Quantitative clonal analysis reveals vast heterogeneity among fallopian tube cells for ovarian cancer-initiation and progression

Abstract

Clonal dynamics of mutant cells during early carcinogenesis result from the intersection between genetic mutations and cell-intrinsic states, and foreshadow the trajectory for further transformation. While fallopian tube (FT) Pax8+ cells are one of the origin for high-grade serous ovarian cancer (HGSOC), their clonal dynamics upon oncogenic mutations remain unknown. Here we use a mouse genetic mosaic system called MADM (Mosaic Analysis with Double Markers) that can generate sporadic mutant cells unequivocally labeled with GFP to gain access to the premalignant stages of HGSOC. The sparseness of mutant cells generated by MADM enabled us to investigate the fate of individual tumor-initiating Pax8+ cells at the clonal level. Surprisingly, we observed a dichotomous progression kinetics among mutant clones: while the vast majority stalls immediately, a small proportion expands significantly. Clonal analysis with wildtype MADM mice revealed the same dichotomy among normal Pax8+ clones, suggesting that cell-intrinsic properties determine its initial expansion capacity. Furthermore, while wildtype clones cease to expand shortly after development, expanded mutant clones manifest divergent fates: some enter quiescence, others maintained high proliferative rate and continue to progress, indicating that oncogenic mutations exaggerate clonal expansion beyond cell-intrinsic potentials. Finally, intra-clonal fate mapping showed that progressive cells have a higher propensity to maintain Pax8+ fate, implying possible prolonged stemness within progressive clones. Taken together, our studies reveal that clonal expansion during tumor initiation of HGSOC seems to be be an oncogenic mutation-induced exaggeration of a small group of Pax8+ cells with intrinsically high expansion potential, and suggest that future early detection and cancer prevention studies should focus on these rare progressing clones.