Genetic Dissection of Genomic Instability and Cellular Differentiation in Zebrafish

ZEBRAFISH: The zebrafish is an inch-long tropical fish with rapidly-developing, transparent embryos and a powerful bag of genetic tricks developed by the late George Streisinger and his colleagues at the University of Oregon. Large scale mutant screens have been completed in zebrafish (see special Zebrafish Issue of Development, December 1996). A dense genetic map and an EST project are in full swing. Recently, a zebrafish genome project has begun, and functional knockdown technology has been established. This and other work has made the zebrafish a premier vertebrate model to study development and other vertebrate processes.

GENOMIC INSTABILITY: We are applying the advantageous genetic features of the zebrafish to the study of mutation and tissue differentiation. In order to discover new vertebrate genes that control mutation, we are studying mutants that show elevated rates of mutation. Genomic instability ("gin") mutants have been discovered by J. Moore in our lab by their increased frequency of somatic loss of heterozygosity at a pigment locus, golden (see figure). We expect genetic instability to be caused by deficiencies in any of a number of functions, including chromosome segregation, recombination, DNA repair, and epigenetic mechanisms of gene regulation.

DIFFERENTIATION: In order to discover new vertebrate genes that control tissue differentiation, we have performed a screen for histological mutants using larval array technology developed in our laboratory. Both organ-specific and multi-organ mutations were found, including one with cytological phenotypes highly reminiscent of cancer. We expect the mutations to affect key decision points in processes including cell polarity, cell proliferation, and cell-cell interaction.

FROM OUR MUTANTS: Critical knowledge will be gained by studying the characteristics of mutants, the structure of the mutated genes, and the biochemical activities of the corresponding proteins. Genomic instability mutants can be used to help the detection of environmental mutagens. Insights gained from these mutants will increase our understanding of the molecular forces that drive evolution and suggest new ways to fight cancer. Mutations that result in a tendency to develop cancer will signal the identification of tumor suppressor genes, and will represent animal models for human genetic syndromes that predispose to cancer.