have to advance the science of nicotine and tobacco research.

Comprehensive catecholaminergic projectome analysis reveals single-neuron integration of zebrafish ascending and descending dopaminergic systems

Essential components of animal behaviour are modulated by dopaminergic (DA) and noradrenergic circuitry. In this study, we reveal at cellular resolution the complete set of projections ('projectome') of every single type of DA and noradrenergio neurons in the central nervous system of zebrafish larvae. The most extensive DA projections are established by posterior tubercular otp-dependent neurons, with individual somata integrating the ascending DA system, the descending diencephalospinal, as well as the endohypothalamic circuitry. These findings suggest a major role in the modulation of physiology and behaviour for otp-dependent DA neurons, which correlate with the mammalian A11 group. We further identified an endogenous subpallial DA system that not only provides most of the local DA projections, but also connects to the ventral diencephalon. The catecholaminergic projectome map provides a framework to understand the evolution and function of these neuromodulatory systems.

Zebrafish: an integrative system for neurogenomics and neurosciences

Rapid technological advances over the past decade have moved us closer to a high throughput molecular approach to neurobiology, where we see the merging of neurogenetics, genomics, physiology, imaging and pharmacology. This is the case more in zebrafish than in any other model organism commonly used. Recent improvements in the generation of transgenic zebrafish now allow genetic manipulation and live imaging of neuronal development and function in early embryonic, larval, and adult animals. The sequenced zebrafish genome and comparative genomics give unprecedented insights into genome evolution and its relation to genome structure and function. There is now information on embryonic and larval expression of over 12,000 genes and just under 1000 mutant phenotypes. We review the remarkable similarity of the zebrafish genetic blueprint for the nervous system to that of mammals and assess recent technological advances that make the zebrafish a model of choice for elucidating the development and function of neuronal circuitry, transgene-based neuroanatomy, and small molecule neuropharmacology.

Characterization of the dopamine system in the brain of the túngara frog, Physalaemus pustulosus

Dopamine is an evolutionarily ancient neurotransmitter that plays an essential role in mediating behavior. In vertebrates, dopamine is central to the mesolimbic reward system, a neural network concerned with the valuation of stimulus salience, and to the nigrostriatal motor system and hypothalamic nuclei involved in the regulation of locomotion and social behavior. In amphibians, dopaminergic neurons have been mapped out in several species, yet the distribution of dopaminoreceptive cells is unknown. The túngara frog, Physalaemus pustulosus, is an excellent model system for the study of neural mechanisms by which valuations of stimuli salience and social decisions are made, especially in the context of mate choice. In order to better understand where dopamine acts to regulate social decisions in this species, we have determined the distribution of putative dopaminergic cells (using tyrosine hydroxylase immunohistochemistry) and cells receptive to dopaminergic signaling (using DARPP-32 immunohistochemistry) throughout the brain of P. pustulosus. The distribution of dopaminergic cells was comparable to other anurans. DARPP-32 immunoreactivity was identified in key brain regions known to modulate social behavior in other vertebrates including the proposed anuran homologues of the mammalian amygdalar complex, nucleus accumbens, hippocampus, striatum, preoptic area, anterior hypothalamus, ventromedial hypothalamus, and ventral tegmental area/substantia nigra pars compacta. Due to its widespread distribution, DARPP-32 likely also plays many roles in non-limbic brain regions that mediate non-social information processing. These results significantly extend our understanding of the distribution of the dopaminergic system in the anuran brain and beyond.

Phylogenetic analysis and evolution of aromatic amino acid hydroxylase

A study was performed to investigate the phylogenetic relationship among AAAH members and to statistically evaluate sequence conservation and functional divergence. In total, 161 genes were identified from 103 species. Phylogenetic analysis showed that well-conserved subfamilies exist. Exon-intron structure analysis showed that the gene structures of AAAH were highly conserved across some different lineage species, while some species-specific introns were also found. The dynamic distribution of ACT domain suggested one gene fusion event has occurred in eukaryota. Significant functional divergence was found between some subgroups. Analysis of the site-specific profiles revealed critical amino acid residues for functional divergence. This study highlights the molecular evolution of this family and may provide a starting point for further experimental verifications.

Rapid dopaminergic modulation of the fish hypothalamic transcriptome and proteome

Background

Dopamine (DA) is a major neurotransmitter playing an important role in the regulation of vertebrate reproduction. We developed a novel method for the comparison of transcriptomic and proteomic data obtained from in vivo experiments designed to study the neuroendocrine actions of DA.

Methods and Findings

Female goldfish were injected (i.p.) with DA agonists (D1-specific; SKF 38393, or D2-specific; LY 171555) and sacrificed after 5 h. Serum LH levels were reduced by 57% and 75% by SKF 38393 and LY 171555, respectively, indicating that the treatments produced physiologically relevant responses in vivo. Bioinformatic strategies and a ray-finned fish database were established for microarray and iTRAQ proteomic analysis of the hypothalamus, revealing a total of 3088 mRNAs and 42 proteins as being differentially regulated by the treatments. Twenty one proteins and mRNAs corresponding to these proteins appeared on both lists. Many of the mRNAs and proteins affected by the treatments were grouped into the Gene Ontology categorizations of protein complex, signal transduction, response to stimulus, and regulation of cellular processes. There was a 57% and 14% directional agreement between the differentially-regulated mRNAs and proteins for SKF 38393 and LY 171555, respectively.

Conclusions

The results demonstrate the applicability of advanced high-throughput genomic and proteomic analyses in an amendable well-studied teleost model species whose genome has yet to be sequenced. We demonstrate that DA rapidly regulates multiple hypothalamic pathways and processes that are also known to be involved in pathologies of the central nervous system.

The comparative neuroanatomy and neurochemistry of zebrafish CNS systems of relevance to human neuropsychiatric diseases

Modulatory neurotransmitters which signal through G protein-coupled receptors control brain functions which deteriorate in degenerative brain diseases. During the past decade many of these systems have been mapped in the zebrafish brain. The main architecture of the systems in zebrafish brain resembles that of the mammals, despite differences in the development of the telencephalon and mesodiencephalon. Modulatory neurotransmitters systems which degenerate in human diseases include dopamine, noradrenaline, serotonin, histamine, acetylcholine and orexin/hypocretin. Although the number of G protein-coupled receptors in zebrafish is clearly larger than in mammals, many receptors have similar expression patterns, binding and signaling properties as in mammals. Distinct differences between mammals and zebrafish include duplication of the tyrosine hydroxylase gene in zebrafish, and presence of one instead of two monoamine oxidase genes. Zebrafish are sensitive to neurotoxins including MPTP, and exposure to this neurotoxin induces a decline in dopamine content and number of detectable tyrosine hydroxylase immunoreactive neurons in distinct nuclei. Sensitivity to important neurotoxins, many available genetic methods, rapid development and large-scale quantitative behavioral methods in addition to advanced quantitative anatomical methods render zebrafish an optimal organism for studies on disease mechanisms.

The sea lamprey tyrosine hydroxylase: cDNA cloning and in situ hybridization study in the brain

Lampreys belong to the oldest group of extant vertebrates, the agnathans or cyclostomes. Thus, they occupy a key phylogenetic position near the root of the vertebrate tree, which makes them important to the study of nervous system evolution. Tyrosine hydroxylase is the rate-limiting enzyme of catecholamine biosynthesis and is considered a marker of catecholaminergic neurons. In the present study, we report partial cloning of the sea lamprey tyrosine hydroxylase (TH) cDNA and the pattern of TH transcript expression in the adult brain by means of in situ hybridization. Sea lamprey TH mRNA is characterized by the presence of a large untranslated sequence in the 3' end that contains a typical polyadenylation signal (ATTAAA). The deduced partial TH protein sequence presents a conserved domain with two His residues coordinating Fe(2+) binding and a conserved cofactor binding site. Neurons expressing the TH transcript were observed in the preoptic, postoptic commissure, dorsal hypothalamic, ventral hypothalamic, mammillary and paratubercular nuclei of the prosencephalon. In situ hybridization experiments also confirmed the existence of a catecholaminergic (dopaminergic) striatal population in the brain of the adult sea lamprey. A few granule-like cells in the olfactory bulbs also showed weak TH transcript expression. No cells showing TH transcript expression were observed in the rostral rhombencephalon, which suggests the absence of a locus coeruleus in the sea lamprey. Comparison of the pattern of TH mRNA expression in the prosencephalon between lampreys and teleost fishes revealed both similarities and differences. Our results suggest that the duplication of the TH gene might have occurred before the separation of agnathans and gnathostomes.

Studying peripheral sympathetic nervous system development and neuroblastoma in zebrafish

The combined experimental attributes of the zebrafish model system, which accommodates cellular, molecular, and genetic approaches, make it particularly well-suited for determining the mechanisms underlying normal vertebrate development as well as disease states, such as cancer. In this chapter, we describe the advantages of the zebrafish system for identifying genes and their functions that participate in the regulation of the development of the peripheral sympathetic nervous system (PSNS). The zebrafish model is a powerful system for identifying new genes and pathways that regulate PSNS development, which can then be used to genetically dissect PSNS developmental processes, such as tissue size and cell numbers, which in the past haves proved difficult to study by mutational analysis in vivo. We provide a brief review of our current understanding of genetic pathways important in PSNS development, the rationale for developing a zebrafish model, and the current knowledge of zebrafish PSNS development. Finally, we postulate that knowledge of the genes responsible for normal PSNS development in the zebrafish will help in the identification of molecular pathways that are dysfunctional in neuroblastoma, a highly malignant cancer of the PSNS.