English: Abnormal neuroblast proliferation and brain tumor formation. (a) (Top), wild-type Drosophilae have “normal neuroblasts” which undergo a regulated self-renewal and differentiation process to generate neurons or glial cells. This proliferation exits at pupal stage. (Bottom), Dysregulated asymmetric cell division in central brain neuroblasts of larval brains with knockdown or knockout of cell-fate determinants results in brain tumor formation [24, 29–32]. The disturbed balance between self-renewal and differentiation results in the generation of self-renewing “tumor neuroblasts” and indefinite proliferation. (b) (Left) wild-type larval brain compared to (right) cell fate determinant (brat/prospero/numb) mutant, overproliferated brain. Transplantation of dissected GFP-labeled neuroblasts from the latter results in tumor formation in host flies and subsequent metastasis [32–34].