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PubMed2005

Kidney development and disease in the zebrafish.

Unraveling the molecular pathogenesis of human disease presents many experimental challenges, not the least of which is that experiments on humans are generally frowned upon. Model organisms, including the zebrafish, allow for experimental analysis of gene function and the detailed characterization of disease processes. Zebrafish have matured as a vertebrate model organism now that genetic tools for targeted "knockdowns" and unbiased mutagenesis approaches are in hand. The fish larval pronephros is a relevant kidney in which to pursue many aspects of human kidney development and disease. This short review outlines recent progress in applying the zebrafish pronephros to issues of human health and development.

Animals↗

PubMed2006

Polycystin-2 immunolocalization and function in zebrafish.

Polycystin-2 functions as a cation-permeable transient receptor potential ion channel in kidney epithelial cells and when mutated results in human autosomal dominant polycystic kidney disease. For further exploration of the in vivo functions of Polycystin-2, this study examined its expression and function during zebrafish embryogenesis. pkd2 mRNA is ubiquitously expressed, and its presence in the larval kidney could be confirmed by reverse transcription-PCR on isolated pronephroi. Immunostaining with anti-zebrafish Polycystin-2 antibody revealed protein expression in motile kidney epithelial cell cilia and intracellular cell membranes. Intracellular localization was segment specific; in the proximal nephron segment, Polycystin-2 was localized to basolateral cell membranes, whereas in the caudal pronephric segment, Polycystin-2 was concentrated in subapical cytoplasmic vesicles. Polycystin-2 also was expressed in muscle cells and in a variety of sensory cells that are associated with mechanotransduction, including cells of the ear, the lateral line organ, and the olfactory placodes. Disruption of Polycystin-2 mRNA expression resulted in pronephric kidney cysts, body axis curvature, organ laterality defects, and hydrocephalus-defects that could be rescued by expression of a human PKD2 mRNA. In-frame deletions in the first extracellular loop and C-terminal phosphofurin acidic cluster sorting protein-1 (PACS-1) binding sites in the cytoplasmic tail caused Polycystin-2 mislocalization to the apical cell surface. Unlike zebrafish intraflagellar transport protein (IFT) mutants, cyst formation was not associated with cilia defects and instead correlated with reduced kidney fluid output, expansion of caudal duct apical cell membranes, and occlusion of the caudal pronephric nephron segment.

Amino Acid Sequence↗

PubMed2005

An environmentally relevant concentration of estrogen induces arrest of male gonad development in zebrafish, Danio rerio.

The aim of the present study was to elucidate how full life-cycle exposure to estrogens impacts zebrafish development and reproduction, compared to partial life-cycle exposure only, and whether the estrogen-induced effects in zebrafish are reversible or irreversible. Zebrafish were exposed in a flow-through system to an environmentally relevant concentration (3 ng/L) of the synthetic estrogen 17alpha-ethinylestradiol (EE2) either from fertilization until the all-ovary stage of gonad development (i.e., 42 d postfertilization [DPF] in our experiment) or from fertilization until the reproductive stage (i.e., 118 DPF). Reversibility of the estrogen-induced effects was assessed after 58 d of depuration in EE2-free water until 176 DPE Early life exposure led to a lasting induction of plasma vitellogenin (VTG) in adult females but altered neither the sex ratio nor the reproductive capabilities. Full life-cycle exposure resulted in elevated VTG concentrations and caused gonadal feminization in 100% of exposed fish and thus inhibited reproduction. Two types of ovaries were observed in continuously exposed adult fish, immature ovaries with primary growth stage oocytes only and mature ovaries containing the full range of all oocyte maturation stages. Fish with immature ovaries had plasma VTG levels like control males, while fish with mature ovaries had female-like VTG levels. The effects of full life cycle exposure were at least partly reversible, and 26% of fish of the previous all-female cohort developed fully differentiated testes. These findings suggest that continuous estrogen exposure had arrested the developmental transition of the gonads of genetic males from the early all-ovary stage to functional testes. After the exposure had ceased, however, these males apparently were able to accomplish testicular differentiation.

Animals↗

PubMed2005

Novel biomarkers of perchlorate exposure in zebrafish.

Perchlorate inhibits iodide uptake by thyroid follicles and lowers thyroid hormone production. Although several effects of perchlorate on the thyroid system have been reported, the utility of these pathologies as markers of environmental perchlorate exposures has not been adequately assessed. The present study examined time-course and concentration-dependent effects of perchlorate on thyroid follicle hypertrophy, colloid depletion, and angiogenesis; alterations in whole-body thyroxine (T4) levels; and somatic growth and condition factor of subadult and adult zebrafish. Changes in the intensity of the colloidal T4 ring previously observed in zebrafish also were examined immunohistochemically. Three-month-old zebrafish were exposed to ammonium perchlorate at measured perchlorate concentrations of 0, 11, 90, 1,131, and 11,480 ppb for 12 weeks and allowed to recover in clean water for 12 weeks. At two weeks of exposure, the lowest-observed-effective concentrations (LOECs) of perchlorate that induced angiogenesis and depressed the intensity of colloidal T4 ring were 90 and 1,131 ppb, respectively; other parameters were not affected (whole-body T4 was not determined at this time). At 12 weeks of exposure, LOECs for colloid depletion, hypertrophy, angiogenesis, and colloidal T4 ring were 11,480, 1,131, 90, and 11 ppb, respectively. All changes were reversible, but residual effects on angiogenesis and colloidal T4 ring intensity were still present after 12 weeks of recovery (LOEC, 11,480 ppb). Whole-body T4 concentration, body growth (length and weight), and condition factor were not affected by perchlorate. The sensitivity and longevity of changes in colloidal T4 ring intensity and angiogenesis suggest their usefulness as novel markers of perchlorate exposure. The 12-week LOEC for colloidal T4 ring is the lowest reported for any perchlorate biomarker in aquatic vertebrates.

Angiogenesis Inducing Agents↗

PubMed2003

Visualization of erythrocytes in the zebrafish brain.

We found that erythrocytes of zebrafish have cytoplasmic peroxidase activity. Blood in the zebrafish brain was visualized using a standard peroxidase staining method after formaldehyde fixation. The erythrocytes in the brain were heavily stained, but neurons and glias were not stained at all. This easy method enables the distribution of erythrocytes in the whole brain to be determined, and enables the actual number of erythrocytes in each area in the brain to be calculated. The paths of major, thick blood vessels in zebrafish brain are similar to those in higher vertebrates, however, the distribution of thin blood vessels is different. We also found that the erythrocytes were unevenly distributed in the brain. For example, the density of erythrocytes in the surface layer of the tectum was more than 30-fold higher than in the deeper granular layer. Very few erythrocytes were found in bundles of axons like cranial nerves and the medial longitudinal fascicle. In general, fewer erythrocytes were found in areas near the ventricle, whereas many more were found closer to the surface of the brain. The distribution of erythrocytes in the brains of sleeping, awake and actively moving fish were compared. In the brains of sleeping fish, most of the erythrocytes were present in large vessels. This was not observed in brains of awake or actively moving fish. We found that the blood supply to motor neurons in the ventral horn of the spinal cord increased during active movement compared to that in awake or sleeping fish.

Animals↗

PubMed2000

Use of an IRES bicistronic construct to trace expression of exogenously introduced mRNA in zebrafish embryos.

To understand gene function in developing vertebrate embryos, co-injection of an mRNA for a reporter protein and an mRNA for a testing factor is widely used. However, because of the mosaic segregation of injected nucleic acids during early embryogenesis, whether both mRNAs are translated in the same cell remains uncertain. In the present study, we tested a new system of tracing the expression of a testing gene in zebrafish using an internal ribosomal entry site (IRES) to express two proteins from the same mRNA template, thus eliminating the problem of independent translation observed in co-injection essays. A DNA construct was made for synthesizing bicistronic mRNA for NeuroD, a neurogenic transcription factor, and the enhanced green fluorescent protein (EGFP) reporter. When the bicistronic mRNA for NeuroD and EGFP was injected into zebrafish embryos at one cell stage, all EGFP-expressing embryos showed ectopic expression of neuroD mRNA and the mRNA of its potential downstream gene, islet-1. Thus, the IRES bicistronic mRNA construct might be a more convincing means of analyzing gene function in developing zebrafish embryos.

Animals↗

PubMed2001

Three-color imaging using fluorescent proteins in living zebrafish embryos.

The zebrafish embryo is especially valuable for cell biological studies because of its optical clarity. In this system, use of an in vivo fluorescent reporter has been limited to green fluorescent protein (GFP). We have examined other fluorescent proteins alone or in conjunction with GFP to investigate their efficacy as markers for multi-labeling purposes in live zebrafish. By injecting plasmid DNA containing fluorescent protein expression cassettes, we generated single-, double-, or triple-labeled embryos using GFP, blue fluorescent protein (BFP, a color-shifted GFP), and red fluorescent protein (DsRed, a wild-type protein structurally related to GFP). Fluorescent imaging demonstrates that GFP and DsRed are highly stable proteins, exhibiting no detectable photoinstability, and a high signal-to-noise ratio. BFP demonstrated detectable photoinstability and a lower signal-to-noise ratio than either GFP or DsRed. Using appropriate filter sets, these fluorescent proteins can be independently detected even when simultaneously expressed in the same cells. Multiple labels in individual zebrafish cells open the door to a number of biological avenues of investigation, including multiple, independent tags of transgenic fish lines, lineage studies of wild-type proteins expressed using polycistronic messages, and the detection of protein-protein interactions at the subcellular level using fluorescent protein fusions.

Animals↗

PubMed2003

Zebrafish sperm cryopreservation with N,N-dimethylacetamide.

High fecundity, rapid generation time, and external development of optically clear embryos make the zebrafish (Danio rerio) a convenient vertebrate model for genetic, developmental, and disease studies. Efficient sperm cryopreservation enhances the zebrafish model system by optimizing productive use of facility space, extending the reproductive lifetime of males, providing an alternative to live stocks for strain recovery, and ensuring the survival of valuable mutant lines. Here we identify a cryoprotective medium, 10% N,N-dimethylacetamide (DMA) (v/v) diluted in buffered sperm motility-inhibiting solution (BSMIS), as well as parameters for zebrafish sperm cryopreservation that enhance cryopreservation efficiency and significantly increase the yield of live embryos from archived stocks. Our experiments emphasize the effect of the ratio of sperm and medium volume and the use of large egg clutches to maximize the recovery of viable embryos.

Acetamides↗

PubMed2005

New ways to admire zebrafish: progress in functional genomics research methodology.

The main challenge of the post-genomic era is to functionally characterize genes identified by the genome sequencing projects. Model organisms, including zebrafish, are indispensable for this demanding task. Zebrafish has been successfully incorporated into large-scale genetic screens due to the optical clarity of the embryos and their accessibility to various experimental techniques throughout development. The attractiveness of the zebrafish as a model organism is enhanced by the availability of continuously improving genomic tools and methodologies for functional characterization of the gene. This article will highlight the current techniques used in the field, with the focus on transgenesis.

Animals↗

PubMed2000

A contig map of the Mhc class I genomic region in the zebrafish reveals ancient synteny.

In contrast to the human and mouse Mhc, in which the clusters of class I and class II loci reside in close vicinity to one another, in the zebrafish, Danio rerio, they are found in different linkage groups. Chromosome walking using BAC (bacterial artificial chromosome) and PAC (P1 artificial chromosome) clones reveals the zebrafish class I region to occupy a segment of approximately 450 kb and to encompass at least 19 loci. These include three class I (Dare-UDA, -UEA, -UFA), five proteasome subunit beta (PSMB8, -9A, -9C, -11, -12), two TAPs (TAP2A, TAP2B), and one TAP binding protein (TAPBP). This arrangement contrasts with the arrangements found in human and mouse Mhc, in which the orthologues of the PSMB, TAP, and TAPBP loci reside within the class II region. In addition to this main zebrafish class I contig, a shorter contig of about 150 kb contains two additional class I (UBA, UCA) and at least five other loci. It probably represents a different haplotype of part of the class I region. The previously identified UAA gene shares an identical 5' part with UEA, but the two genes differ in their 3' parts. One of them is probably the result of an unequal crossing over. The described organization has implications for the persistence of syntenic relationships, coevolution of loci, and interpretation of the origin of the human/mouse Mhc organization.

Animals↗

PubMed2005

Specific RNAi mediated gene knockdown in zebrafish cell lines.

Here we demonstrate highly efficient RNA interference in ZFL, SJD and ZF4 cell lines derived from adult and embryonic zebrafish Danio rerio. Microinjection of siRNAs resulted in silencing in almost 100% of cells while transfection using cationic liposomes led to silencing in 30%. Use of siRNAs against zebrafish lamin A, lamin B2 and the motor protein Eg5, led to knockdown of the target genes with the specific phenotypes expected from prior studies in mammalian cells. In contrast injection of lamin A, GL2 and eGFP siRNAs into zebrafish embryos resulted in morphological defects, abnormal development and early death of most embryos. The results indicate unspecific responses to siRNAs in the embryo but a fully developed and active RNAi machinery in cell lines.

Animals↗

PubMed1999

Stimulus dependence of the development of the zebrafish (Danio rerio) vestibular system.

It has been suggested that stimulus dependence is a general feature of all developing sensory systems. We tested this idea for the developing zebrafish vestibular system using a bioreactor the National Aeronautic and Space Agency designed to simulate microgravity for cells in culture on earth. We replaced the culture medium with aquarium water and maintained zebrafish eggs/hatchlings in the bioreactor for either 72 or 96 h postfertilization. These experimental animals displayed a swimming behavior that was indistinguishable from the control animals when illuminated from above. However, when illuminated from below, experimental animals swam not only dorsal surface up, but also lying on their side; they corkscrewed, swam vertical loops, and occasionally even swam upside down. When incubated in the bioreactor for 96 h, the saccular otolith was significantly smaller than normal, suggesting that otolith development was either delayed or slower than normal. When incubated in the bioreactor for 72 h, some animals were missing one or more otoliths. In contrast, control animals all had two otoliths on each side. This supports the idea that otolith development was delayed. Immediately upon removal from the bioreactor at 96 h, experimental animals showed some signs of compensatory eye rotation, but with a much less clear relationship between the orientation of the eye and the direction of gravity than the age-matched control animals. This difference was still obvious 1 day later. These results support the idea that development of the vestibular system in zebrafish is dependent on the presence of the normal stimulus the system is designed to detect.

Animals↗

PubMed1999

Defective calmodulin-dependent rapid apical endocytosis in zebrafish sensory hair cell mutants.

Vertebrate mechanosensory hair cells contain a narrow "pericuticular" zone which is densely populated with small vesicles between the cuticular plate and cellular junctions near the apical surface. The presence of many cytoplasmic vesicles suggests that the apical surface of hair cells has a high turnover rate. The significance of intense membrane trafficking at the apical surface is not known. Using a marker of endocytosis, the styryl dye FM1-43, this report shows that rapid apical endocytosis in zebrafish lateral line sensory hair cells is calcium and calmodulin dependent and is partially blocked by the presence of amiloride and dihydrostreptomycin, known inhibitors of mechanotransduction channels. As seen in lateral line hair cells, sensory hair cells within the larval otic capsule also exhibit rapid apical endocytosis. Defects in internalization of the dye in both lateral line and inner ear hair cells were found in five zebrafish auditory/vestibular mutants: sputnik, mariner, orbiter, mercury, and skylab. In addition, lateral line hair cells in these mutants were not sensitive to prolonged exposure to streptomycin, which is toxic to hair cells. The presence of endocytic defects in the majority of zebrafish mechanosensory mutants points to a important role of apical endocytosis in hair cell function.

Acridine Orange↗

PubMed2000

Vertebrate ancient-long opsin: a green-sensitive photoreceptive molecule present in zebrafish deep brain and retinal horizontal cells.

Nonretinal/nonpineal photosensitivity has been found in the brain of vertebrates, but the molecular basis for such a "deep brain" photoreception system remains unclear. We conducted an extensive search for brain opsin cDNAs of the zebrafish (Danio rerio), a useful animal model for genetic studies, and we have isolated a partial cDNA clone encoding an ortholog of vertebrate ancient (VA) opsin, the function of which is unknown. Subsequent characterization revealed the occurrence of two kinds of mRNAs encoding putative splicing variants, VA and VA-Long (VAL) opsin, the latter of which is a novel variant of the former. Both opsins shared a common core sequence in the membrane-spanning domains, but VAL-opsin had a C-terminal tail much longer than that of VA-opsin. Functional reconstitution experiments on the recombinant proteins showed that VAL-opsin with bound 11-cis-retinal is a green-sensitive pigment (lambdamax approximately 500 nm), whereas VA-opsin exhibited no photosensitivity even in the presence of 11-cis-retinal. Immunoreactivity specific to this functionally active VAL-opsin was localized at a limited number of cells surrounding the diencephalic ventricle of central thalamus, and these cells were distributed over approximately 200 micrometer along the rostrocaudal axis. Taken together with the previous study on the locus of the teleost brain photosensitivity (von Frisch K, 1911), it is strongly suggested that the VAL-positive cells in the zebrafish brain represent the deep brain photoreceptors. The VAL-specific immunoreactivity was also detected in a subset of non-GABAergic horizontal cells in the zebrafish retina. The existence of VAL-opsin, a new member of the rhodopsin superfamily, in these tissues may indicate its multiple roles in visual and nonvisual photosensory physiology.

Animals↗

PubMed2000

Chitin oligosaccharides as candidate patterning agents in zebrafish embryogenesis.

In this work we investigate the possible function of N-acetyl-chitooligosaccharides (NACOs) produced during zebrafish (Danio rerio) development. First, we show that NACOs are synthesized in vivo during early embryogenesis in the zebrafish. Second, we demonstrate that injection of a pure bacterial chitinase into one-cell stage embryos elicits developmental defects in which the posterior trunk and tail of developing embryo are severely affected. In addition, an endogenous chitinase activity detected both intra- and extracellularly is described, suggesting that cells may secrete it into the extracellular space. Moreover, this compartmentalization appears to be functionally relevant as inhibition of the extracellular, but not the intracellular, endogenous chitinase activity causes morphological defects similar to those seen in embryos injected with chitinase 63. Finally, analysis of the expression of the zebrafish ZDG42 gene, which has been suggested to be involved in synthesis of NACOs, is described. Transcripts are detected from late blastula stage, during gastrulation, and move as an anterior-posterior wave of expression in adaxial mesoderm during somitogenesis.

Acetylglucosamine↗

PubMed2001

Analysis of the activity-deprived zebrafish mutant macho reveals an essential requirement of neuronal activity for the development of a fine-grained visuotopic map.

The formation of a retinotopic map is thought to involve an activity-independent molecular phase for early steps of both axon pathfinding and projection and a later phase in which cross talk between retinal ganglion cells (RGCs) and tectal neurons modifies and refines the neuronal connections. We report that the maturation of the retinotopic map in the zebrafish tectum involves activity-dependent processes. Zebrafish larvae mutant for the gene macho (mao) lack neuronal activity in RGCs and also display an enlarged retinotectal projection field but no significant increase in single axon length. This morphological defect can be phenocopied by raising larvae under TTX-induced neural impulse blockade. The effect of activity deprivation is dependent on the developmental stage. The projection phenotype in mao as well as in the TTX-treated larvae develops between 4 and 6 d post-fertilization (dpf), after complete tectal coverage is first achieved. Electrophysiological recordings of RGCs in wild-type and mao zebrafish larvae reveal a temporally regulated reduction of sodium current in the mutant between 5 and 6 dpf. This coincides with the time of the axonal projection shifting on the tectum to compensate for the disparate growth patterns of the retina and the tectum. Our genetic and physiological analyses suggest a model in which neuronal activity in RGCs is needed for the establishment of morphological plasticity.

Animals↗

PubMed2001

Cytoplasmic expression of ribozyme in zebrafish using a T7 autogene system.

A cytoplasmic ribozyme expression system, based on codelivery of a ribozyme vector, a T7 autogene vector, and T7 RNA polymerase (RNAP), has been developed and used to generate a specific phenotype in zebrafish by targeting a no tail (ntl) mRNA. The expression of the no tail ribozyme sequence is under the control of a tandem of two promoters: The T7 promoter and an adenoviral va 1 (pol III) promoter. The coinjection of the ribozyme vector pT7vaRz, the T7 autogene vector pT7T7, and the T7 RNAP resulted in rapid synthesis of the ribozyme against the ntl mRNA in the cytoplasm of the injected zebrafish embryos, generating no tail phenotypes in up to 10-20% of the injected embryos. The phenotypic change rates have been found to be related to the concentrations of the plasmid vectors and T7 RNAP injected and to the ratios of the three injected components. This cytoplasmic ribozyme expression system may be useful for efficiently targeting other mRNA and for various biomedical applications. These potential applications may include rapid identification of biological functions of novel genes from zebrafish and humans based on partial gene sequence information and gene therapy of genetic and acquired diseases.

Adenoviridae↗

PubMed2002

Repellent guidance of regenerating optic axons by chondroitin sulfate glycosaminoglycans in zebrafish.

We analyzed the role of chondroitin sulfate (CS) glycosaminoglycans, putative inhibitors of axonal regeneration in mammals, in the regenerating visual pathway of adult zebrafish. In the adult, CS immunoreactivity was not detectable before or after an optic nerve crush in the optic nerve and tract but was constitutively present in developing and adult nonretinorecipient pretectal brain nuclei, where CSs may form a boundary preventing regenerating optic fibers from growing into these inappropriate locations. Enzymatic removal of CSs by chondroitinase ABC after optic nerve crush significantly increased the number of animals showing erroneous growth of optic axons into the nonretinorecipient magnocellular superficial/posterior pretectal nucleus (83% vs 42% in controls). In vitro, a substrate border of CSs, but not heparan sulfates, strongly repelled regenerating retinal axons from adult zebrafish. We conclude that CSs contribute to repellent axon guidance during regeneration of the optic projection in zebrafish.

Animals↗