Hh and EGFR-Ras signaling promote distinct steps of tumor progression in the Drosophila follicle epithelium
Controlled signaling activity is vital for normal tissue homeostasis and oncogenic signaling activation facilitates tumorigenesis. Here we combine single-cell transcriptomics with in-depth genetic and imaging analysis to investigate the role of the EGFR-Ras and Hedgehog signaling pathways in homeostasis of the Drosophila follicle stem cell lineage. We find that Hedgehog signaling simultaneously promotes an undifferentiated state and induces differentiation via activation of the epithelial-mesenchymal-transition associated transcription factor Zfh1. Overactivation of Hedgehog signaling generates a mixed transcriptional state comparable to partial epithelial-mesenchymal-transition. EGFR-Ras overactivation induces cell cycle defects by activating the transcription factors Pointed and E2f1 and impedes differentiation. Overactivation of both pathways blocks differentiation and induces tumor-like growth where follicle cells exhibit a loss of tissue architecture, sustained proliferation and a reduced lifespan of the host. These findings provide new insight into how signaling pathways converge at the transcriptional level to prevent malignant cell behavior. Overall design: Females of the appropriate genotype were raised at 18°C and shifted to 29°C for 14 days and fed wet yeast daily in the presence of males. Ovaries were dissected and late stages were removed. A single cell suspension was prepared and subjected to single-cell RNA-seqencig using 10x Chromium Single-Cell 3' Reagent Version 2 Kit. The resulting libraries were sequenced using Illumina HiSeq 2500 (Illumina).