Targeted transgenic RNAi knockdown of cell fate determinants induces neoplastic tumor growth and metastasis in a Drosophila transplantation model of neural stem cell derived cancer

Genetic models such as Drosophila have sophisticated transgenic and molecular genetic tools available to investigate proliferation control in normal and tumorigenic neural stem cells. In this report, we adapted a targeted transgenic RNAi knockdown approach based on the Gal4/UAS expression system to the study of neoplastic tumor formation and metastatic growth in the Drosophila brain tissue transplantation model. Transgenic RNAi driven knockdown of numb, brain tumor (brat) and prospero (pros) in all neuroblasts (type I and type II) resulted in a high incidence of neoplastic tumor formation after transplantation that was comparable to that of loss-of-function mutations in these cell fate determinants. RNAi knockdown of numb and brat specifically restricted to type II neuroblast lineages also resulted in tumor formation after transplantation. A marked temperature dependence of tumor formation after transplantation was documented and quantified for RNAi-induced knockdown of numb, brat and pros. An in vivo assay for micrometastasis formation in ovarioles revealed significant metastatic potential of transplanted overproliferating brain tissue induced by RNAi knockdown of these cell fate determinants. These findings establish the foundation for RNAi-based investigations of the mechanisms which underlie the proliferation, invasion and metastastic potential of neural stem cell induced tumors in the Drosophila model.