Progressive heterogeneity of cancer-initiating cells revealed by quantitative clonal analysis

Different cellular compartments within a tissue present distinct cancer-initiating capacity. Current approach to dissect cellular heterogeneity in cancer-initiating capacity requires a well-understood tissue lineage hierarchy and highly-specific promoters, which are lacking for most tissues. Here, utilizing a genetic tool called Mosaic Analysis with Double Markers (MADM), we induced scattered GFP-labeled single mutant cells in a broad category of cell types and quantitatively traced their expansion at clonal level, to pinpoint cells susceptible for cancer initiation within under-defined tissues. We dissected the heterogeneous cancer-initiating capacity of fallopian tube Pax8+ cells, which are thought to be the origin for high-grade serous ovarian cancer. We revealed that only a rare primitive subset enriched in the fimbriae can fuel ovarian cancer initiation, and oncogenic mutations exaggerate their intrinsic potential and bias their differentiation for further progression. Collectively, we demonstrated a scheme to dissect cellular heterogeneity in cancer-initiating capacity in tissues lacking established lineage hierarchy. Overall design: To compare the expression profile of small clones and large clones, from each MADM-wildtype mouse at 4 weeks old (n=6), 200 cells from small clones were collected and pooled, and another 200 cells from large clones were collected and pooled. The samples were then subjected to cDNA library construction, followed by amplifications and sequencing.