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PubMed2006

The developmental neurotoxicity of fipronil: notochord degeneration and locomotor defects in zebrafish embryos and larvae.

Fipronil is a phenylpyrazole insecticide designed to selectively inhibit insect gamma-aminobutyric acid (GABA) receptors. Although fipronil is often used in or near aquatic environments, few studies have assessed the effects of this neurotoxicant on aquatic vertebrates at sensitive life stages. We explored the toxicological effects of fipronil on embryos and larvae using the zebrafish (Danio rerio) experimental model system. Embryos exposed to fipronil at nominal concentrations at or above 0.7 microM (333 mug/l) displayed notochord degeneration, shortening along the rostral-caudal body axis, and ineffective tail flips and uncoordinated muscle contractions along the body axis in response to touch. This phenotype closely resembles zebrafish locomotor mutants of the accordion class and is consistent with loss of reciprocal inhibitory neurotransmission by glycinergic commissural interneurons in the spinal cord. Consistent with the hypothesis that notochord degeneration may be due to abnormal mechanical stress from muscle tetany, the expression patterns of gene and protein markers specific to notochord development were unaffected by fipronil. Moreover, the degenerative effects of fipronil (1.1 microM) were reversed by coexposure to the sodium channel blocker MS-222 (0.6mM). The notochord effects of fipronil were phenocopied by exposure to 70 microM strychnine, a glycinergic receptor antagonist. In contrast, exposure to gabazine, a potent vertebrate GABA(A) antagonist, resulted in a hyperactive touch response but did not cause notochord degeneration. Although specifically developed to target insect GABA receptors with low vertebrate toxicity, our results suggest that fipronil impairs the development of spinal locomotor pathways in fish by inhibiting a structurally related glycine receptor subtype. This represents an unanticipated and potentially novel mechanism for fipronil toxicity in vertebrates.

Animals↗

PubMed2005

Dichloroacetate-induced developmental toxicity and production of reactive oxygen species in zebrafish embryos.

Dichloroacetate (DCA) is one of the toxic by products that are formed during the chlorine disinfection process of drinking water. In this study, the developmental toxicity of DCA has been determined in zebrafish (Danio rerio) embryos. Embryos were exposed to different concentrations (4, 8, 16, and 32 mM) of the compound at the 4 h postfertilization (hpf) stage of development, and were observed for different developmental toxic effects at 8, 24, 32, 55, 80, and 144 hpf. Exposure of embryos to 8-32 mM of DCA resulted in significant increases in the heart rate and blood flow of the 55 and 80 hpf embryos that turned into significant decreases at the 144 hpf time point. At 144 hpf, malformations of mouth structure, notochord bending, yolk sac edema and behavioral effects including perturbed swimming and feeding behaviors were also observed. DCA was also found to produce time- and concentration-dependent increases in embryonic levels of superoxide anion (O2*-) and nitric oxide (NO), at various stages of development. The results of the study suggest that DCA-induced developmental toxic effects in zebrafish embryos are associated with production of reactive oxygen species in those embryos.

Animals↗

PubMed1998

Notochord regulates cardiac lineage in zebrafish embryos.

We focus here upon regulation by the notochord of myocardial cell fate in zebrafish. Myocardial precursors, defined by lineage tracing in the living embryo, are in the lateral plate mesoderm adjacent to the notochord-prechordal plate junction. Interestingly, the anterior end of the notochord corresponds to the posterior extent of the heart progenitor field, defined by this lineage analysis. This suggested that the notochord might suppress, or the prechordal plate might enhance, the cardiogenic fate. Nkx2.5 expression is, in the zebrafish embryo, closely correlated with the position of myocardial precursors, which reside adjacent to the notochord-prechordal plate junction. This expression, however, is extinguished in the region posterior to this junction, a region normally not contributing cells to the heart. Laser ablation of the notochord tip between the 4-somite and 12-somite stage causes posterior expansion of the Nkx2. 5-expressing region. The ntl mutation of the notochord is associated with posterior extension of Nkx2.5 expression. Lineage tracking, by laser activation of caged fluoresceinated dextran, confirms that, normally, lateral plate cells next to the notochord do not contribute progeny to the heart. After anterior notochord ablation, these cells are redirected to a heart cell fate. These data suggest that the anterior notochord delimits the posterior extent of the heart field by suppressing the heart cell fate.

Animals↗

PubMed2002

2,3,7,8-tetrachlorodibenzo-p-dioxin toxicity in the zebrafish embryo: local circulation failure in the dorsal midbrain is associated with increased apoptosis.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on local circulation and apoptosis in the midbrain were investigated in zebrafish (Danio rerio) embryos during early development. Embryos were exposed to TCDD from 24 h post fertilization (hpf) until observation, in water maintained at 28.5 degrees C. TCDD decreased blood flow in the mesencephalic vein, the only vessel perfusing the dorsal midbrain of the embryo. At 50 hpf, blood flow was maximally reduced in this vessel and gradually returned to the control level at 60 hpf. In contrast, blood flows in the trunk and in other vessels of the head of the embryo did not significantly change until 72 hpf. Furthermore, TCDD exposure caused apoptosis in the midbrain at 60 hpf, and the TCDD dose response relationship for this effect was similar to that for reduced blood flow in the mesencephalic vein at 50 hpf. The effects of TCDD on apoptosis in the midbrain, but not on blood flow, were abolished by Z-VAD-FMK, a general caspase inhibitor. TCDD effects on both endpoints were mimicked by beta-naphthoflavone (BNF), an aryl hydrocarbon receptor (AHR) agonist, and almost abolished by concomitant exposure to TCDD and alpha-naphthoflavone (ANF), an AHR antagonist. Concomitant exposure to TCDD and either an inhibitor of cytochrome P450 (CYP) (SKF525A or miconazole) or an antioxidant (N-acetylcysteine or ascorbic acid) inhibited these effects of TCDD. The incidence of apoptosis in the midbrain was inversely related to blood flow in this brain region following these various treatments and graded TCDD exposure concentrations (r = -0.91). The same range of TCDD exposure concentrations that reduced blood flow and increased apoptosis in the midbrain greatly enhanced CYP1A mRNA expression and immunoreactivity at 50 hpf in endothelial cells of blood vessels including the mesencephalic vein and the heart, but not the brain parenchyma. Taken together, these results suggest that TCDD induces apoptosis in the midbrain of the zebrafish embryo secondary to local circulation failure, which could be related to AHR activation, induction of CYP1A, and oxidative stress.

Animals↗

PubMed2006

Supraspinal input is dispensable to generate glycine-mediated locomotive behaviors in the zebrafish embryo.

The anatomy of the developing zebrafish spinal cord is relatively simple but, despite this simplicity, it generates a sequence of three patterns of locomotive behaviors. The first behavior exhibited is spontaneous movement, then touch-evoked coiling, and finally swimming. Previous studies in zebrafish have suggested that spontaneous movements occur independent of supraspinal input and do not require chemical neurotransmission, while touch-evoked coiling and swimming depend on glycinergic neurotransmission as well as supraspinal input. In contrast, studies in other vertebrate preparations have shown that spontaneous movement requires glycine and other neurotransmitters and that later behaviors do not require supraspinal input. Here, we use lesion analysis combined with high-speed kinematic analysis to re-examine the role of glycine and supraspinal input in each of the three behaviors. We find that, similar to other vertebrate preparations, supraspinal input is not essential for spontaneous movement, touch-evoked coiling, or swimming behavior. Moreover, we find that blockade of glycinergic neurotransmission decreases the rate of spontaneous movement and impairs touch-evoked coiling and swimming, suggesting that glycinergic neurotransmission plays critical yet distinct roles for individual patterns of locomotive behaviors.

Animals↗

PubMed2005

Muscular contractions in the zebrafish embryo are necessary to reveal thiuram-induced notochord distortions.

Dithiocarbamates form a large group of chemicals that have numerous uses in agriculture and medicine. It has been reported that dithiocarbamates, including thiuram (tetramethylthiuram disulfide), cause wavy distortions of the notochord in zebrafish and other fish embryos. In the present study, we investigated the mechanism underlying the toxicity of thiuram in zebrafish embryos. When embryos were exposed to thiuram (2-1000 nM: 0.48-240 microg/L) from 3 h post fertilization (hpf) (30% epiboly) until 24 hpf (Prim-5), all embryos develop wavy notochords, disorganized somites, and have shortened yolk sac extensions. The thiuram response was specific and did not cause growth retardation or mortality at 24 hpf. The thiuram-dependent responses showed the same concentration dependence with a waterborne EC50 values of approximately 7 nM. Morphometric measurements revealed that thiuram does not affect the rate of notochord lengthening. However, the rate of overall body lengthening was significantly reduced in thiuram-exposed animals. Other dithiocarbamates, such as ziram, caused similar malformations to thiuram. While expression of genes involved in somitogenesis was not affected, the levels of notochord-specific transcripts were altered after the onset of malformations. Distortion of the notochord started precisely at 18 hpf, which is concomitant with onset of spontaneous rhythmic trunk contractions. Abolishment of spontaneous contractions using tricaine, alpha-bungarotoxin, and a paralytic mutant sofa potato, resulted in normal notochord morphology in the presence of thiuram. These results indicate that muscle activity is necessary to reveal the underlying functional deficit and suggest that the developmental target of dithiocarbamates impairs trunk plasticity through an unknown mechanism.

Animals↗

PubMed2000

Motoneuron activity patterns related to the earliest behavior of the zebrafish embryo.

As a first step in the study of the developing motor circuitry of the embryonic zebrafish spinal cord, we obtained patch-clamp recordings in vivo from identified motoneurons in curarized embryos from the onset of the first motor behavior. At an early developmental stage in which embryos showed slow and repetitive spontaneous contractions of the trunk, motoneurons showed periodic depolarizations that triggered rhythmic bursts of action potentials with a frequency and duration that were consistent with those of the spontaneous contractions. The periodic depolarizations were blocked by tetrodotoxin or Cd(2+). Surprisingly, the contractions and periodic depolarizations were insensitive to general blockade of synaptic transmission (by elevated Mg(2+) and reduced Ca(2+), or by Co(2+)) and to selective blockade of the major neurotransmitter receptors of the mature spinal cord (acetylcholine, GABA(A), NMDA, AMPA/kainate, and glycine). The periodic depolarizations were suppressed by heptanol or by intracellular acidification, treatments that are known to uncouple gap junctions, indicating that electrotonic synapses could underlie the earliest motor behavior. A few hours later, most motoneurons already showed a new pattern of repetitive activity consisting of bursts of glycinergic synaptic events, but these were not necessary for the spontaneous contractions. Transecting the spinal cord at the hindbrain border did not affect the rhythmic activity patterns of the motoneurons. We suggest that spontaneous contractions of the zebrafish embryo are mediated by an early spinal circuit that is independent of the main neurotransmitter systems and descending hindbrain projections that are required for locomotion in the mature vertebrate spinal cord.

Aging↗

PubMed1997

Musculoskeletal patterning in the pharyngeal segments of the zebrafish embryo.

The head skeleton and muscles of the zebrafish develop in a stereotyped pattern in the embryo, including seven pharyngeal arches and a basicranium underlying the brain and sense organs. To investigate how individual cartilages and muscles are specified and organized within each head segment, we have examined their early differentiation using Alcian labeling of cartilage and expression of several molecular markers of muscle cells. Zebrafish larvae begin feeding by four days after fertilization, but cartilage and muscle precursors develop in the pharyngeal arches up to 2 days earlier. These chondroblasts and myoblasts lie close together within each segment and differentiate in synchrony, perhaps reflecting the interdependent nature of their patterning. Initially, cells within a segment condense and gradually become subdivided into individual dorsal and ventral structures of the differentiated arch. Cartilages or muscles in one segment show similar patterns of condensation and differentiation as their homologues in another, but vary in size and shape in the most anterior (mandibular and hyoid) and posterior (tooth-bearing) arches, possibly as a consequence of changes in the timing of their development. Our results reveal a segmental scaffold of early cartilage and muscle precursors and suggest that interactions between them coordinate their patterning in the embryo. These data provide a descriptive basis for genetic analyses of craniofacial patterning.

Animals↗

PubMed2004

fgf17b, a novel member of Fgf family, helps patterning zebrafish embryos.

Fibroblast growth factors (Fgfs) play important roles in the pattern formation of early vertebrate embryos. We have identified a zebrafish ortholog of human FGF17, named fgf17b. The first phase of fgf17b expression occurs in the blastodermal margin of late blastulae and in the embryonic shield of early gastrulae. The second phase starts after the onset of segmentation, mainly in the presomitic mesoderm and newly formed somites. Injection of fgf17b mRNA into one-cell embryos induces expression of the mesodermal marker no tail (ntl) and rescues ntl expression suppressed by overexpression of lefty1 (lft1). Overexpression of fgf17b dorsalizes zebrafish gastrulae by enhancing expression of chordin (chd), which is an antagonist of the ventralizing signals BMPs. In addition, overexpression of fgf17b posteriorizes the neuroectoderm. Simultaneous knockdown of fgf17b and fgf8 with antisense morpholinos results in reduction of chd and ntl. Knockdown of fgf17b can alleviate inhibitory effect of ectopic expression of fgf3 on otx1. These data together suggest that Fgf17b plays a role in early embryonic patterning. We also demonstrate that fgf17b and fgf8 have stronger mesoderm inducting activity than fgf3, whereas fgf17b and fgf3 have stronger activity in posteriorizing the neuroectoderm than fgf8. Like fgf8, activation of fgf17b expression depends on Nodal signaling.

Animals↗

PubMed2002

Patterning of angiogenesis in the zebrafish embryo.

Little is known about how vascular patterns are generated in the embryo. The vasculature of the zebrafish trunk has an extremely regular pattern. One intersegmental vessel (ISV) sprouts from the aorta, runs between each pair of somites, and connects to the dorsal longitudinal anastomotic vessel (DLAV). We now define the cellular origins, migratory paths and cell fates that generate these metameric vessels of the trunk. Additionally, by a genetic screen we define one gene, out of bounds (obd), that constrains this angiogenic growth to a specific path. We have performed lineage analysis, using laser activation of a caged dye and mosaic construction to determine the origin of cells that constitute the ISV. Individual angioblasts destined for the ISVs arise from the lateral posterior mesoderm (LPM), and migrate to the dorsal aorta, from where they migrate between somites to their final position in the ISVs and dorsal longitudinal anastomotic vessel (DLAV). Cells of each ISV leave the aorta only between the ventral regions of two adjacent somites, and migrate dorsally to assume one of three ISV cell fates. Most dorsal is a T-shaped cell, based in the DLAV and branching ventrally; the second constitutes a connecting cell; and the third an inverted T-shaped cell, based in the aorta and branching dorsally. The ISV remains between somites during its ventral course, but changes to run mid-somite dorsally. This suggests that the pattern of ISV growth ventrally and dorsally is guided by different cues. We have also performed an ENU mutagenesis screen of 750 mutagenized genomes and identified one mutation, obd that disrupts this pattern. In obd mutant embryos, ISVs sprout precociously at abnormal sites and migrate anomalously in the vicinity of ventral somite. The dorsal extent of the ISV is less perturbed. Precocious sprouting can be inhibited in a VEGF morphant, but the anomalous site of origin of obd ISVs remains. In mosaic embryos, obd somite causes adjacent wild-type endothelial cells to assume the anomalous ISV pattern of obd embryos. Thus, the launching position of the new sprout and its initial trajectory are directed by inhibitory signals from ventral somites. Zebrafish ISVs are a tractable system for defining the origins and fates of vessels, and for dissecting elements that govern patterns of vessel growth.

Animals↗

PubMed1995

Wnt4 affects morphogenesis when misexpressed in the zebrafish embryo.

The Wnts are a family of secreted glycoproteins involved in cell-cell signalling and pattern formation during development, although the extent to which various Wnts are functionally equivalent remains unclear. We have cloned zebrafish (Danio rerio) wnt4, characterized its expression, and compared its activity relative to other Wnts. The wnt4 transcript is first detected early in somitogenesis, in the dorsocaudal region of the forebrain, and then appears in the dorsal and lateral regions of the caudal hindbrain and neural keel. During somitogenesis, wnt4 appears in the floor plate, and this expression is absent in cyclops mutants, which lack floor plate. wnt4 is also expressed in the developing pronephros and gill slit. To characterize the biological activity of wnt4, synthetic zebrafish wnt4 mRNA was injected into embryos of zebrafish and Xenopus laevis. The phenotypic effects of misexpression in the zebrafish include cyclopia, misfolding in the brain, and an anteriorly forking notochord. Comparison of the phenotypes arising from misexpression of wnt4 and Xwnt-5A in both organisms suggests close parallels in the response to these Wnts. Our data suggest that wnt4, like Xwnt-5A, inhibits cell movements, and that these Wnts define a functional class distinct from the class which includes Wnt-1, Xwnt-3A and Xwnt-8.

Amino Acid Sequence↗

PubMed2001

Analysis of pancreatic development in living transgenic zebrafish embryos.

Using DNA constructs containing regulatory sequences of the zebrafish Pdx-1 and insulin genes, germline transgenic zebrafish expressing the green fluorescent protein (GFP) reporter gene in the pancreas were generated. For both constructs, the GFP expression patterns in transgenic embryos were consistent with the mRNA expression patterns detected by RNA in situ hybridization. A deletion promoter analysis revealed that positive and negative cis-acting elements were involved in regulation of insulin gene expression. Three-dimensional reconstructions imaged from living embryos using two-photon laser-scanning microscopy (TPLSM) demonstrated that the zebrafish pancreas is formed from a single dorsal pancreatic cell mass. This is in contrast to mammals where the pancreas derives from both dorsal and ventral anlage. These transgenic fish should be useful for in vivo studies of factors involved in specifying and regulating pancreatic development and function.

5' Untranslated Regions↗

PubMed2006

Trout Ea4- or human Eb-peptide of pro-IGF-I disrupts heart, red blood cell, and vasculature development in zebrafish embryos.

E-peptide of the pro-insulin-like growth factor (pro-IGF)-I is produced by proteolytic cleavage of the pro-hormone in post-translational processing. Introduction of a transgene encoding a secreted form of rtEa4- or hEb-peptide into newly fertilized zebrafish (Danio rerio) eggs by electroporation or microinjection resulted in embryos with abnormal cardiovascular features and reduced red blood cells and vasculature. Two different phenocopies of heart developmental defects were observed: (i) Group I embryos exhibited heart development arrested at the heart muscle stage and (ii) group II embryos exhibited heart development arrested at the heart tube stage. Both groups of embryos also exhibited reduction of red blood cells and vasculature. The mRNA levels of genes essential for heart development (GATA 5 and NKX2.5), hematopoiesis (GATA 1 and GATA 2), and vasculogenesis (VEGF) in normal and defective embryos were determined by quantitative real-time RT-PCR at 36 hr post-fertilization (hpf). Significant reduction of GATA 5, NKX2.5, GATA 1, GATA 2, and VEGF mRNA levels was observed in both groups of defective embryos. These results suggest that overexpression of rtEa4 or hEb transgene in zebrafish embryos disrupts heart development, hematopoiesis, and vasculogenesis by reducing the levels of GATA 5, NKX2.5, GATA 1, GATA 2, and VEGF mRNA.

Animals↗

PubMed2003

Expression of a novel type I keratin, DAPK-1 in the dorsal aorta and pronephric duct of the zebrafish embryos.

We isolated a novel cytokeratin gene of zebrafish (Danio rerio), DAPK-1 closely related to other vertebrate type I cytokeratin genes. Zygotic transcription starts at the sphere stage. After the mid-blastula stage, DAPK-1 is expressed in all surface cells, notably in those of the outer enveloping layer. DAPK-1 messages are also present specifically during the segmentation, pharyngula, and hatching periods. In particular, after 24 h post-fertilization, its expression is restricted to the developing eye region, otic vesicle, pectoral fin, dorsal aorta, and pronephric duct. In the mindbomb mutant embryo that has defects in the dorsal aorta development, DAPK-1 transcripts are not detected in the dorsal aorta and pronephric duct. The characteristic expression pattern of DAPK-1 may facilitate more detailed studies related to the morphogenesis of dorsal aorta and pronephric duct.

Amino Acid Sequence↗

PubMed2005

Destabilization of DeltaNp63alpha by Nedd4-mediated ubiquitination and Ubc9-mediated sumoylation, and its implications on dorsoventral patterning of the zebrafish embryo.

We have recently identified the p53-related DeltaNp63 gene as a transcriptional target of Bmp signaling that encodes a transcriptional repressor blocking neural development in the zebrafish ectoderm. However, in contrast to Bmps, the neural-repressing effect of forced DeltaNp63alpha expression is restricted to the presumptive forebrain, while posterior regions of the brain are not affected. Here, we show that this is due to instability of DeltaNp63alpha protein on the dorsal side of the embryo. In a yeast-two-hybrid screen, we isolated two DeltaNp63alpha-modifying enzymes, the SUMO-conjugating enzyme Ubc9 and the ubiquitin ligase Nedd4. The proteins bind to distinct sites in the C-terminal region of DeltaNp63alpha, which are absent in the shorter and more stable DeltaNp63gamma isoform. Similarly, mutant versions of DeltaNp63alpha unable to bind Nedd4 or Ubc9 are stabilized. DeltaNp63alpha is sumoylated and ubiquitinated both in HEK293 cells and in zebrafish embryos, and Nedd4 promotes ubiquitination and instability of DeltaNp63alpha protein, with lysine residue 637 serving as a potential alternative sumoylation and ubiquitination site that is crucial for DeltaNp63alpha destabilization. In zebrafish, ubc9.1 and nedd4 show restricted expression on the dorsal side of the embryo, where DeltaNp63alpha instability can be overcome upon blockage of endogenous Nedd4 activity, or upon injection of mutant versions of DeltaNp63alpha that are unable to bind Nedd4 or Ubc9. This results in a more widespread neural repression, affecting the entire Bmp-sensitive neuroectoderm. In sum, our data indicate that DeltaNp63alpha is ubiquitinated in a Nedd4- and sumoylated in a Ubc9-dependent fashion, and that these modifications can regulate DeltaNp63alpha stability in the zebrafish ectoderm.

Amino Acid Sequence↗

PubMed2006

The Na+/PO4 cotransporter SLC20A1 gene labels distinct restricted subdomains of the developing pronephros in Xenopus and zebrafish embryos.

The embryonic pronephric kidneys of Xenopus and zebrafish serve as models to study vertebrate nephrogenesis. Recently, multiple subdomains within the Xenopus pronephros have been defined based on the expression of several transport proteins. In contrast, very few studies on the expression of renal transporters have been conducted in zebrafish. We have recently shown that the anterior and posterior segments of the zebrafish pronephric duct may correspond to the proximal tubule and distal tubule/duct compartments of the Xenopus and higher vertebrate pronephros, respectively. Here, we report the embryonic expression pattern of the Na(+)/PO(4) cotransporter SLC20A1 (PiT1/Glvr-1) gene encoding a type III sodium-dependent phosphate cotransporter in Xenopus and zebrafish. In Xenopus, SLC20A1 mRNA is expressed in the somitic mesoderm and lower level of expression is detected in the neural tube, eye, and neural crest cells. From stage 25, SLC20A1 is also detectable in the developing pronephros where expression is restricted to the late portion of the distal pronephric tubules. In zebrafish, SLC20A1 is transcribed from mid-somitogenesis in the anterior part of the pronephros where its expression corresponds to the rostral portion of the expression of other proximal tubule-specific markers. Outside the pronephros, lower level of SLC20A1 expression is also observed in the posterior cardinal and caudal veins. Based on the SLC20A1 expression domain and that of other transporters, four segments have been defined within the zebrafish pronephros. Together, our data reveal that the zebrafish and Xenopus pronephros have non-identical proximo-distal organizations.

Animals↗

PubMed1997

Water distribution and permeability of zebrafish embryos, Brachydanio rerio.

Teleost embryos have not been successfully cryopreserved. To formulate successful cryopreservation protocols, the distribution and cellular permeability to water must be understood. In this paper, the zebrafish (Brachydanio rerio) was used as a model for basic studies of the distribution to permeability to water. These embryos are a complex multi-compartmental system composed of two membrane-limited compartments, a large yolk (surrounded by the yolk syncytial layer) and differentiating blastoderm cells (each surrounded by a plasma membrane). Due to the complexity of this system, a variety of techniques, including magnetic resonance microscopy and electron spin resonance, was used to measure the water in these compartments. Cellular water was distributed unequally in each compartment. At the 6-somite stage, the percent water (V/V) was distributed as follows: total in embryo = 74%, total in yolk = 42%, and total in blastoderm = 82%. A one-compartment model was used to analyze kinetic, osmotic shrinkage data and determine a phenomenological water permeability parameter, Lp, assuming intracellular isosmotic compartments of either 40 or 300 mosm. This analysis revealed that the membrane permeability changed (P < 0.05) during development. During the 75% epiboly to 3-somite stage, the mean membrane permeability remained constant (Lp = 0.022 +/- 0.002 micron x min-1atm-1 [mean +/- S.E.M.] assuming isosmotic is 40 mosm or Lp = 0.049 +/- 0.008 micron x min-1atm-1 assuming isosmotic is 300 mosm). However, at the 6-somite stage, Lp increased twofold (Lp = 0.040 +/- 0.004 micron x min-1atm-1 assuming isosmotic is 40 mosm or Lp = 0.100 +/- 0.017 micron x min-1atm-1 assuming isosmotic is 300 mosm). Therefore, the low permeability of the zebrafish embryo coupled with its large size (and consequent low area to volume ratio) led to a very slow osmotic response that should be considered before formulating cryopreservation protocols.

Animals↗

PubMed1987

Early development of photoreceptors in the ventral retina of the zebrafish embryo.

The first photoreceptor outer segments in the retina of the zebrafish Brachydanio rerio appear in the embryo 2.5 days after fertilization, as revealed by scanning and transmission electron microscopy. These outer segments arise in a small region ventral to the exit of the optic nerve. Ultrastructural features of the developing photoreceptor cells, especially those that distinguish the rods and cones, are described. By 3 days after fertilization, the time of hatching, photoreceptor outer segments are widespread in the retina. However, at this time and in the young larva the early developing ventral region remains distinctive because of its conspicuous population of rods.

Animals↗