Cancer is a major health problem, and over 500,000 people die of the disease each year in the United States. Various model systems have been utilized to define abnormalities in cell cycle or genome stability associated with cancer, and these studies have resulted in the isolation of oncogenes, cell cycle control genes, checkpoint genes and tumor suppressor genes. Although mice and humans are excellent systems in which to study cancer, a large-scale forward genetic approach to define other factors involved in cancer biology is not feasible in these systems. We plan to use the zebrafish as a model to examine genes that participate in and/or disrupt the cancer phenotype. The zebraflsh is an attractive developmental model due to its optical clarity during embryogenesis. Genetics of this model system are aided by the ability to house large numbers of zebrafish (currently greater than 100,000 in a small area at our institution). In addition, each female lays up to 200 eggs weekly. In an effort to establish the zebraflsh system as a model for cancer biology, a preliminary screen for mutations affecting the cell cycle has been undertaken using whole embryo immunohistochemical analysis of the phosphorylated form of histone H3. This antibody delineates cells in late G2 to anaphase of the cell cycle. Mutants have been isolated with both increased and decreased phospho-histone H3 (pH3) staining, which suggests the presence of defects in the cell cycle. Several of these mutants are prone to developing cancer in a carcinogenesis assay. We have also created a zebrafish p53 mutant and will characterize its role in cell cycle control and carcinogenesis. We plan to perform genetic and chemical modifier screens on the cell cycle mutants to identify suppressors of the embryonic cell cycle defect. We will further establish if these suppressors lead to a decrease in cancer rates in fish treated with carcinogens. These studies should provide new insight into the vertebrate cell cycle and cancer biology, and may delineate pharmaceutical targets for patients with cancer.
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