![aging zebrafish circuli aging zebrafish circuli](https://i0.wp.com/scene.geneseo.edu/wp-content/uploads/2018/08/19-Zebarafish-7D0A8952-KEITH-WALTERS-web.jpg)
This species was initially described by the Scottish physician and naturalist Hamilton ( 5) in a survey on South Asian flora and fauna. Zebrafish, the most frequently employed non-mammalian vertebrate animal model, is a freshwater bony fish, belonging to the Cyprinidae family and to the Teleostei infraclass of ray-finned fish which arose ~340 million years ago ( 4). In these organisms in vivo techniques can be applied with the simplicity and versatility of in vitro assays and therefore they are frequently used in fundamental and biomedical research to quickly define gene functions and to develop novel therapeutic options ( 3). Furthermore, in most countries the adoption of the “Three R's” principles: Replacement, Reduction, and Refinement ( 2) for animal research is mandatory and encourages the use of alternative models, such as Danio rerio (zebrafish), Xenopus laevis/tropicalis (clawed toad), Drosophila melanogaster (fruit fly), and Caenorhabditis elegans (nematode). However, their use is costly and studies at early developmental stages raise ethical concerns. Mammals such as mice and non-human primates are traditionally the preferred models for biomedical research due to their close evolutionary relationship with humans. Preclinical animal models can be used to elucidate gene and protein function in ways often impossible in humans, by means of genome sequencing, advances in DNA manipulation and high resolution live-imaging ( 1). This review aims to discuss the techniques that make zebrafish a powerful model to investigate the molecular and physiological basis of skeletal disorders. Finally, the permeability of embryos to chemicals dissolved in water, together with the availability of large numbers of small-sized animals makes zebrafish a perfect model for high-throughput bone anabolic drug screening. The ability of adult zebrafish to remodel skeletal tissues can be exploited as a unique tool to investigate bone formation and repair. Despite the small size of the zebrafish, many traditional techniques for skeletal phenotyping, such as x-ray and microCT imaging and histological approaches, can be applied using the appropriate equipment and custom protocols. In addition, transgenic lines expressing fluorescent proteins under bone cell- or pathway- specific promoters enable in vivo imaging of differentiation and signaling at the cellular level. In the last decades, the use of both forward and new reverse genetics techniques has resulted in the generation of many mutant lines carrying skeletal phenotypes associated with human diseases. Furthermore, zebrafish share similar skeletal cells and ossification types with mammals. The zebrafish has been used as an efficient alternative vertebrate model for the study of human skeletal diseases, thanks to its easy genetic manipulation, high fecundity, external fertilization, transparency of rapidly developing embryos, and low maintenance cost.
![aging zebrafish circuli aging zebrafish circuli](https://thumbs-prod.si-cdn.com/GC-0SgOcT992FbkRcRsaUCVb6F0=/fit-in/1600x0/https://public-media.si-cdn.com/filer/97/9d/979d9257-273c-43f1-8505-220ed060b82f/zebrafish_26436913602.jpg)
Traditionally, mice have been the most common model organism in biomedical research, but their use is hampered by several limitations including complex generation, demanding investigation of early developmental stages, regulatory restrictions on breeding, and high maintenance cost. 2Department of Biomolecular Medicine, Center of Medical Genetics, Ghent University-University Hospital, Ghent, BelgiumĪnimal models are essential tools for addressing fundamental scientific questions about skeletal diseases and for the development of new therapeutic approaches.1Biochemistry Unit, Department of Molecular Medicine, University of Pavia, Pavia, Italy.Coucke 2, Andy Willaert 2 ‡ and Antonella Forlino 1 * ‡ Francesca Tonelli 1 †, Jan Willem Bek 2 †, Roberta Besio 1 †, Adelbert De Clercq 2 †, Laura Leoni 1, Phil Salmon 3, Paul J.