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1.  Diffusion of small molecules into medaka embryos improved by electroporation 
BMC Biotechnology  2013;13:53.
Diffusion of small molecules into fish embryos is essential for many experimental procedures in developmental biology and toxicology. Since we observed a weak uptake of lithium into medaka eggs we started a detailed analysis of its diffusion properties using small fluorescent molecules.
Contrary to our expectations, not the rigid outer chorion but instead membrane systems surrounding the embryo/yolk turned out to be the limiting factor for diffusion into medaka eggs. The consequence is a bi-phasic uptake of small molecules first reaching the pervitelline space with a diffusion half-time in the range of a few minutes. This is followed by a slow second phase (half-time in the range of several hours) during which accumulation in the embryo/yolk takes place. Treatment with detergents improved the uptake, but strongly affected the internal distribution of the molecules. Testing electroporation we could establish conditions to overcome the diffusion barrier. Applying this method to lithium chloride we observed anterior truncations in medaka embryos in agreement with its proposed activation of Wnt signalling.
The diffusion of small molecules into medaka embryos is slow, caused by membrane systems underneath the chorion. These results have important implications for pharmacologic/toxicologic techniques like the fish embryo test, which therefore require extended incubation times in order to reach sufficient concentrations in the embryos.
PMCID: PMC3716799  PMID: 23815821
Medaka; Small molecules; Diffusion; Toxicology; Electroporation; LiCl
2.  Side chain modified peptide nucleic acids (PNA) for knock-down of six3 in medaka embryos 
BMC Biotechnology  2012;12:50.
Synthetic antisense molecules have an enormous potential for therapeutic applications in humans. The major aim of such strategies is to specifically interfere with gene function, thus modulating cellular pathways according to the therapeutic demands. Among the molecules which can block mRNA function in a sequence specific manner are peptide nucleic acids (PNA). They are highly stable and efficiently and selectively interact with RNA. However, some properties of non-modified aminoethyl glycine PNAs (aegPNA) hamper their in vivo applications.
We generated new backbone modifications of PNAs, which exhibit more hydrophilic properties. When we examined the activity and specificity of these novel phosphonic ester PNAs (pePNA) molecules in medaka (Oryzias latipes) embryos, high solubility and selective binding to mRNA was observed. In particular, mixing of the novel components with aegPNA components resulted in mixed PNAs with superior properties. Injection of mixed PNAs directed against the medaka six3 gene, which is important for eye and brain development, resulted in specific six3 phenotypes.
PNAs are well established as powerful antisense molecules. Modification of the backbone with phosphonic ester side chains further improves their properties and allows the efficient knock down of a single gene in fish embryos.
PMCID: PMC3469332  PMID: 22901024
PNA; Knock down; Medaka; Six3
3.  Magnetic field-controlled gene expression in encapsulated cells 
Journal of Controlled Release  2012;158(3):424-432.
Cell and gene therapies have an enormous range of potential applications, but as for most other therapies, dosing is a critical issue, which makes regulated gene expression a prerequisite for advanced strategies. Several inducible expression systems have been established, which mainly rely on small molecules as inducers, such as hormones or antibiotics. The application of these inducers is difficult to control and the effects on gene regulation are slow. Here we describe a novel system for induction of gene expression in encapsulated cells. This involves the modification of cells to express potential therapeutic genes under the control of a heat inducible promoter and the co-encapsulation of these cells with magnetic nanoparticles. These nanoparticles produce heat when subjected to an alternating magnetic field; the elevated temperatures in the capsules then induce gene expression. In the present study we define the parameters of such systems and provide proof-of-principle using reporter gene constructs. The fine-tuned heating of nanoparticles in the magnetic field allows regulation of gene expression from the outside over a broad range and within short time. Such a system has great potential for advancement of cell and gene therapy approaches.
Graphical abstract
Cells containing a heat inducible promoter construct (a) are encapsulated with magnetic nanoparticles (b+c). An alternating magnetic field produces heat (d), which allows controlled gene expression in patients (e).
PMCID: PMC3329627  PMID: 22197778
Magnetic nanoparticles; Hyperthermia; Inducible gene expression; Cell encapsulation; Cell therapy; Gene therapy
4.  Induction of otic structures by canonical Wnt signalling in medaka 
Development Genes and Evolution  2009;219(8):391-398.
The Wnt family of signalling proteins is known to participate in multiple developmental decisions during embryogenesis. We misexpressed Wnt1 in medaka embryos and observed anterior truncations, similar to those described for ectopic activation of canonical Wnt signalling in other species. Interestingly, when we induced a heat-shock Wnt1 transgenic line exactly at 30% epiboly, we observed multiple ectopic otic vesicles in the truncated embryos. The vesicles then fused, forming a single large ear structure. These “cyclopic ears” filled the complete anterior region of the embryos. The ectopic induction of otic development can be explained by the juxtaposition of hindbrain tissue with anterior ectoderm. Fibroblast growth factor (Fgf) ligands are thought to mediate the otic-inducing properties of the hindbrain. However, signals different from Fgf3 and Fgf8 are necessary to explain the formation of the ectopic ear structures, suggesting that Wnt signalling is involved in the otic induction process in medaka.
Electronic supplementary material
The online version of this article (doi:10.1007/s00427-009-0302-z) contains supplementary material, which is available to authorized users.
PMCID: PMC2773112  PMID: 19760182
Wnt1; Otic induction; Cyclopic ear; Medaka
5.  Rapid identification of PAX2/5/8 direct downstream targets in the otic vesicle by combinatorial use of bioinformatics tools 
Genome Biology  2008;9(10):R145.
A novel bioinformatics pipeline is used to discover PAX2/5/8 direct downstream targets involved in inner ear development.
The pax2/5/8 genes belonging to the PAX family of transcription factors are key developmental regulators that are involved in the patterning of various embryonic tissues. More particularly, their function in inner ear specification has been widely described. However, little is known about the direct downstream targets and, so far, no global approaches have been performed to identify these target genes in this particular tissue.
Here we present an original bioinformatics pipeline composed of comparative genomics, database querying and text mining tools, which is designed to rapidly and specifically discover PAX2/5/8 direct downstream targets involved in inner ear development. We provide evidence supported by experimental validation in medaka fish that brain 2 (POU domain, class 3, transcription factor 2), claudin-7, secretory pathway component sec31-like and meteorin-like precursor are novel direct downstream targets of PAX2/5/8.
This study illustrates the power of extensive mining of public data repositories using bioinformatics methods to provide answers for a specific biological question. It furthermore demonstrates how the usage of such a combinatorial approach is advantageous for the biologist in terms of experimentation time and costs.
PMCID: PMC2760872  PMID: 18828907
6.  Wnt/Axin1/β-Catenin Signaling Regulates Asymmetric Nodal Activation, Elaboration, and Concordance of CNS Asymmetries 
Neuron  2007;55(3):393-405.
Nodal activity in the left lateral plate mesoderm (LPM) is required to activate left-sided Nodal signaling in the epithalamic region of the zebrafish forebrain. Epithalamic Nodal signaling subsequently determines the laterality of neuroanatomical asymmetries. We show that overactivation of Wnt/Axin1/β-catenin signaling during late gastrulation leads to bilateral epithalamic expression of Nodal pathway genes independently of LPM Nodal signaling. This is consistent with a model whereby epithalamic Nodal signaling is normally bilaterally repressed, with Nodal signaling from the LPM unilaterally alleviating repression. We suggest that Wnt signaling regulates the establishment of the bilateral repression. We identify a second role for the Wnt pathway in the left/right regulation of LPM Nodal pathway gene expression, and finally, we show that at later stages Axin1 is required for the elaboration of concordant neuroanatomical asymmetries.
PMCID: PMC1940036  PMID: 17678853
7.  Gbx2 and Otx2 Interact with the WD40 Domain of Groucho/Tle Corepressors▿ ‡  
Molecular and Cellular Biology  2006;27(1):340-351.
One of the earliest organizational decisions in the development of the vertebrate brain is the division of the neural plate into Otx2-positive anterior and Gbx2-positive posterior territories. At the junction of these two expression domains, a local signaling center is formed, known as the midbrain-hindbrain boundary (MHB). This tissue coordinates or “organizes” the development of neighboring brain structures, such as the midbrain and cerebellum. Correct positioning of the MHB is thought to depend on mutual repression involving these two homeobox genes. Using a cell culture colocalization assay and coimmunoprecipitation experiments, we show that engrailed homology region 1 (eh1)-like motifs of both transcription factors physically interact with the WD40 domain of Groucho/Tle corepressor proteins. In addition, heat shock-induced expression of wild-type and mutant Otx2 and Gbx2 in medaka embryos demonstrates that Groucho is required for the repression of Otx2 by Gbx2. On the other hand, the repressive functions of Otx2 on Gbx2 do not appear to be dependent on corepressor interaction. Interestingly, the association of Groucho with Otx2 is also required for the repression of Fgf8 in the MHB. Therefore Groucho/Tle family members appear to regulate key aspects in the MHB development of the vertebrate brain.
PMCID: PMC1800652  PMID: 17060451

Results 1-7 (7)