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Superficial appeal: The surface of live cells and zebrafish embryos can be modified by a supramolecular method. A peptide pair that forms a coiled coil at the cell membrane can be used to dock liposomes in in vitro and in vivo environments (see scheme). This tool can be used in biophysical studies of biological processes occurring at membranes.

BackgroundThe zebrafish embryo is an important in vivo model to study the host innate immune response towards microbial infection. In most zebrafish infectious disease models, infection is achieved by micro-injection of bacteria into the embryo. Alternatively, Edwardsiella tarda, a natural fish pathogen, has been used to treat embryos by static immersion. In this study we used transcriptome profiling and quantitative RT-PCR to analyze the immune response induced by E. tarda immersion and injection.ResultsMortality rates after static immersion of embryos in E. tarda suspension varied between 25-75%, while intravenous injection of bacteria resulted in 100% mortality. Quantitative RT-PCR analysis on the level of single embryos showed that expression of the proinflammatory marker genes il1b and mmp9 was induced only in some embryos that were exposed to E. tarda in the immersion system, whereas intravenous injection of E. tarda led to il1b and mmp9 induction in all embryos. In addition, microarray expression profiles of embryos subjected to immersion or injection showed little overlap. E. tarda-injected embryos displayed strong induction of inflammatory and defense genes and of regulatory genes of the immune response. E. tarda-immersed embryos showed transient induction of the cytochrome P450 gene cyp1a. This gene was also induced after immersion in Escherichia coli and Pseudomonas aeruginosa suspensions, but, in contrast, was not induced upon intravenous E. tarda injection. One of the rare common responses in the immersion and injection systems was induction of irg1l, a homolog of a murine immunoresponsive gene of unknown function.ConclusionsBased on the differences in mortality rates between experiments and gene expression profiles of individual embryos we conclude that zebrafish embryos cannot be reproducibly infected by exposure to E. tarda in the immersion system. Induction of il1b and mmp9 was consistently observed in embryos that had been systemically infected by intravenous injection, while the early transcriptional induction of cyp1a and irg1l in the immersion system may reflect an epithelial or other tissue response towards cell membrane or other molecules that are shed or released by bacteria. Our microarray expression data provide a useful reference for future analysis of signal transduction pathways underlying the systemic innate immune response versus those underlying responses to external bacteria and secreted virulence factors and toxins.

The increasing use of zebrafish larvae for biomedical research applications is resulting in versatile models for a variety of human diseases. These models exploit the optical transparency of zebrafish larvae and the availability of a large genetic tool box. Here we present detailed protocols for the robotic injection of zebrafish embryos at very high accuracy with a speed of up to 2000 embryos per hour. These protocols are benchmarked for several applications: (1) the injection of DNA for obtaining transgenic animals, (2) the injection of antisense morpholinos that can be used for gene knock-down, (3) the injection of microbes for studying infectious disease, and (4) the injection of human cancer cells as a model for tumor progression. We show examples of how the injected embryos can be screened at high-throughput level using fluorescence analysis. Our methods open up new avenues for the use of zebrafish larvae for large compound screens in the search for new medicines.

dThe translational value of zebrafish high-throughput screens can be improved when more knowledge is available on uptake characteristics of potential drugs. We investigated reference antibiotics and 15 preclinical compounds in a translational zebrafish-rodent screening system for tuberculosis. As a major advance, we have developed a new tool for testing drug uptake in the zebrafish model. This is important, because despite the many applications of assessing drug efficacy in zebrafish research, the current methods for measuring uptake using mass spectrometry do not take into account the possible adherence of drugs to the larval surface. Our approach combines nanoliter sampling from the yolk using a microneedle, followed by mass spectrometric analysis. To date, no single physicochemical property has been identified to accurately predict compound uptake; our method offers a great possibility to monitor how any novel compound behaves within the system. We have correlated the uptake data with high-throughput drug-screening data from Mycobacterium marinum-infected zebrafish larvae. As a result, we present an improved zebrafish larva drug-screening platform which offers new insights into drug efficacy and identifies potential false negatives and drugs that are effective in zebrafish and rodents. We demonstrate that this improved zebrafish drug-screening platform can complement conventional models of in vivo Mycobacterium tuberculosis-infected rodent assays. The detailed comparison of two vertebrate systems, fish and rodent, may give more predictive value for efficacy of drugs in humans.

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BackgroundMicroRNAs (miRNAs) have recently been shown to play important roles in development of the immune system and in fine-tuning of immune responses. Human miR-146 family members are known as inflammation-inducible miRNAs involved in negative feedback regulation of Toll-like receptor (TLR) signalling. Dysregulation of the miR-146 family has often been linked to inflammatory diseases and malignancies. This study reports on miR-146a and miR-146b as infection-inducible miRNAs in zebrafish, which has emerged as a model species for human disease.ResultsUsing a custom-designed microarray platform for miRNA expression we found that both members of the zebrafish miR-146 family, miR-146a and miR-146b, were commonly induced by infection of zebrafish embryos with Salmonella typhimurium and by infection of adult fish with Mycobacterium marinum. The induction of these miRNAs was confirmed by Taqman miRNA assays. Subsequently, we used zebrafish embryos, in which adaptive immunity is not yet active, as an in vivo system to investigate the role of miR-146 in the innate immune response to S. typhimurium infection. Knockdown of traf6 and use of myd88 mutants demonstrated that the induction of miR-146a and miR-146b by S. typhimurium infection was affected by disruption of the MyD88-Traf6 pathway that mediates transduction of TLR signals and cytokine responses. In turn, knockdown of miR-146 itself had no major effects on the expression of known targets of MyD88-Traf6 signalling. Instead, RNA sequencing analysis showed that miR-146 knockdown led to an increased induction of six members of the apolipoprotein gene family in S. typhimurium-infected embryos.ConclusionBased on microarray analysis and Taqman miRNA assays we conclude that members of the miR-146 family, which is highly conserved between fish and human, are induced by bacterial infection in zebrafish in a MyD88 and Traf6 dependent manner. The combined knockdown of miR-146a and miR-146b in zebrafish embryos infected with S. typhimurium had no major effect on the expression of pro-inflammatory genes and transcription factors known to be downstream of the MyD88-Traf6 pathway. In contrast, apolipoprotein-mediated lipid transport emerged as an infection-inducible pathway under miR-146 knockdown conditions, suggesting a possible function of miR-146 in regulating lipid metabolism during inflammation.

Zebrafish larvae (Danio rerio) are increasingly used to translate findings regarding drug efficacy and safety from in vitro-based assays to vertebrate species, including humans. However, the limited understanding of drug exposure in this species hampers its implementation in translational research. Using paracetamol as a paradigm compound, we present a novel method to characterize pharmacokinetic processes in zebrafish larvae, by combining sensitive bioanalytical methods and nonlinear mixed effects modeling. The developed method allowed quantification of paracetamol and its two major metabolites, paracetamol-sulfate and paracetamol-glucuronide in pooled samples of five lysed zebrafish larvae of 3 days post-fertilization. Paracetamol drug uptake was quantified to be 0.289 pmole/min and paracetamol clearance was quantified to be 1.7% of the total value of the larvae. With an average volume determined to be 0.290 μL, this yields an absolute clearance of 2.96 × 107 L/h, which scales reasonably well with clearance rates in higher vertebrates. The developed methodology will improve the success rate of drug screens in zebrafish larvae and the translation potential of findings, by allowing the establishment of accurate exposure profiles and thereby also the establishment of concentration–effect relationships.