Our results show that ectopic YAP expression accelerates medulloblastoma onset and aggressiveness, and also confers a survival advantage after tumor radiation. This has particularly important implications for medulloblastomas; due to their radiosensitivity, radiation therapy is a standard in children older than 3 years of age (Mueller and Chang 2009). We show here that 3 hours after radiation, YAP-driven SmoA1 medulloblastomas feature higher levels of proliferation markers and reduced apoptosis. In vitro, we found a similar effect when we irradiated GFP- or YAP-over-expressing CGNPs. CGNPs expressing YAP not only proliferated more than GFP-expressing cells after radiation, but also failed to arrest in response to radiation, skipping the G2/M checkpoint.