Drosophila imaginal discs are able to regenerate and thus provide us with a model system to study multipotency of cells. Under certain conditions a small set of cells in the """"""""weak point"""""""" of each imaginal disc change their fate. This switch, known as transdetermination (TD), occurs with high frequency when wg is overexpressed or when a disc is cut through the """"""""weak point"""""""". Expression profiling of these cells identified candidate genes which in functional tests significantly modified TD. Some of these candidates are chromatin-remodeling genes. Furthermore, we identified putative regeneration genes such as alr-like, a gene orthologous to the mouse gene augmenter of liver regeneration (alr), Matrix metalloproteinase 1 (Mmp1), and dReg, a novel gene that contains a C-lectin domain. Although the mammalian orthologs of these three genes have been linked to regeneration of specific tissues, the mechanism by which they act is not well understood. We propose to continue and complete the functional tests, including the generation of mutations in novel candidate Drosophila genes. Dr. Moon will test homologous zebrafish genes. In examining regeneration, the issue of stem cells must be addressed. Do TD cells divide like stem cells? Cell clones will be induced in TD cells to assay for asymmetrical divisions, a landmark of stem cell behavior. These analyses will then be performed in the presence and absence of characterized enhancers and suppressors of TD to test whether these genes affect developmental plasticity by modifying the cell lineage pattern, the number of founder cells or the cell-doubling times. This proposal will contribute to the understanding of which molecular signals increase regeneration potential to ensure normal tissue maintenance and repair. Short summary A few specific cells in each imaginal disc of Drosophila have stem cell properties. If challenged by injury they regenerate. We will test whether these cells divide asymmetrically, a landmark of stem-cell behavior. In addition, we will identify the genes that mediate developmental plasticity and test how their gene products affect multipotent cells and their surroundings. Drosophila has been used as a model system to study human disease and we see here an opportunity to gain insight into stem-cell biology and regeneration. ? ? ?
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