Zebrafish as a model of genetic disease.

Abstract

The zebrafish is rapidly becoming a vital tool in studies of genetic disease. Use of the zebrafish embryo as an experimental model combines the efficiency of techniques specific to invertebrates with the human applicability of vertebrate studies, along with a number of other advantages such as optical transparency and high spawn number. Sequencing maps and mutant screen data are available, and gene ontology annotation is progressing. Furthermore, a number of highly important projects are underway to expand the utility of the zebrafish still further (eg. Mutant screens and TILLING projects; see (Lieschke and Currie, 2007) for review). As such the zebrafish has become a vital model organism for study of a variety of genetic defects, toxicology and pharmacological screens etc. These papers trace the development of zebrafish embryos as a model organism for both genetic disease and, as part of this, the development of a relatively high throughput approach to analysing relative levels of apoptosis. The first paper describes the fmr1 gene family in zebrafish (fmr1, and its orthologs fxr1 and fxr2). This paper includes a phylogenetic analysis of the gene family that demonstrates the high conservation between human and zebrafish, in the context of Drosophila. We then describe expression of the genes in the embryo (using in situ hybridisation) and adult (using real time pcr). The conclusions are that the zebrafish is an appropriate model in which to study Fragile X Mental Retardation genetic disease. The second paper builds upon this conclusion and further establishes the appropriateness of the model by recapitulating elements of the disease that had already been modelled in other model organisms. The research is validated using a number of controls. We describe a number of original findings that extended the body of knowledge regarding pharmacological rescue of the FMRP loss phenotypes. A craniofacial phenotype is identified, the first such discovery in a model of Fragile X syndrome. These findings are a vital step toward understanding the pathway from gene, to molecular phenotype, to cellular morphology, to gross morphology. As part of these studies, we found it necessary to analyse apoptosis. The technique developed to facilitate this analysis is described in our third paper. Given the highly stochastic nature of the apoptotic patterns we developed a method to take full advantage of the characteristics of zebrafish embryos, primarily their transparency and availability in large numbers. As the zebrafish becomes more widely accepted as a model for a diverse range of scientific questions, the development of such a technique is doubly important given the necessity of a cheap, reliable and simple generalizable method of analysing processes affecting cell viability in fish. This has clear importance for pharmacological studies, but is also a long overdue addition to the battery of controls available for highly invasive techniques such as microinjection, in which apoptosis is regularly found among its non specific effects.