"Complex biological systems such as a developing embryo, a regenerating tissue, or a tumor are composed of heterogeneous cell types. The complex behavior of these systems is often dominated by a minority cell population such as the embryonic stem cells in a developing organism or cancer stem cells in tumors. Thus, in order to properly understand development, tissue regeneration, and cancer, a single cell approach must be taken: the biological sample must be ""dissected"" into many individual cells and each single cell has to be characterized independently. In this study we will develop and apply high throughput genomic methods for measuring gene expression in hundreds of individual cells in order to characterize transcriptional heterogeneity in tissues and tumors. This approach will allow us to find unique markers to identify cancer stem cells, elucidate their interactions with other cell types in the tumor, and systematically discover key gene circuits responsible for their long-term survival, self-renewal, and proliferation. As a starting point, we will focus on Wilms’ tumor, which is a common pediatric renal malignancy."