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PubMed2000

Zebrafish neural induction and patterning.

Formation of a functional nervous system requires that distinct types of cells develop at quite precise times and places. A goal of developmental neurobiologists is to understand the nature of the patterning mechanisms that specify neural cells for particular fates. In recent years, zebrafish has emerged as new model system for investigating vertebrate neural development, offering a unique combination of genetic, cellular, and molecular tools. Studies using zebrafish provide important new insights concerning the source and nature of molecular signals that induce and pattern the central nervous system.

Animals↗
PubMed1992

A specific brain tract guides follower growth cones in two regions of the zebrafish brain.

Neurons of the nucleus of the posterior commissure (nuc PC), an identifiable cluster of neurons in the embryonic zebrafish brain, project growth cones ventrally along the posterior commissure to the anterior tegmentum where the PC intersects two longitudinal tracts, the tract of the postoptic commissure (TPOC) and the medial longitudinal fasciculus (MLF). Once at the intersection, nuc PC growth cones turn posteriorly onto the TPOC in the dorsal tegmentum and follow it to the hindbrain. Previously we showed that in the absence of the TPOC, nuc PC growth cones often extended along aberrant pathways suggesting that fasciculation, that is, contact with TPOC axons is an important factor in guiding growth cones along their normal pathway. However, a significant number of nuc PC growth cones also followed their normal pathway suggesting that cues associated with the dorsolateral tegmentum, independent of the TPOC, can also guide nuc PC growth cones. We have now confirmed using electron microscopy that nuc PC growth cones fasciculate with axons in the TPOC. In the absence of the TPOC, the nuc PC growth cones that extend along their normal pathway do so in contact with dorsolateral neuroepithelial cells. This suggests that cues associated with these cells can also guide the nuc PC growth cones. Furthermore, in the absence of the TPOC axons, these growth cones now inappropriately turn onto axons that normally intersect the TPOC near the border of the midbrain and hindbrain, that is, at a second intersection of tracts. This suggests that fasciculation with TPOC axons may also guide nuc PC growth cones in this second region of the brain.

Animals↗
PubMed2004

Distribution of prospective glutamatergic, glycinergic, and GABAergic neurons in embryonic and larval zebrafish.

Zebrafish are an excellent model for studies of the functional organization of neuronal circuits, but little is known regarding the transmitter phenotypes of the neurons in their nervous system. We examined the distribution in spinal cord and hindbrain of neurons expressing markers of transmitter phenotype, including the vesicular glutamate transporter (VGLUT) genes for glutamatergic neurons, the neuronal glycine transporter (GLYT2) for glycinergic neurons, and glutamic acid decarboxylase (GAD65/67) for GABAergic neurons. All three markers were expressed in a large domain in the dorsal two-thirds of spinal cord, with additional, more ventral expression domains for VGLUT2 and GAD/GABA. In the large dorsal domain, dual in situ staining showed that GLYT2-positive cells were intermingled with VGLUT2 cells, with no dual-stained neurons. Many of the neurons in the dorsal expression domain that were positive for GABA markers at embryonic stages were also positive for GLYT2, suggesting that the cells might use both GABA and glycine, at least early in their development. The intermingling of neurons expressing inhibitory and excitatory markers in spinal cord contrasted markedly with the organization in hindbrain, where neurons expressing a particular marker were clustered together to form stripes that were visible running from rostral to caudal in horizontal sections and from dorsomedial to ventrolateral in cross sections. Dual labeling showed that the stripes of neurons labeled with one transmitter marker alternated with stripes of cells labeled for the other transmitter phenotypes. The differences in the distribution of excitatory and inhibitory neurons in spinal cord versus hindbrain may be tied to differences in their patterns of development and functional organization.

Amino Acid Transport Systems, Neutral↗
PubMed2002

Development of pigment cells in the zebrafish embryo.

In recent years, the zebrafish Danio rerio has emerged as a powerful model organism for the study of vertebrate embryogenesis. Zebrafish, like other vertebrates, possess pigment cells that arise from two distinct embryonic sources: those of the dermis and epidermis originate from the neural crest, while those that comprise the outermost layer of the retina, the retinal pigment epithelium or RPE, derive from the optic cup. A better understanding of processes behind the specification and differentiation of these cells will provide insight to the evolutionary diversification of all classes of vertebrates and will have clinical relevance to human disorders of pigmentation and certain retinopathies. In the first part of this review, the present knowledge of the ontogeny of both of these populations of pigment cells in the embryonic zebrafish is summarized, in terms of both genetics and molecular markers. The final part of the review focuses on duplicate zebrafish genes encoding orthologs of the basic helix-loop-helix/leucine zipper protein Mitf (Microphthalmia-associated transcription factor), and presents a hypothesis concerning their divergent roles in neural crest and retinal pigment cells.

Animals↗
PubMed2004

Development of the nervus terminalis: origin and migration.

The origin of the nervus terminalis is one of the least well understood developmental events involved in generating the cranial ganglia of the forebrain in vertebrate animals. This cranial nerve forms at the formidable interface of the anteriormost limits of migrating cranial neural crest cells, the terminal end of the neural tube and the differentiating olfactory and adenohypophyseal placodes. The complex cellular interactions that give rise to the various structures associated with the sensory placode (olfactory) and endocrine placode (adenohypophysis) surround and engulf this enigmatic cranial nerve. The tortured history of nervus terminalis development (see von Bartheld, this issue, pages 13-24) reflects the lack of consensus on the origin (or origins), as well as the experimental difficulties in uncovering the origin, of the nervus terminalis. Recent technical advances have allowed us to make headway in understanding the origin(s) of this nerve. The emergence of the externally fertilized zebrafish embryo as a model system for developmental biology and genetics has shed new light on this century-old problem. Coupled with new developmental models are techniques that allow us to trace lineage, visualize gene expression, and genetically ablate cells, adding to our experimental tools with which to follow up on studies provided by our scientific predecessors. Through these techniques, a picture is emerging in which the origin of at least a subset of the nervus terminalis cells lies in the cranial neural crest. In this review, the data surrounding this finding will be discussed in light of recent findings on neural crest and placode origins.

Animals↗
PubMed2004

Patterns of spatial and temporal visceral arch muscle development in the Mexican axolotl (Ambystoma mexicanum).

Vertebrate head development is a classical topic that has received renewed attention during the last decade. Most reports use one of a few model organisms (chicken, mouse, zebrafish) and have focused on molecular mechanisms and the role of the neural crest, while cranial muscle development has received less attention. Here we describe cranial muscle differentiation and morphogenesis in the Mexican axolotl, Ambystoma mexicanum. To determine the onset of differentiation we use antibodies against desmin and optical sectioning using confocal laser scanning microscopy on whole-mount immunostained embryos. This technique makes it possible to document the cranial muscle in three dimensions while keeping the specimens intact. Desmin expression starts almost simultaneously in the first, second, and third visceral arch muscles (as in other amphibians studied). Muscle anlagen divide up early into the different elements which constitute the larval cranial musculature. We extend and refine earlier findings, e.g., by documenting a clear division between interhyoideus and interhyoideus posterior. The timing of cranial muscle differentiation differs among vertebrate groups, but seems to be constant within each group. This study provides a morphological foundation for further studies of muscle cell fate and early differentiation.

Ambystoma mexicanum↗
PubMed2004

Comparative study on the in vitro/in vivo estrogenic potencies of 17beta-estradiol, estrone, 17alpha-ethynylestradiol and nonylphenol.

The estrogenic activity of compounds was evaluated in a comparative approach both with in vitro and in vivo assays. By comparing simultaneously obtained experimental data, we evaluated the differences in response sensitivity (by EC10) and concentration-response relationships (including EC50) in order to get an idea about the predictive value of in vitro assays for in vivo estrogenic potencies or effects in fish. Two human estrogen receptor-based assays, the MVLN-assay (transformed MCF-7 human breast cancer cell line) and the yeast estrogen screen (YES-screen) were used for the in vitro evaluation of the estrogenic potencies. An in vivo model with the female zebrafish (Danio rerio) with plasma vitellogenin (VTG) as a biomarker for exposure and the ovarian somatic index (OSI) as an effect endpoint was used for the in vivo work. Compounds tested were 17beta-estradiol (E2), estrone (E1), 17alpha-ethynylestradiol (EE2) and the alkylphenolic compound nonylphenol (NP). All compounds were found to be estrogenic in both in vitro assays and were able to induce VTG and to reduce the ovarian somatic index in female zebrafish. The MVLN-assay appeared up to 15 times more sensitive than the YES-screen. Concentration-response relationships, determined by EC10 and EC50 (concentration of test compound causing 10% or 50% effect compared to control) for VTG and OSI were of the same order of magnitude, indicating that VTG induction as an exposure biomarker can be predictive for effects on ovaries in females. We further demonstrated that for E1 and NP, the in vitro observed estrogenic potencies, based on EC50 values, were of the same order of magnitude as the in vivo estrogenic potencies. For EE2, a difference between in vitro and in vivo relative estrogenic potency was observed, being about 25 times more potent in vivo than could be expected based on the in vitro results. These experimental results showed the suitability of in vitro assays for screening purposes with qualitative assessment of estrogenicity, but they meanwhile point to the need of in vivo tests for an accurate hazard assessment for wildlife.

Analysis of Variance↗
PubMed2006

Small molecule screening by imaging.

Useful small molecule tools can be discovered in imaging screens that measure phenotype in single cells or small organisms. Recent examples include identification of small molecule inhibitors of processes such as cell migration, cytokinesis, mitotic spindle length determination, melanogenesis, aggresome formation, membrane transport and nuclear export. Imaging screens are currently limited by challenges in the areas of image analysis and target identification. We discuss the use of model organisms such as zebrafish in screens and review different methods of target identification. The emerging field of automated image analysis is also introduced.

Animals↗
PubMedDate not supplied

Transcriptome study in China.

The Chinese genome project was initiated in 1993 with the goal of contributing 1% to the Human Genome Program. The study of gene expression profiles with cDNA microarrays, and large-scale sequencing and analysis of 130928 expressed sequence tags (ESTs), allowed isolation and characterization of over 1000 novel full-length human cDNAs derived from human hematopoietic stem/progenitor cells, neuroendocrine tissues, liver, and cardiovascular cells. In addition, EST sequencing for model organisms, including rat, zebrafish, Schistosoma japonicum and rice was performed, aiming at identifying genes associated with physiological and/or pathological characteristics.

Animals↗
PubMed2025

ELFN1 deficiency: The mechanistic basis and phenotypic spectrum of a neurodevelopmental disorder with epilepsy.

PURPOSE: Synaptic communication deficits are central to many neurodevelopmental disorders. However, for rare monogenic conditions, these disorders remain poorly defined, with limited understanding of their molecular etiology. A homozygous frameshift variant in the synaptic cell adhesion molecule ELFN1 was reported in a family with 3 affected siblings with epileptic encephalopathy, alongside a missense variant of uncertain significance in a cohort study involving a family with intellectual disability. Therefore, we sought to evaluate the role and mechanism of biallelic ELFN1 variants in disease pathogenesis. METHODS: We describe 8 newly identified individuals from 5 unrelated families, all carrying homozygous ELFN1 variants, including frameshift and in-frame deletions. By integrating data from these cases with clinical details from 6 previously reported individuals, we delineate the phenotypic spectrum associated with ELFN1 variants. RESULTS: Clinical features include varying degrees of developmental delay/intellectual disability, epilepsy, and movement disorders. Molecular investigations reveal that these variants disrupt ELFN1 protein trafficking to the cell surface, resulting in loss of function. Functional modeling in mice and zebrafish demonstrates the role of Elfn1 loss in motor activity abnormalities and seizures. CONCLUSION: Our findings establish ELFN1 deficiency as the cause of a distinct, rare neurodevelopmental disorder, providing a foundation for future investigations into its pathophysiology and therapeutic strategies.

Humans↗
PubMed2004

Characterization of mutations affecting embryonic hematopoiesis in the medaka, Oryzias latipes.

In a genetic screen for mutations affecting organogenesis in the medaka, Oryzias latipes, we identified eight mutants with defects in embryonic hematopoiesis. These mutations were classified into seven complementation groups. In this paper, we characterize the five mutants that were confirmed in the next generation. The beni fuji mutant was defective in the generation of blood cells, exhibiting reduced blood cells at the initiation of circulation. Mutations in two genes, lady finger and ryogyoku, caused abnormal morphology of blood cells, i.e., deformation, along with a progressive decrease in the number of blood cells. The sekirei mutant exhibited photosensitivity with autofluorescent blood cells. Mutations in kyoho resulted in huge blood cells that were approximately three times longer than the wild-type blood cells. The spectrum of phenotypes identified in this study is similar to that of the zebrafish hematopoietic mutants except for the huge blood cells in kyoho. Our results demonstrate that medaka, as well as zebrafish, is a useful model to study hematopoiesis.

Animals↗
PubMed2005

Genetics moving to neuronal networks.

Neuronal circuits are essential components of the nervous system and determine various body functions. To understand how neuronal circuits operate it is necessary to identify the participating neuronal subpopulations and to dissect the function of the neurons at the molecular level. The locomotor central pattern generator that coordinates body movements is well suited for elucidating the assembly and identity of the participating neurons. Remarkable advances in the field of genetics are making studies in neuroscience more efficient and precise so that now, using nematode worms, fruit flies, zebrafish and mice as model organisms, a genetic approach can be used to identify molecules and neurons crucial for locomotor network functionality.

Animals↗
PubMed2001

Green fluorescent protein (GFP) transgenic fish and their applications.

The coupling of the GFP reporter system with the optical clarity of embryogenesis in model fish such as zebrafish and medaka is beginning to change the picture of transgenic fish study. Since the advent of first GFP transgenic fish in 1995, GFP transgenic fish technology have been quickly employed in many areas such as analyses of gene expression patterns and tissue/organ development, dissection of promoters/enhancers, cell lineage and axonal pathfinding, cellular localization of protein products, chimeric embryo and nuclear transplantation, cell sorting, etc. The GFP transgenic fish also have the potentials in analysis of upstream regulatory factors, mutagenesis screening and characterization, and promoter/enhancer trap. Our own studies indicate that GFP transgenic fish may become a new source of novel variety of ornamental fish. Efforts are also being made in our laboratory to turn GFP transgenic fish into biomonitoring organisms for surveillance of environmental pollution.

Animals↗
PubMed2002

Skeletal muscle fibre type specification during embryonic development.

In the last 10 years an increasing number of studies have provided an insight in the signalling mechanisms underlying myogenesis and fibre type specification during embryonic development: this paper aims to review the most relevant findings. In vertebrates a central role in muscle differentiation is played by the MyoD family, a group of transcription factors which activate transcription of muscle specific genes. In turn MyoD family is expressed in response to inductive signals coming from tissues adjacent to somites, in the first place the notochord and the neural tube. Hedgehog and Wnt are among these inductive signals and they find in the future myoblasts a response pathway which includes Ptc, Smu and Gli. The signalling mechanisms have been analysed in model organisms: mouse, chick. zebrafish and Drosophila. For some factors the orthologs in different species have been found to accomplish similar function, but for some other factors important differences are present: for example in Drosophila twist codes for a transcription factor which promotes myogenesis, whereas its ortholog in mouse tends to prevent or inhibit myogenesis. Conversely, nautilus which is the orholog of MyoD in Drosophila does not have a general function in muscle differentiation, but is required for the differentiation of a limited group of muscle fibres.

Animals↗
PubMed2006

Microarray studies of gene expression in fish.

The use of microarrays for the study of various aspects of fish physiology has seen a spectacular increase in recent years. From early studies with model species, such as zebrafish, to current studies with commercially important species, such as salmonids, catfish, carp, and flatfish, microarray technology has emerged as a key tool for understanding developmental processes as well as basic physiology. In addition, microarrays are being applied to the fields of ecotoxicology and nutrigenomics. A number of different platforms are now available, ranging from microarrays containing cDNA amplicons to oligomers of various sizes. High-density microarrays containing hundreds of thousands of distinct oligomers have been developed for zebrafish and catfish. As this exciting technology advances, so will our understanding of global gene expression in fish. Furthermore, lessons learned from this experimentally tractable group of organisms can also be applied to more advanced organisms such as humans.

Animals↗
PubMed1998

Characterization of whole genome radiation hybrid mapping resources for non-mammalian vertebrates.

Radiation hybrid panels are already available for genome mapping in human and mouse. In this study we have used two model organisms (chicken and zebrafish) to show that hybrid panels that contain a full complement of the donor genome can be generated by fusion to hamster cells. The quality of the resulting hybrids has been assessed using PCR and FISH. We confirmed the utility of our panels by establishing the percentage of donor DNA present in the hybrids. Our hybrid resources will allow inexpensive gene mapping and we expect that this technology can be transferred to many other species. Such successes are providing the basis for a new era of mapping tools, in the form of whole genome radiation hybrid panels, and are opening new possibilities for systematic genome analysis in the animal genetics community.

Animals↗