MicroXRF tomographic visualization of zinc and iron in the zebrafish embryo at the onset of the hatching period

Behavioral changes and transcriptomic effects at embryonic and post-embryonic stages reveal the toxic effects of 2,2',4,4'-tetrabromodiphenyl ether on neurodevelopment in zebrafish (Danio rerio)

Polybrominated biphenyl ethers (PBDEs) are new persistent pollutants that are widely exist in the environment and have many toxic effects. However, their toxicity mechanisms on neurodevelopment are still unclear. In this study, zebrafish embryos were exposed to 2, 2', 4, 4'-tetrabromodiphenyl ether (BDE-47) (control, 10, 50 and 100 μg/L) at 2 h postfertilization (hpf) - 7 dpf. Locomotion analysis indicated that BDE-47 increased spontaneous coiling activity in zebrafish embryos under high-intensity light stimuli and decreased locomotor in zebrafish larvae. RNA-Seq analysis revealed that most of the up-regulated pathways were related to the metabolism of cells and tissues, while the down-regulated pathways were related to neurodevelopment. Consistent with the locomotion and KEGG results, BDE-47 affected the expression of genes for central nervous system (gfap, mbpa, bdnf & pomcb), early neurogenesis (neurog1 & elavl3), and axonal development (tuba1a, tuba1b, tuba1c, syn2a, gap43 & shha). Furthermore, BDE-47 interfered with gene expression of the Wnt signaling pathway, especially during embryonic stages, suggesting that the mechanisms of BDE-47 toxicity to zebrafish at various stages of neurodevelopment may be different. In summary, early neurodevelopment effects and metabolic disturbances may have contributed to the abnormal neurobehavioral changes induced by BDE-47 in zebrafish embryos/larvae, suggesting the neurodevelopmental toxicity of BDE-47.

Towards routine 3D characterization of intact mesoscale samples by multi-scale and multimodal scanning X-ray tomography

Non-invasive multi-scale and multimodal 3D characterization of heterogeneous or hierarchically structured intact mesoscale samples is of paramount importance in tackling challenging scientific problems. Scanning hard X-ray tomography techniques providing simultaneous complementary 3D information are ideally suited to such studies. However, the implementation of a robust on-site workflow remains the bottleneck for the widespread application of these powerful multimodal tomography methods. In this paper, we describe the development and implementation of such a robust, holistic workflow, including semi-automatic data reconstruction. Due to its flexibility, our approach is especially well suited for on-the-fly tuning of the experiments to study features of interest progressively at different length scales. To demonstrate the performance of the method, we studied, across multiple length scales, the elemental abundances and morphology of two complex biological systems, Arabidopsis plant seeds and mouse renal papilla samples. The proposed approach opens the way towards routine multimodal 3D characterization of intact samples by providing relevant information from pertinent sample regions in a wide range of scientific fields such as biology, geology, and material sciences.

The effect of combined exposure of zinc and nickel on the development of zebrafish

Excessive accumulation of Zn²⁺ or Ni²⁺ can cause various problems to aquatic animals. In this study, the developmental toxicity induced by individual or combined exposure of Zn²⁺ and Ni²⁺ to zebrafish embryos and larvae were evaluated to better understand the interaction between Zn²⁺ and Ni²⁺ . Both of individual and combined exposure of Zn²⁺ and Ni²⁺ could cause obvious developmental toxicity, which mainly occurred after hatching, at a concentration-dependent manner. The calculated 168-h LC₅₀ were 2.79 mg/L for Zn²⁺ and 7.44 mg/L for Ni²⁺ . The interaction of Zn²⁺ and Ni²⁺ based on mortality was found to be an antagonism. Various malformations, including tail curving, spinal curvature, pericardial edema, and yolk sac edema, were observed with significant effects on body length and heartbeat rates after exposure of Zn²⁺ and Ni²⁺ . Meanwhile, some genes related to cardiovascular development and bone formation were mainly down-regulated by the individual and combined exposure of Zn²⁺ and Ni²⁺ . The individual exposure was more toxic than combined exposure because the interaction of Zn²⁺ and Ni²⁺ was determined to be an antagonism. The down-regulation of genes related to cardiovascular development and bone formation may contribute to the observed malformation and decreases of body length and heartbeat rates.

The zebrafish Znt1asa17 mutant reveals roles of zinc transporter-1a in embryonic development

BACKGROUND

Zinc is one of the vital micronutrients required through various developmental stages in animals. Zinc transporter-1 (ZnT1; Slc30a1) is essential in vertebrates for nutritional zinc uptake and cellular zinc extrusion. Knockout of ZnT1 is lethal in vertebrates and there are therefore few functional studies of this protein in vivo.

METHODS

In the present study we characterised the embryonic development in a zebrafish Znt1a mutant (Znt1a^sa17) which is lacking the last 40 amino acids of Znt1a as generated by TILLING. In parallel experiments, we compared the development of a zebrafish embryo Znt1a morphant (Znt1a^MO) which was generated by knockdown of Znt1a using morpholino-modified oligonucliotides.

RESULTS

The homozygous Znt1a^sa17 embryo is viable, but displays a subtle phenotype informing on the biological roles of Znt1a. The Znt1a^sa17 fish have delayed development, including attenuated epiboly. They further show a decrease in phosphorylated extracellular signal-regulated kinases 1 and 2 (pERK1/2), retarded yolk resorption, and impaired clearance of free Zn²⁺ from the vitelline fluid and its storage in hatching gland cells. All these aberrations are milder versions of those observed upon knockdown of Znt1a by morpholinos. Interestingly, the phenotype could be rescued by addition of the cell-permeable zinc chelator, N,N,N',N'-tetrakis(2-pyridinylmethyl)-1,2-ethanediamine (TPEN) to the incubation medium and was aggravated by addition of zinc(II). Thus, the Znt1a^sa17 mutant has a reduced ability to handle zinc and can be characterised as a hypomorph.

CONCLUSION

This study is the first to show that the last 40 amino acids of Znt1a are of importance for its role in zinc homeostasis and ability to activate the MAPK/ERK pathway contrary to what was previously thought.

Novel Insights into the Role of Copper in Critical Life Stages of Oysters Revealed by High-Resolution NanoSIMS Imaging

Copper (Cu) is a key trace element for many biological processes, but there is little available information regarding its requirements and functions in critical life stages of marine bivalves, during which dramatic morphological and physiological changes occur. In this study, the ontogeny pattern of Cu accumulation across the life history of oysters was explored for the first time and the distributions of Cu in oysters at critical life stages (pediveliger and early settled spat) were in situ mapped by nanoscale secondary ion mass spectrometry (NanoSIMS) with high lateral resolution. We first demonstrated that the late pelagic stage to early settled stage was the critical stage requiring Cu during oyster development. NanoSIMS imaging revealed a significant elevation of intercellular Cu levels along with mitochondrial calcium overload and obvious structural degradation of mitochondria in velar cells at the pediveliger stage, implying the possible role of Cu in cell apoptosis of the velum during larval metamorphosis. Furthermore, an obvious enrichment of Cu together with calcium was observed in the nucleus and mitochondria of ciliated cells of gill tissue at the early settled stage. Their accumulation in the gill cells was significantly higher than that in the juveniles, indicating the potential role of Cu in sustaining the fast growth of the gill filament and the concomitant acceleration of energy metabolism during early benthic development. Our findings offer new insights into the understanding of the interactions between trace metals and marine bivalves.

Evaluation of laser ablation microtomy for correlative microscopy of hard tissues

Laser ablation machining or microtomy (LAM) is a relatively new approach to producing slide mounted sections of translucent materials. We evaluated the method with a variety of problems from the bone, joint and dental tissues fields where we require thin undecalcified and undistorted sections for correlative light microscopy (LM) and backscattered electron scanning electron microscopy (BSE SEM). All samples were embedded in poly-methylmethacrlate (PMMA) and flat block surfaces had been previously studied by BSE-SEM and confocal scanning light microscopy (CSLM). Most were also studied by X-yay microtomography (XMT). The block surface is stuck to a glass slide with cyanoacrylate adhesive. Setting the section thickness and levelling uses inbuilt optical coherence tomographic imaging. Tight focusing of near-infrared laser radiation in the sectioning plane gives extreme intensities causing photodisruption of material at the focal point. The laser beam is moved by a fast scanner to write a cutting line, which is simultaneously moved by an XY positioning unit to create a sectioning plane. The block is thereby released from the slide, leaving the section stuck to the slide. Light, wet polishing on the finest grade (4000 grit) silicon carbide polishing paper is used to remove a 1-2 μm thick damaged layer at the surface of the section. Sections produced by laser cutting are fine in quality and superior to those produced by mechanical cutting and can be thinner than the 'voxel' in most laboratory X-ray microtomography systems. The present extensive pilot studies have shown that it works to produce samples which we can study by both light and electron microscopy.