PTF1A and neoplasm: In contrast to control cerebellum of Tg(ptf1a:eGFP) fish (supplementary material Fig. S1A,B), the tumor appears as sheet-like areas of small, round, blue cells with scant cytoplasm and dense hyperchromatic nuclei (supplementary material Fig. S1C,D), resembling classic human cerebellar cancer (supplementary material Fig. S1E,F), which originates from granule cell progenitors located in the external granular layer (EGL) of the cerebellum (Marino, 2005).