PTF1A and medulloblastoma: As expected by eGFP-KRASG12D tissue-specific expression driven by ptf1a, we found the hallmark features of an undifferentiated medulloblastoma in both the external granular layer and ventricular zone in 5 out of 35 samples analyzed at 1 mpf (Aldinger and Elsen, 2008; Pascual et al., 2007).