Fish skin is a multi-purpose tissue that serves numerous vital functions including chemical and physical protection, sensory activity, behavioural purposes or hormone metabolism. Further, it is an important first-line defense system against pathogens, as fish are continuously exposed to multiple microbial challenges in their aquatic habitat. Fish skin excels in highly developed antimicrobial features, many of which have been preserved throughout evolution, and infection defense principles employed by piscine skin are still operative in human skin. This review argues that it is both rewarding and important for investigative dermatologists to revive their interest in fish skin biology, as it provides insights into numerous fundamental issues that are of major relevance to mammalian skin. The basic molecular insights provided by zebrafish in vivo-genomics for genetic, regeneration and melanoma research, the complex antimicrobial defense systems of fish skin and the molecular controls of melanocyte stem cells are just some of the fascinating examples that illustrate the multiple potential uses of fish skin models in investigative dermatology. We synthesize the essentials of fish skin biology and highlight selected aspects that are of particular comparative interest to basic and clinically applied human skin research.

The signal-mediated and spatially controlled assembly and dynamics of actin are crucial for maintaining shape, motility, and tip growth of eukaryotic cells. We report that a novel Armadillo repeat protein in Arabidopsis thaliana, ARMADILLO REPEAT ONLY1 (ARO1), is of fundamental importance for polar growth and F-actin organization in tip-growing pollen tubes. ARO1 is specifically expressed in the vegetative cell of pollen as well as in the egg cell. ARO1-GFP (for green fluorescent protein) fusion proteins accumulate most notably in pollen tube tips and partially colocalize with F-actin in the shank of pollen tubes. ARO1 knockout results in a highly disorganized actin cytoskeleton, growth depolarization, and ultimately tube growth arrest. Tip-localized ARO1-GFP is spatially shifted toward the future site of tip growth, indicating a role of ARO1 in the signaling network controlling tip growth and regulating actin organization. After the pollen tube discharges its contents into the receptive synergid, ARO1-GFP colocalizes with emerging F-actin structures near the site of sperm cell fusion, suggesting additional participation in the mechanism of sperm cell tracking toward the female gametes. The variable localization of ARO1 in the cytoplasm, the nucleus, and at the plasma membrane, however, indicates a multifunctional role like that of β-catenin/Armadillo and the p120 catenins.

Background/Aims: Cellular models are an interesting tool to study human heart diseases. To date, research groups mainly focus on mouse models, but important murine physiology is different from human characteristics. Recently, scientists found that the electrophysiology of fish cardiomyocytes largely resembles that of humans. So far, cardiomyocyte models were generated using differentiation medium, were stimulated electrically or, when contracting spontaneously, only did so over a short time period. We established an in vitro spontaneously, long-term beating heart model generated from rainbow trout, with the potential to be used as a new human heart model system because of its electrophysiology. Methods: Spontaneously contracting 3D cell layers from rainbow trout were generated in vitro and analyzed using PCR and immunochemistry. Further, electrophysiology was measured via intra – and extracellular recordings. Results: Contracting cardiomyogenic aggregates were generated without differentiation medium and were beating autonomously for more than one month. Electrophysiological measurements exhibit that the action potential properties of fish cardiomyocytes in part resemble the characteristics of human cardiomyocytes. The sensitivity of the beating cell aggregates to drugs could also be confirmed. Conclusion: Spontaneously contracting cardiomyogenic cell aggregates from rainbow trout generated in vitro are suitable for human heart research and pharmacology.

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We describe a method for fast and easy isolation of cells via trypsin digestion from larvae of Atlantic sturgeon Acipenser oxyrinchus oxyrinchus resulting in a stable, well-proliferating cell culture. The culture conditions for these cells were optimized with the aim of supporting the production of high amounts of biomass. To enhance cell growth and cell density, 4 different cultivation temperatures as well as commercially available carp serum (CS) and fetal calf serum (FCS) at different concentrations were tested and evaluated. Cell growth was measured via an impedancebased online cell-monitoring system (xCELLigence). These results showed the best cultivation temperature to be at 25°C and a media composition of Dulbecco's modified Eagle's medium (DMEM) supplemented with either 10 or 20% FCS or 5% CS. The cells were stable in the process of longterm cultivation over 33 passages and could be cryo-preserved. Immunocytochemical analysis revealed that the cells expressed proteins of different blastodermic layers. Ectodermic glia fibrilliary acid protein, vigilin (mRNA transport protein), and pan cytokeratin were abundant. This fastgrowing cell culture provides an important tool for research on Atlantic sturgeon populations.